Patent Publication Number: US-2021194319-A1

Title: Power tool with compact motor assembly

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/950,409 filed Dec. 19, 2019, content of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This disclosure relates to a power tool, such as an impact driver or impact wrench, with a compact motor assembly, such as a low-profile and compact brushless motor assembly. 
     BACKGROUND 
     Power tools such as impact drivers and impact wrenches may be used for driving threaded fasteners into workpieces. Such power tools may lack sufficient power to drive a threaded fastener into a workpiece or may be too large in length or girth to fit into a desired location. In such power tools, it is desirable to reduce the girth and/or length of the tool, including the motor assembly and related components, without sacrifice power performance. 
     SUMMARY 
     In a first aspect, a power tool includes a housing having a rearward end portion and a forward end portion and a brushless motor received in the housing. The motor includes a rotor configured to rotate about a rotor axis and a stator assembly having a stator core and conductive windings. The motor defines a motor envelope bounded by a rear plane at a rearmost point of the stator assembly and the rotor, a front plane at a frontmost point of the stator assembly and the rotor, and a generally cylindrical boundary extending from the rear plane to the front plane and surrounding a radially outermost portion of the stator assembly and the rotor. A rotor shaft extends along the rotor axis and is coupled to and configured to be rotatably driven by rotation of the rotor. A transmission is received in the housing and includes an input member coupled to and configured to be rotatably driven by rotation of the rotor shaft, and an output member configured to be driven by rotation of the input member. A first bearing is configured to support the rotor shaft and is at least partially received within the motor envelope. A second bearing is configured to support a component of the transmission and is at least partially received within the motor envelope. 
     In a second aspect, a power tool includes a housing having a rearward end portion and a forward end portion and a brushless motor received in the housing. The motor includes a rotor configured to rotate about a rotor axis and a stator assembly having a stator core and conductive windings. A rotor shaft extends along the rotor axis and is coupled to and configured to be rotatably driven by rotation of the rotor. A transmission is received in the housing and includes an input member coupled to and configured to be rotatably driven by rotation of the rotor shaft. An output member is configured to be driven by rotation of the input member. A first bearing is configured to support the rotor shaft and at least partially nested inside the stator assembly. A second bearing is configured to support a component of the transmission and at least partially nested inside the stator assembly. 
     Implementations of the first and second aspects may include one or more of the following features. The stator may at least partially surround the rotor. The input member may comprise a gear rotatably driven by the rotor shaft. The transmission may comprise a planetary gear set with the input member including a sun gear rotatably driven by the rotor shaft, the output member including a carrier, and the planetary gear set further including a planet gear rotatably mounted to the carrier and meshed with the sun gear and a ring gear meshed with the planet gear and held non-rotatably relative to the housing. The second bearing may be configured to support the carrier. The second bearing may be configured to support the sun gear. The second bearing may be configured to support the output member and may further comprise a third bearing configured to support the rotor shaft. The rearward end portion of the housing may include a rear cap defining a recess and the third bearing may be disposed at least partially in the recess. A fan may be coupled to the rotor shaft. The fan may be disposed between the stator and the rear end wall. The fan may include a hub and a vane portion extending radially outward from the hub. The hub may be at least partially received in the stator assembly. 
     A support plate may be configured to support at least a portion of the transmission and held non-rotatably relative to the housing. The support plate may include a nested portion at least partially received within the motor envelope. The nested portion of the support plate may support the first bearing. The nested portion of the support plate may support the second bearing. The nested portion of the support plate may include a rearward projection of the support plate. The nested portion may be at least partially received within the stator. The nested portion may be at least partially received within a recess in the rotor. The first bearing may be nested at least partially within at least a portion of the rotor. The rotor may define a central recess and the first bearing may be received at least partially within the recess. 
     An output spindle may have a front end proximal a front end portion of the housing and a rotational impact mechanism coupled to the output member of the transmission and to the output spindle. The impact mechanism may be configured to transmit continuous rotary motion without impacts from the transmission to the output spindle when a torque on the output spindle does not exceed a transition torque, and to transmit rotational impacts from the motor to the output spindle when a torque on the output spindle exceeds the transition torque. The mechanism may include a cam shaft extending forward from the output member, a hammer received over the cam shaft and configured to move axially and rotationally relative to the cam shaft, a spring disposed between the hammer and the output member and configured to bias the hammer away from the cam shaft, and an anvil coupled to the output spindle, the hammer configured to transmit continuous rotary motion to the anvil when the torque on the output spindle does not exceed a transition torque and the hammer configured to apply rotational impacts to the anvil when the torque on the output spindle exceeds a transition torque. 
     The power tool may have a maximum power output of at least 430 Watts and a length of the tool from a rear end of the housing to a front end of the output spindle of less than or equal to 110 mm. A ratio of the maximum power output of the motor to the length of the tool may be at least 4.5 Watts/mm. The power tool may have a maximum output torque of at least 1820 inch-pounds and a length of the tool from a rear end of the housing to a front end of the output spindle is less than or equal to 110 mm. A ratio of the maximum output torque of the tool to the length of the tool may be at least 18.0 inch-pounds/mm. 
     In a third aspect, a power tool includes a housing having a rearward end portion, a forward end portion, and defining a tool axis. A brushless motor is received in the housing. The motor includes a rotor configured to rotate about a rotor axis and a stator assembly having a stator core and conductive windings. A rotor shaft extends along the rotor axis and is configured to be rotatably driven by rotation of the rotor. A transmission is received in the housing and includes an input member configured to be rotatably driven by rotation of the rotor shaft and an output member configured to be driven by rotation of the input member. An output spindle has a front end proximate the front end portion of the housing. A rotational impact mechanism is coupled to the output member of the transmission and to the output spindle. The impact mechanism is configured to transmit continuous rotary motion without impacts from the transmission to the output spindle when a torque on the output spindle does not exceed a transition torque, and to transmit rotational impacts from the motor to the output spindle when a torque on the output spindle exceeds the transition torque. A ratio of maximum power output to a length of the tool from a rear end of the housing to a front end of the output spindle is at least 4.5 Watts/mm. 
     In a fourth aspect, a power tool includes a housing having a rearward end portion, a forward end portion, and defining a tool axis. A brushless motor is received in the housing. The motor includes a rotor configured to rotate about a rotor axis and a stator assembly having a stator core and conductive windings. A rotor shaft extends along the rotor axis and is configured to be rotatably driven by rotation of the rotor. A transmission is received in the housing and includes an input member configured to be rotatably driven by rotation of the rotor shaft and an output member configured to be driven by rotation of the input member. An output spindle has a front end proximate the front end portion of the housing. A rotational impact mechanism is coupled to the output member of the transmission and to the output spindle. The impact mechanism is configured to transmit continuous rotary motion without impacts from the transmission to the output spindle when a torque on the output spindle does not exceed a transition torque, and to transmit rotational impacts from the motor to the output spindle when a torque on the output spindle exceeds the transition torque. A ratio of a maximum output torque of the tool to a length of tool from a rear end of the housing to a front end of the output spindle is at least 18.0 inch-pounds/mm. 
     Implementations of the third and fourth aspects may include one or more of the following features. The stator may at least partially surround the rotor. The input member may comprise a gear rotatably driven by the rotor shaft. The transmission may comprise a planetary gear set with the input member including a sun gear rotatably driven by the rotor shaft, the output member including a carrier, and the planetary gear set further including a planet gear rotatably mounted to the carrier and meshed with the sun gear and a ring gear meshed with the planet gear and held non-rotatably relative to the housing. A first bearing may be configured to support the motor output shaft and may be at least partially nested within the stator assembly. A second bearing may be configured to support at least one of the rotor shaft and a portion of the transmission. At least a portion of the second bearing may be nested within the stator assembly. The second bearing may be configured to support the rotor shaft. A third bearing may be configured to support the input member of the transmission. The second bearing may be configured to support the input member of the transmission. The third bearing may be configured to support the rotor shaft. The third bearing may be positioned rearward of the stator. The housing may include a rear end wall with a recess and the third bearing may be disposed at least partially in the recess. 
