Patent Publication Number: US-2021194316-A1

Title: Battery-powered stand-alone motor unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to co-pending U.S. Provisional Patent Application No. 62/952,563 filed on Dec. 23, 2019, the entire content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to motor units, and more particularly to motor units for use with power equipment. 
     BACKGROUND OF THE INVENTION 
     Small, single or multi-cylinder gasoline engines can be mounted to power equipment to drive the equipment with a power take-off shaft. 
     SUMMARY OF THE INVENTION 
     The present invention provides, in one aspect, a stand-alone motor unit for use with a piece of power equipment. The motor unit comprises a housing, a flange coupled to the housing on a first side thereof and a slot in the flange. The slot is configured to receive a protrusion of the piece of power equipment. The motor unit further comprises an electric motor located within the housing and a power take-off shaft receiving torque from the motor and protruding from a second side of the housing adjacent the first side. The motor unit further comprises a battery pack to provide power to the motor. 
     The present invention provides, in another aspect, a power equipment assembly comprising a stand-alone motor unit including a housing, a flange coupled to the housing on a first side thereof, a slot in the flange, an electric motor located within the housing, a power take-off shaft receiving torque from the motor and protruding from a second side of the housing adjacent the first side, and a battery pack to provide power to the motor. The power equipment assembly further comprises a power equipment unit configured to receive torque form the power take-off shaft when the stand-alone motor unit is coupled to the power equipment unit. The power equipment unit including a protrusion configured be received in the slot when the stand-alone motor unit is coupled to the power equipment unit. 
     The present invention provides, in yet another aspect, a method of assembling a stand-alone motor unit and a piece of power equipment. The method comprises moving the motor unit in a first direction onto the piece of power equipment, such that a protrusion of the piece of power equipment is received in a slot of the motor unit. The method further comprises moving the motor unit along the piece of power equipment in a second direction that is perpendicular to the first direction, such that the protrusion moves within the slot from a first position to a second position, in which the protrusion is inhibited from moving in a direction opposite the first direction. The method further comprises coupling a power take-off shaft of the motor unit to a rotational input of the piece of power equipment, such that torque from the motor unit can be transferred to the rotational input to operate the piece of power equipment. 
     The present invention provides, in yet another aspect, a power equipment assembly comprising a stand-alone motor unit including a housing, an electric motor arranged in the housing, a battery pack to provide power to the motor, and a gear train receiving torque from the motor and including a drive gear having a passage with a first plurality splines and a plurality of detents biased toward the passage. The motor unit assembly also comprises a power equipment unit including a shaft that is removably receivable in the passage of the drive gear. The shaft includes a circumferential recess and a second plurality of splines configured to mate with the first plurality of splines when the shaft is received in the passage, such that the shaft is coupled for rotation with the drive gear and the power equipment unit can be driven by the stand-alone motor unit. When the shaft is received in the passage, the detents are biased into the circumferential recess of the power take-off shaft, inhibiting removal of the shaft from the passage of the drive gear. 
     The present invention provides, in yet another aspect, a stand-alone motor unit for use with a piece of power equipment having a first pulley and a belt. The motor unit comprises a housing, an electric motor located within the housing, a power take-off shaft receiving torque from the motor and protruding from the housing, and a second pulley arranged on the power take-off shaft and configured to receive the belt, such that the second pulley can drive the first pulley via the belt. The motor unit further comprises an idler pulley configured to increase tension within the belt between the first and second pulleys, and a battery pack to provide power to the motor. 
     The present invention provides, in yet another aspect, a stand-alone motor unit for use with a piece of power equipment having a first pulley and a belt. The motor unit comprises a housing, an electric motor arranged in the housing, a power take-off shaft receiving torque from the motor and protruding from a side of the housing, and a second pulley arranged on the power take-off shaft and configured to receive the belt, such that the second pulley can drive the first pulley via the belt. The stand-alone motor unit further comprises a battery pack to provide power to the electric motor, a tension arm coupled to the housing and biased toward the belt, and an idler pulley coupled to the tension arm, such that the idler pulley is engaged with the belt and configured to increase tension within the belt between the first and second pulleys. 
     The present invention provides, in yet another aspect, a stand-alone motor unit for use with a piece of power equipment having a first pulley and a belt. The motor unit comprises a housing, an electric motor arranged in the housing, a power take-off shaft receiving torque from the motor and protruding from a side of the housing, and a second pulley arranged on the power take-off shaft and configured to receive the belt, such that the second pulley can drive the first pulley via the belt. The motor unit further comprises a battery pack to provide power to the electric motor, and a first plurality of holes in the side of the housing from which the power take-off shaft protrudes. The first plurality of holes defines a first hole pattern. The motor unit further comprises a tensioner assembly including a mounting plate including a second plurality of holes defining a second hole pattern that is identical to the first hole pattern, such that the mounting plate is configured to be coupled to the side of the housing from which the power take-off shaft protrudes. The mounting plate also includes a through-bore for passage of the power take-off shaft when the mounting plate is coupled to the side of the housing. The tensioner assembly further includes a tension arm pivotably coupled to the mounting plate. The tension arm is biased toward the belt. The tensioner assembly further includes an idler pulley coupled to the tension arm, such that the idler pulley is engaged with the belt and configured to increase tension within the belt between the first and second pulleys. 
     The present invention provides, in yet another aspect, a power equipment assembly comprising a stand-alone motor unit including a housing including a side with a threaded annular recess, an electric motor arranged in the housing, a power take-off shaft receiving torque from the motor and protruding from a through-bore in the housing that passes through the threaded annular recess, and a battery pack to provide power to the motor. The motor unit assembly further comprises a piece of power equipment that includes a first flange and a rotational input configured to receive the power take-off shaft, such that the power take-off shaft can drive the rotational input. The motor unit assembly further comprises a collar that is threadably coupled to the threaded annular recess. The collar includes a second flange that is engageable with the first flange of the piece of power equipment to axially fix the piece of power equipment to the motor unit. 
     Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a stand-alone motor unit in accordance with an embodiment of the invention. 
         FIG. 2  is a plan view of the stand-alone motor unit of  FIG. 1 . 
         FIG. 3  is a schematic view of the stand-alone motor unit of  FIG. 1 . 
         FIG. 4  is a perspective view of a battery pack of the stand-alone motor unit of  FIG. 1 . 
         FIG. 5  is a cross-sectional view of the battery pack of  FIG. 4 . 
         FIG. 6  is a cross-sectional view of a battery receptacle of the stand-alone motor unit of  FIG. 1 . 
         FIG. 7  is a cross-sectional view of a motor of the stand-alone motor unit of  FIG. 1 . 
         FIG. 8  is a schematic view of a motor of the stand-alone motor unit of  FIG. 1 . 
         FIG. 9  is a schematic view of a motor, a gear train, and a power take-off shaft of the stand-alone motor unit of  FIG. 1 . 
         FIG. 10  is a schematic view of a motor, a gear train, and a power take-off shaft of the stand-alone motor unit of  FIG. 1  in a first configuration. 
         FIG. 11  is a schematic view of a motor, a gear train, and a power take-off shaft of the stand-alone motor unit of  FIG. 1  in a second configuration. 
         FIG. 12  is a schematic view of a motor, a gear train, and a power take-off shaft of the stand-alone motor unit of  FIG. 1  in a third configuration. 
         FIG. 13  is a plan view of a stand-alone motor unit in accordance with another embodiment of the invention. 
         FIG. 14  is a plan view of the stand-alone motor unit of  FIG. 13 . 
         FIG. 15  is a schematic view of a first side of the stand-alone motor unit of  FIG. 1 . 
         FIG. 16  is a schematic view of a second side of the stand-alone motor unit of  FIG. 1 . 
         FIG. 17  is an enlarged plan view of a first slot of the stand-alone motor unit of  FIG. 1 . 
         FIG. 18  is an enlarged plan view of a second slot of the stand-alone motor unit of  FIG. 1 . 
         FIG. 19  is a schematic view of a motor, a gear train, and a power take-off shaft of the stand-alone motor unit of  FIG. 1  in a fourth configuration. 
         FIG. 20  is a block diagram of the stand-alone motor unit of  FIG. 1 . 
         FIG. 21  is a block diagram of a user equipment communicating with the motor unit of  FIG. 1 . 
         FIG. 22  is a flowchart of a method for no-load operation of the motor unit of  FIG. 1 . 
         FIG. 23  is a graphical illustration of power savings offered by the motor unit of  FIG. 1  implementing the method of  FIG. 22 . 
         FIG. 24  is a flowchart of a method for providing simulated bog-down operation of the motor unit of  FIG. 1  that is similar to actual bog-down experienced by gas engines. 
         FIG. 25  is a schematic diagram of the motor unit of  FIG. 1  that shows how an electronic processor of the motor unit implements the methods of  FIG. 24 . 
         FIG. 26  is a schematic diagram of the motor unit of  FIG. 1  that shows how an electronic processor of the motor unit implements the method of  FIG. 24  with user customization. 
         FIG. 27  is a flowchart of a method for checking compatibility of the motor unit of  FIG. 1  for a user-selected application. 
         FIG. 28  is a perspective view of a pump system including a stand-alone motor unit of  FIG. 42 . 
         FIG. 29  is a perspective view of a jetter including the stand-alone motor unit of  FIG. 42 . 
         FIG. 30  is a perspective view of a compactor including the stand-alone motor unit of  FIG. 42 . 
         FIG. 31  is a schematic view of a vibration mechanism of the compactor of  FIG. 30 . 
         FIG. 32  is a perspective view of a rammer including the stand-alone motor unit of  FIG. 42 . 
         FIG. 33  is a schematic view of coupling arrangement for a gear train of the motor unit of  FIG. 42  and a female shaft subassembly. 
         FIG. 34  is a schematic view of coupling arrangement for a gear train of the motor unit of  FIG. 42  and a male shaft subassembly. 
         FIG. 35  is a perspective view of a half-circle shaft with female bore coupling arrangement for the coupling mechanism of  FIG. 33 or 34 . 
         FIG. 36  is a perspective view of a tongue and groove coupling arrangement for the coupling mechanism of  FIG. 33 or 34 . 
         FIG. 37  is a perspective view of a double D coupling arrangement for the coupling mechanism of  FIG. 33 or 34 . 
         FIG. 38  is a perspective view of a serrated coupling arrangement for the coupling mechanism of  FIG. 33 or 34 . 
         FIG. 39  is a perspective view of a peg coupling arrangement for the coupling mechanism of  FIG. 33 or 34 . 
         FIG. 40  is a perspective view of a female collar with radial fasteners coupling arrangement for the coupling mechanism of  FIG. 33 or 34 . 
         FIG. 41  is a cross-sectional view of a coupling arrangement for a gear train of the motor unit of  FIG. 1  and a male shaft subassembly. 
         FIG. 42  is a perspective view of a motor unit according to another embodiment of the invention. 
         FIG. 42 a    is another perspective view of the motor unit of  FIG. 42   
         FIG. 43  is a cross-sectional view of a coupling arrangement for a gear train of the motor unit of  FIG. 1  and a shaft subassembly. 
         FIG. 44  is a cross-sectional view of a coupling arrangement for a gear train of the motor unit of  FIG. 1  and a shaft subassembly. 
         FIG. 45  is a schematic view of a mounting arrangement for a motor and a gearbox of the motor unit of  FIG. 42 . 
         FIG. 46  is a schematic view of a gearbox and geartrain of the motor unit of  FIG. 42 . 
         FIG. 47  is a perspective view of an arrangement of a motor and a geartrain of the motor unit of  FIG. 42 . 
         FIG. 48  is a perspective view of a motor unit according to another embodiment of the invention. 
         FIG. 49  is a schematic view of a coupling arrangement between a power take-off shaft of the motor unit of  FIG. 42  and a tool input shaft. 
         FIG. 50  is a schematic view of a gearbox of the motor unit of  FIG. 42 . 
         FIG. 51  is a perspective view of the battery of  FIG. 4  in a cover. 
         FIG. 52  is a perspective view of a battery for the motor unit of  FIG. 42 . 
         FIG. 53  is a plan view of a remote control for use with the motor unit of  FIG. 42 . 
         FIG. 54  is a perspective view of a stand-alone motor unit according to another embodiment of the invention, with a battery module in a first position. 
         FIG. 55  is a perspective view of the stand-alone motor unit of  FIG. 54 , with a battery module removed from a base. 
         FIG. 56  is a perspective view of the stand-alone motor unit of  FIG. 54 , with a battery module in a second position, for a horizontal mounting application. 
         FIG. 57  is a perspective view of the stand-alone motor unit of  FIG. 54 , with a battery module in a second position, for a vertical mounting application. 
         FIG. 58  is a plan view of the stand-alone motor unit of  FIG. 54 , with a battery module removed from a base. 
         FIG. 59  is a perspective view of another embodiment of a motor of the stand-alone motor unit of  FIG. 1 . 
         FIG. 60  is a plan view of the motor of  FIG. 59 . 
         FIG. 61  is a cross-sectional view of the motor of  FIG. 59 . 
         FIG. 62  is a plan view of the motor of  FIG. 59  coupled to a first gearbox. 
         FIG. 63  is a plan view of the motor of  FIG. 59  coupled to a second gearbox. 
         FIG. 64  is a plan view of the motor of  FIG. 59  coupled to a third gearbox. 
         FIG. 65  is a plan view of the motor of  FIG. 59  coupled to a piece of power equipment. 
         FIG. 66  is a plan view of the motor of  FIG. 59  coupled to a piece of power equipment. 
         FIG. 67  is a cross-sectional view of the stand-alone motor unit of  FIG. 42 . 
         FIG. 68  is a cross-sectional view of a stand-alone motor unit of  FIG. 54 . 
         FIG. 69  is a perspective view of the stand-alone motor unit of  FIG. 42  with an adapter plate configured to be coupled thereto. 
         FIG. 70  is a perspective view of the adapter plate of  FIG. 69 . 
         FIG. 71  is a perspective view of the stand-alone motor unit of  FIG. 42  with an another embodiment of an adapter plate coupled thereto. 
         FIG. 71 a    is a perspective view of the stand-alone motor unit of  FIG. 42  with a a pair of power-take off shafts configured to be coupled removably thereto. 
         FIG. 72  is a cross-sectional view of a power take-off shaft coupled to a drive gear of the stand-alone motor unit of  FIG. 42 . 
         FIG. 73  is a cross-sectional view of a power take-off shaft coupled to another embodiment of a drive gear of the stand-alone motor unit of  FIG. 42 . 
         FIG. 74  is a cross-sectional view of a power take-off shaft coupled to another embodiment of a drive gear of the stand-alone motor unit of  FIG. 42 . 
         FIG. 75  is a cross-sectional view of a power take-off shaft coupled to another embodiment of a drive gear of the stand-alone motor unit of  FIG. 42 . 
         FIG. 76  is a cross-sectional view of a power take-off shaft coupled to another embodiment of a drive gear of the stand-alone motor unit of  FIG. 42 . 
         FIG. 77  is a perspective view of an adapter plate configured to be coupled to the stand-alone motor unit of  FIG. 42 . 
         FIG. 78  is a perspective view a stand-alone motor unit according to another embodiment of the invention, with an external gearbox configured to be coupled thereto. 
         FIG. 79  is a schematic view of a stand-alone motor unit according to another embodiment of the invention, with a legacy gearbox configured to be coupled thereto. 
         FIG. 80  is a perspective view of the stand-alone motor unit of  FIG. 79 , with the legacy gearbox configured to be coupled thereto. 
         FIG. 81  is a schematic view of a stand-alone motor unit according to another embodiment of the invention, with an gearbox configured to be coupled thereto. 
         FIG. 82  is a perspective view of the stand-alone motor unit of  FIG. 81 , with the external gearbox configured to be coupled thereto. 
         FIG. 83  is a perspective view of a pulley unit with a shaft configured to be received in the stand-alone motor unit of  FIG. 42 . 
         FIG. 84  is a perspective view of an impeller unit with a shaft configured to be received in the stand-alone motor unit of  FIG. 42 . 
         FIG. 85  is a perspective view of a pump unit with a shaft configured to be received in the stand-alone motor unit of  FIG. 42 . 
         FIG. 86  is a perspective view of a stand-alone motor unit according to another embodiment of the invention. 
         FIG. 87  is a plan view of a slot in a flange of the stand-alone motor unit of  FIG. 86 . 
         FIG. 88  is a plan view of the stand-alone motor unit of  FIG. 86  above a piece of power equipment. 
         FIG. 89  is a plan view of the stand-alone motor unit of  FIG. 86  received onto a piece of power equipment, with a protrusion of the piece of power equipment received in a first portion of a slot on a flange of the stand-alone motor unit. 
         FIG. 90  is a cross-sectional view of the protrusion of  FIG. 89  in the first portion of the slot. 
         FIG. 91  is a plan view of the stand-alone motor unit of  FIG. 86  received onto a piece of power equipment, with a protrusion of the piece of power equipment received in a second portion of a slot on a flange of the stand-alone motor unit. 
         FIG. 92  is a cross-sectional view of the protrusion of  FIG. 91  in the second portion of the slot. 
         FIG. 93  is a perspective view of a tensioner assembly coupled to the stand-alone motor unit of  FIG. 42 . 
         FIG. 94  is a cross-sectional view of a collar configured to couple the stand-alone motor unit of  FIG. 42  to a piece of power equipment. 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1, 2, 14 and 15 , a stand-alone motor unit  10  for use with a piece of power equipment includes a housing  14  with a first side  18 , a second side  22  adjacent the first side  18 , a third side  26  opposite the second side  22 , a fourth side  28  opposite the first side  18 , a fifth side  30  extending between the second and third sides  22 ,  26 , and a sixth side  32  opposite the fifth side  30 . The motor unit  10  also includes a flange  34  coupled to the housing  14  on the first side  18 , an electric motor  36  located within the housing  14 , and a power take-off shaft  38  that protrudes from the second side  22  and receives torque from the motor  36 . As explained in further detail below, in some embodiments, the power take-off shaft  38  protrudes from the first side  18  and from the flange  34 . As shown in  FIGS. 3 and 16 , the motor unit  10  also includes control electronics  42  positioned within the housing  14  and including wiring and a controller  46  that is electrically connected to the motor  36 . In some embodiments, the control electronics  42  has a volume of up to about 820 mm 3 . In some embodiments, the control electronics  42  has a weight of up to about 830 g.  FIGS. 42 and 42   a  illustrate another embodiment of the motor unit  10 , described in greater detail below. 
     As shown in  FIGS. 1-6 , the motor unit  10  also includes a battery pack  50  that is removably received in a battery receptacle  54  in the housing  14  to transfer current from the battery pack  50  to the motor  36  via the control electronics  42 . With reference to  FIGS. 4-6 , the battery pack  50  includes a battery pack housing  58  with a support portion  62  and a first terminal  66  that is electrically connected to a plurality of battery cells  68  supported by the pack housing  58 . The support portion  62  provides a slide-on arrangement with a projection/recess portion  70  cooperating with a complementary projection/recess portion  74  (shown in  FIG. 6 ) of the battery receptacle  54 . In the embodiment illustrated in  FIGS. 4-6 , the projection/recess portion  70  of the battery pack  50  is a guide rail and the projection/recess portion  74  of the battery receptacle  54  is a guide recess. A similar battery pack is described and illustrated in U.S. patent application Ser. No. 16/025,491 filed Jul. 2, 2018, the entire content of which is incorporated herein by reference. In some embodiments, the battery cells  68  have a nominal voltage of up to about 80 V. In some embodiments, the battery cells  68  have a nominal voltage of up to about 120 V. In some embodiments, the battery pack  50  has a weight of up to about 6 lb. In some embodiments, each of the battery cells  68  has a diameter of up to 21 mm and a length of up to about 71 mm. In some embodiments, the battery pack  50  includes up to twenty battery cells  68 . In some embodiments, the battery cells  68  are connected in series. In some embodiments, the battery cells  68  are operable to output a sustained operating discharge current of between about 40 A and about 60 A. In some embodiments, each of the battery cells  68  has a capacity of between about 3.0 Ah and about 5.0 Ah. 
       FIG. 6  illustrates the battery receptacle  54  of the motor unit  10  in accordance with some embodiments. The battery receptacle  54  includes the projection/recess  74 , a second terminal  78 , a latching mechanism  82 , and a power disconnect switch  86 . The projection/recess  74  cooperates with the projection/recess  70  of the battery pack  50  to attach the battery pack  50  to the battery receptacle  54  of the motor unit  10 . When the battery pack  50  is attached to the motor unit  10 , the second terminal  78  and the first terminal  66  are electrically connected to each other. The latching mechanism  82  protrudes from a surface of the battery receptacle  54  and is configured to engage the battery pack  50  to maintain engagement between the battery pack  50  and the battery receptacle  54 . Thus, the battery pack  50  is connectable to and supportable by the battery receptacle  54  such that the battery pack  50  is supportable by the housing  14  of the stand-alone motor unit  10 . In some embodiments, the battery pack receptacle  54  is arranged on the housing  14  in a position to create a maximum possible distance of separation between the motor  36  and the battery pack  50 , in order to inhibit vibration transferred from the motor  36  to the battery pack  50 . In some embodiments, elastomeric members are positioned on the battery pack receptacle  54  in order to inhibit vibration transferred from the motor  36 , via the housing  14 , to the battery pack  50 . 
     In other embodiments (not shown), the latching mechanism  82  may be disposed at various locations (e.g., on a sidewall, an end wall, an upper end wall etc., of the battery receptacle  54 ) such that the latching mechanism  82  engages corresponding structure on the battery pack  50  to maintain engagement between the battery pack  50  and the battery receptacle  54 . The latching mechanism  82  includes a pivotable actuator or handle  90  operatively engaging a latch member  94 . The latch member  94  is slidably disposed in a bore  98  of the receptacle  54  and is biased toward a latching position by a biasing member  102  (e.g., a spring) to protrude through a surface of the battery receptacle  54  and into a cavity in the battery pack  50 . 
     The latching mechanism also  82  includes the power disconnect switch  86  (e.g., a micro-switch) facilitating electrical connecting/disconnecting the battery pack  50  from the battery receptacle  54  during actuation of the handle  90  to withdraw the latch member  94  from the battery pack  50 . The power disconnect switch  86  may act to electrically disconnect the battery pack  50  from the motor unit  10  prior to removal of the battery pack  50  from the battery receptacle  54 . The power disconnect switch  86  is actuated when the latch member  94  is moved from the latched position (i.e., when the latch member  94  is completely within the cavity of the battery pack  50 ) to an intermediate position. The power disconnect switch  86  is electrically connected to the controller  46  and may generate an interrupt to indicate that the battery pack  50  is being disconnected from the motor unit  10 . When the controller  46  receives the interrupt, the controller  46  begins a power down operation to safely power down the control electronics  42  of the motor unit  10 . A similar latching mechanism and disconnect switch is described and illustrated in U.S. patent application Ser. No. 16/025,491, which has been incorporated herein by reference. 
     As shown in  FIG. 7 , the motor  36  includes a motor housing  96  having an outer diameter  97 , a stator  98  having a nominal outer diameter  102  of up to about 80 mm, a rotor  102  having an output shaft  106  and supported for rotation within the stator  98 , and a fan  108 . A similar motor is described and illustrated in U.S. patent application Ser. No. 16/025,491, which has been incorporated herein by reference. In some embodiments, the motor  36  is a brushless direct current motor. In some embodiments, the motor  36  has a power output of at least about 2760 W. In some embodiments, the power output of the motor  36  may drop below 2760 W during operation. In some embodiments, the fan  108  has a diameter  109  that is larger than the diameter  97  of the motor housing  96 . In some embodiments, the motor  36  can be stopped with an electronic clutch (not shown) for quick overload control. In some embodiments, the motor  36  has a volume of up to about 443,619 mm 3 . In some embodiments, the motor has a weight of up to about 4.6 lb. The housing  14  includes an inlet vent and an outlet vent, such that the motor fan  108  pulls air through the inlet vent and along the control electronics  42  to cool the control electronics  42 , before the air is exhausted through the outlet vent. In the embodiment illustrated in  FIG. 7 , the motor is a 36 is an internal rotor motor, but in other embodiments, the motor  36  can be an outer rotor motor with a nominal outer diameter (i.e. the nominal outer diameter of the rotor) of up to about 80 mm. 
     With reference to  FIGS. 8-12 , the motor  36  can transfer torque to the power take-off shaft  38  in a variety of configurations. In the embodiment shown in  FIG. 8 , the output shaft  106  is also the power take-off shaft  38 , such that the motor  36  directly drives the power take-off shaft  38  without any intermediate gear train. For example, the motor  36  may be a direct drive high pole count motor. As shown in  FIG. 9 , in other embodiments, the motor unit  10  includes a gear train  110  that transfers torque from the motor  36  to the power take-off shaft  38 . In some embodiments, the gear train  110  can include a mechanical clutch (not shown) to discontinue the transfer of torque from the motor  36  to the power take-off shaft  38 . In the embodiment shown in  FIG. 10 , the gear train  110  includes a planetary transmission  114  that transfers torque from the output shaft  106  to the power take-off shaft  38 , and a rotational axis  118  of the output shaft  106  is coaxial with a rotational axis  122  of the power take-off shaft  38 . In the embodiment shown in  FIG. 11 , the gear train  110  includes a spur gear  126  engaged with the output shaft  106  of the rotor, such that the rotational axis  118  of the output shaft  106  is offset from and parallel to the rotational axis  122  of the power take-off shaft  38 . In the embodiment shown in  FIG. 12 , the gear train  110  includes a bevel gear  130 , such that the rotational axis  118  of the output shaft  106  is perpendicular to the rotational axis  122  of the power take-off shaft  38 . Thus, in the embodiment of  FIG. 12 , the rotational axis  118  of the output shaft  106  intersects the second side  22  of the housing  14  and the power take-off shaft  38  protrudes from the flange  34 . In other embodiments utilizing a bevel gear, the rotational axis  118  of the output shaft  106  is not perpendicular, parallel, or coaxial to the rotational axis  122  of the power take-off shaft  38 , and the power-take off shaft  38  protrudes from the flange  34 . 
     In the embodiment illustrated in  FIG. 19 , the gear train  110  includes a first gear  111  and a second gear  112  making up a first gear set  113  with a first reduction stage  115 , and a third gear  116  and a fourth gear  117  making up second gear set  119  with a second reduction stage  120 . The first gear  111  has a rotational center C 1  and is coupled for rotation with the output shaft  106  of the motor  36 . The second and third gears  112 ,  116  have respective rotational centers C 2 , C 3  and are coupled for rotation with a second shaft  121  that is parallel to the output shaft  106  and the power take-off shaft  38 . The power take-off shaft  38  is coupled for rotation with the fourth gear  117 , which has a rotational center C 4 . A first center distance CD 1  is defined between the rotational centers C 1  and C 2  of the first and second gears  111 ,  112 . A second center distance CD 2  is defined between the rotational centers C 3  and C 4  of the third and fourth gears  116 ,  117 . In the illustrated embodiment, the first center distance CD 1  is equal to the second center distance CD 2 . However, in other embodiments, the first center distance CD 1  may be different than the second center distance CD 2 . 
     With continued reference to the embodiment illustrated in  FIG. 19 , the housing  14  includes a removable faceplate  124  that allows the operator to remove the faceplate  124  to access the first, second, third, and fourth gears  111 ,  112 ,  115 ,  116  and to slide them off the output shaft  106 , the second shaft  120  and the power take-off shaft  38 . Thus, the operator may replace the first gear set  113  with a different gear set with two gears having the same first center distance CD 1  between their rotational centers to change the reduction ratio of the first reduction stage  115 . Similarly, the operator may replace the second gear set  119  with a different gear set with two gears having the same second center distance CD 2  between their rotational centers to change the reduction ratio of the second reduction stage  120 . Thus, the motor unit  10  can implement a variety of reduction ratios to work with a broad range of power equipment, and the removable faceplate  124  makes it easy for an operator to quickly change these reduction ratios. Also the faceplate  124  makes it easy for an operator to change out the power take-off shaft  38  to replace it with a custom power take-off shaft for any given application. Also, the faceplate  124  is easily replaced with a different faceplate to fit a unique or custom mounting configuration. 
     In the embodiment shown in  FIGS. 13 and 14 , the power-take off shaft  38  is a first power take-off shaft and the motor unit  10  includes a second power take-off shaft  134  that also extends along the rotational axis  122  of the first power take off shaft  38 . The motor  36  drives the first and second power take-off shafts  38 ,  134  simultaneously, such that the motor unit  10  can be used with, for example, tillers, saws, and snow blowers. 
       FIGS. 15 and 16  illustrate embodiments of the motor unit  10  in which the power take-off shaft  38  protrudes through the second side  22  of the housing  14 . As shown in  FIG. 15 , a plane  138  is defined on the first side  18  of the housing  14  on which the flange  34  is coupled. The plane  138  contains orthogonal X and Y axes that intersect at an origin O. As shown in  FIG. 16 , the power take-off shaft  38  extends parallel to the Y-axis and as shown in  FIG. 15 , the power take-off shaft  38  has an end  140 . The X-axis extends parallel to the second and third sides  22 ,  26  and the Y-axis extends parallel to the fifth and sixth sides  30 ,  32 . 
     With continued reference to  FIG. 15 , the flange  34  includes a plurality of apertures therethrough, including a first hole  142  having a center  144 , a second hole  146  having a center  148 , a first slot  150 , and a second slot  154 . The plurality of apertures collectively define a first bolt pattern that matches an “identical”, second bolt pattern defined in a piece of power equipment to which the motor unit  10  can be mounted. “Identical” does not mean that each of the plurality of apertures defining the first bolt pattern identically aligns with each of the plurality of apertures defining the second bolt pattern. In other words, not all of the first hole  142 , second hole  146 , first slot  150 , and second slot  154  need align with a corresponding aperture in the second bolt pattern. Rather, at least two of the first hole  142 , second hole  146 , first slot  150 , and second slot  154  will at least partially align with two corresponding apertures in the second bolt pattern, such that at least two fasteners, such as bolts, may be respectively inserted through at least two of the at least partially-aligned respective apertures of the first and second bolt patterns in order to couple the motor unit  10  to the piece of power equipment. Thus, for the first bolt pattern to match an “identical” second bolt pattern, at least two apertures in the first bolt pattern are configured to at least partially align with two apertures of the second bolt pattern. In the disclosed embodiment, the plurality of apertures defining the first bolt pattern includes four apertures (first hole  142 , second hole  146 , first slot  150 , and second slot  154 ) but in other embodiments, the plurality of apertures defining the first bolt pattern could include more or fewer apertures. 
     In some embodiments, the flange  34  may include one or more intermediate mounting members or adapters arranged between the flange  34  itself and the flange of the piece of power equipment having the second bolt pattern, such that the adapter(s) couple the flange  34  to the piece of power equipment. In these embodiments, the adapter includes both the second bolt pattern and the first bolt pattern, such that the first bolt pattern of the flange  34  aligns with the first bolt pattern of the adapter and the second bolt pattern of the adapter aligns with the second bolt pattern defined in the piece of power equipment, thereby allowing the flange  34  of the motor unit  10  to be coupled to the piece of power equipment. 
     As shown in  FIG. 17 , the first slot  150  includes a first semi-circular portion  158  having a radius R 1 , a second semi-circular portion  162  having a radius R 2 , and a straight portion  166  that connects the first and second semi-circular portions  158 ,  162 . The first semi-circular portion  158  has a center  170  from which radius R 1  is defined and the second semi-circular portion  162  has a center  174  from which radius R 2  is defined. The centers  170 ,  174  can define points where a bolt is inserted through the first slot  150  when the first slot  150  is aligned with a corresponding aperture in the second bolt pattern in the piece of power equipment, but the bolt may also be inserted anywhere along the straight portion  166 . 
     As also shown in  FIG. 18 , the second slot  154  includes a first semi-circular portion  178  having a radius R 3 , a second semi-circular portion  182  having a radius R 4 , and a straight portion  186  that connects the first and second semi-circular portions  178 ,  182 . The first semi-circular portion  178  has a center  190  from which radius R 3  is defined and the second semi-circular portion  182  has a center  194  from which radius R 4  is defined. The centers  170 ,  174  can define points where a bolt is inserted through the second slot  154  when the second slot  154  is aligned with a corresponding aperture in the second bolt pattern in the piece of power equipment, but the bolt may also be inserted anywhere along the straight portion  186 . In the embodiment illustrated in  FIGS. 15 and 17 , R 1 , R 2 , R 3 , and R 4  are all equal, but in other embodiments, one or more of the radii R 1 , R 2 , R 3 , R 4  may be different from one another. 
     With reference again to  FIG. 15 , Table 1 below lists the distances of various components and reference points with respect to the X-axis and the Y-axis. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Distance 
                 Distance 
               