     A fan may be coupled to the rotor shaft. The fan may be disposed between the stator and the rear end cap. The rotor may define a central recess and the first bearing may be received at least partially within the recess. A support plate may be configured to support at least a portion of the transmission and held non-rotatably relative to the housing. The support plate may be at least partially received within the stator. The support plate may support a first bearing that supports the rotor shaft and a second bearing that supports at least one of the rotor shaft and a portion of the transmission. The support plate may have a rearward projection that is at least partially received within a recess in the rotor. 
     The impact mechanism may include a cam shaft extending forward from the output member, a hammer received over the cam shaft and configured to move axially and rotationally relative to the cam shaft, a spring disposed between the hammer and the output member and configured to bias the hammer away from the cam shaft, and an anvil coupled to the output spindle, the hammer configured to transmit continuous rotary motion to the anvil when the torque on the output spindle does not exceed a transition torque and the hammer configured to apply rotational impacts to the anvil when the torque on the output spindle exceeds a transition torque. The power tool may have a maximum power output of at least 430 Watts and a length of the tool from a rear end of the housing to a front end of the output spindle may be less than or equal to 110 mm. The power tool may have a maximum output torque of at least 1820 inch-pounds and a length of the tool from a rear end of the housing to a front end of the output spindle of less than or equal to 110 mm. 
     In a fifth aspect, a power tool includes a housing having a rear end portion and a front end portion and a brushless motor received in the housing. The motor includes a rotor configured to rotate about a rotor axis and a stator assembly having a stator core and conductive windings. The motor defines a motor envelope bounded by a rear plane at a rearmost point of the stator assembly and the rotor, a front plane at a frontmost point of the stator assembly and the rotor, and a generally cylindrical boundary extending from the rear plane to the front plane and surrounding a radially outermost portion of the stator assembly and the rotor. A rotor shaft extends along the rotor axis and is coupled to and configured to be rotatably driven by rotation of the rotor. A transmission is received in the housing and includes an input member configured to be rotatably driven by rotation of the rotor shaft, and an output member configured to be driven by rotation of the input member. A support plate is configured to support at least a portion of the transmission, where the support plate is held non-rotatably relative to the housing and has a rearward portion at least partially received within the motor envelope. 
     In a sixth aspect, a power tool includes a housing having a rear end portion and a front end portion and a brushless motor received in the housing. The motor includes a rotor configured to rotate about a rotor axis and a stator assembly having a stator core and conductive windings. A rotor shaft extends along the rotor axis and is coupled to and configured to be rotatably driven by rotation of the rotor. A transmission is received in the housing and includes an input member configured to be rotatably driven by rotation of the rotor shaft, and an output member configured to be driven by rotation of the input member. A support plate is configured to support at least a portion of the transmission, where the support plate is held non-rotatably relative to the housing and has a rearward portion at least partially nested within the stator assembly. 
     In a seventh aspect, a power tool includes a power tool includes a housing having a rear end portion and a front end portion and a brushless motor received in the housing. The motor includes a rotor configured to rotate about a rotor axis and a stator assembly having a stator core and conductive windings. A rotor shaft extends along the rotor axis and is coupled to and configured to be rotatably driven by rotation of the rotor. A transmission is received in the housing and includes an input member configured to be rotatably driven by rotation of the rotor shaft, and an output member configured to be driven by rotation of the input member. A support plate is configured to support at least a portion of the transmission, where the support plate is held non-rotatably relative to the housing and has a rearward portion at least partially received within the rotor. 
     Implementations of the fifth, sixth, and seventh aspects may include one or more of the following features. The stator may at least partially surround the rotor. The input member may comprise a gear rotatably driven by the rotor shaft. A first bearing may be configured to support the rotor shaft and a second bearing may be configured to support one of the rotor shaft and a portion of the transmission. Each of the first bearing and the second bearing may be at least partially received in the stator assembly. The transmission may include a planetary gear set with the input member including a sun gear rotatably driven by the rotor shaft, the output member including a carrier, and the planetary gear set further including a planet gear rotatably mounted to the carrier and meshed with the sun gear and a ring gear meshed with the planet gear and held non-rotatably relative to the housing. 
     The second bearing may be configured to support the carrier. The second bearing is may be configured to support the sun gear. The second bearing may be configured to support the rotor shaft. The second bearing may be configured to support the output member of the transmission. A third bearing may be configured to support the rotor shaft. The rearward end portion of the housing may include a rear cap defining a recess and the third bearing may be disposed at least partially in the recess. A fan may be coupled to the rotor shaft. The fan may be disposed between the stator and the rear end wall. The fan may include a hub and a vane portion extending radially outward from the hub, the hub being at least partially received in the stator assembly. The first bearing may be nested at least partially within at least a portion of the rotor. The rotor may define a central recess and the first bearing may be received at least partially within the recess. 
     An output spindle may have a front end proximal a front end portion of the housing and a rotational impact mechanism coupled to the output member of the transmission and to the output spindle. The impact mechanism may be configured to transmit continuous rotary motion without impacts from the transmission to the output spindle when a torque on the output spindle does not exceed a transition torque, and to transmit rotational impacts from the motor to the output spindle when a torque on the output spindle exceeds the transition torque. The impact mechanism may include a cam shaft extending forward from the output member, a hammer received over the cam shaft and configured to move axially and rotationally relative to the cam shaft, a spring disposed between the hammer and the output member and configured to bias the hammer away from the cam shaft, and an anvil coupled to the output spindle, the hammer configured to transmit continuous rotary motion to the anvil when the torque on the output spindle does not exceed a transition torque and the hammer configured to apply rotational impacts to the anvil when the torque on the output spindle exceeds a transition torque. 
     The power tool may have a maximum power output of at least 430 Watts and a length of the tool from a rear end of the housing to a front end of the output spindle may be less than or equal to 110 mm. a ratio of the maximum power output of the motor to the length of the tool may be at least 4.5 Watts/mm. The power tool may have a maximum output torque of at least 1820 inch-pounds and a length of the tool from a rear end of the housing to a front end of the output spindle of less than or equal to 110 mm. A ratio of the maximum output torque of the tool to the length of the tool is at least 18.0 inch-pounds/mm. 
     Advantages may include one or more of the following. At least a portion of each of a motor bearing and a second bearing that supports a portion of the transmission or the rotor shaft is received in the motor envelope and at least partially nested within the stator assembly, reducing the overall length of the power tool along the tool axis. Also, at least a portion of at least one of the motor bearings and/or the transmission bearing is received in and nested within the rotor, reducing the overall length of the power tool. In addition, at least a portion of the support plate 130 is received in and nested within the stator assembly and the rotor, reducing the overall length of the power tool. At the same time, the power tool may be configured to produce a maximum power output of at least approximately 450 Watts and a maximum output torque of at least approximately 1800 inch-pounds. Thus, the power tool is able to produce much greater power and torque than would be expected in an impact power tool of comparable size (e.g., a ratio of power output to tool length of at least approximately 4.5 Watts/mm and/or a ratio of output torque to tool length of at least approximately 18.0 inch-pounds/mm. These and other features and advantages will become apparent and within the scope of this application. 