               
                   
                 from X-axis 
                 from Y-axis 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Center 144 of first hole 142 
                 E 
                 G 
               
               
                 Center 148 of second hole 146 
                 E 
                 H 
               
               
                 Center 170 of first semi-circular portion 
                 C 
                 G 
               
               
                 158 of first slot 150 
               
               
                 Center 174 of second semi-circular 
                 D 
                 G 
               
               
                 portion 162 of first slot 150 
               
               
                 Center 190 of first semi-circular portion 
                 C 
                 H 
               
               
                 178 of second slot 154 
               
               
                 Center 194 of second semi-circular 
                 D 
                 H 
               
               
                 portion 182 of second slot 154 
               
               
                 Second side 22 of housing 14 
                 A 
                 Perpendicular 
               
               
                   
                   
                 to Y-axis 
               
               
                 Third side 26 of housing 14 
                 B 
                 Perpendicular 
               
               
                   
                   
                 to Y-axis 
               
               
                 End 140 of power take-off shaft 38 
                 F 
                 Perpendicular 
               
               
                   
                   
                 to Y-axis 
               
               
                 Fifth side 30 of housing 14 
                 Perpendicular 
                 I 
               
               
                   
                 to X-axis 
               
               
                 Sixth side 32 of housing 14 
                 Perpendicular 
                 J 
               
               
                   
                 to X-axis 
               
               
                   
               
            
           
         
       
     
     Table 2 below lists five different embodiments of the stand-alone motor unit  10  of  FIG. 1 , which is also schematically illustrated in  FIGS. 15 and 16 , in which the values of the distances from Table 1, in millimeters, are provided: 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
                 I 
                 J 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Embodiment 1 
                 75.2-75.5 
                 168.6 
                 34.5 
                 39.5 
                 40.5 
                 115.4 
                 66 
                 96 
                 115 
                 231 
               
               
                 Embodiment 2 
                 75.2-75.5 
                 175.6 
                 34.5 
                 39.5 
                 40.5 
                 139.9 
                 66 
                 96 
                 123 
                 239 
               
               
                 Embodiment 3 
                 75.2-75.5 
                 184.6 
                 34.5 
                 39.5 
                 40.5 
                 136.9 
                 66 
                 96 
                 123 
                 253 
               
               
                 Embodiment 4 
                 75.2-75.5 
                 203.1 
                 34.5 
                 39.5 
                 40.5 
                 128.4 
                 66 
                 96 
                 135.3 
                 278.3 
               
               
                 Embodiment 5 
                 75.2-75.5 
                 221.5 
                 34.5 
                 39.5 
                 40.5 
                 128.4 
                 66 
                 96 
                 147.6 
                 303.6 
               
               
                   
               
            
           
         
       
     
     In some embodiments, dimension F, the length to the end  140  of the power take-off shaft  38 , can be modified or customized besides the dimensions listed in Table 2. 
     As shown in  FIG. 16 , a Z-axis intersects the origin O of plane  138  and the first and fourth sides  18 ,  28  of the housing  14 . The Z-axis is arranged perpendicular to the X-axis and Y-axis of the plane  138 . The Z-axis is also arranged perpendicular to the first and fourth  18 ,  28  sides of the housing  14 . The Z-axis is also arranged parallel to the fifth and sixth sides  30 ,  32  of the housing  14 . As also shown in  FIG. 16 , a radius R 5  extending from the rotational axis  122  of the power take-off shaft  38  defines a circle  198 . The rotational axis  118  of the output shaft  106  of the rotor  102  is intersected by the circle  198 , such that a distance R 5  is defined between the rotational axis  118  of the output shaft  106  and the rotational axis  122  of the power take-off shaft  38 . Table 3 below identifies the distances of various components and reference points with respect to the X-axis and Z-axis. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Distance 
                 Distance 
               
               
                   
                 from X-axis 
                 from Z-axis 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Rotational axis 118 of output shaft 106 
                 L 
                 K 
               
               
                 Rotational axis 122 of power 
                 M 
                 Intersected 
               
               
                 take-off shaft 38 
                   
                 by Z-axis 
               
               
                 Fourth side 28 of housing 14 
                 N 
                 Perpendicular 
               
               
                   
                   
                 to Z-axis 
               
               
                 Fifth side 30 of housing 14 
                 Perpendicular 
                 I 
               
               
                   
                 to X-axis 
               
               
                 Sixth side 32 of housing 14 
                 Perpendicular 
                 J 
               
               
                   
                 to X-axis 
               
               
                   
               
            
           
         
       
     
     Table 4 below lists the five different embodiments from Table 2 and provides the values of the distances from Table 3, as well as R 5 , in millimeters, for each embodiment: 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 K 
                 L 
                 M 
                 N 
                 I 
                 J 
                 R5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Embodiment 1 
                 46.9 
                 95.3 
                 106 
                 329 
                 115 
                 231 
                 48.1 
               
               
                 Embodiment 2 
                 46.9 
                 95.3 
                 106 
                 346 
                 123 
                 239 
                 48.1 
               
               
                 Embodiment 3 
                 46.9 
                 95.3 
                 106 
                 346 
                 123 
                 253 
                 48.1 
               
               
                 Embodiment 4 
                 46.9 
                 95.3 
                 106 
                 380.6 
                 135.3 
                 278.3 
                 48.1 
               
               
                 Embodiment 5 
                 46.9 
                 95.3 
                 106 
                 415.2 
                 147.6 
                 303.6 
                 48.1 
               
               
                   
               
            
           
         
       
     
     With continued reference to the embodiment illustrated in  FIG. 16 , the control electronics  42  are vertically oriented relative to flange  34  and positioned between the Z-axis and the fifth side  30  of the housing  14 , while being closer to the fifth side  30  of the housing  14 . As also shown in the embodiment illustrated in  FIG. 16 , the battery pack  50  is horizontally oriented relative to flange  34  and positioned between the rotational axis  122  of the power take-off shaft  38  and the fourth side  28  of the housing  14 , while being closer to the fourth side  28  of the housing  14 . However, in other embodiments, the battery pack  50  may be closer to the rotational axis  122  of the power take-off shaft  38 . Thus, in all five embodiments, even when the design envelope of the housing  14  of the motor unit  10  is changed, each of the battery  50 , the battery receptacle  54 , the control electronics  42 , and the motor  36  fit within the housing  14 . In some embodiments, the total weight of the motor unit  10  including each of the battery  50 , the battery receptacle  54 , the control electronics  42 , and the motor  36 , is 37.05 lbs. In contrast, when fully loaded with fluids, some 120 cc gas engine units can weigh up to 33.50 lbs, some 160 cc gas engine units can weigh up to 40.10 lbs, and some 200 cc gas engine units can weigh up to 41.30 lbs. 
     In some embodiments, the motor unit  10  includes a “kill switch” (not shown) that can be used when the motor unit  10  is coupled to, e.g., a riding lawnmower with a seat. Thus, when an operator intentionally or inadvertently gets off the seat, the kill switch discontinues power to the motor  36  and/or control electronics  42 . In some embodiments, the kill switch stops the motor  36  and/or power take-off shaft  38 , but maintains power to the power electronics  42  so that the motor unit  10  may be kept in an armed or ready state. In some embodiments, the motor unit  10  requires two or more actions required to turn on the motor  36  because unlike a gas engine, it may be difficult to determine whether the electric motor  36  is on or not. Specifically, the electric motor  36  is much quieter than a gas engine. Thus, simply hitting an “on” switch may not be enough to indicate to the operator that the motor  36  has been turned on, because of its relative silence. Thus, by forcing the operator to make two actions, such as holding an “on” switch and then depressing a second actuator, the operator is made to feel more certain that the motor  36  has been turned on. 
     In some embodiments, a control interface to control the power equipment and/or the motor unit  10  is built into the motor unit  10 . In some embodiments, the motor unit  10  includes a communication port and a wiring harness electrically connects the motor unit  10  to the piece of power equipment, thus allowing the operator to control the motor unit  10  from the piece of power equipment  10 , or vice versa. For example, if the motor unit  10  is mounted to a lawn mower, the operator may arrange the wiring harness between the lawn mower and the communication port on the motor unit  10 . The wiring harness could electrically connect a kill switch on a handlebar of the lawnmower, for example, to the motor  36  of the motor unit  10 . Thus, if the kill switch is intentionally or inadvertently released during operation of the lawn mower, the motor  36  of the motor unit  10  stops via the electrical communication through the wiring harness and communication port on the motor unit  10 . Thus, the control interface and communication port allow the operator flexibility in controlling the motor unit  10  and/or the piece of power equipment. 
     In some embodiments, the motor unit  10  includes ON/OFF indicators (not shown). In some embodiments, the motor unit  10  includes a filter (not shown) to keep airborne debris out of the motor  36  and control electronics  42 . In some embodiments, the filter includes a dirty filter sensor (not shown) and a self-cleaning mechanism (not shown). In some embodiments, the motor  36  will mimic a gas engine response when encountering resistance, such as slowing down or bogging. In some embodiments, the motor unit  10  includes a heat sink  202  in the housing  14  for air-cooling the control electronics  42  ( FIGS. 1 and 2 ). In some embodiments, the motor unit  10  is liquid cooled. 
     In some embodiments, the output shaft  106  of the rotor  102  has both forward and reverse capability. In some embodiments, the forward and reverse capability is controllable without shifting gears of the gear train  110 , in comparison to gas engines, which cannot achieve forward/reverse capability without extra gearing and time delay. Thus, the motor unit  10  provides increased speed, lower weight, and lower cost. Because the motor unit  10  has fewer moving parts and no combustion system, as compared with a gas engine, it also provides additional speed, weight, and cost advantages. 
     In some embodiments, the motor unit  10  is able to start under a “heavy” load. For example, when the motor unit  10  is mounted to a riding lawnmower and the lawnmower is started over a patch of thick grass, the motor unit  10  is able to start the motor  36  in the thick grass. Thus, unlike gas engines, the motor unit  10  does not require a centripetal clutch. Rather, the motor  36  would always be engaged. Additionally, the motor unit  10  does not need a centrifugal clutch, in comparison to gas engines, which need a centrifugal clutch to idle and disengage from the load, or risk stalling. 
     The motor unit  10  is able to operate in any orientation (vertical, horizontal, upside down) with respect to a ground surface for a prolonged period of time, giving it an advantage over four-cycle gas engines, which can only be operated in one orientation and at slight inclines for a shorter period of time. Because the motor unit  10  does not require gas, oil, or other fluids, it can run, be transported, and be stored upside down or on any given side without leaking or flooding 
     In operation, the motor unit  10  can be used to replace a gas engine system. Specifically, the motor unit  10  can be mounted to the piece of power equipment having the second bolt pattern by aligning the first bolt pattern defined by the plurality of apertures in the flange  34  with the second bolt pattern. Thus, the power take-off shaft  38  of the motor unit  10  can be used to drive the equipment. 
     During operation, the housing  14  of the motor unit  10  is comparably much cooler than the housing of an internal combustion unit because there is no combustion in the motor unit  10 . Specifically, when a gas engine unit runs, the housing of the gas engine unit is 220 degrees Celsius or higher. In contrast, when the motor unit  10  runs, all of the exterior surfaces of the housing  14  are less than 95 degrees Celsius. Tables 5 and 6 below list with further specificity the temperature limits of different components on the housing  14  of the motor unit  10 . 
     Table 5 below lists the Underwriter&#39;s Laboratories (UL) temperature limits of different components typically used in power tools, with respect to whether those components are formed of metal, plastic, rubber, wood, porcelain, or vitreous. The plastic rated temperatures are never exceeded. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                   
                 Plastic/ 
                 Porcelain/ 
               
               
                   
                 Metal 
                 Rubber/Wood 
                 Vitreous 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Casual Contact 
                 85° C. 
                 85° C. 
                 85° C. 
               
               
                 Handles and knobs that are 
                 55° C. 
                 75° C. 
                 65° C. 
               
               
                 continuously held 
               
               
                 Handles and knobs that are only 
                 60° C. 
                 80° C. 
                 70° C. 
               
               
                 briefly held (i.e. switches) 
               
               
                   
               
            
           
         
       
     
     Table 6 below lists the UL temperature limits of different components of the battery pack housing  58  of the battery pack  50 , with respect to whether those components are formed of metal, plastic or rubber. The plastic rated temperatures are never exceeded. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Metal 
                 Plastic/Rubber 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Casual Contact 
                 70° C. 
                 95° C. 
               
               
                 Handles and knobs that are continuously held 
                 55° C. 
                 75° C. 
               
               
                 Handles and knobs that are only briefly held 
                 60° C. 
                 85° C. 
               
               
                 (i.e. switches) 
               
               
                   
               
            
           
         
       
     