     According to an aspect of this disclosure, a power tool is provided including a tool housing, a support plate provided within the tool housing, a rear tool cap mounted on a rear end of the tool housing. and a brushless direct-current (BLDC) motor received within the housing. The BLDC motor includes a stator assembly including a stator core, stator teeth radially extending from the stator core and defining slots therebetween, and stator windings wound around the stator teeth. The BLDC motor further includes a rotor shaft extending along a longitudinal axis, a front motor bearing mounted on the rotor shaft and supported by the support plate, a rear motor bearing mounted on the rotor shaft and supported by the rear tool cap, and a rotor. The rotor includes a rotor core mounted on the rotor shaft within the stator assembly and a magnet ring mounted around the rotor core. The rotor core defines an annular recess within which at portion of the front bearing and a portion of the support plate are located such that the a radial plane intersects the front bearing, the magnet ring, and the stator core. 
     In an embodiment, the magnet ring includes a sintered permanent magnet. 
     In an embodiment, rotor core includes at least two alignment rings on an outer surface thereof defining one or more annular grooves therebetween. In an embodiment, an adhesive is provided within the annular grooves to secure the magnet ring to the rotor core. 
     In an embodiment, the rotor core includes at least two axial pads on an outer surface thereof defining one or more axial channels therebetween. In an embodiment, an adhesive is provided within the axial channels to secure the magnet ring to the rotor core. 
     In an embodiment, the support plate includes a radial wall provided adjacent the stator assembly, a bearing pocket formed at a center portion of the radial wall to receive the front motor bearing, and a stator piloting feature extending from the radial wall to engage a portion of the stator assembly to radially support the support plate relative to the stator assembly. 
     In an embodiment, the stator piloting feature includes axial posts axially extending from the radial wall around the bearing pocket into the slots of the stator assembly in engagement with at least one of the stator core or tip portions of the stator teeth to radially support the support plate relative to the stator assembly. 
     In an embodiment, a transmission assembly is disposed forward of the BLDC motor, and the support plate includes a radial wall provided adjacent the stator assembly, a first bearing pocket formed at a center portion of a first surface of the radial wall received within the annular recess of the rotor core and configured to receive the front motor bearing, and a second bearing pocket formed on a second surface of the radial wall facing the transmission assembly and configured to receive a component of the transmission assembly. 
     In an embodiment, the BLDC motor further includes a terminal block arranged on an outer surface of the stator core intersecting the radial plane, the terminal block including terminals each extending parallel to the longitudinal axis and each including a tang portion to which at least one of the stator windings is connected. 
     In an embodiment, the BLDC motor further includes a circuit board on which at least one magnetic sensor is mounted to magnetically sense the magnet ring, where the circuit board is oriented along a second radial plane that intersects the stator windings. 
     In an embodiment, a fan is mounted on the rotor shaft, and an inner portion of the fan is recessed to allow the rear bearing to be radially aligned with at least a portion of the fan. 
     In an embodiment, the rear tool cap includes a radial body that includes a central bearing pocket arranged to receive the rear motor bearing, a peripheral portion extending form the radial body arranged to be mate with the tool housing, and at least one constraining member projecting from the radial body to engage the stator assembly and radially secure the stator assembly relative to the rear tool cap independently of the tool housing. 
     In an embodiment, the rear tool cap is integrally formed as a part of the tool housing. 
     According to another aspect of this disclosure, a brushless direct-current (BLDC) motor is provided including a stator assembly. The stator assembly includes a stator core, stator teeth radially extending from the stator core and defining slots therebetween, and stator windings wound around the stator teeth. The motor further includes a rotor shaft that extends along a longitudinal axis and a rotor including a rotor core mounted on the rotor shaft, a permanent magnet ring mounted on an outer surface of the rotor core, and an adhesive material disposed between the rotor core and the permanent magnet ring. The rotor core includes a first portion having an outer diameter that substantially corresponds to an inner diameter of the permanent magnet ring to allow the first portion of the rotor core to be form-fittingly received within the permanent magnet ring in direct contact therewith and to radially secure the permanent magnet ring to the stator core, and a second portion having an outer diameter that is smaller than the inner diameter of the permanent magnet ring. The adhesive material is disposed between the second portion of the rotor core and the permanent magnet ring to axially secure the permanent magnet ring to the stator core. 
     In an embodiment, the first portion of the rotor core includes at least two annular alignment rings and the second portion of the rotor core includes at least one annular groove formed between the at least two annular alignment rings. In an embodiment, the adhesive material is disposed within the annular groove. 
     In an embodiment, the first portion of the rotor core includes at least one annular axial pad and the second portion of the rotor core includes at least one axial channel. In an embodiment, the adhesive material is disposed within the at least one axial channel. 
     In an embodiment, the permanent magnet ring includes a sintered magnet. 
     In an embodiment, the rotor core defines an annular recess within which at portion of a bearing of the rotor shaft is located. 
     In an embodiment, the rotor core includes uniformly shaped laminations bonded together and shaped to form the first portion and the second portion of the rotor core. 
     In an embodiment, the rotor core includes a first set of laminations shaped to form the first portion of the rotor core and a second set of laminations shaped to form the second portion of the rotor core. 
     In an embodiment, a power tool is provided including a tool housing a brushless direct-current (BLDC) motor as described above received within the housing. 
     According to another embodiment, a brushless direct-current (BLDC) motor is provided including a stator assembly. The stator assembly includes a stator core, stator teeth radially extending from the stator core and defining slots therebetween, and stator windings wound around the stator teeth. The motor further includes a rotor shaft that extends along a longitudinal axis and a rotor including a rotor core mounted on the rotor shaft, a permanent magnet ring mounted on an outer surface of the rotor core, and an adhesive material disposed between the rotor core and the permanent magnet ring. In an embodiment, the rotor core includes annular grooves formed in the outer surface within which the adhesive material is disposed to axially secure the permanent magnet ring to the stator core. 
     In an embodiment, the rotor core has an outer diameter that substantially corresponds to an inner diameter of the permanent magnet ring to allow the rotor core to be form-fittingly received within the permanent magnet ring in direct contact therewith and to radially secure the permanent magnet ring to the stator core. 
     In an embodiment, the rotor core has an outer diameter that is smaller than an inner diameter of the permanent magnet ring to form a gap within which the adhesive material is received. 
     In an embodiment, a power tool provided including a tool housing and a BLDC motor as described disposed within the housing. 
     According to another aspect of this disclosure, a brushless direct-current (BLDC) motor is provided including a stator assembly including a stator core, stator teeth radially extending from the stator core and defining slots therebetween, and stator windings wound around the stator teeth; a rotor shaft extending along a longitudinal axis; and a rotor including a rotor core mounted on the rotor shaft. The rotor core supports at least one permanent magnet that magnetically interacts with the stator windings to cause a rotation of the rotor relative to the stator assembly. A circuit board is provided having a main body and at least one leg radially projecting from the main body to support at least one magnetic sensor in close proximity to the at least one permanent magnet. In an embodiment, the leg is oriented along a radial plane that intersects the stator windings. 
     In an embodiment, the stator assembly further includes an end insulator mounted on an end surface of the stator core to insulate the stator core from the stator windings. In an embodiment, the circuit board is mounted and fastened to the end insulator. 
     In an embodiment, the circuit board at least three legs radially projecting from the main body to support three magnetic sensors. In an embodiment, each leg extends between two adjacent stator windings in the direction of the rotor towards a center of the stator assembly. 
     In an embodiment, each of the three magnetic sensors is substantially circumferentially aligned with inner portions of the stator windings. 
     In an embodiment, the main body of the circuit board includes a first portion that is curved and extends along the end of the stator assembly but does not extend peripherally beyond an outer surface of the stator core, and a second portion that extends peripherally beyond the outer surface of the stator core and through which at least one fastener is provided to secure the circuit board to the end insulator. 
     In an embodiment, a connector is mounted on the second portion of the main body of the circuit board and signal wires are coupled to the connector. 