       FIG. 20  illustrates a simplified block diagram of the motor unit  10  according to one example embodiment. As shown in  FIG. 20 , the motor unit  10  includes an electronic processor  302 , a memory  306 , the battery pack  50 , a power switching network  310 , the motor  36 , a rotor position sensor  314 , a current sensor  318 , a user input device (e.g., a trigger or power button)  322 , a transceiver  326 , and indicators (e.g., light-emitting diodes)  330 . In some embodiments, the motor unit  10  includes fewer or additional components than those shown in  FIG. 20 . For example, the motor unit  10  may include a battery pack fuel gauge, work lights, additional sensors, kill switch, the power disconnect switch  86 , etc. In some embodiments, elements of the motor unit  10  illustrated in  FIG. 20  including one or more of the electronic processor  302 , memory  306 , power switching network  310 , rotor position sensor  314 , current sensor  318 , user input device (e.g., a trigger or power button)  322 , transceiver  326 , and indicators (e.g., light-emitting diodes)  330  form at least part of the control electronics  42  shown in  FIG. 3 , with the electronic processor  302  and the memory  306  forming at least part of the controller  46  shown in  FIG. 3 . 
     The memory  306  includes read only memory (ROM), random access memory (RAM), other non-transitory computer-readable media, or a combination thereof. The electronic processor  302  is configured to communicate with the memory  306  to store data and retrieve stored data. The electronic processor  302  is configured to receive instructions and data from the memory  306  and execute, among other things, the instructions. In particular, the electronic processor  302  executes instructions stored in the memory  306  to perform the methods described herein. 
     As described above, in some embodiments, the battery pack  50  is removably attached to the housing of the motor unit  10  such that a different battery pack  50  may be attached and removed to the motor unit  10  to provide different amount of power to the motor unit  10 . Further description of the battery pack  50  (e.g., nominal voltage, sustained operating discharge current, size, number of cells, operation, and the like), as well as the motor  36  (e.g., power output, size, operation, and the like), is provided above with respect to  FIGS. 1-19 . 
     The power switching network  310  enables the electronic processor  302  to control the operation of the motor  36 . Generally, when the user input device  322  is depressed (or otherwise actuated), electrical current is supplied from the battery pack  50  to the motor  36 , via the power switching network  310 . When the user input device  322  is not depressed (or otherwise actuated), electrical current is not supplied from the battery pack  50  to the motor  36 . In some embodiments, the amount in which the user input device  322  is depressed is related to or corresponds to a desired speed of rotation of the motor  36 . In other embodiments, the amount in which the user input device  322  is depressed is related to or corresponds to a desired torque. In other embodiments, a separate input device (e.g., slider, dial, or the like) is included on the motor unit  10  in communication with the electronic processor  302  to provide a desired speed of rotation or torque for the motor  36 . 
     In response to the electronic processor  302  receiving a drive request signal from the user input device  322 , the electronic processor  302  activates the power switching network  310  to provide power to the motor  36 . Through the power switching network  310 , the electronic processor  302  controls the amount of current available to the motor  36  and thereby controls the speed and torque output of the motor  36 . The power switching network  310  may include numerous field-effect transistors (FETs), bipolar transistors, or other types of electrical switches. For instance, the power switching network  310  may include a six-FET bridge that receives pulse-width modulated (PWM) signals from the electronic processor  302  to drive the motor  36 . 
     The rotor position sensor  314  and the current sensor  318  are coupled to the electronic processor  302  and communicate to the electronic processor  302  various control signals indicative of different parameters of the motor unit  10  or the motor  36 . In some embodiments, the rotor position sensor  314  includes a Hall sensor or a plurality of Hall sensors. In other embodiments, the rotor position sensor  314  includes a quadrature encoder attached to the motor  36 . The rotor position sensor  314  outputs motor feedback information to the electronic processor  302 , such as an indication (e.g., a pulse) when a magnet of a rotor of the motor  36  rotates across the face of a Hall sensor. In yet other embodiments, the rotor position sensor  314  includes, for example, a voltage or a current sensor that provides an indication of a back electro-motive force (back emf) generated in the motor coils. The electronic processor  302  may determine the rotor position, the rotor speed, and the rotor acceleration based on the back emf signals received from the rotor position sensor  314 , that is, the voltage or the current sensor. The rotor position sensor  314  can be combined with the current sensor  318  to form a combined current and rotor position sensor. In this example, the combined sensor provides a current flowing to the active phase coil(s) of the motor  36  and also provides a current in one or more of the inactive phase coil(s) of the motor  36 . The electronic processor  302  measures the current flowing to the motor based on the current flowing to the active phase coils and measures the motor speed based on the current in the inactive phase coils. 
     Based on the motor feedback information from the rotor position sensor  314 , the electronic processor  302  can determine the position, velocity, and acceleration of the rotor. In response to the motor feedback information and the signals from the user input device  322 , the electronic processor  302  transmits control signals to control the power switching network  310  to drive the motor  36 . For instance, by selectively enabling and disabling the FETs of the power switching network  310 , power received from the battery pack  50  is selectively applied to stator windings of the motor  36  in a cyclic manner to cause rotation of the rotor of the motor  36 . The motor feedback information is used by the electronic processor  302  to ensure proper timing of control signals to the power switching network  310  and, in some instances, to provide closed-loop feedback to control the speed of the motor  36  to be at a desired level. For example, to drive the motor  36 , using the motor positioning information from the rotor position sensor  314 , the electronic processor  302  determines where the rotor magnets are in relation to the stator windings and (a) energizes a next stator winding pair (or pairs) in the predetermined pattern to provide magnetic force to the rotor magnets in a direct of desired rotation, and (b) de-energizes the previously energized stator winding pair (or pairs) to prevent application of magnetic forces on the rotor magnets that are opposite the direction of rotation of the rotor. 
     The current sensor  318  monitors or detects a current level of the motor  36  during operation of the motor unit  10  and provides control signals to the electronic processor  302  that are indicative of the detected current level. The electronic processor  302  may use the detected current level to control the power switching network  310  as explained in greater detail below. 
     The transceiver  326  allows for communication between the electronic processor  302  and an external device (for example, the user equipment  338  of  FIG. 21 ) over a wired or wireless communication network  334 . In some embodiments, the transceiver  326  may comprise separate transmitting and receiving components. In some embodiments, the transceiver  326  may comprise a wireless adapter attached to the motor unit  10 . In some embodiments, the transceiver  326  is a wireless transceiver that encodes information received from the electronic processor  302  into a carrier wireless signal and transmits the encoded wireless signal to the user equipment  338  over the communication network  334 . The transceiver  326  also decodes information from a wireless signal received from the user equipment  338  over the communication network  334  and provides the decoded information to the electronic processor  302 . 
     The communication network  334  provides a wired or wireless connection between the motor unit  10  and the user equipment  338 . The communication network  334  may comprise a short range network, for example, a BLUETOOTH network, a Wi-Fi network or the like, or a long range network, for example, the Internet, a cellular network, or the like. 
     As shown in  FIG. 20 , the indicators  330  are also coupled to the electronic processor  302  and receive control signals from the electronic processor  302  to turn on and off or otherwise convey information based on different states of the motor unit  10 . The indicators  330  include, for example, one or more light-emitting diodes (“LEDs”), or a display screen. The indicators  330  can be configured to display conditions of, or information associated with, the motor unit  10 . For example, the indicators  330  are configured to indicate measured electrical characteristics of the motor unit  10 , the status of the motor unit  10 , the mode of the motor unit  10 , etc. The indicators  330  may also include elements to convey information to a user through audible or tactile outputs. In some embodiments, the indicators  330  include an eco-indicator that indicates an amount of power being used by the load during operation. 
     The connections shown between components of the motor unit  10  are simplified in  FIG. 20 . In practice, the wiring of the motor unit  10  is more complex, as the components of a motor unit are interconnected by several wires for power and control signals. For instance, each FET of the power switching network  310  is separately connected to the electronic processor  302  by a control line; each FET of the power switching network  310  is connected to a terminal of the motor  36 ; the power line from the battery pack  50  to the power switching network  310  includes a positive wire and a negative/ground wire; etc. Additionally, the power wires can have a large gauge/diameter to handle increased current. Further, although not shown, additional control signal and power lines are used to interconnect additional components of the motor unit  10 . 
       FIG. 21  illustrates a simplified block diagram of the user equipment  338  according to one example embodiment. The user equipment  338  is, for example, a smart telephone, a tablet computer, a laptop computer, a personal digital assistant, and the like, and may also be referred to as a personal electronic communication device. The user equipment  338  allows the user to customize settings of the motor unit  10  and receive operation information from the motor unit  10 . As shown in  FIG. 20 , the user equipment  338  includes an equipment electronic processor  342 , an equipment memory  346 , an equipment transceiver  350 , and an input/output interface  354 . The equipment electronic processor  342 , the equipment memory  346 , the equipment transceiver  350 , and the input/output interface  354  communicate over one or more control and/or data buses (e.g., a communication bus  358 ). The equipment electronic processor  342 , the equipment memory  346 , and the equipment transceiver  350  may be implemented similar to the electronic processor  302 , the memory  306 , and the transceiver  326  of the motor unit  10 . Particularly, the equipment electronic processor  342  executed a motor unit application stored on the equipment memory  346  to perform functionality described herein. The input/output interface  354  includes one or more input components (e.g., a keypad, a mouse, and the like), one or more output components (e.g., a speaker, a display, and the like), or both (e.g., a touch screen display). 
       FIG. 22  illustrates a flowchart of a method  362  for no-load operation of the motor unit  10 . In the example illustrated, the method  362  includes measuring, using the current sensor  318 , a motor current (at block  366 ). The electronic processor  302  detects the current flowing through the motor using the current sensor  318  as described above. The current sensor  318  may detect the current level at discrete time intervals, for example, every 2 milli-seconds, and provide the control signals indicating the current level at the discrete time intervals to the electronic processor  302 . The method  362  also includes measuring, using the rotor position sensor  314 , the motor speed (at block  370 ). The electronic processor  302  receives feedback from the rotor position sensor  314  when a magnet of the rotor rotates across the face of a Hall sensor. The electronic processor  302  determines the speed of the motor  36  based on the frequency of the pulses received from the rotor position sensor  314 . 
     The method  362  further includes determining, using the electronic processor  302 , a point on the motor power curve corresponding to the measured motor current and the measured motor speed (at block  374 ). In one example, the electronic processor  302  constructs a motor power graph having motor speed on the X-axis and motor current on the Y-axis. The point on the motor power curve is the point corresponding to the measured motor current and the measured motor speed on the motor power graph. 
     The method  362  also includes determining, using the electronic processor  302 , whether the motor unit  10  is operating in a no-load condition for a pre-determined period of time based on the point on the motor power curve (at block  378 ). The motor  36  may be operating at full power (or 100% duty cycle) or at a selected power or duty cycle corresponding to the position of the user input device  322 . The amount of current flowing to the motor  36  is proportional to the load on the motor  36 . That is, when there is a high load on the motor unit  10 , the motor  36  draws higher current from the battery pack  50  and when there is a lighter load on the motor unit  10 , the motor  36  draws lower current from the battery pack  50 . The electronic processor  302  determines the load on the motor unit  10  based on the point on the motor power curve. For example, for a measured speed, the electronic processor  302  determines whether the measured current is below a current threshold corresponding to the measured speed. When the measured current is below the current threshold, the electronic processor  302  determines that the motor unit  10  is operating in a no-load condition and, when the measured current is above the current threshold, the electronic processor  302  determines that the motor unit  10  is not operating in a no-load condition. The electronic processor  302  may then further determine whether the motor unit  10  is operating in the no-load condition for the pre-determined period of time. For example, the electronic processor  302  determines whether the measured current is below the current threshold corresponding to the measured speed for the pre-determined period of time. 
     The method  362  further includes, in response to determining that the motor unit  10  is operating in the no-load condition for a pre-determined period of time, reducing, using the electronic processor  302 , the motor speed of the motor  36  to a no-load speed (at block  382 ). As discussed above, the electronic processor  302  may provide control signals to the power switching network  310  to control the speed of the motor  36  by selecting a particular pulse width modulated (PWM) duty cycle for driving the power switching network  310 . The speed control may be open loop or closed loop. The electronic processor  302  may also shut-off (i.e., reduce the duty cycle to zero) the motor when the electronic processor  302  determines that the motor unit  10  is operating in the no-load condition for the pre-determined period of time. In one example, the electronic processor  302  reduces the speed of the motor  36  to a no-load speed by reducing a duty cycle of the pulse width modulated signals provided to the power switching network  310  to 5%, 10%, or 15%. The method  362  also includes, in response to determining that the motor unit  10  is not operating in the no-load condition for the pre-determined period of time, operating, using the electronic processor  302 , the motor  36  at a loaded speed that is greater than the no-load speed (at block  386 ). For example, to operate at the loaded speed, the electronic processor  302  controls the power switching network  310  to operate the motor  36  according to the power or speed corresponding to the position of the user input device  322  or at full power (i.e., 100% duty cycle) (for example, when the motor unit  10  does not include a variable speed trigger). After block  382  and  386 , respectively, the electronic processor  302  may loop back to execute block  366 , thus providing continued load-based operation control throughout an operation of the motor unit  10 . 
     Typical gasoline engines that drive power equipment are not controlled to reduce speed or power when the gasoline engine is operating in a no-load condition. Accordingly, gasoline engines continue to burn excess amounts of fuel and expend energy even when the gasoline engines are operating under no-load. The electronic processor  302  executing the method  362  detects when the motor unit  10  is operating under no-load and reduces the motor speed or power to provide additional energy savings and then returns to normal power when loaded to meet the demand of a task. In one example, as shown in  FIG. 23 , by reducing the duty cycle to 10% in the no-load condition, the motor unit  10  provides energy savings of about 5 times that of a gasoline engine operating at no-load. Energy saving resulting from other reduced duty cycle levels are also illustrated in  FIG. 23 . 
     During operation of gas engines, an excessive input force exerted on the gas engine or a large load encountered by the power equipment powered by the gas engine may cause a resistive force impeding further operation of the gas engine. For example, a gas engine encountering higher than usual loads may have its motor slowed or bogged-down because of the excessive load. This bog-down of the motor can be sensed (e.g., felt and heard) by a user, and is a helpful indication that an excessive input, which may potentially damage the gas engine or the power equipment, has been encountered. In contrast, high-powered electric motor driven units, similar to the motor unit  10 , for example, do not innately provide the bog-down feedback to the user. Rather, in these high-powered electric motor driven units, excessive loading of the motor unit  10  causes the motor to draw excess current from the power source or battery pack  50 . Drawing excess current from the battery pack  50  may cause quick and potentially detrimental depletion of the battery pack  50 . 
     Accordingly, in some embodiments, the motor unit  10  includes a simulated bog-down feature to provide an indication to the user that excessive loading of the motor unit  10  or power equipment is occurring during operation.  FIG. 24  illustrates a flowchart of a method  390  for providing simulated bog-down operation of the motor unit  10  that is similar to actual bog-down experienced by gas engines. 
     The method  390  includes controlling, using the electronic processor  302 , the power switching network  310  to provide power to the motor  36  in response to determining that the user input device  322  has been actuated (at block  394 ). For example, the electronic processor  302  provides a PWM signal to the FETs of the power switching network  310  to drive the motor  36  in accordance with the drive request signal from the user input device  322 . The method  390  further includes detecting, using the current sensor  318 , a current level of the motor  36  (at block  398 ). Block  398 , at least in some embodiments, may be performed using similar techniques as described above for block  366  with respect to  FIG. 22 . The method  390  also includes comparing, using the electronic processor  302 , the current level to a bog-down current threshold (at block  402 ). In response to determining that the current level is lower than the bog-down current threshold, the method  390  proceeds back to block  398  such that the electronic processor  302  repeats blocks  398  and  402  until the current level is greater than the bog-down current threshold. 
     In response to determining that the current level is greater than the bog-down current threshold, the method  390  includes controlling, using the electronic processor  302 , the power switching network  310  to simulate bog-down (at block  406 ). In some embodiments, the electronic processor  302  controls the power switching network  310  to decrease the speed of the motor  36  to a non-zero value. For example, the electronic processor  302  reduces a duty cycle of the PWM signal provided to the FETs of the power switching network  302 . In some embodiments, the reduction in the duty cycle (i.e., the speed of the motor  36 ) is proportional to an amount that the current level is above the bog-down current threshold (i.e., an amount of excessive load). In other words, the more excessive the load of the motor unit  10 , the further the speed of the motor  36  is reduced by the electronic processor  302 . For example, in some embodiments, the electronic processor  302  determines, at block  406 , the difference between the current level of the motor  36  and the bog-down current threshold to determine a difference value. The electronic processor  302  determines the amount of reduction in the duty cycle based on the difference value (e.g., by using a look-up table that maps the difference value to a motor speed or duty cycle). 
     In some embodiments, at block  406 , the electronic processor  302  controls the power switching network  310  in a different or additional manner to provide an indication to the user that excessive loading of the motor unit  10  is occurring during operation. In such embodiments, the behavior of the motor  36  may provide a more noticeable indication to the user that excessive loading of the motor unit  10  is occurring than the simulated bog-down described above. As one example, the electronic processor  302  controls the power switching network  310  to oscillate between different motor speeds. Such motor control may be similar to a gas engine-powered power equipment stalling and may provide haptic feedback to the user to indicate that excessive loading of the motor unit  10  is occurring. In some embodiments, the electronic processor  302  controls the power switching network  310  to oscillate between different motor speeds to provide an indication to the user that very excessive loading of the motor unit  10  is occurring. For example, the electronic processor  302  controls the power switching network  310  to oscillate between different motor speeds in response to determining that the current level of the motor  36  is greater than a second bog-down current threshold that is greater than the bog-down current threshold described above with respect to simulated bog-down. As another example, the electronic processor  302  controls the power switching network  310  to oscillate between different motor speeds in response to determining that the current level of the motor  36  has been greater than the bog-down current threshold described above with respect to simulated bog-down for a predetermined time period (e.g., two seconds). In other words, the electronic processor  302  may control the power switching network  310  to simulate bog-down when excessive loading of the motor unit  10  is detected and may control the power switching network  310  to simulate stalling when excessive loading is prolonged or increases beyond a second bog-down current threshold. 
     With respect to any of the embodiments described above with respect to block  406 , other characteristics of the motor unit  10  and the motor  36  may provide indications to the user that excessive loading of the motor unit  10  is occurring (e.g., tool vibration, resonant sound of a shaft of the motor  36 , and sound of the motor  36 ). In some embodiments, these characteristics change as the electronic processor  302  controls the power switching network  310  to simulate bog-down or to oscillate between different motor speeds as described above. 
     The method  390  further includes detecting, using the electronic processor  302 , the current level of the motor  36  (at block  410 ). The method  390  also includes comparing, using the electronic processor  302 , the current level of the motor  36  to the bog-down current threshold (at block  414 ). When the current level remains above the bog-down current threshold, the method  362  proceeds back to block  402  such that the electronic processor  302  repeats blocks  402  through  414  until the current level decreases below the bog-down current threshold. In other words, the electronic processor  302  continues to simulate bog-down until the current level decreases below the bog-down current threshold. Repetition of blocks  402  through  414  allows the electronic processor  302  to simulate bog-down differently as the current level changes but remains above the bog-down current threshold (e.g., as mentioned previously regarding proportional adjustment of the duty cycle of the PWM provided to the FETs). 
     When the current level of the motor  36  decreases below the bog-down current threshold (e.g., in response to the user reducing the load on the motor unit  10 ), the method  390  includes controlling, using the electronic processor  302 , the power switching network  310  to cease simulating bog-down and operate in accordance with the actuation of the user input device  322  (i.e., in accordance with the drive request signal from the user input device  322 ) (at block  416 ). In other words, the electronic processor  302  controls the power switching network  310  to increase the speed of the motor  36  from the reduced simulated bog-down speed to a speed corresponding to the drive request signal from the user input device  322 . For example, the electronic processor  302  increases the duty cycle of the PWM signal provided to the FETs of the power switching network  310 . In some embodiments, the electronic processor  302  gradually ramps the speed of the motor  36  up from the reduced simulated bog-down speed to the speed corresponding to the drive request signal from the user input device  322 . Then, the method  390  proceeds back to block  394  to allow the electronic processor  302  to continue to monitor the motor unit  10  for excessive load conditions. In some embodiments of the method  390 , in block  414 , a second current threshold different than the bog-down threshold of block  402  is used. For example, in some embodiments, the bog-down threshold is greater than the second current threshold. 
       FIG. 25  illustrates a schematic control diagram of the motor unit  10  that shows how the electronic processor  302  implements the method  390  according to one example embodiment. The electronic processor  302  receives numerous inputs, makes determinations based on the inputs, and controls the power switching network  310  based on the inputs and determinations. As shown in  FIG. 25 , the electronic processor  302  receives a drive request signal  418  from the user input device  322  as explained previously herein. In some embodiments, the motor unit  10  includes a slew rate limiter  422  to condition the drive request signal  418  before the drive request signal  418  is provided to the electronic processor  302 . The drive request signal  418  corresponds to a first drive speed of the motor  36  (i.e., a desired speed of the motor  36  based on an amount of depression of the user input device  322  or based on the setting of a secondary input device). In some embodiments, the drive request signal  418  is a desired duty ratio (e.g., a value between 0-100%) of the PWM signal for controlling the power switching network  310 . 
     The electronic processor  302  also receives a motor unit current limit  426  and a battery pack current available limit  430 . The motor unit current limit  426  is a predetermined current limit that is, for example, stored in and obtained from the memory  306 . The motor unit current limit  426  indicates a maximum current level that can be drawn by the motor unit  10  from the battery pack  50 . In some embodiments, the motor unit current limit  426  is stored in the memory  306  during manufacturing of the motor unit  10 . The battery pack current available limit  430  is a current limit provided by the battery pack  50  to the electronic processor  302 . The battery pack current available limit  430  indicates a maximum current that the battery pack  50  is capable of providing to the motor unit  10 . In some embodiments, the battery pack current available limit  430  changes during operation of the motor unit  10 . For example, as the battery pack  50  becomes depleted, the maximum current that the battery pack  50  is capable of providing decreases, and accordingly, as does the battery pack current available limit  430 . The battery pack current available limit  430  may also be different depending on the temperature of the battery pack  50  and/or the type of battery pack  50 . Although the limits  426  and  430  are described as maximum current levels for the motor unit  10  and battery pack  50 , in some embodiments, these are firmware-coded suggested maximums or rated values that are, in practice, lower than true maximum levels of these devices. 
     As indicated by floor select block  434  in  FIG. 25 , the electronic processor  302  compares the motor unit current limit  426  and the battery pack current available limit  430  and determines a lower limit  438  using the lower of the two signals  426  and  430 . In other words, the electronic processor  302  implementing a function, floor select  434 , determines which of the two signals  426  and  430  is lower, and then uses that lower signal as the lower limit  438 . The electronic processor  302  also receives a detected current level of the motor  36  from the current sensor  318 . At node  442  of the schematic diagram, the electronic processor  302  determines an error (i.e., a difference)  446  between the detected current level of the motor  36  and the lower limit  438 . The electronic processor  302  then applies a proportional gain to the error  446  to generate a proportional component  450 . The electronic processor  302  also calculates an integral of the error  446  to generate an integral component  454 . At node  458 , the electronic processor  302  combines the proportional component  450  and the integral component  454  to generate a current limit signal  462 . The current limit signal  462  corresponds to a drive speed of the motor  36  (i.e., a second drive speed) that is based on the detected current level of the motor  36  and one of the motor unit current limit  426  and the battery pack current available limit  430  (whichever of the two limits  426  and  430  is lower). In some embodiments, the current limit signal  462  is in the form of a duty ratio (e.g., a value between 0-100%) for the PWM signal for controlling the power switching network  310 . 
     As indicated by floor select block  466  in  FIG. 25 , the electronic processor  302  compares the current limit signal  462  and the drive request signal  418  and determines a target PWM signal  470  using the lower of the two signals  462  and  418 . In other words, the electronic processor  302  determines which of the first drive speed of the motor  36  corresponding to the drive request signal  418  and the second drive speed of the motor  36  corresponding to the current limit signal  462  is less. The electronic processor  302  then uses the signal  418  or  462  corresponding to the lowest drive speed of the motor  36  to generate the target PWM signal  470 . 
     The electronic processor  302  also receives a measured rotational speed of the motor  36 , for example, from the rotor position sensor  314 . At node  474  of the schematic diagram, the electronic processor  302  determines an error (i.e., a difference)  478  between the measured speed of the motor  36  and a speed corresponding to the target PWM signal  470 . The electronic processor  302  then applies a proportional gain to the error  478  to generate a proportional component  482 . The electronic processor  302  also calculates an integral of the error  478  to generate an integral component  486 . At node  490 , the electronic processor  302  combines the proportional component  482  and the integral component  486  to generate an adjusted PWM signal  494  that is provided to the power switching network  310  to control the speed of the motor  36 . The components of the schematic diagram implemented by the electronic processor  302  as explained above allow the electronic processor  302  to provide simulated bog-down operation of the motor unit  10  that is similar to actual bog-down experienced by gas engines. In other words, in some embodiments, by adjusting the PWM signal  494  in accordance with the schematic control diagram, the motor unit  10  lowers and raises the motor speed in accordance with the load on the motor unit  10 , which is perceived by the user audibly and tactilely, to thereby simulate bog down.  FIGS. 25 and 26  illustrate a closed loop speed control of the motor  36 . In some embodiments, the method  390  uses open loop speed control of the motor  36 . For example, in  FIGS. 25 and 26 , the method  390  can be adapted for open loop speed control by eliminating node  474 , the proportional component  482 , the integral component  486 , the node  490 , and the feedback signal from the rotor positions sensor  314 . 
       FIG. 26  illustrates a schematic control diagram of the motor unit  10  that shows how the electronic processor  302  implements the method  390  according to another example embodiment. The control process illustrated in  FIG. 26  is similar to the control process illustrated in  FIG. 25 . However, rather than determining the lower limit  438  based on the motor unit current limit  426  and the battery pack current available limit  430 , the electronic processor  302  determines the lower limit  438  based on an input received from the user equipment  338 . For example, the user may define the motor performance on the user equipment  338  by providing current, power, torque, or performance parameters (referred to as motor performance parameters) over the input/output interface of the user equipment  338 . The user equipment  338  communicates the motor performance parameters defined by the user to the electronic processor  302  over the communication network  334 . The electronic processor  302  determines the lower limit  438  based on the motor performance parameters. For example, the electronic processor  302  uses the current defined in the motor performance parameters as the lower limit  438 . The control process shown in  FIG. 26  provides the user the ability to customize performance of the motor unit  10  according to the needs of the power equipment. 
     In some embodiments, the motor performance parameters may be defined based on an application of the motor unit  10 . The motor unit  10  may be used to power different kinds of power equipment for different applications. The user may select the application that the motor unit  10  is being used for on the input/output interface  354  of the user equipment  338 . The equipment electronic processor  342  may determine the motor performance parameters based on the application selected by the user. For example, the equipment electronic processor  342  may refer to a look-up table in the equipment memory  346  mapping each application of the motor unit  10  to a set of motor performance parameters. The equipment electronic processor  342  may then provide the motor performance parameters to the electronic processor  302 . In some embodiments, the user equipment  338  may provide the application selected by the user to the electronic processor  302 . The electronic processor  302 , rather than the equipment electronic processor  338 , may determine the motor performance parameters based on the application selected by the user. For example, the electronic processor  302  may refer a look-up table in the memory  306  mapping each application of the motor unit  10  to a set of motor performance parameters. 
     In some embodiments, the electronic processor  302  may perform a system compatibility check prior to each power-up to determine whether the motor unit  10  is capable of the power outputs defined by the user.  FIG. 27  is a flowchart of a method  498  for system compatibility check according to one example embodiment. As shown in  FIG. 27 , the method  498  includes receiving, via the transceiver  326 , a load command from the user equipment  338  (at block  502 ). For example, the electronic processor  302  receives the motor performance parameters from the equipment electronic processor  342  as described above. The motor performance parameters may include an output power requirement (i.e., the load command) of the motor unit  10 . In some embodiments, the load command is a rotation speed of the motor unit  10  (e.g., 5000 RPM). For example, the user may select the rotation speed or an application that maps to the rotation speed on the user equipment  338 . The electronic processor  302  determines the amount of load or current draw required to operate the motor at the selected speed (i.e., the load command). The method  498  also includes determining, using the electronic processor  302 , a load limit of the battery pack  50  (at block  506 ). The electronic processor  302  determines the load limit based on, for example, battery type, battery state of charge, battery age, and the like. In some embodiments, the electronic processor  302  determines the load limit based on the battery pack current available limit  430 . In some embodiments, the load limit is a maximum speed that can be attained based on the battery conditions. For example, the electronic processor may determine that the maximum rotational speed that can be achieved based on the power available through the battery pack  50  is 4000 RPM. 
     The method  498  further includes determining, using the electronic processor  302 , whether the load command exceeds the load limit (at block  510 ). The electronic processor  302  compares the load command to the load limit to determine whether the load command exceeds the load limit. In response to determining that the load command does not exceed the load limit, the method  498  includes performing, using the electronic processor  302 , normal operation of the motor unit  10  (at block  514 ). Performing normal operation of the motor unit  10  includes controlling the power switching network  310  to operate the motor  36  according to the load command provided by the user and the input from the user input device  322 . For example, the electronic processor  302  provides a PWM signal to the FETs of the power switching network  310  to drive the motor  36  in accordance with the drive request signal from the user input device  322 . In response to determining that the load command exceeds the load limit, the method  498  includes performing, using the electronic processor  302 , limited operation of the motor unit  10  (at block  518 ). Performing limited operation may include for example, turning off the motor  36 , running the motor  36  with limited power within the load limit of the battery pack  50 , or the like. In one example, performing limited operation may include simulating bog-down of the motor unit  10  as described above. In some embodiments, the electronic processor  302  may also warn the user that the load command exceeds the load limit. For example, the electronic processor  302  may provide an indication to the user equipment  338  that the load command exceeds the load limit. The user equipment  338  in response to receiving the indication from the electronic processor  302  provides an audible, tactile, or visual feedback to the user indicating that the load command exceeds the load limit. For example, the user equipment  338  displays a warning text on the input/output interface  354  that the load command exceeds the load limit. In some embodiments, the electronic processor  302  activates the indicators  330  to warn the user that the load command exceeds the load limit. The user may then adjust the load command based on the warning received from the electronic processor  302 . After block  514  and  518 , respectively, the electronic processor  302  loops back to the block  502 . 
       FIG. 28  illustrates a pump system  520  including a frame  524  supporting the stand-alone motor unit  10  and a pump  528  with the motor unit  10  operable to drive the pump  528 . The illustrated pump  528  is a centrifugal pump having an impeller positioned within a housing  532  of the pump  528  that is rotatable about an axis to move material from an inlet  536  of the pump  528  to an outlet  540  of the pump  528 . Specifically, the pump  528  is a “trash pump” that includes enough clearance between the impeller of the pump  528  and the housing  532  (e.g., 8 millimeters) to provide a mixture of a liquid (e.g., water) and debris (e.g., solid material like mud, small rocks, leases, sand, sludge, etc.) to pass through the pump  528  from the inlet  536  to the outlet  540  without the debris getting trapped within the pump  528  and decreasing the performance of the pump system  520 . The pump system  520  driven by the motor unit  10  includes many advantages over a conventional pump driven by an internal combustion engine, some of which are discussed below. 
     The motor unit  10  of the pump system  520 :
         drives the pump  528  in two different directions to clear the pump  528  if debris is stuck within the pump  528  (without utilizing a transmission including a forward gear and a rearward gear);   is operable by AC power (e.g., from a standard 120 volt outlet) or DC power (e.g., from a battery pack) to drive the pump  528  to eliminate a downtime refueling period of the internal combustion engine;   eliminates an air intake and an exhaust outlet such that the motor unit  10  can be fluidly sealed in a water proof housing;   is operable in a wider speed range than a comparable internal combustion engine, for example, the motor unit  10  is operable at a lower speed range (e.g., less than 2,000 revolutions per minute) than a comparable internal combustion engine to increase runtime of the motor unit  10 , and the motor unit  10  is also operable at a higher speed range (e.g., greater than 3,600 revolutions per minute) than a comparable internal combustion engine to provide a broader output capability;   operates the pump  528  regardless of the orientation of the motor unit  10 , unlike an internal combustion engine that can only can operate in one orientation (e.g., an upright orientation); and   eliminates fuel and oil to operate—unlike an internal combustion engine—allowing the pump system  520  to run, be transported, or stored at any orientation (e.g., upside down or on its side) without the motor unit  10  leaking oil or flooding with fuel.       

     In addition, the electronic processor  302  of the motor unit  10  can, for example:
         via first sensors  541  in the pump  528  that are in communication with the electronic processor  302 , detect an amount of liquid being moved through the pump  528  to enable operation of the pump  528  if the amount of liquid is at or above a threshold level and automatically stops operation of the pump  528  if the amount of liquid is below the threshold level. However, in other embodiments, the electronic processor  302  can simply monitor the current drawn by the motor  36  to determine whether to slow down or stop the motor  36 ;   provide a battery status that at least represents a power level of the battery pack of the motor unit  10 ;   be in communication with a remote control to start or stop the motor unit  10  remotely with the remote control including status indicators of the motor unit  10 ;   turn ON/OFF the motor unit  10 —and ultimately the pump  528 , change a speed of the motor unit  10 , change a flow rate of liquid and debris exiting the outlet  540 , provide a timer (e.g., automatically turn OFF the motor unit  10 ), provide a delayed start of the motor unit  10 —all of which can occur without direct user input (e.g., via sensors or programs);   be in communication with other power tools to provide tool-to-tool communication and coordination;   be in communication with a wireless network to track the location of the pump system  520 , report the pump system  520  usage and performance data, disable/enable the pump system  520  remotely, change the performance of the pump system  520  remotely, etc.;   be in communication with digital controls on a customizable user interface (e.g., a touch display) that control, regulate, measure different aspects of the motor unit  10  and/or the pump  528 ;   via second sensors  542  on the pump  528  that are in communication with the electronic processor  302  and arranged in an impeller reservoir, monitor suction or fluid level in the impeller reservoir and signal that the pump  528  is not adequately primed or automatically shut off the pump  528  to protect the pump system  520 ;   electronically control a valve  543  on the pump  528  to adjust an exhaust opening to support an auto-priming capability;   electronically control the valve  543  to adjust the exhaust opening so that only air exits and slowly reopen the valve  543  until suction is established;   adjust pressure or flow rate of the pump  528  with the speed of the motor unit  10  instead of a throttle; and   control a priming mode or “soft start” that optimizes the speed of the impeller of the pump  528  for self-priming, and governing to a slower speed until full suction is achieved.       

     Test specifications of the pump system  520  appear in Table 7 below: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Full Speed 
                 Low Speed 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Motor Speed (RPM) 
                 19,627 
                 7,452 
               
               
                 Average Current (Amperes) 
                 38.0 
                 2.11 
               
               
                 Peak Current (95%) (Amperes) 
                 43 
                 2 
               
               
                 Instantaneous Peak Current (Amperes) 
                 46 
                 43 
               
               
                 Average Voltage (V) 
                 69.9 
                 76.41 
               
               
                 Average Power (HP) 
                 3.56 
                 0.22 
               
               
                 Peak Power (95%) (HP) 
                 4.16 
                 0.23 
               
               
                 Runtime (Minutes) 
                 9.20 
                 96.86 
               
               
                 Flow Rate (Gallons per Minute) 
                 120.3 
                 48.9 
               
               
                 Total Pumped (Gallons) 
                 1,098 
                 4,753 
               
               
                   
               
            
           
         
       
     
     The values listed in Table 7 were measured during a full discharge cycle of the battery pack  50  (i.e., full charge to shutoff due to the voltage of the battery pack  50  dropping below a predetermined value). 
       FIG. 29  illustrates a jetter  544  including a frame  545  with a pair of wheels  546  and a handle  548 . The frame  545  supports the stand-alone motor unit  10  and a pump  550  driven by the motor unit  10 . The pump  550  includes an inlet  551  that receives fluid from an inlet line  552  connected to a fluid source  553  (e.g. a spigot or reservoir). The pump  550  also includes an outlet  554  from which an outlet line  556  extends. The frame  545  supports a hose reel  558  that supports a hose  559  that is fluidly coupled to the outlet line  556  and includes a jetter nozzle  560 . The hose  559  and jetter nozzle  560  are fluidly coupled with the pump  550  via the outlet line  556 , such that the pump  550  pumps fluid from the fluid source  553  to the jetter nozzle  560 . The jetter nozzle  560  includes back jets  564  and one or more front jets  568 . 
     In operation, the motor unit  10  drives the pump  550 , which supplies water or another fluid from the fluid source  553  to the nozzle  560 , such that the back jets  564  of the jetter nozzle  560  propel the jetter nozzle  560  and  559  hose through a plumbing line while front jets  568  of the nozzle  560  are directed forward to break apart clogs in the plumbing line, blasting through sludge, soap, and grease. Once propelled a sufficient distance through the plumbing line, an operator may use the hose reel  558  to retract the hose  559  and jetter nozzle  560  back through the plumbing line, while the pump  550  continues to supply fluid to the back and front jets  564 ,  568  to break up debris in the line and flush debris therethrough. The jetter  544  including the motor unit  10  possesses advantages over a conventional jetter with an internal combustion engine, some of which are discussed below. For instance, the motor unit  10  can be pulsed to clear a jam in the plumbing line. 
     In addition, the electronic processor  302  of the motor unit  10  can, for example:
         Communicate with fluid level sensors  572  on the pump  550  to detect whether an adequate level of fluid is available;   Communicate with inlet and outlet sensors  573 ,  574  respectively located at the inlet and outlet lines  552 ,  556  to prevent the motor unit  10  from being activated until the inlet and outlet lines  552 ,  556  for the pump  550  are sufficiently bled of air;   adjust pressure or flow rate of the pump  550  with the speed of the motor unit  10  instead of a throttle or regulator; and   turn ON/OFF the motor unit  10 —and ultimately the pump  550 , change a speed of the motor unit  10 , change a flow rate of liquid through the pump  550 , provide a timer (e.g., automatically turn OFF the motor unit  10 ), provide a delayed start of the motor unit  10 —all of which can occur without direct user input (e.g., via sensors or programs).       

     Test specifications of the jetter  544  appear in Table 8 below: 
     
       
         
           
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Full Speed 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Motor Speed (RPM) 
                 17,773 
               
               
                   
                 Average Current (Amperes) 
                 55.7 
               
               
                   
                 Peak Current (95%) (Amperes) 
                 64 
               
               
                   
                 Instantaneous Peak Current (Amperes) 
                 67 
               
               
                   
                 Average Voltage (V) 
                 65.4 
               
               
                   
                 Average Power (HP) 
                 5.29 
               
               
                   
                 Peak Power (95%) (HP) 
                 6.18 
               
               
                   
                 Runtime (Minutes) 
                 5.7 
               
               
                   
                 Peak Jet Pressure (PSI) 
                 2070 
               
               
                   
                   
               
            
           
         
       
     
     The values listed in Table 8 were measured during a full discharge cycle of the battery pack  50  (i.e., full charge to shutoff due to the voltage of the battery pack  50  dropping below a predetermined value). 
       FIG. 30  illustrates a compactor  576  including a frame  580  supporting the stand-alone motor unit  10 , a vibrating plate  584 , and a vibration mechanism  588  intermediate the motor unit  10  and vibrating plate  584 , such that the motor unit  10  can drive the vibration mechanism  588  to drive the vibrating plate  584 . The frame  580  includes a handle  592  and also supports a water tank  596  with a valve  600  through which water or other liquid can be applied to the surface to be compacted or the vibrating plate  584 . In some embodiments, the compactor  576  includes a paint sprayer  604  to spray and demarcate lines or boundaries in and around the compacting operation. 
     In operation, an operator can grasp the handle  592  and activate the motor unit  10  to drive the vibrating plate  584  to compact soil or asphalt, including granular, mixed materials that are mostly non-cohesive. During operation, the operator may control the valve  600  to allow water from the water tank  596  to be applied to the compacted surface, such that in some applications, the water allows the compacted particles to create a paste and bond together, forming a denser or tighter finished surface. In addition, the water from the water tank  596  prevents asphalt or other material from adhering to the vibrating plate  584  during operation. 
     The compactor  576  can be used in parking lots and on highway or bridge construction. In particular, the compactor  576  can be used in construction areas next to structures, curbs and abutments. The compactor  576  can also be used for landscaping for subbase and paver compaction. The compactor  576  including the motor unit  10  possesses advantages over a conventional compactor with by an internal combustion engine, some of which are discussed below. For instance, the motor  36  of the motor unit  10  can run forward or reverse, allowing the operator to shift directional bias of the vibration mechanism  588 . Thus the vibration mechanism  588  is configured to move or “walk” itself forward or reverse, depending on how the operator has shifted the directional bias of the vibration mechanism  588 . 
     In addition, the electronic processor  302  of the motor unit  10  can, for example:
         sense the levelness of compaction, such as the grade or pitch, by communicating with an auxiliary sensor device such as a surveying and grading tool  608 ;   sense the degree of compactness, such as whether the material being compacted is loose or sufficiently tight, by communicating with an auxiliary or onboard device  610  such as a durometer probe, ultrasound, accelerometer, or gyroscope. However, in other embodiments, the electronic processor  302  can simply monitor the current drawn by the motor  36  to sense the level of compactness;   turn ON/OFF the motor unit  10 —and ultimately the vibration mechanism  588 , change a speed of the motor unit  10 , and output direction and steering of the compactor system  576 ;   use sensors  611  on the compactor system  576  that are in communication with the electronic processor  302  to detect where a compacted surface dips and in response, control the paint sprayer  604  to mark where more material is needed at the detected dip; and   control the valve  600  of the water tank  596  to adjust the flow rate to the vibrating plate or compacted surface.       

     Test specifications of the compactor  576  appear in Table 9 below: 
     
       
         
           
               
               
             
               
                   
                 TABLE 9 
               
               
                   
                   
               
               
                   
                 Full Speed 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Motor Speed (RPM) 
                 19,663 
               
               
                   
                 Average Current (Amperes) 
                 26.4 
               
               
                   
                 Peak Current (95%) (Amperes) 
                 32 
               
               
                   
                 Instantaneous Peak Current (Amperes) 
                 52 
               
               
                   
                 Average Voltage (V) 
                 71.9 
               
               
                   
                 Average Power (HP) 
                 2.55 
               
               
                   
                 Peak Power (95%) (HP) 
                 3.24 
               
               
                   
                 Runtime (Minutes) 
                 12.78 
               
               
                   
                   
               
            
           
         
       
     
     The values listed in Table 9 were measured during a full discharge cycle of the battery pack  50  (i.e., full charge to shutoff due to the voltage of the battery pack  50  dropping below a predetermined value). 
     In another embodiment of a compactor  576  shown schematically in  FIG. 31 , the vibration mechanism  588  is a multi-motor drive system with four separate vibration mechanisms  588   a ,  588   b ,  588   c ,  588   d , each having its own motor and each configured to respectively vibrate an individual quadrant  612 ,  614 ,  616 ,  618  of the vibrating plate  584 . Each vibration mechanism  588   a ,  588   b ,  588   c ,  588   d , is controlled by a controller  620  of the compactor  576 . Thus, depending on readings from the auxiliary or onboard sensor devices  608 ,  610  described above, the controller  620  can select which quadrant  612 ,  614 ,  616 ,  618  requires vibration. In some embodiments, the controller  620  may receive instructions from an operator via, e.g., a remote control. In some embodiments, the controller  620  can control the vibration mechanisms  588   a ,  588   b ,  588   c ,  588   d  to move the compactor  576  forward or reverse, as well as steer or turn the compactor  576  via the vibration plate  584 . 
       FIG. 32  illustrates a rammer  624  including a body  628  supporting the stand-alone motor unit  10 , a vibrating plate  632 , and a vibration mechanism  636  intermediate the motor  10  and vibrating plate  632 , such that the motor unit  10  can drive the vibration mechanism  636  to drive the vibrating plate  632 . The rammer  624  includes a handle  640  extending from the body  628  to enable an operator to manipulate the rammer  624 . 
     In operation, an operator can grasp the handle  640  and activate the motor unit  10  to drive the vibrating plate  632  to compact cohesive and mixed soils in compact areas, such as trenches, foundations and footings. The rammer  624  including the motor unit  10  possesses advantages over a conventional rammer driven with an internal combustion engine, some of which are discussed below. 
     For instance, the electronic processor  302  of the motor unit  10  can, for example:
         turn ON/OFF the motor unit  10 —and ultimately the vibration mechanism  636 , change a speed of the motor unit  10 ;   provide a delayed start of the motor unit  10 —all of which can occur without direct user input (e.g., via sensors or programs); and   utilize preset modes for compacting soft, hard, loose, or tight material.       

     The electronic processor  302  can also input data from sensors  642  on the rammer  624  to detect whether the frequency and/or amplitude of the vibrating plate is within a predetermined range, such that the control electronics  42  can precisely control the speed of the motor unit  10  and adjust the frequency of vibration of the vibration mechanism  636 . In this manner, the electronic processor  302  can prevent amplified vibration or resonance and ensure that the rammer  624  is under control when the operator wishes to lower the output speed and reduce the rate of compaction. Also, this ensures that vibration energy is being efficiently transferred into the surface material instead of the operator. 
     Test specifications of the rammer  624  appear in Table 10 below: 
     
       
         
           
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                 Full Speed 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Motor Speed (RPM) 
                 19,863 
               
               
                   
                 Average Current (Amperes) 
                 19.7 
               
               
                   
                 Peak Current (95%) (Amperes) 
                 28 
               
               
                   
                 Instantaneous Peak Current (Amperes) 
                 56 
               
               
                   
                 Average Voltage (V) 
                 72.7 
               
               
                   
                 Average Power (HP) 
                 1.92 
               
               
                   
                 Peak Power (95%) (HP) 
                 2.76 
               
               
                   
                 Runtime (Minutes) 
                 15.73 
               
               
                   
                   
               
            
           
         
       