     In an embodiment, the fastener is peripherally provided beyond the outer surface of the stator core. 
     In an embodiment, a retention feature provided on the first portion of the main body of the circuit board and arranged to make a mechanical connection with a portion of the end insulator, wherein no portion of the retention feature projects over a rear surface of the circuit board in a direction opposite the stator core. 
     In an embodiment, the second portion covers an angular distance in the range of approximately 60 degrees to 90 degrees. 
     In an embodiment, the first portion is provided within a part of the main body of the circuit board that covers an angular distance in the range of approximately 35 degrees to 55 degrees. 
     In an embodiment, inner tips of the three legs of the circuit board are circumferentially aligned with inner ends of the stator teeth. 
     In an embodiment, overmold or glue material is arranged to secure the inner tips of the three legs of the circuit board to inner teeth portions of the end insulator. 
     According to another aspect of the disclosure, a brushless direct-current (BLDC) motor is provided including a rotor shaft extending along a longitudinal axis, a stator assembly, and a rotor. The stator assembly includes a stator core, stator teeth radially extending from the stator core and defining slots therebetween, stator windings wound around the stator teeth, and an end insulator mounted on an end surface of the stator core to insulate the stator core from the stator windings, the end insulator having a radial body and a retention post projecting from the radial body. The rotor includes a rotor core mounted on the rotor shaft, the rotor core supporting at least one permanent magnet that magnetically interacts with the stator windings to cause a rotation of the rotor relative to the stator assembly. In an embodiment, a circuit board is mounted to the end insulator, the circuit board including a front surface facing the end insulator, a rear face, and at least one magnetic sensor mounted on the front face and configured to generate a signal associated with an angular position of the rotor. A retention feature is provided on a front surface of the circuit board facing the stator core and arranged to make a mechanical connection with the retention post of the end insulator. In an embodiment, no portion of retention post of the end insulator or the retention feature projects substantially over the rear surface of the circuit board. 
     In an embodiment, the circuit board includes an arcuate main body and at least one leg projecting radially inwardly from the main body to support at least one magnetic sensor in close proximity to the at least one permanent magnet. In an embodiment, the at least one leg is oriented along a radial plane that intersects the plurality of stator windings. 
     In an embodiment, the retention post includes a snap head and the circuit board includes a slot arranged to receive the snap head of the retention post. In an embodiment, the snap head does not substantially project out of the slot over the rear surface of the circuit board. 
     In an embodiment, the retention feature includes an overmold layer formed on the front surface of the circuit board facing the stator core. In an embodiment, the overmold layer forms a lip arranged at a distance from the front surface of the circuit board and configured to make a snap-fit connection with the snap head of the retention post. 
     In an embodiment, the retention feature includes a metal trap including two legs mounted on the front surface of the circuit board and a main body distanced from the front face of the circuit board partially overlapping the slot of the circuit board. In an embodiment, the main body is configured to make a snap-fit connection with the snap head of the retention post. 
     In an embodiment, the retention feature includes a place pad having a planar body mounted on the front face of the circuit board, the place pad including at least one snap projecting from the planar body overlapping the slot of the circuit board, the at least one snap being resiliently flexible to make a snap-fit connection with the retention post. 
     In an embodiment, the retention post includes a recess and the retention feature includes a clip disposed on the front surface of the circuit board. In an embodiment, the retention feature has an engagement edge extending from an edge of the circuit board that is received within the recess of the retention post. 
     In an embodiment, a power tool is provided including a tool housing and a BLDC motor as described in any of the embodiments above. 
     According to another aspect of this disclosure, a power tool is provided including a tool housing, a support plate provided within the tool housing, a rear tool cap separately formed from the tool housing and mounted on a rear end of the tool housing, and a brushless direct-current (BLDC) motor received within the housing. The BLDC motor includes a stator assembly including a stator core having an outer surface, stator teeth radially extending from the stator core and defining slots therebetween, and stator windings wound around the stator teeth. The BLDC motor further includes a rotor shaft extending along a longitudinal axis, a front motor bearing mounted on the rotor shaft and supported by the support plate, a rear motor bearing mounted on the rotor shaft and supported by the rear tool cap, and a rotor including a rotor core mounted on the rotor shaft to rotate relative to the stator assembly. The rear end cap includes a radial body, a bearing pocket formed on or within the radial body to support the rear motor bearing, a peripheral portion that mates with the rear end of the tool housing, and a constraining member configured to engage a portion of the stator assembly to pilot the stator assembly and the rear motor bearing relative to the rear end cap independently of the tool housing. 
     In an embodiment, the constraining member includes at least one constraining wall extending axially along a first circumference radially outward of the outer surface of the stator core. In an embodiment, the first circumference is radially inward of the peripheral portion of the rear end cap. 
     In an embodiment, the constraining wall includes tuning pads having inner surfaces oriented along a second circumference that substantially corresponds to the outer surface of the stator core to form-fittingly receive the outer surface of the stator assembly within the rear end cap. 
     In an embodiment, the constraining wall includes two or more spaced apart arcuate constraining walls forming circumferential gaps therebetween. 
     In an embodiment, a motor fan is mounted on the rotor shaft within the rear end cap between the stator assembly and the radial body of the rear end cap. The fan includes a main body oriented radially in line with the peripheral portion of the rear end cap and fan blades projecting towards the stator assembly. 
     In an embodiment, at least one exhaust vent is formed in the peripheral portion of the rear end cap radially aligned with the fan blades. 
     In an embodiment, the motor fan has a diameter that is smaller than a diameter of the outer surface of the stator core. 
     In an embodiment, the motor is an inner-rotor motor. 
     In an embodiment, the retention feature includes axial posts arranged to penetrate at least some of the stator slots in sliding contact with a portion of the stator assembly. 
     In an embodiment, each axial post engages an inner surface of the stator core forming the corresponding stator slot. 
     In an embodiment, each axial post engages tooth tips of adjacent ones of the stator teeth. 
     In an embodiment, the axial posts traverse substantially an entire length of the stator core. 
     In an embodiment, a motor fan is mounted on the rotor shaft between the stator assembly and a transmission mechanism of the power tool. 
     In an embodiment, the rotor core defines an annular recess within which at portion of the rear bearing and the bearing pocket of the rear end cap are located such that the a radial plane intersects the rear bearing, the axial posts, and the rotor core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure. 
         FIG. 1  depicts a side view of a first embodiment of a power tool, in this example an impact tool, according to an embodiment. 
         FIG. 2A  depicts a partial cross-sectional view of an exemplary impact tool according to an embodiment. 
         FIG. 2B  depicts an exploded view of an impact mechanism of an exemplary impact tool according to an embodiment. 
         FIG. 3  depicts a zoomed-in partial cross-sectional view of an exemplary power tool, according to an embodiment. 
         FIG. 4  depicts a side cross-sectional view of a second embodiment of a power tool including a motor assembly and support plate sized and optimized to reduce the length of the power tool, according to an embodiment. 
         FIG. 5  depicts a zoomed-in side cross-sectional view of the support plate and the motor assembly, according to an embodiment. 
         FIG. 6  depicts a perspective cross-sectional view of the motor assembly, according to an embodiment. 
         FIGS. 7A and 7B  depicts perspective and side views of the motor assembly respectively, according to an embodiment. 
         FIGS. 8A and 8B  depict two perspective exploded views of the same motor assembly, according to an embodiment. 
         FIG. 9  depict a side view of the motor assembly of  FIG. 2  to illustrate an advantage of the support plate and nested rotor bearing configuration, according to an embodiment. 
         FIG. 10  depicts a side view of a prior art motor without a nested rotor bearing. 
         FIG. 11  depicts a side cross-sectional view of the rotor, according to an embodiment. 
         FIG. 12  depicts a perspective exploded view of the rotor, according to an embodiment. 