     
     The values listed in Table 10 were measured during a full discharge cycle of the battery pack  50  (i.e., full charge to shutoff due to the voltage of the battery pack  50  dropping below a predetermined value). 
     As shown in  FIG. 33 , in some embodiments, the gear train  110  of the motor unit  10  includes a terminal male shaft section  644  to which a first female shaft subassembly  648  can mount within a gearbox  650  of the motor unit  10 . The first female shaft subassembly  648  includes a first power take-off shaft  38   a  configured to drive a first tool and a female socket  652  that mates with the male shaft section  644 . In the embodiment of  FIG. 33 , a second female shaft subassembly  656  is provided with the female socket  652  and a second power take-off shaft  38   b  configured to drive a second tool that is different than the first tool. Thus, the first and second female shaft subassemblies  648 ,  656  may be conveniently swapped in and out of mating relationship with the male shaft section  644  to allow an operator to quickly and conveniently adapt the motor unit  10  to drive different first and second tools. In contrast, a typical gas engine does not permit such quick or convenient replacement of the power take-off shaft. 
     As shown in  FIG. 34 , in some embodiments, the gear train  110  of the motor unit  10  includes a terminal female shaft section  660  to which a first male shaft subassembly  664  can mount within the gearbox  650  of the motor unit  10 . The first male shaft subassembly  664  includes the first power take-off shaft  38   a  configured to drive the first tool and a male shaft section  668  that mates with the female shaft section  660 . In the embodiment of  FIG. 34 , a second male shaft subassembly  672  is provided with the male shaft section  668  and the second power take-off shaft  38   b  configured to drive the second tool. Thus, the first and second male shaft subassemblies  664 ,  672  may be conveniently swapped in and out of mating relationship with the female shaft section  660  to allow an operator to quickly and conveniently adapt the motor unit  10  to drive different first and second tools. In contrast, a typical gas engine does not permit such quick or convenient replacement of the power take-off shaft. In some embodiments, the male shaft section  668  mates with the female shaft section  660  via a splined connection. In the embodiment illustrated in  FIG. 34 , the first and second male shaft subassemblies  664 ,  672  are axially retained to the gearbox  650  via a retaining ring  673  on the gearbox  650 . 
     In some embodiments, the female socket  652  mates with the male shaft section  644 , and the male shaft section  668  mates with the female shaft section  660 , via any of the following connection methods: spline-fit ( FIG. 34 ), keyed, half-circle shaft w/ female bore ( FIG. 35 ), tongue &amp; groove ( FIG. 36 ), double “D” ( FIG. 37 ), face ratchet bolted together, Morse taper, internal/external thread, pinned together, flats and set screws, tapered shafts, or serrated connections ( FIG. 38 ). 
     In some embodiments, different types of power take-off shaft subassemblies  38  may couple to the gear train  110  using a quick-connect structure similar to any of the following applications: modular drill, pneumatic quick connect, socket set-style, ball-detent hex coupling, drill chuck, pins filling gaps around shaft, hole saw arbor. In some embodiments, different types of power take-off shaft subassemblies  38  may couple to the gear train  110  using one of the following coupling structures: Spring coupling, c-clamp style, love joy style, plates w/ male/female pegs ( FIG. 39 ), or female collar with radial fasteners ( FIG. 40 ). 
     In another embodiment shown in  FIG. 41 , the geartrain  110  includes a female shaft section  674  with a gear  674   a  and an elongate bore  675  for receiving a stem  676   a  of a first male shaft subassembly  676  having the first power take-off shaft  38   a . The female shaft section  674  is rotatably supported in the gearbox  650  by first and second bearings  677 ,  678 . Once received in the elongate bore  675 , the first male shaft subassembly  676  is axially secured to the female shaft section  674  via a fastener  679  inserted into the stem  676   a  of the first male shaft subassembly  676   a  while securing a washer  680  between the fastener  679  and the stem  676   a  of the first male shaft subassembly  676 . Thus, unlike the embodiments of  FIGS. 33 and 34 , the embodiment of  FIG. 41  requires the operator to access a side  681  of the gearbox  650  opposite the faceplate  124  to access the fastener  679 . In the embodiment of  FIG. 41 , a second male shaft subassembly having the second power take-off shaft  38   b  can be inserted in lieu of the first male shaft subassembly  676  to allow an operator to conveniently adapt the motor unit  10  to drive different first and second tools. In contrast, a typical gas engine does not permit such quick or convenient replacement of the power take-off shaft. 
     In an embodiment shown in  FIG. 43 , a shaft subassembly  682  may be removably coupled to the gearbox  650 . Specifically, the shaft subassembly  682  includes the faceplate  124 , the power take-off shaft  38  rotatably supported by a first bearing  688  in the faceplate  124 , and a first gear  692  arranged on and coupled for rotation with the power take-off shaft  38 . In some embodiments, the power take-off shaft  38  is axially constrained with respect to the faceplate  124  with a retaining ring  694 . The shaft subassembly  682  is removably received in a recess  696  of the gearbox  650 . The recess  696  includes a second bearing  700  for rotatably supporting an end  704  of the power take-off shaft  38  within the recess  696  when the shaft subassembly  682  is received in the recess  696  and coupled to the gearbox  650 . 
     Also, when the shaft subassembly  682  is received in the recess  696  and coupled to the gearbox  650 , the first gear  692  is engaged with an upstream gear  706  of the gear train  110 , the faceplate  124  covers the gear train  110  and the first gear  692  is the final drive gear of the gear train  110 , such that the gear train  110  can drive the power take-off shaft  38  using a first overall reduction ratio. When the shaft subassembly  682  is removed from the gearbox  650 , the first gear  692  can be replaced with a second gear, and the upstream gear  706  of the gear train  110  that engages with the first gear  692  can be changed as well. Using the second gear with the shaft subassembly  682  and a different gear as the upstream gear results in a second overall reduction ratio of the gear train  110 . The second overall reduction ratio is different than the first overall reduction ratio, such that an operator can reconfigure the shaft subassembly  682  for driving different tools by swapping between the first gear  692  and the second gear. Also, when the shaft subassembly  682  is removed from the gearbox  650 , at least a portion of the gear train  110  is exposed, thus enabling an operator to replace, repair, or access certain gears within the gear train  110 , such as the upstream gear  706 . In other embodiments, instead of just the first gear  692 , the entire shaft subassembly  682  can be changed out for a different subassembly to change the reduction ratio. 
     As shown in  FIG. 43 , the motor  36  mounts to a portion of the gearbox  650  that has a generally C-shaped cross-section, and the faceplate  124  is part of a shaft subassembly  682  including the power take-off shaft  38 , with the faceplate  124  being generally planar. In an alternative embodiment shown in  FIG. 44 , the geometries are swapped from those of the embodiment of  FIG. 43 . Specifically, the motor  36  mounts to a portion of the gearbox  650  having a generally planar cross-section and the faceplate  124  has a generally reverse-C-shaped cross-section. 
     As shown in  FIG. 45 , in some embodiments, a first gearbox  650   a  with a first gear train  110   a  is removably attachable to an adapter plate  712  adjacent the motor  36  in the housing  14 , such that the output shaft  106  of the motor  36  can drive the first gear train  110   a  when the first gearbox  650   a  is attached to the adapter plate  712 . A second gearbox  650   b  with a second gear train  110   b  that has a different reduction ratio than the first gear train  110   a  is also removably attachable to the adapter plate  712 . Thus, depending on what tool an operator wishes to drive with the motor unit  10 , an operator can select either the first or second gearboxes  650   a ,  650   b . In some embodiments, the first and second gearboxes  650   a ,  650   b  can attach to the adapter plate  712  via a bayonet connection. In some embodiments, there are a plurality of additional gearboxes respectively having different gear trains than the first and second gear trains  110   a ,  110   b , each of the additional gearboxes being attachable to the adapter plate  712 . 
     Instead of swappable gearboxes  650   a ,  650   b  as in the embodiment of  FIG. 45 , and instead of embodiments of  FIGS. 19 and 43  that allow an operator to change or replace individual gears, in some embodiments the gear train  110  in the gearbox  650  includes a transmission allowing an operator to shift gear sets to change the reduction ratio. In some embodiments, the gear train  110  in the gearbox  650  has a predetermined number of stages that can be arranged in different combinations to produce different outputs. For example, as shown in  FIG. 46 , the gearbox  650  might include three slots  716 ,  720 ,  724  for accepting cartridge-style gear stages  728 ,  732 ,  736 ,  740 ,  744  (e.g., planetary stages). Thus, depending on the output that an operator desires from the gear train  110 , the operator can selectively insert three of the five stages  728 ,  732 ,  736 ,  740 ,  744  into the three slots  716 ,  720 ,  724  in a particular order depending on which tool the operator wishes the motor unit  10  to drive. 
     As shown in  FIG. 47 , in some embodiments, the motor  36  is enveloped within the gear train  110  in the gearbox  650 . Specifically, the output shaft  106  of the motor  36  acts as a sun gear with three planetary gears  748 ,  752 ,  756  between the output shaft  106  and a ring gear  760  that includes a first face gear  764 . First and second spur gear  768 ,  772  are arranged between the first face gear  764  and a second face gear  776 . 
     As shown in  FIG. 48 , in some embodiments, the flange  34  is configured to translate all or part of the housing  14  and gearbox  650  with respect to the flange  34  to provide freedom for varying geometries of the power take-off shaft  38 . For instance, the flange  34  may include a groove  777  for receipt of a tongue  778  of the housing or gearbox  650  to permit lateral translation. In some embodiments, a locking mechanism  779  may be included to lock the housing  14  at a particular position with respect to the flange  34 . The lateral translation of housing  14  with respect to flange  34  permits an operator to slide the housing  14  in a direction away from the tool to which the motor unit  10  is mounted, then service or remove the power take-off shaft  38 , without having to decouple the flange  34  from the tool. In some embodiments, the housing  14  can translate with respect to the flange  34  in a direction parallel to, perpendicular to, or both parallel and perpendicular to the rotational axis  122  of the power take-off shaft  38 . 
     As shown in  FIG. 49 , in some embodiments, the power take-off shaft  38  is coupled to an input shaft  780  of a tool via an endless drive member  784  (e.g., a belt or chain) that is coupled to first and second pulleys  785 ,  786  that are respectively arranged on the power take-off shaft  38  and input shaft  780 . In the embodiment of  FIG. 49 , the motor unit  10  also includes a tensioner  788  with a spring  792  to adjust the tension of the endless drive member  784 . In some embodiments, the first pulley  785  can be arranged on the input shaft  780  and the second pulley  786  can be arranged on the power take-off shaft  38  to produce a different gear reduction ratio. 
     As shown in  FIG. 50 , in some embodiments, the gearbox  650  is sectioned to have a quartile faceplate  124  that allows for access to only the power take-off shaft  38 . 
     As shown in  FIG. 51 , in some embodiments, the battery  50  can be stored within a cover  796  to protect the electronics from the ingress of water or moisture. In some embodiments, the cover  796  is a hard case cover  796 . As shown in  FIG. 52 , in some embodiments, the battery  50  includes a system lock out apparatus, such as a keypad  797  or a key, which can be utilized to prevent unauthorized individuals from accessing the battery  50 , for example, in a scenario in which the battery  50  has been rented along with the motor unit  10 . 
     Because the control electronics  42  of the motor unit  10  don&#39;t require intake of ambient air for combustion or exhaust of noxious gases, the control electronics  42  can be fully sealed within a fully sealed waterproof compartment within housing  14 . As shown in  FIG. 42 a   , in some embodiments, the housing  14  includes doors  798  that can open and close at various locations on the housing  14  to allow an operator to quickly reconfigure where the air intake and exhaust ports are located for cooling of the motor  36 . In some embodiments, the motor unit  10  can operate using AC power from a remote power source, or DC power via the battery  50 . Additionally, the motor unit  10  may include an AC power output  799 , as a passthrough or inverted to AC power, for connection with an AC power cord of a power tool. In some embodiments, the housing  14  includes inlets  801  ( FIG. 42 a   ) for pressurized air for cleaning or to supplement a cooling airflow. 
     In some embodiments, the motor unit  10  can be mated with a new tool (e.g. one of the pump system  520 , jetter  544 , compactor  576 , or rammer  624 ) and the memory  306  can be reprogrammed to optimize the motor unit  10  for operation with the new tool. In some embodiments, the electronic processor  302  automatically recognizes which type of new tool the motor unit  10  has been mated with, and governs operation of the motor unit  10  accordingly. In some embodiments, the electronic processor  302  can automatically detect with which tool the motor unit  10  has been mated via Radio Frequency Identification (RFID) communication with the new tool. In another embodiment, the tool may be detected with a resistor inserted into a plug connected to the electronic processor  302 . For example, a resistor between 10K and 20K ohms would indicate to the electronic processor  302  that the motor unit  10  system was connected to a power trowel or other tool. 
     In yet another embodiment, the tool may be detected with a multi-position switch (e.g., a 10-position rotary switch). Each position on the switch would correspond with a different type of tool system. 
     In yet another embodiment, the tool may be detected with a user interface on the motor unit  10  in which a user selects, from a pre-programmed list, the make and model of tool to which the motor unit  10  is attached. The motor unit  10  would then apply the appropriate system controls for the tool. 
     In some embodiments, the memory  306  is reprogrammable via either BLUETOOTH or Wi-Fi communication protocols. In some embodiments, the electronic processor  302  has control modes for different uses of the same tool. The control modes may be preset or user-programmable, and may be programmed remotely via BLUETOOTH or Wi-Fi. In some embodiments, the electronic processor  302  utilizes master/slave tool-to-tool communication and coordination, such that the motor unit  10  can exert unidirectional control over a tool, or an operator can use a smartphone application to exert unidirectional control over the motor unit  10 . 
     In some embodiments, the operator or original equipment manufacturer (OEM) is allowed limited access to control the speed of the motor unit  10  through the electronic processor  302  via, e.g., a controller area network (CAN)-like interface. In some embodiments, the electronic processor  302  is capable of a wider range of speed selection with a single gear set in the gear train  110  than a gasoline engine. For example, the control electronics  42  are configured to drive the motor  36  at less than 2,000 RPM, which is lower than any speed a gasoline engine is capable of, which permits the associated tool to have a greater overall runtime over a full discharge of the battery  50 , than a gasoline engine. Additionally the control electronics  42  are configured to drive the motor at more than 3,600 RPM, which is higher than any speed a gasoline engine is capable of, and with the capability to deliver more torque. The wider range of speeds of motor  36  offers greater efficiency and capability than a gasoline engine. In some embodiments, the operator could have access to control the current drawn by the motor  36  in addition to the speed. 
     In some embodiments, the electronic processor  302  is configured to log and report data. For example, the electronic processor  302  is configured to provide wired or wireless diagnostics for monitoring and reading the status of the motor unit  10 . For example, the electronic processor  302  can monitor and log motor unit  10  runtime for example, in a rental scenario. In some embodiments, the motor  36  and the electronic processor  302  use regenerative braking to charge the battery  50 . In some embodiments, the motor unit  10  includes a DC output  803  for lights or accessories ( FIG. 42 ). In some embodiments, the electronic processor  302  can detect anomalies or malfunctions of the motor unit  10  via voltage, current, motion, speed, and/or thermocouples. In some embodiments, the electronic processor  302  can detect unintended use of or stoppage of the motor unit  10 . If the tool driven by the motor unit  10  (e.g. one of the pump system  520 , jetter  544 , compactor  576 , or rammer  624 ) is not running with the intended characteristics or is not being used correctly or safely, the electronic processor  302  can detect the anomaly and deactivate the motor unit  10 . For example, the motor unit  10  can include one or more accelerometers to sense if the motor unit  10  and tool is in the intended orientation. And, if the electronic processor  302  determines that the motor unit  10  is not in the intended orientation (i.e. the tool has fallen over), the electronic processor  302  can deactivate the motor unit  10 . 
     In some embodiments, the motor unit  10  includes accessible sensor ports  802  ( FIG. 42 ) to electrically connect with user-selected sensors for use with the piece of power equipment, such as accelerometers, gyroscopes, GPS units, or real time clocks, allowing an operator to customize the variables to be sensed and detected by the electronic processor  302 . In some embodiments, the electronic processor  302  can indicate the status of the battery  50 , such as when the battery is running low, to an operator via visual, audio, or tactile notifications. In some embodiments, the electronic processor  302  can operate an auxiliary motor that is separate from the motor  36  to drive an auxiliary device such as a winch. The auxiliary motor may be internal or external to the motor unit  10 . 
     In some embodiments, the motor unit  10  can include digital controls on a customizable user interface, such as a touch display or a combination of knobs and buttons. In contrast, an analog gasoline engine does not include such digital controls. In some embodiments, the user interface for the motor unit  10  can be modular, wired, or wireless and can be attachable to the motor unit  10  or be hand held. In some embodiments, the motor unit  10  can be controlled with a remote control  804  that includes status indicators for certain characteristics of the motor unit  10 , such as charge of the battery  50  and the temperature, as shown in  FIG. 53 . In some embodiments, the motor unit  10  can provide status indications with a remote, programmable device. In some embodiments, the remote control  804  can include a USB cord  808  that plugs into a USB port  812  on the battery  50  ( FIG. 52 ), or a USB port elsewhere on the motor unit  10 , such that the remote control  804  can be charged by the battery  50 . In some embodiments the remote control  804  can be charged wirelessly from the battery  50 . The remote control  804  can include a variety of controls, such as:
         a button  816  to turn the motor unit  10  on or off;   a joystick  820  to steer the tool (e.g., the compactor  576 );   a dial  824  to adjust the flow rate of the tool (e.g. the pump system  520  or jetter  544 );   a timer  828  for a delayed start or stop of the tool; and   a switch  832  to select forward or reverse directions of the power take-off shaft  38 .       