         FIG. 13  depicts a perspective exploded view of the rotor, according to another embodiment. 
         FIG. 14  depicts a perspective exploded view of the rotor, according to yet another embodiment. 
         FIG. 15  depicts a rear axial view of the stator assembly and the Hall board, according to an embodiment. 
         FIG. 16  depicts a front axial view of the stator assembly and the Hall board, according to an embodiment. 
         FIG. 17  depicts a side view of the stator assembly and the Hall board, according to an embodiment. 
         FIG. 18  depicts a cross-sectional side view of the stator assembly and the Hall board from a different angle, according to an embodiment. 
         FIG. 19  depicts a cut-off perspective front view of the stator assembly and the Hall board, according to an embodiment. 
         FIG. 20  depicts a rear perspective view of the stator assembly and the Hall board, according to an embodiment. 
         FIG. 21  depicts a perspective view of the motor assembly including the fan and support plate, according to an embodiment. 
         FIG. 22  includes a rear view of the motor assembly including the fan  18 , according to an embodiment. 
         FIG. 23  depicts a partial perspective view of the end insulator including a snap post, according to an embodiment. 
         FIG. 24A  depicts a partial perspective view of the Hall board, depicting a first embodiment of the retention feature. 
         FIG. 24B  depicts a partial side cross-sectional view of the Hall board with retention feature in engagement with snap post of rear end insulator, according to the first embodiment. 
         FIG. 25A  depicts a partial perspective view of the Hall board, depicting a second embodiment of the retention feature. 
         FIG. 25B  depicts a partial side cross-sectional view of the Hall board with retention feature in engagement with snap post of the rear end insulator, according to the second embodiment. 
         FIG. 26  depicts a partial perspective view of the Hall board, depicting a third embodiment of the retention feature. 
         FIG. 27  depicts a perspective view of the place pad of the third embodiment, according to an embodiment. 
         FIG. 28A  depicts a partial perspective view of the place pad and snap post, according to an embodiment. 
         FIG. 28B  depicts a perspective view of the Hall board, depicting the plate pad in a bent position, according to an embodiment. 
         FIG. 29  depicts a partial perspective view of the end insulator including a clip post, according to an embodiment. 
         FIG. 30  depicts a perspective frontal view of the Hall board depicting a fourth embodiment of the retention feature in the form of a clip. 
         FIG. 31A  depicts a perspective view of the Hall board secured to the clip post of the insulator via the clip, according to an embodiment. 
         FIG. 31B  depicts a perspective view of the clip secured to the clip post of the insulator depicted without the Hall board, according to an embodiment. 
         FIG. 32  depicts a side view of a third embodiment of a power tool including an improved rear tool cap provided for interfacing with the motor assembly, according to an embodiment. 
         FIG. 33  depicts a perspective exploded view an improved rear tool cap provided for interfacing with the motor assembly, according to an embodiment. 
         FIG. 34  depicts a perspective view of the rear tool cap, according to an embodiment. 
         FIG. 35  depicts an axial view of the motor assembly received within the rear tool cap, according to an embodiment. 
         FIG. 36  depicts a side cross-sectional view of the motor assembly received within the rear tool cap, according to an embodiment. 
         FIG. 37  depicts a frontal perspective view of the motor assembly received within the rear tool cap, according to an embodiment. 
         FIG. 38  depicts a rear perspective view of the motor assembly received within the rear tool cap, according to an embodiment. 
         FIG. 39  depicts a perspective view of rear tool cap, according to an embodiment. 
         FIG. 40  depicts an axial view of the motor assembly mounted on the rear tool cap, according to an embodiment. 
         FIG. 41  depicts a side cross-sectional view of the motor assembly mounted on the rear tool cap, according to an embodiment. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide an explanation of various embodiments of the present teachings. 
       FIG. 1  depicts a side view of a power tool  10 , in this example an impact tool, according to an embodiment.  FIG. 2A  depicts a partial cross-sectional view of the exemplary impact tool  10  according to an embodiment.  FIG. 2B  depicts an exploded view of the exemplary impact tool  10  according to an embodiment.  FIG. 3  depicts a zoomed-in partial cross-sectional view of the exemplary power tool  10 , according to an embodiment. 
     In an embodiment, the exemplary impact tool  10  includes a housing  12  having a motor housing portion  23  including two clamshells that come together to house a motor  100  rotatably driving a rotor shaft  102  and a transmission housing portion  21  coupled to the motor housing portion  23  that houses a transmission assembly  20  and an impact mechanism  40  that together selectively impart rotary motion and/or a rotary impact motion to an output spindle  26 . Coupled to the output spindle  26  is a tool holder  28  for retaining a tool bit (e.g., a drill bit, a screw driving bit, or a socket wrench, not shown). Further details regarding exemplary tool holders are set forth in U.S. patent application Ser. No. 12/394,426, which is incorporated herein by reference. The power tool further includes a handle  13  that extends transverse to the housing  12  and accommodates a trigger switch  15 , a control and/or power module (not shown) that includes control electronics and switching components for driving the motor  100 , and a battery receptacle  17  that receives a removeable power tool battery pack for supplying electric power to the motor  100 . The handle  13  has a proximal portion coupled to the housing  12  and a distal portion coupled to the battery receptacle  17 . The motor  100  may be powered by an electrical power source, such as a DC power source or battery (not shown), that is coupled to the battery receptacle  17 , or by an AC power source. The trigger  15  is coupled to the handle  13  adjacent the housing  12 . The trigger  15  connects the electrical power source to the motor  100  via the control and/or power module, which controls power delivery to the motor  100 . 
     In an embodiment, the transmission assembly  20  may comprise a planetary transmission and may include, among other features, a pinion or sun gear  24  that is coupled to an end of the rotor shaft  102  of the motor  100  and that extends along a tool axis X. One or more planet gears  48  surround and have teeth that mesh with the teeth on the sun gear  24 . An outer ring gear  30  is rotationally fixed to the housing  12  and centered on the tool axis X with internal teeth meshing with the teeth on the planet gears  48 . A cam carrier  22  includes a pair of carrier plates  22 A,  22 B that support the planet gears  48  with pins  55  so that the planet gears  48  can rotate about the pins  55 . The cam carrier  52  further includes a rearward protrusion  57  that extends axially rearward from the rear carrier plate  22 A along the axis X and a cam shaft  59  that extends axially forward from the front carrier plate  22 B along the axis X. 
     When the motor  100  is energized, the rotor shaft  102  and the sun gear  24  rotate about the axis X. Rotation of the sun gear  24  causes the planet gears  48  to orbit the sun gear  24  about the axis X, which in turn causes the cam carrier  22  to rotate about the axis X at a reduced speed relative to the rotational speed of the rotor shaft  102 . In the illustrated embodiment, only a single planetary stage is shown. It should be understood that the transmission may include multiple planetary stages that may provide for multiple speed reductions, and that each stage can be selectively actuated to provide for multiple different output speeds of the planet carrier. Further, the transmission may include a different type of gear system such as a parallel axis transmission or a spur gear transmission. 
     The impact mechanism  40  includes the cam shaft  59 , a generally cylindrical hammer  42  received over the cam shaft  59 , and an anvil  44  fixedly coupled to the output spindle  26 . The hammer  42  has two lugs  45  configured to engage two radial projections  46  on the anvil  44  in a rotating direction. Formed on an outer surface of the cam shaft  59  is a pair of rear-facing V-shaped cam grooves  47  with their open ends facing toward transmission assembly  20 . A corresponding pair of forward-facing V-shaped cam grooves (not shown) is formed on an interior surface of the hammer  42  with their open ends facing toward the output spindle  26 . Balls  49  are received in and rides along each of the cam grooves  47  to movably couple the hammer  42  to the cam shaft  59 . A compression spring  41  is received in a cylindrical recess in the hammer  42  and abuts a forward face of the front carrier plate  22 B. The spring  41  biases the hammer  42  toward the anvil  44 so that the so hammer lugs  45  engage the corresponding anvil projections  44 . 
     At low torque levels, the impact mechanism  40  transmits torque from the transmission assembly  20  to the output spindle  26  in a rotary mode. In the rotary mode, the compression spring  41  maintains the hammer  42  in a forward position so that the hammer lugs  45  continuously engage the anvil projections  46 . This causes the cam shaft  59 , the hammer  42 , the anvil  44 , and the output spindle  26  to rotate together as a unit about the axis X. As torque increases, the impact mechanism  40  may transition to transmitting torque to the output spindle  26  in an impact mode. In the impact mode, the hammer  44  moves axially rearwardly against the force of the spring  41 , decoupling the hammer lugs  45  from the anvil projections  46 . The anvil  44  continues to spin freely on about the axis X without being driven by the motor assembly  100  and the transmission assembly  20 , so that the anvil  44  coasts to a slower speed. Meanwhile, the hammer  42  continues to be driven at a higher speed by the motor assembly  100  and transmission assembly  20 , while the hammer  42  moves axially rearwardly relative to the anvil  44  by the movement of the balls  49  in the V-shaped cam grooves  47 . When the balls  49  reach their rearmost position in the V-shaped cam grooves  47 , the spring  41  drives the hammer  42  axially forward with a rotational speed that exceeds the rotational speed of the anvil  44 . This causes the hammer lugs  45  to rotationally strike the anvil projections  46 , imparting a rotational impact to the output spindle  26 . 
     In an embodiment, the motor  100  is a brushless direct-current (BLDC) motor that includes an inner rotor  104  having surface-mount magnets  106  on a rotor core  108  and a stator assembly  110  located around the rotor  104 . The stator assembly  110  includes a stator core  112  having a series of teeth  114  projecting radially inwardly from the stator core  112 , and a series of conductive windings  113  wound around the stator teeth  114  to define three phases connected in a wye or a delta configuration. As the phases of the stator assembly  110  are sequentially energized, they interact with the rotor magnets  106  to cause rotation of the rotor  104  relative to the stator assembly  110 . 
     In an embodiment, the rotor core  108  is mounted on the rotor shaft  102  and includes an annular recess  116  around the rotor shaft  102  on one side of the rotor core  104 . Specifically, the rotor  104  is provided with what is referred to in this disclosure as an open-core construction, where the rotor magnet  106  is mounted around the rotor core  112  and the annular recess  116  is provided within the rotor core  112  for positioning of one or more of the rotor bearings. The rotor core  112  may be made of a solid core piece of metal or lamination stack that includes a series of parallel laminations. The annular recess  116  may be carved or stamped out of the rotor core  112 , or it may be formed using ring-shaped laminations. 
     In an embodiment, the rotor magnet  106  is a ring surface-mounted on the outer surface of the rotor core  108  and magnetized in a series of poles, e.g., four poles having a S-N-S-N orientation. Alternatively, rotor magnet  106  may be provided as a series of discrete magnet segments that may be pre-magnetized prior to assembly. The outer surface of the rotor core  108  may be shaped for proper retention of the magnet segments. In yet another embodiment, the rotor magnets  106  may be fully or partially embedded within the rotor core  108 . 
     In an embodiment, a fan  118  is mounted on the rotor shaft  102  behind the motor assembly  100 . In an embodiment, a rear tool cap  14  is mounted to the end of the housing  12  to contain the end of the motor  100 . The rear tool cap  14  may be provided integrally with the housing  12  or as a separate piece. In an embodiment, the fan  118  is positioned between the motor  100  and the rear tool cap  14 . The fan  118  generates airflow through the motor  100  and (preferably) the transmission assembly  20  to cool the components. 
     In an embodiment, a support plate  130  supports front and rear motor bearings  158  and  160  that support the rotor shaft  102 . At least the rear motor bearing  160  is located within the stator assembly  110  and within the annular recess  116  of the rotor core  108  along the axial direction of the motor  100  such that the rear motor bearing  160  intersects a portion of the rotor core  108  along a radial plane. The support plate  130  includes a cylindrical portion  132  that receives the outer races of the motor bearings  158  and  160  and a radial portion  134  that extends radially from the cylindrical portion  132  and includes radial ends supported by the tool housing  12 . The stator assembly  110  is also supported by the tool housing  12 , thus being axially and radially secure with respect to the support plate  130 . In this manner, the support plate  130  axially and radially supports the rotor  104  within the stator assembly  110 . In an embodiment, the support plate  130  and the stator assembly  110  may be independently supported by the tool housing  12 . In another embodiment, the support plate may be formed integrally as a part of two clamshells that form the tool housing  12 . Alternatively, the support plate  130  may be piloted to and retained by the stator assembly  110  directly and independently of the tool housing  12 . 
     In an embodiment, as shown in  FIGS. 2A and 3 , the support plate  130  also has a front lip  131  that supports a component of the transmission assembly  20 , such as supporting the ring gear  30 , to inhibit axially and rotational movement of the ring gear  30  relative to the housing  12 . In addition, the support plate  130  supports a cam carrier bearing  32  that supports the cam carrier  22  relative to the support plate  130 , and therefore relative to the motor  100  and the tool housing  12 . The cam carrier bearing  32  is nested within the support plate  130  adjacent the motor  100 . Specifically, the support plate  130  is positioned between the motor assembly  100  and transmission assembly  20  and provides support for the motor bearings  158  and  160  on one side and for the cam carrier bearing  32  on the other side. In an embodiment, the support plate  130  includes a recessed portion  136  that includes a larger diameter than the cylindrical portion  134  and is sized to receive the cam carrier bearing  32  therein. The cam carrier bearing  32  is thus located axially forward of the entire motor assembly  100 . 
     At least a portion of the support plate  130  is received within the stator assembly  110  and within the rotor core  108 . In this embodiment, the rear cylindrical projection of the support plate that supports the motor bearings  158  and  160  is at least partially received within the stator assembly  110  and within the motor core  108 . In this embodiment, the nested arrangement of the one or more motor bearings  158  and  160  and the support plate  130  provide a compact motor assembly  100  compared to conventionally available brushless motors. Disposition of the one or more bearings  158  and  160  and at least a portion of the support plate  130  within the stator assembly  110  and within the rotor core  108  reduces the length of the motor assembly  100  and the overall power tool and improves power density. 
     In an embodiment, motor assembly  100  defines a motor envelope  120  bounded by a rear plane  122  at a rearmost point of the motor assembly  100  (i.e., at the rearmost point of the stator assembly  110 ), a front plane  124  at a frontmost point of the motor assembly  100  (i.e., at the frontmost point of the stator assembly  110 ), and a generally cylindrical boundary  126  extending from the rear plane  122  to the front plane  124  and surrounding a radially outermost portion of the motor assembly  100  (e.g., a radially outermost portion of the stator assembly  110 ) not including terminal block  121 . In the illustrated embodiment, the rear plane  122  is at a rearmost point of the stator assembly  110  (including its windings  113 ), the front plane  124  is at a frontmost point of the stator assembly  110  (including its windings  113 ), and the generally cylindrical boundary  126  surrounds a radially outermost portion of the stator assembly  110 . However, it should be understood that the rear plane may be at a rearmost point of the rotor  104  (if that extends further rearward than the stator assemblyl 10 ), the front plane may be at a frontmost point of the rotor  104  (if that extends further frontward than the stator assemblyl 10 ), and the generally cylindrical boundary may be at an outermost point of the rotor  104  (if that extends further radially outward than the stator assembly  110 , e.g., in an outer rotor motor). The motor envelope  120  may have a length L 1  from the rear plane  122  to the front plane  124  of approximately 16 mm to 20 mm (e.g., approximately 18.4 mm) and a diameter D 1  of the cylindrical boundary  126  of approximately 40 mm to 60 mm (e.g., approximately 51 mm), with a volume of approximately 20 cm 2  to 56 cm 2  (e.g., approximately 38 cm 2 ). In an embodiment, at least a portion of at least one of the motor bearings  158  and  160  and at least a portion of the support plate  130  are received within the motor envelope  120 . 