     The remote control  804  can also control the operating pressure of the tool (e.g. the pump system  520  or jetter  544 ), or other operating characteristics of the tool. 
     In an embodiment shown in  FIGS. 54-58 , the housing  14  of the motor unit  10  is split into a base  836  having the first, second, third, fourth, fifth, and sixth sides, 18, 22, 26, 28, 30, 32, and a battery module  840  that is removably coupled to the base  836 . As explained in further detail below (with ref to  FIGS. 78-82 ), the motor unit  10  of  FIGS. 54-58  has a different faceplate  124 ′ than the faceplate  124 . The battery module  840  includes the battery receptacle  54  for receiving the battery pack  50 , as described above. The battery module  840  also includes a pair of opposed side walls  844 , a rear wall  848 , and a front wall  852  opposite the rear wall  848 . The side walls  844  are longer than the rear and front walls  848 ,  852 , such that the battery module  844  defines a battery module axis  854  that is parallel to the side walls  844 . The battery pack  50  is removable from the battery receptacle  54  by sliding the battery pack  50  in a direction away from the rear wall  848 . 
     The battery module  840  also includes a plurality of coupling members, such as fasteners  856  ( FIGS. 55 and 58 ), configured to mate with a plurality of receiving elements, such as bores  860  on the fourth side  28  of the base  836 , such that the battery module  840  can be secured to the fourth side  28  of base  836 . The bores  860  are arranged on the fourth side  28  such that the battery module  840  is configured to be coupled to the base  836  in a first position ( FIG. 54 ) or a second position ( FIGS. 56 and 57 ). Thus, in some embodiments, there may be twice as many bores  860  as fasteners  856 , to facilitate the two different positions of the battery module  840  with respect to the base  836 . In some embodiments, one of the base  836  and the battery module  840  may include, e.g., an extended wire harness  858  ( FIG. 58 ) to facilitate the electrical connection between the second terminal  78  of the battery receptacle  54 , which is in the battery module  840 , and the control electronics  42 , which are in the base  836 . 
     In the first position of the battery module  840  shown in  FIG. 54 , the side walls  844  of the battery module  840  are parallel to the second and third sides  22 ,  26  of the base  836 , the battery module axis  854  is perpendicular to the rotational axis  122  of the power take-off shaft  38 , the rear and front walls  848 ,  852  of the battery module  840  are perpendicular to the second side and third sides  22 ,  26  of the base  836 , and the battery module  840  is removable in a direction away from the fifth side  30  of the base  836 . In the second position of the battery module shown in  FIGS. 56 and 57 , the side walls  844  of the battery module  840  are perpendicular to the second and third sides  22 ,  26  of the base  836 , the battery module axis  854  is parallel to the rotational axis  122  of the power take-off shaft  38 , the rear and front walls  848 ,  852  of the battery module  840  are parallel to the second and third sides  22 ,  26  of the base  836 , and the battery module  840  is removable in a direction away from the second side  22  of the base  836 . 
     Thus, when the operator or original equipment manufacturer (OEM) wants the motor unit  10  in an arrangement in which the battery pack  50  needs to be removable in the space above the sixth side  32  of the base  836 , or there needs to be free space above the power take-off shaft  38  and second side  22  of the base  836 , the operator or OEM can elect to couple the battery module  840  to the base  836  in the first position shown in  FIG. 54 . Thus, the first position of the battery module  840  may be useful in, e.g., high vibration applications, horizontal power take-off shaft  38  applications ( FIG. 54 ), or vertical power take-off shaft  38  applications. 
     Alternatively, when the operator or OEM wants the motor unit  10  in an arrangement in which the battery pack  50  needs to be removable in a space above the third side  26  of the base  836 , or there needs to be free space above the fifth and sixth sides  30 ,  32  of the base  836 , the operator or OEM can elect to couple the battery module  840  to the base  836  in the second position shown in  FIGS. 56 and 57 . Thus, the second position of the battery module  840  may be useful in, e.g., high vibration applications, horizontal power take-off shaft  38  applications ( FIG. 56 ), or vertical power take-off shaft  38  applications ( FIG. 57 ). 
     As shown in  FIGS. 55 and 58 , in some embodiments, the base  836  includes a plurality of vibration damping members, such as springs  864  and/or elastomeric spacers  868 , that inhibit vibration transferred from the base  836  to the battery module  840  during operation of the motor unit  10 . Thus, vibration transferred to the battery pack  50  is inhibited, increasing the lifespan of the battery pack  50 , the battery receptacle  54 , and the base  836 . 
       FIGS. 59-66  illustrate a motor  36   a  for the motor unit  10  that is different than the motor  36 . The motor  36   a  includes a stator  872 , a rotor  876  rotatable relative to the stator  872 , and a housing  880  in which the rotor  876  and stator  872  are arranged. The motor  36   a  also includes an adapter plate  884  coupled to the housing  880  and a back cover  888  coupled to the housing  880 . The housing  880  is sized to accommodate the specific diameter of the rotor  876 . In some embodiments, the rotor  876  has a diameter ranging from 70 mm to 120 mm. 
     An output shaft  892  of the rotor  876  protrudes from the adapter plate  884 . As shown in  FIGS. 59 and 60 , the adapter plate  884  includes first plurality of holes  896  defining a first hole pattern. As shown in  FIG. 60 , each of the holes  896  is the same distance D away from a rotational axis  900  defined by the output shaft  892 . A variety of different gearboxes  650   x  ( FIG. 62 ),  650   y  ( FIGS. 63 ), and  650   z  ( FIG. 64 ) each have a second plurality of holes defining a second hole pattern that is identical to the first hole pattern defined by the first plurality of holes  896 . Thus, when at least two holes of the second hole pattern of one of the gearboxes  650   x ,  650   y ,  650   z  are aligned with at least two of the first plurality of holes  896 , the selected gearbox  650  may be coupled to the adapter plate  884  by, e.g., inserting fasteners through the aligned holes in the first and second hole patterns. In some embodiments, the fasteners may extend through the back cover  888 , the housing  880 , the adapter plate  884 , and the selected gearbox  650 . When one of the gearboxes  650   x ,  650   y ,  650   z  is coupled to the adapter plate  884 , the output shaft  892  extends into the selected gearbox  650 . In some embodiments, in addition to being coupled to the adapter plate  884  of the motor  36   a , the selected gearbox  650  is also coupled to the housing  14  of the motor unit  10 . In some embodiments, the selected gearbox  650  is not coupled to the housing  14  of the motor unit  10 . In some embodiments, the gearbox  650  is coupled to the housing  14  and the motor  36   a  is coupled to the gearbox  650 , but not the housing  14 . In some embodiments, the motor  36   a  is coupled to the housing  14 , as well as the gearbox  650 . 
     A power take-off shaft  38  extends from each of the gearboxes  650   x ,  650   y ,  650   z  and the gearboxes  650   x ,  650   y ,  650   z  respectively include different gear trains  110   x ,  110   y ,  110   z  for transferring torque from the output shaft  892  to the power take-off shaft  38 . For instance, the gear train  110   x  may be a planetary gear train, the gear train  110   y  may be a 2-stage gear train, and the gear train  110   z  may be a transmission. Thus, depending on the piece of power equipment the operator wants to use with the motor unit  10 , and the type of speed reduction from the motor  36   a  to the power take-off shaft  38  the operator wants to achieve, the operator can couple one of the gearboxes  650   x ,  650   y ,  650   z  to the adapter plate  884  of the motor  36   a.    
     In some embodiments, the first hole pattern defined by the first holes  896  is identical to a second hole pattern on the piece of power equipment  904  itself. Thus, when the at least two holes of the second hole pattern of the power equipment  904  are aligned with at least two holes of the first hole pattern defined by the plurality of holes  896 , the power equipment  904  may be coupled to the adapter plate  884  by, e.g., inserting the fasteners  900  through aligned holes in the first and second hole patterns. Thus, the output shaft  892  drives the power equipment  904  directly ( FIG. 65 ) or via a pulley  908  ( FIG. 66 ) used to drive a belt  912 . 
       FIG. 67  illustrates an embodiment similar to the embodiment shown in  FIG. 43 , with the following difference explained below. Specifically, the first gear  692  is meshingly engaged with and driven by a pinion  916  on the output shaft  106  of the motor  36  when the shaft subassembly  682  is coupled to the gearbox  650 . The motor  36  is coupled to the gearbox  650  and the output shaft  106  is supported by a bearing  918  in the gearbox  650 . 
     In an embodiment shown in  FIG. 68 , an internal ring gear  920  is coupled to or integrally formed on the power take-off shaft  38 , which is supported by a first bearing  924  in the removable faceplate  124  and a second bearing  928  in the gearbox  650 . The internal ring gear  920  is meshingly engaged with and driven by the pinion  916  on the output shaft  106  of the motor  36 , and the motor  36  is coupled to the gearbox  650 . Thus, the removable faceplate  124  may be removed to swap out the internal ring gear  920  for other gears. For instance, in other embodiments, instead of the internal ring gear  920 , the gear train  110  could include single or multiple stage spur ( FIGS. 11 and 47 ) or helical gear sets, single or multistage planetary gearset planetary gears ( FIGS. 10, 46, 47, and 62 ), hydraulic coupling, or a belt/chain drive ( FIGS. 49 and 66 ). In the embodiments illustrated in  FIGS. 67 and 68 , the rotational axis  118  of the output shaft  106  is parallel to the rotational axis  122  of the power take-off shaft  38 . However, in other embodiments, the rotational axis  118  of the output shaft  106  is coaxial with the inline with the rotational axis  122  of the power take-off shaft  38 . In still other embodiments, the rotational axis  118  of the output shaft  106  is perpendicular to the rotational axis  122  of the power take-off shaft  38 . In still other embodiments, the rotational axis  118  of the output shaft  106  forms an oblique angle with respect to the rotational axis  122  of the power take-off shaft  38  with the use of bevel gears or worm gears. 
     As discussed in many embodiments above, the motor unit  10  includes a gear train  110  to lower the rotational speed output by the power take-off shaft  38 , as compared with the rotational speed of the motor  36 . Generally, DC brushless motors, such as the motor  36 , operate most efficiently at high speeds, ranging between 15,000 and 30,000 RPM. However, the desired output speed of the power take-off shaft  38  is generally in a range of 2,000-3,600 RPM, which is roughly equivalent to the speed of a power take-off shaft of a 150-250 cc class V small combustion engine that the motor unit  10  is intended to replace. 
     In some embodiments, other electric motors could be used, such as outer rotor motors, AC induction motors, or brushed motors. In some embodiments, the gear train  110  could include internal ring gear(s) (e.g.  FIG. 68 ), planetary gears ( FIGS. 10, 46, 47, and 62 ), belts and/or chains ( FIGS. 49 and 66 ), bevel gears ( FIG. 12 ), helical or spur gears ( FIGS. 11 and 47 ) or even viscous fluid coupling. 
     In addition to using a gear train  110  to provide a reduced rotational speed to the power take-off shaft  38 , motor speed control can be used to reduce the rotational speed of the motor  36 , and thus the power take-off shaft  38 . Because the exact gear reduction ratio of the gear train  110  is known, the electronic processor  302  of the motor unit  10  can accurately control the speed of the motor  36  to achieve the desired speed of the power take-off shaft  38 . Also, as shown in the embodiments of  FIGS. 8, 65, and 66 , the output shaft  106  is also the power take-off shaft  38 , such that the motor  36  directly drives the power take-off shaft  38  without any intermediate gear train. Thus, in the embodiments of  FIGS. 8, 65 and 66 , the rotational speed of the motor  36  is the same as the rotational speed of the power take-off shaft  38 . In some embodiments, the gear train  110  may be configured to increase the rotational speed of the power take-off shaft  38  to a value greater than the rotational speed of the motor  36 . “Gearing up” may be useful in, e.g., applications in which the piece of power equipment is a vacuum cleaner being driven by the power take-off shaft  38 . 
     In an embodiment shown in  FIGS. 69-71 , the faceplate  124  includes a first plurality of holes  932  defining a first hole pattern. In other embodiments, the faceplate  124  is omitted and the first plurality of holes  932  defining the first hole pattern can be on the second side  22  of the housing  14  or the gearbox  650 . An adapter plate  936  includes a second plurality of holes  940  defining a second hole pattern that is identical to the first hole pattern, such that when the second holes  940  are aligned with the first holes  932 , the adapter plate  936  is configured to be coupled to the faceplate  124 . 
     In some embodiments, the first and second hole patterns are the hole patterns shown in the Flange A mounting pattern from the SAE International Surface Vehicle Recommended Practice Manual, J609, section (R) “Mounting Flanges and Power Take-Off Shafts for Small Engines”, issued May 1958 and revised July 2003 (“the SAE J609”), which is incorporated herein by reference. Thus, the adapter plate  936  is not needed when the motor unit  10  is to be used with a piece of power equipment utilizing the SAE J609 Flange A mounting pattern, because the first plurality of holes  932  defining the SAE J609 Flange A mounting pattern can be used to mount the piece of power equipment directly to the faceplate  124 . In other embodiments, the first plurality of holes  932  could define other mounting patterns besides the SAE J609 Flange A mounting pattern, such as the SAE J609 Flange Patterns B, C, D, E or F mounting patterns. 
     The adapter plate  936  also includes a first set of mounting elements  944  configured to align with a second set of mounting elements on a piece of power equipment, such that the adapter plate  936  can be coupled to the piece of power equipment. The adapter plate  936  of  FIGS. 69 and 70  has mounting elements  944  that are dowel pins configured to align with a second set of mounting elements on, for example, a rammer. However, a different adapter plate  936   a  of  FIG. 71  has mounting elements  944   a  that are protrusions  946  with holes  947  configured to align with a second set of mounting elements on, for example, a lawn mower, log splitter, or earth auger, in a vertical power take-off shaft  38  mounting arrangement. The mounting elements  944   a  could have a pattern of holes as laid out in the SAE J609 Flange Patterns B, C, D, E or F mounting patterns. 
     In other embodiments, the mounting elements  944  may include studs or fasteners. In some embodiment, the studs could be threaded. The adapter plate  936  also includes a through bore  948  for passage of the power take-off shaft  38 . In some embodiments, the adapter plate  936  includes a piloting member configured to pilot the adapter plate  936  onto the piece of power equipment, such that first set of mounting elements  944  of the adapter plate  936  are forced to align with the second set of mounting elements on the piece of power equipment. In some embodiments, the second holes  940  are recessed mounting holes so that fasteners can be arranged sub-flush on equipment side  948  of the adapter plate  936  to allow the adapter plate  936  to sit flat on the power equipment to which it is mounted. 
     As shown in  FIG. 71 a   , the motor unit  10  can be provided to an OEM without a power take-off shaft  38  assembled. The OEM could then select an appropriate power take-off shaft  38 ′,  38 ″ for the application needed and assemble the selected power take-off shaft  38  to the motor unit  10 . In some embodiments, the faceplate  124  of the gearbox  650  would need to be removed to assemble the different power take-off shafts  38 ′,  38 ″. 
     When swapping out different power take-off shafts  38 , a variety of different methods can be used to axially retain the power take off shaft  38 , as shown in  FIGS. 72-76 . In  FIG. 72 , a final drive gear  952  of the gear train  110  has a journal  956  rotatably supported by a first bearing  960 , a shaft carrier  964  rotatably supported by a second bearing  968 , a recess  972  in the shaft carrier  964 , and a plurality of ball detents  976  biased into the recess  972  by, e.g., springs  978 . A power take-off shaft  38   x  shown in  FIG. 72  includes a splined portion  980  having splines  982  configured to be received in the recess  972 , and a driving end  984  configured to drive the piece of power equipment. The splined portion  980  includes a circumferential recess  988 . 
     When the splined portion  980  of the power-take off shaft  38   x  is inserted into the recess  972  of the final drive gear  952 , the splines  982  engage with corresponding splines of the recess  972 , such that the power-take off shaft  38   x  is coupled for rotation with the final drive gear  952 . In other embodiments, instead of a splined portion  980  with splines  982 , the power take-off shaft  38   x  could include a D-shape, hex shape, or other key and keyway mating connection with the recess  972  to enable co-rotation with the drive gear  952 . Also, when the splined portion  980  is received into the recess  972 , the ball detents  976  are biased into the circumferential recess  988 , such that the power take-off shaft  38   x  is axially locked with respect to the final drive gear  952 . When the power-take off shaft  38   x  is secured in the final drive gear  952 , the power take-off shaft  38   x  is rotatably supported with respect to the gearbox  650  (illustrated), faceplate  124 , or adapter plate  936  by a third bearing  992 . The power take-off shaft  38   x  can be removed by the operator pulling on the driving end  984  to overcome the biasing force of the detents  976  and move them out of the circumferential recess  988 . Then the operator can insert a different power take-off shaft that also has the splined portion  980  with the circumferential recess  988 , but has a different driving end configured to drive a different piece of power equipment than the power take-off shaft  38   x.    
     In another embodiment shown in  FIG. 73 , a final drive gear  996  of the gear train  110  has a journal  1000  rotatably supported by a first bearing  1004 , a shaft carrier  1008 , and a recess  1012  in the shaft carrier  1008 . A power take-off shaft  38   y  shown in  FIG. 74  includes a splined portion  1016  having splines  1020  configured to be received in the recess  1012 , and a driving end  1024  configured to drive the piece of power equipment. In other embodiments, instead of a splined portion  1016  with splines  1020 , the power take-off shaft  38   y  could include a D-shape, hex shape, or other key and keyway mating connection with the recess  1012  to enable co-rotation with the drive gear  996 . The power take-off shaft  38   y  includes a snap ring  1028 , or clip, configured to axially retain the power take-off shaft  38   y  to one of the gear box  650 , faceplate  124 , or adapter plate  936 , depending on how the motor unit  10  is configured for that particular application. The power take-off shaft  38   y  is rotatably supported with respect to the snap ring  1028  by a second bearing  1032 . 
     In another embodiment shown in  FIG. 74 , a final drive gear  1036  of the gear train  110  has a first journal  1040  supported by a first bearing  1044 , a second journal  1048  supported by a second bearing  1052 , a shaft carrier  1054 , and a circumferential recess  1056  between the shaft carrier  1054  and the second journal  1048 . A quick release collar  1060  is arranged in the recess  1056  and is biased away from the first journal  1040  by a compression spring  1064 , but is prevented from being biased out of the recess  1056  by a retaining clip  1068  set in the recess  1056 . The collar  1060  includes a circumferential lip  1072  and circumferential recess  1076  adjacent the circumferential lip  1072 . A plurality of ball detents  1080  are set in a plurality of radial bores  1084  extending through the shaft carrier  1054 . The collar  1060  is biased by the spring  1064  to a first position ( FIG. 74 ), in which the circumferential lip  1072  is axially aligned with the ball detents  1080 , such that the detents  1080  are forced into a passage  1088  in the shaft carrier  1054 . The collar  1060  is moveable from the first position to a second position, in which the circumferential recess  1076  is axially aligned with the ball detents  1080 . A power take-off shaft  38   z  includes a splined portion  1092  with splines  1096  and a circumferential groove  1100 , and a driving end  1104  configured to drive the piece of power equipment. 
     In operation of the embodiment shown in  FIG. 74 , the collar  1060  is moved to the second position by the operator and the splined portion  1092  of the power take-off shaft  38   z  is inserted into the passage  1088  of the shaft carrier  1054 , such that splines  1096  of the splined portion  1092  mate with corresponding splines in the passage  1088 , thus coupling the power take-off shaft  38   z  for rotation with the final drive gear  1036 . In other embodiments, instead of a splined portion  1092  with splines  1096 , the power take-off shaft  38   z  could include a D-shape, hex shape, or other key and keyway mating connection with the passage  1088  to enable co-rotation with the drive gear  1036 . As the power take-off shaft  38   z  is inserted, the ball detents  1080  are pushed by the power take-off shaft  38   z  radially outward into the circumferential recess  1076  of the collar  1060 . Once the power take-off shaft  38   z  has been inserted, the collar  1060  is released and biased back to the first position by the spring  1064 , causing the detents  1080  to be pushed by the circumferential lip  1072  of the collar  1060  to a radially inward position in which they are arranged in the circumferential grove  1100  of the power take-off shaft  38   z , thus axially locking the power take-off shaft  38   z  with respect to the final drive gear  1036 . If the power take-off shaft  38   z  is attempted to be removed from the passage  1088  before moving the collar  1060  to the second position, the circumferential lip  1072  prevents the detents  1080  from moving radially outward, and thus the power take-off shaft  38   z  cannot be moved axially. 
     To remove the power take-off shaft  38   z  from the final drive gear  1036 , the collar  1060  is first moved to the second position by the operator and the power take-off shaft  38   z  is then pulled from the passage  1088 . As the power take-off shaft  38   z  moves out of the passage  1088 , the detents  1080  are pushed by the power take-off shaft  38   z  radially outward into the circumferential recess  1076  of the collar  1060 . Then the operator can insert a different power take-off shaft that also has the splined portion  1092  with the circumferential recess  1100 , but has a different driving end configured to drive a different piece of power equipment than the power take-off shaft  38   z.    
     In another embodiment shown in  FIG. 75 , a final drive gear  1100  of the gear train  110  has a first journal  1104  supported by a first bearing  1108 , a shaft carrier  1112  supported by a second bearing  116  arranged in the faceplate  124  of the gear box  650 . A quick release collar  1120  is arranged around the shaft carrier  1112  and is biased away from the first journal  1104  by a compression spring  1124  seated in a recess  1126  in the final drive gear  1100 . The release collar  1120  abuts against the second bearing  1116  when the faceplate  124  is coupled to the gearcase  650 . 
     The collar  1120  includes a circumferential lip  1128  and circumferential recess  1132  adjacent the circumferential lip  1128 . A plurality of ball detents  1136  are set in a plurality of bores  1140  extending through the shaft carrier  1112 . As noted above, when the faceplate  124  is coupled to the gearbox  650 , the collar  1120  is biased by the spring  1124  to a first position, in which the collar  1120  abuts the second bearing  1116 , such that the circumferential lip  1128  is axially aligned with the ball detents  1136 , and the detents  1136  are thus forced by the circumferential lip  1128  into a passage  1144  in the shaft carrier  1112 . When the faceplate  124 , and thus the second bearing  1116 , is removed from the gearbox  650 , the collar  1120  is moveable from the first position to a second position, in which the circumferential recess  1132  is axially aligned with the ball detents  1136 . 
     In operation of the embodiment shown in  FIG. 75 , the faceplate  124  is not yet coupled to the gearbox and the collar  1120  is thus in the second position. The splined portion  1092  of the power take-off shaft  38   z  is inserted into the passage  1144  of the shaft carrier  1112 , such that splines  1096  of the splined portion  1092  mate with corresponding splines in the passage  1144 , thus coupling the power take-off shaft  38   z  for rotation with the final drive gear  1100 . In other embodiments, instead of a splined portion  1092  with splines  1096 , the power take-off shaft  38   z  could include a D-shape, hex shape, or other key and keyway mating connection with the passage  1144  to enable co-rotation with the drive gear  1100 . Once the power take-off shaft  38   z  has been inserted, the faceplate  124  is coupled to the gearbox  650 , thus causing the collar  1120  to be moved from the second position to the first position, causing the detents  1136  to be pushed by the circumferential lip  1128  of the collar  1120  to a radially inward position in which they are arranged in the circumferential recess  1100  of the power take-off shaft  38   z , thus axially locking the power take-off shaft  38   z  with respect to the final drive gear  1100 . If the power take-off shaft  38   z  is attempted to be removed from the passage  1144  before moving the collar  1120  to the second position, the circumferential lip  1128  prevents the detents  1136  from moving radially outward, and thus the power take-off shaft  38   z  cannot be moved axially. 
     To remove the power take-off shaft  38   z  from the final drive gear  1100 , the faceplate  124 , and thus the second bearing  1116 , is removed from the gearbox  650 . As the faceplate  124  is removed, the collar  1120  is biased by the spring  1124  from the first position to the second position, in which the circumferential recess  1132  is axially aligned with the ball detents  1136 . The operator then pulls the power take-off shaft  38   z  from the passage  1144 . As the power take-off shaft  38   z  is pulled from the passage  1144 , the detents  1136  are pushed by the power take-off shaft  38   z  radially outward into the circumferential recess  1132  of the collar  1120 . Then the operator can insert a different power take-off shaft  38  that also has the splined portion  1092  with the circumferential recess  1100 , but has a different driving end configured to drive a different piece of power equipment than the power take-off shaft  38   z.    
     In another embodiment shown in  FIG. 76 , a final drive gear  1148  of the gear train  110  has a first journal  1152  supported by a first bearing  1156  and a shaft carrier  1160  supported by a second bearing  1116  arranged in the faceplate  124  of the gear box  650 . The shaft carrier  1160  includes a threaded bore  1164  for a set screw  1168  that is radially moveable into or out of a passage  1172  in the shaft carrier  1160 . To install a power take-off shaft  38   w , an operator inserts the power take-off shat  38   w  into the passage  1172  until a circumferential groove  1176  in the shaft  38   w  is axially and circumferentially aligned with the bore  1164  of the shaft carrier  1160 . The operator then screws the set screw  1168  radially inward to engage the circumferential recess  1176  of the power take-off shaft  38   w , such that the power take-off shaft  38   w  is axially coupled to the final drive gear  1148 . Also, because the power take-off shaft  38   w  has a splined portion  1180  having splines  1182  that mates with a corresponding splined portion in the passage  1172 , the power take-off shaft  38   w  is coupled for rotation with the final drive gear  1148 . In other embodiments, instead of a splined portion  1180  with splines  1182 , the power take-off shaft  38   z  could include a D-shape, hex shape, or other key and keyway mating connection with the passage  1172  to enable co-rotation with the drive gear  148 . 
     In order to remove the power take-off shaft  38   w , the operator simply unscrews the set screw  1168  until it is out of the circumferential groove  1176  and passage  1172 , and then removes the power take-off shaft  38   w . Then the operator can insert a different power take-off shaft  38  that also has the splined portion  1180  with the circumferential groove  1176 , but has a different driving end configured to drive a different piece of power equipment than the power take-off shaft  38   w . In other embodiments, instead of a circumferential groove  1176 , the power take-off shaft  38   w  could include a radial bore to receive the set screw  1168 , thus enabling both axial retention and co-rotation with the drive gear  1148 . 
     Thus, with interchangeable adapter plates  936 ,  936   a , and interchange power take-off shafts  38 , such as the power take-off shaft  38   a ,  38   b ,  38   w ,  38   x ,  38   y ,  38   z  and their corresponding mounting arrangements described above and shown in  FIGS. 33, 34 and 72-76 , the motor unit  10  can be customized to mate with and drive a variety of different pieces of power equipment. Indeed, the power take-off shaft  38  could have the dimensions of any of the power take-off shaft Extensions for horizontal crankshaft engines defined in the SAE J609, such as the dimensions of Extensions 1, 2, 3, 4, 4a, 4b, 6, 6a, 6b, or 8. 
     In another embodiment shown in  FIG. 77 , like the embodiment of  FIGS. 69-71 , the faceplate  124  includes the first plurality of holes  932  defining a first hole pattern. However, unlike the embodiment of  FIGS. 69-71 , instead of a through bore  948 , the embodiment of  FIG. 77  includes an adapter plate  1184  having a rotatable power take-off shaft  38 . Depending on the desired application, the power take-off shaft  38  could have the dimensions of any of the extensions defined in the SAE J609, such as extensions 1, 2, 3, 4, 4a, 4b, 6, 6a, 6b, or 8. 
     Like the adapter plate  936  of  FIGS. 69-71 , the adapter plate  1184  includes the second plurality of holes  940  defining the second hole pattern that is identical to the first hole pattern, such that when the second holes  940  are aligned with first holes  932  of the faceplate  124 , the adapter plate  1104  is configured to be coupled to the faceplate  124 . 
     The adapter plate  1104  also includes a third plurality of holes  1188  defining a third hole pattern that is different than the first and second hole patterns and identical to a fourth hole pattern on a certain piece of power equipment. Thus, after the adapter plate  1104  has been coupled to the faceplate  124 , the adapter plate  1104  is configured to be coupled to the piece of power equipment when the third hole pattern is aligned with the fourth hole pattern. When the adapter plate  1104  is coupled to both the faceplate  124  and the piece of power equipment, the power take-off shaft  38  is configured to receive torque from the motor  36  via the geartrain  110  to thereby drive the piece of power equipment. In some embodiments, the third hole pattern could be one of the SAE J609 Flange Patterns B, C, D, E or F mounting hole patterns. 
     Unlike the adapter plate  936 , the adapter plate  1184  does not require an operator to swap out power take-off shafts  38 , because the power take-off shaft  38  is included as part of the adapter plate  1184 . Thus, different adapter plates  1184  can be created with different combinations of third hole patterns and power take-off shafts  38  directed to certain types of equipment. Some examples are listed in Table 11 below. However, the combinations and permutations of the adapter plate  1184  are not limited to these examples, and the adapter plate  1184  can have its third hole pattern and power take-off shaft  38  modified to mate with any application. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 11 
               
               
                   
                   
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Third hole pattern of adapter 
                 SEA J609 
                 SEA J609 
                 SEA J609 
                 SEA J609 
                 SEA J609 
               
               
                 plate 1104 
                 Flange A 
                 Flange A 
                 Flange A 
                 Flange B 
                 Flange C 
               
               
                 Type of power take-off shaft 
                 SAE J609 
                 SAE J609 
                 SAE J609 
                 SAE J609 
                 SAE J609 
               
               
                 38 for adapter plate 1104 
                 Extension 3 
                 Extension 5 
                 Extension 7 
                 Extension 3 
                 Extension 7 
               
               
                   
               
            
           
         
       
     
     In an embodiment of the motor unit  10  shown in  FIG. 78 , the motor unit  10  includes the gearbox  650  with the faceplate  124 , and the power take-off shaft  38  with a pinion  1192 . An external gearbox  650   e  is coupled to the faceplate  124  via the first plurality of holes  932  defining a first hole pattern, which match a corresponding pattern of holes  1196  on the external gearbox  650   e . The external gearbox  650   e  has a faceplate  124 ′ that also has the first plurality of holes  932  defining the first hole pattern, such that the faceplate  124 ′ can couple to the piece of power equipment by aligning the first hole pattern with an identical hole pattern on the piece of power equipment. The external gearbox  650   e  has a power take-off shaft  38   e  that receives torque via the motor  36 , the gear train  110  of the gearbox  650 , the power take-off shaft  38  with pinion  1192 , and a second gear train  110   s  of external gearbox  650   e . Thus, the external gear box  650   e  can be coupled to the faceplate  124  and used to achieve additional gear reduction that would not be achievable with the gearbox  650  alone. 
     In an embodiment of the motor unit  10  shown in  FIGS. 79 and 80 , the first plurality of holes  932  of the face plate  124  has a SAE J609 Flange A mounting hole pattern. Thus, the motor unit  10  is ready, without alteration, to be coupled to a legacy gearbox  6501  of a piece of power equipment that has a corresponding pattern of holes  1120  that align with the first plurality of holes  932 . Thus, the legacy gearbox  6501  could be easily installed to the motor unit  10  and/or serviced. 
     In an embodiment shown in  FIGS. 81 and 82 , the motor unit  10  includes the gearbox with a faceplate  124 ′, and the power take-off shaft  38  having a keyway shaft, such as the J609 Extension 3 shaft. The external gearbox  650   e  is coupled to the faceplate  124 ′ via the first plurality of holes  932  defining a first hole pattern, which match the corresponding pattern of holes  1196  on the external gearbox  650   e . The external gearbox  650   e  has the same faceplate  124 ′ as the faceplate  124 ′ of the gearbox  650 , and thus the same first plurality of holes  932 . Thus, the external gear box  650   e  can be coupled to the faceplate  124 , and then to the piece of power equipment by aligning the first plurality of holes  932  of the gearbox  650  with the piece of power equipment. The external gear box  650   e  can thus be used to achieve additional gear reduction that would not be achievable with the gearbox  650  alone. The faceplate  124 ′ also has the same power take-off shaft  38  as the power take-off shaft  38  of the motor unit  10 , such that these parts would be easy to swap between the gearbox  650  and external gearbox  650   e . Thus, an operator or OEM could use the external gearbox  650   e  to achieve a mechanical reduction, but still have the option to swap the power take-off shaft  38  to be the J609 Extension 5 shaft, and to replace faceplate  124 ′ to utilize a new J609 flange mounting pattern. Also, the power take-off shaft  38  of the external gearbox  650   e  thus receives torque via the motor  36 , the gear train  110  of the gearbox  650 , the power take-off shaft  38  of the motor unit  10 , and the second gear train  110   s  of external gearbox  650   e.    
     As shown in  FIGS. 83-85 , in some embodiments, instead of removable and swappable power take-off shafts  38   w ,  38   z , each having the splined portion  1092  with splines  1096  and the circumferential groove  1100 , a plurality of power equipment units  1184   a ,  1184   b ,  1184   c  each have a shaft  1188  with the splined portion  1092  with splines  1096  and the circumferential groove  1100 . For instance, as shown in  FIG. 83 , the power equipment unit  1184   a  includes a pulley  1192  coupled for rotation with the shaft  1188 . As shown in  FIG. 84 , the power equipment unit  1184   b  includes an impeller  1196  coupled for rotation with the shaft  1188 . As shown in  FIG. 85 , the power equipment unit  1184   c  includes a pump  1200  configured to be driven by the shaft  1188 . 
     Thus, instead of needing to exchange different power take-off shafts (e.g.  38   w ,  38   z ) with different driving ends configured to drive different pieces of power equipment, in the embodiment of  FIGS. 83-85 , the operator can rely on the different power equipment units  1184   a ,  1184   b ,  1184   c  having a common shaft  1188  that is receivable and axially retainable in the passages  1144 ,  1172  of the final drive gears  1100 ,  1148  of the gear train  110  in the same manner as power take-off shafts  38   w ,  38   z  described above. Thus, to switch between power equipment units  1184   a ,  1184   b ,  1184   c  the operator need only remove the shaft  1188  of the power equipment unit coupled to the motor unit  10 , and then insert the new shaft  1188  of the next power equipment unit into the passages  1144 ,  1172  of the final drive gears  1100 ,  1148 . 
     As shown in  FIGS. 86-92 , in some embodiments, the flange  34  includes a slot  1204  configured to receive a protrusion  1206  of a piece of power equipment  1208 , for mounting the motor unit  10  to the piece of power equipment  1208 . In some embodiments, the flange  34  may include more than one slot  1204  to respectively accommodate more than one protrusion  1206  on the piece of power equipment  1208 . The slot  1204  has a slot depth SD that is defined between an outer surface  1212  of the flange  34  and a base  1216  of the slot  1204 , which is parallel to the rotational axis  122  of the power take-off shaft  38 . The slot  1204  also includes a first portion  1220  having a first surface width SW 1  at the outer surface  1212  of the flange and a first base width BW 1  at the base  1216  of the slot  1204 . In the illustrated embodiment, the first surface width SW 1  is equal to the first base width BW 1 . The slot  1204  also includes a second portion  1222  having a second surface width SW 2  at the outer surface  1212  of the flange  34 , and a second base width BW 2  at the base  1216  of the slot  1204 . 
     As shown in  FIGS. 90 and 92 , the second base width BW 2  is less than the first base width BW 1 . As shown in  FIGS. 87, 90 and 92 , the second surface width SW 2  is less than the first surface width SW 1  and the second base width BW 2 . As shown in  FIG. 87 , the surface width of the slot  1204  tapers from the first portion  1220  to the second portion  1222 , such a pair of recesses  1224  are defined between a pair of overhangs  1228  (shown in  FIGS. 87 and 92 ) and the base  1216  in the second portion  1222 . As shown in  FIGS. 90 and 92 , the protrusion  1206  has a height H that is nominally smaller than the slot depth SD of the slot  1204 , and includes a stem  1232  and a pair of legs  1236  extending orthogonal to the stem  1232 . Together, the legs  1236  define a protrusion width PW that is nominally smaller than the second base width BW 2 . 
     In operation, to mount the motor unit  10  to the piece of power equipment  1208 , the motor unit  10  is moved in a first direction D 1  toward the piece of power equipment  1208 , with the first portion  1220  of the slot  1204  arranged over the protrusion  1206 , as shown in  FIG. 88 . Once the flange  34  contacts the piece of power equipment  1208 , the protrusion  1206  is arranged in a first position in the first portion  1220  of the slot  1204 , as shown in  FIGS. 89 and 90 . Next, as shown in  FIG. 90 , the motor unit  10  is moved in a second direction D 2  that is perpendicular to the first direction D 1  and parallel to the rotational axis  122  of the power take-off shaft  38 . Movement in the second direction D 2  causes the power take-off shaft  38  to mate with a rotational input  1240  of the piece of power equipment  1208  and the slot  1204  to move along the protrusion  1206  until the legs  1236  are arranged in the recesses  1224  of the second portion  1222  of the slot  1204 , such that the protrusion  1206  is in a second position in the slot  1204 , as shown in  FIGS. 91 and 92 . Now, movement of the motor unit  10  off the power equipment  1208  in a third direction D 3  opposite the first direction D 1  is inhibited, because the overhangs  1228  block the legs  1236  and thereby inhibit the protrusion  1206  from being removed from the slot  1204  in the direction D 3 . Thus, the operator can now operate the motor unit  10  to drive the rotational input  1240  of the piece of power equipment  1208  via the power take-off shaft  38 . Specifically, once the power take-off shaft  38  is coupled to the rotational input  1240 , torque from the motor unit  10  can be transferred to the rotational input  1240  to operate the piece of power equipment  1208 . 
     In order to remove the motor unit  10  from the piece of power equipment  1208 , the motor unit  10  is moved in a direction opposite the second direction D 2  until the protrusion  1206  is in the first position in the slot  1204  and the power take-off shaft  38  is decoupled from the rotational input  1240 . Now, because the overhangs  1228  no longer block the legs  1236  and because the first surface width SW 1  of the first portion  1220  of the slot  1204  is greater than the protrusion width PW, the motor unit  10  may be removed from the piece of power equipment by moving the motor unit  10  in the direction D 3 . 
     As shown in  FIG. 93 , in some embodiments, the motor unit  10  includes a tensioner assembly  1232  configured to tension a belt  1236  that is arranged on a first, driven pulley  1242  of a piece of power equipment and a second, driving pulley  1244  on the power take-off shaft  38 . The tensioner assembly  1232  includes a mounting plate  1248  having a plurality of holes  1252  defining a second hole pattern that is identical to the first hole pattern of the faceplate  124  (defined by first holes  932 , as shown in  FIG. 69 ), such that when the second holes  1252  are aligned with the first holes  932 , the mounting plate  1248  is configured to be coupled to the faceplate  124  via a plurality of coupling elements such as, e.g. fasteners. 
     The mounting plate  1248  also includes a through-bore  1250  to allow the power take-off shaft  38  to extend therethrough. The tensioner assembly  1232  also includes a tension arm  1256  that is pivotably coupled to the mounting plate  1248  and biased toward the belt  1236  by, e.g., a torsion spring arranged at a pivot post  1260  on the mounting plate  1248 . An idler pulley  1264  is arranged on the tension arm  1256 , such that the tension pulley  1264  is biased into engagement with the belt  1236  to increase a tension within the belt  1236 . The tensioner assembly  1232  of  FIG. 93  is particularly advantageous when the motor unit  10  is used to drive a piece of power equipment having the first pulley  1242 , and a distance  1268  between the first and second pulleys  1242 ,  1244  cannot be adjusted due to the mounting relationship between the motor unit  10  and the piece of power equipment. In other embodiments, the tensioner assembly  1232  does not include the mounting plate  1248  and instead, the tension arm  1256  is coupled to another location on the motor unit  10 , such as the housing  14 . 
     In an embodiment shown in  FIG. 94 , the OEM may want to prevent an operator from retrofitting a gas engine to the OEM&#39;s piece of power equipment  1272 , thus requiring the operator to use the motor unit  10  to drive the piece of power equipment  1272 . Thus, the motor unit  10  includes a threaded annular recess  1276  coaxial with and surrounding a first through-bore  1280  in the faceplate  124  for the power take-off shaft  38 . The piece of power equipment  1272  includes an annular radially outward-extending first flange  1284 . 
     A collar  1292  has a threaded end  1296  that is threadably received into the threaded annular recess  1276 , and an annular radially inward-extending second flange  1300  opposite the threaded end  1296  and configured to engage the first flange  1284  of the piece of power equipment  1272 . Specifically, after the power take-off shaft  38  is arranged on the motor unit  10  and the collar  1292  is arranged on the first flange  1284  of the piece of power equipment  1272 , the threaded end  1296  of the collar  1292  is threaded into the threaded annular recess  1276 , thus bringing the piece of power equipment  1272  closer to or into contact with the faceplate  124  of the motor unit  10 , until a rotational input  1286  of the piece of power equipment  1272  receives the power take-off shaft  38 , such that the piece of power equipment  1272  can be driven thereby. Also, the collar  1292  axially locks the piece of power equipment  1272  with respect to the motor unit  10 , because the second flange  1300  of the collar  1292  inhibits the first flange  1284 , and thus the piece of power equipment  1272 , from moving away from the faceplate  124 . 
     Thus, in order to drive the piece of power equipment  1272 , the operator must mount the motor unit  10  to the piece of power equipment  1272  using the collar  1292 . In other words, the operator could not use a gas engine unit to drive the piece of power equipment  1272 , because a gas engine unit would not have the threaded annular recess  1276  capable of receiving the collar  1292  with the second flange  1300  that engages with the first flange  1284  of the piece of power equipment  1272 . 
     Various features of the invention are set forth in the following claims.