     An alternative embodiment of a power tool  50  is described herein with reference to  FIGS. 4-10 .  FIG. 4  depicts a side cross-sectional view of the power tool  50  including a motor assembly  200  and support plate  230  sized and optimized to reduce the length of the power tool  50 , according to an embodiment. In an embodiment, power tool  50  includes many of the same features as power tool  10  described above, such as transmission assembly  20 , impact mechanism  40 , output spindle  26 , tool holder  28 , handle  13 , trigger  15 , battery receptacle  17 , etc., details of which are not repeated here, except as necessary to describe this alternative embodiment. In an embodiment, a rear end cap  50  is mounted on a rear end of the housing  52  rearward of the motor assembly  200 . In this embodiment, the support plate  130  is designed to locate the cam carrier bearing  32  along the same radial plane as at least an end of the stator windings, so the cam carrier bearing  32  is located at least partially within an envelope formed by the ends of the motor assembly  200 . 
     In an embodiment, motor assembly  200  includes many of the same features described above with reference to  FIG. 1 . In an embodiment, motor assembly  200  includes a rotor shaft  202 , an inner rotor  204  mounted on the rotor shaft  202  having a surface-mount magnet ring  206  on a rotor core  208 , and a stator assembly  210  located around the rotor  204 . The stator assembly  210  includes a stator core  212 , a series of stator teeth  214  radially projecting inwardly from the stator core  212 , and a series of conductive windings  113  wound around the stator teeth  214  to define three phases connected in a wye or a delta configuration. 
     In an embodiment, the motor assembly  200  defines a tool axis X extending through the center of the rotor shaft  202  extending from a rear of the power tool  50  (i.e., where the rear end cap  50  is located) to a front of the power tool (i.e., where tool holder  28  is located). In this disclosure, the terms “rear” and “front” are used to describe positions of various components along the tool axis X in the direction A shown in  FIG. 4 . Thus, as an example, the motor assembly  200  is disposed rearwardly of the transmission assembly  20 . 
     In an embodiment, the rotor core  208  is mounted on the rotor shaft  202  and includes an annular recess  216  around the rotor shaft  202  on one side of the rotor core  208  for positioning of one or more of the rotor bearings  258  and  260 . The rotor core  212  may be made of a solid core piece of metal or lamination stack that includes a series of parallel laminations. The annular recess  216  may be carved or stamped out of the rotor core  212 , or it may be formed using ring-shaped laminations. The rotor magnet  106  may be ring-sized or segmented, and it may be surface-mounted or embedded within the rotor core  208 . 
       FIG. 5  depicts a zoomed-in side cross-sectional view of the support plate  230  and the motor assembly  200 , according to an embodiment.  FIG. 6  depicts a perspective cross-sectional view of the motor assembly  200 , according to an embodiment.  FIGS. 7A and 7B  depicts perspective and side views of the motor assembly  200  respectively, according to an embodiment.  FIGS. 8A and 8B  depict two perspective exploded views of the same motor assembly  200 , according to an embodiment. Various aspects of the motor assembly  200  ant the support plate  230  are described with reference to these figures. 
     In an embodiment, the support plate  230  includes a first bearing pocket  232  formed as a cylindrical or rim-shaped projection from a radial portion  234  for supporting at least the front motor bearing  258 . The first bearing pocket  232  of the support plate  230  at least partially projects into and is received within the annular recess  216  of the rotor  204 . This allows the front bear motor bearing  258  to be received at least partially within the stator assembly  210  and within an envelope of the rotor core  208  defined by the radial surfaces of the rotor core  208 . 
     In an embodiment, the support plate  230  further includes a second bearing pocket  236  for supporting the cam carrier bearing  32 . The second bearing pocket  236  may be formed as a recessed portion of the radial portion  234  of the support plate  230  facing away from the first bearing pocket  232 . In an embodiment, second bearing pocket  236  is formed as an intermediate annular portion formed between the radial portion  234  and a radial wall  235 , where the radial portion  234  is located along a radial plane that intersects a portion of the stator assembly  210 , and the radial wall  235  is located adjacent a front end of the stator assembly  210 . As such, the radial portion  234  extends between a front end of the first bearing pocket  232  and a rear end of the second bearing pocket  236 . In an embodiment, the radial wall  235  extends from the front end of the second bearing pocket  236  radially outwardly and is supported by either the tool housing  52  or the stator assembly  210 . In an embodiment, support plate  230  further includes an outer rim portion or lip  237  projecting axially forward from an outer circumference of the radial wall  235  for coupling with an outer portion of the transmission housing  21  and/or the tool housing  52  and for receiving and supporting a component of the transmission assembly  20 , such as the ring gear  30  of the transmission assembly  20 . 
     In an embodiment, the second bearing pocket  236  has a larger inner diameter than the first bearing pocket  232 . In an embodiment, second bearing pocket  236  has approximately the same inner diameter as the outside surface of the rotor core  208 . In an embodiment, the outer surface of the second bearing pocket  236  is received within the opening of the stator  210 , i.e., within the inner diameter formed by front ends of the stator windings  224  adjacent the rotor  204 . In an embodiment, the outer annular surface of the second bearing pocket  236  may be in physical contact with the stator windings  224  or a front end insulator  220  of the stator assembly  210 , though in the illustrated figured, a small air gap  217  radially separates the outer annular surface of the second bearing pocket  236  from the stator windings  224  and the front end insulator  220  of the stator assembly  210 . 
     In an embodiment, the cam carrier bearing  32  is received within the second bearing pocket  236  so that it is at least partially nested within the stator assembly  210  along a radial plane A′ that intersects the front ends of the stator windings  224 . 
     In an embodiment, the motor assembly  200  defines a motor envelope  240  similar to the motor envelope  120  of the motor  100 , described above. The motor envelope  240  is bounded by a rear plane  242  at a rearmost point of the motor assembly  200  (i.e., at the rearmost point of the stator assembly  210 ), a front plane  244  at a frontmost point of the motor assembly  200 , and a generally cylindrical boundary  246  extending from the rear plane  242  to the front plane  244  and surrounding a radially outermost portion of the motor assembly  200 (e.g., a radially outermost portion of the stator assembly  210 ). In the illustrated embodiment, the rear plane  242  is at a rearmost point of the stator assembly  210  (including its stator windings  224 ), the front plane  244  is at a frontmost point of the stator assembly  210  (including its stator windings  224 ), and the generally cylindrical boundary  246  surrounds a radially outermost portion of the stator assembly  210  (not including the terminal block  221 ). However, it should be understood that the rear plane may be at a rearmost point of the rotor  204  (if that extends further rearward than the stator assembly  210 ), the front plane may be at a frontmost point of the rotor  204  (if that extends further frontward than the stator assembly  210 ), and the generally cylindrical boundary may be at an outermost point of the rotor  204  (if that extends further radially outward than the stator assembly  210 , e.g., in an outer rotor motor). As shown in  FIGS. 4 and 5 , the motor envelope  240  may have a length L 3  from the rear plane  242  to the front plane  244  of approximately 16 mm to 20 mm (e.g., approximately 18.4 mm) and a diameter D 1  of the cylindrical boundary  246  of approximately 40 mm to 60 mm (e.g., approximately 51 mm), with a volume of approximately 20 cm 2  to 56 cm 2  (e.g., approximately 38 cm 2 ). In an embodiment, at least a portion of the front motor bearing  258  and at least a portion of the support plate  230  are received within the motor envelope  120 . 
     In an embodiment, as best seen in  FIGS. 8A and 8B , support plate  230  is provided with radially outwardly extending axial posts or fins  238  provided for piloting and supporting the support plate  230  relative to the stator assembly  210 . In an embodiment, axial posts  238  are received within respective slots of the stator assembly  210  formed circumferentially between stator windings  224 . In an embodiment, axial posts  238  come into contact with the inner surface of the stator core  212  or adjacent inner tips of the stator teeth  214 . In this manner, the support plate  230  is radially supported with respect to the stator assembly  210  independently of the power tool housing  52 . In an embodiment, support plate  230  further includes one or more circumferential projections  239  that engage a portion of the tool housing  52  to provide axial support for the support plate  230  relative to the stator assembly  210 . In an embodiment, a series of six axial posts  238  are provided, each project from a rear surface of the radial wall  235  around the first bearing pocket  232 . In an embodiment, length of the axial posts  238  is approximately equal to or greater than the length of the first bearing pocket  232  in the direction of the stator assembly  210  to allow the axial posts  238  to extend into the slots of the stator assembly  210 . Reference is made to US Patent Publication No. 2017/0294819A1, which is incorporated herein by reference in its entirety, for a description of the axial posts for piloting and support of a bearing support structure relative to the inner diameter of the stator. 
     In an alternative embodiment not shown here, instead of axial posts  238 , the support plate  230  may be piloted and supported via one or more circumferential constraining walls that extend over the outside surface of the stator core  212 . Reference is made to U.S. Pat. No. 10,056,806, which is incorporated herein by reference in its entirety, for a description of the peripheral walls for piloting and support of a bearing support structure relative to the outer diameter of the stator. 
     In an embodiment, stator assembly  210  includes front and rear end insulators  220  and  222  disposed on axial ends of the stator core  212  to electrically insulate the stator windings  224  from the stator core  212 . In an embodiment, one or more of the end insulators  220  and  222  support a terminal block  221  on the lower surface of the stator core  212 . The terminal block  221  includes a series of motor terminals that connect via a series of wires to a power module (not shown) disposed in the tool housing  52  to receive electric power. The motor terminals are also electrically connected to the stator windings  224 . In an embodiment, the terminal block  221  is provided along a radial plane A″ that also intersects the front motor bearing  258  and the rotor magnet ring  206 . 
     In an embodiment, both motor bearings  258  and  260  may be supported at least partially within the rotor annular recess  216  if the length of the stator core  212  and the corresponding length of the rotor core  208  is sufficiently large to accommodate both motor bearings  258  and  260 . Alternatively, in an embodiment as shown in  FIG. 2 , where the length of the rotor core  208  is not sufficiently large to receive both bearings  258  and  260  within the annular recess  216 , the front motor bearing  258  is supported within the annular recess  216  of the rotor core  212  while the rear motor bearing  260  is supported in rear tool cap  54  of the tool housing  52 . In an embodiment, rear tool cap  54  includes a radial body that includes a central bearing pocket  56  for supporting the rear motor bearing  260 . In an embodiment, rear tool cap  54  includes a peripheral portion  58  that is secured to the tool housing  52 . Alternatively, the rear tool cap  54  may be formed integrally as a part of the clamshell that forms the tool housing  52 . 
     In an embodiment, fan  218  is mounted on the rotor shaft  202  to rotate with the rotation of the motor  200 . The fan  218  includes a radial main body and a plurality of blades facing the stator assembly  210 . In an embodiment, an inner portion of the fan  218  is recessed to allow the rear motor bearing  260  to be nested at least partially in the axial directed within the fan  218  to be aligned radially with the main body of the fan  218 . The central bearing pocket  56  of the rear tool cap  54  is axially received within the recess portion of the fan  218  around the rear motor bearing  260 . In this manner, positioning of the rear motor bearing  260  within the rear tool cap  54  does not pose a significant increase in the overall length of the motor assembly  200 . 
       FIG. 9  depict a side view of the motor assembly  200  of  FIG. 2  to illustrate an advantage of the support plate configuration described above, where the front motor bearing  258  is nested within the envelope of the stator assembly  210  and at least partially within the rotor  204 . In the event of egregious movement of the rotor shaft  202  due to a fall, high vibration, or high impact, the rotor shaft  202  may be pivoted away from the longitudinal axis relative to the stator assembly  210 . This pivoting movement may take place around a pivot point  262  aligned with the front motor bearing  258 . The pivot point  262  is associated with tolerances in the bearings of the front motor bearing  258 , tolerances between the front motor bearing  258  and the rotor  204 , and/or tolerances between the front motor bearing  258  and the stator assembly  210 . Since the pivot point  262  is located within the envelope of the stator assembly  210 , in the event of such a pivoting movement of the rotor shaft  202 , the likelihood that the rotor shaft  202  makes physical contact with the stator assembly  210  is significantly reduced. 
     By comparison,  FIG. 10  depicts a side view of a prior art motor  300 , in which the front rotor bearing  358  is not nested within the rotor  304  and therefore provided outside the envelope of the stator assembly  310 . In an embodiment, in the event of egregious rotor shaft movement, the pivot point  362  for pivoting movement of the rotor shaft  302  relative to the longitudinal axis is located away from the stator assembly  310 . Thus, in the event of a pivoting movement of the rotor shaft  302 , there is a likelihood that the rotor shaft  302  makes physical contact with a portion of the stator assembly  310 . 
     Various embodiments of the rotor  204  including the outer magnet ring  206  are described here with reference to  FIGS. 11-14 . 
       FIG. 11  depicts a side cross-sectional view of the rotor  204 , according to an embodiment.  FIG. 12  depicts a perspective exploded view of the rotor  204 , according to an embodiment. In an embodiment, as described briefly previously, the rotor  204  includes a permanent magnet ring  206  that is sized to be received over an outside surface of the rotor core  208 . The magnet ring  206  may be made of sintered, hot-extrusion (MQ3), bonded, and/or injection-molded magnetic material. In another embodiment, the magnet ring  206  comprises a sintered magnet including magnet alloy that is pulverized, magnetically aligned within a magnetic field for magnetization, press molded, and then sintered. In an embodiment, magnet ring  206  may comprise a series of discrete permanent magnets mounted on the rotor core  208  as a unit. In an embodiment, the discrete magnets may be bonded together before or after magnetization. In an embodiment, the rotor core  208  may include a fully annular body. 
     In an embodiment, to properly secure the magnet ring  206 , a thin layer of adhesive is provided between the magnet ring  206  and the rotor core  208 . To accommodate the adhesive, in an embodiment, the inner diameter of the magnet ring  206  in this case is slightly greater than the outer diameter of the rotor core  208 . This may cause the magnet ring  206  to be acentric relative to the rotor core  208 . 
     Alternatively, in an embodiment, as shown in  FIGS. 11 and 12 , the rotor core  208  includes two annular alignment rings  280  at its two axial ends. Annular alignment rings  280  may be provided by carving out a middle area  282  of the rotor core  208  such that each of the annular alignment rings  280  have a slightly greater diameter than the middle area  282 , e.g., by approximately 0.1 mm to 0.6 mm, preferably 0.1 mm to 0.3 mm. The adhesive (not shown) is applied on the middle area  282  of the outer surface of the rotor core  208  for retaining the magnet ring  206 . Annular alignment rings  280  have approximately the same diameter as the inner diameter of the magnet ring  206  to ensure a tight fit and proper alignment between the magnet ring  206  and the rotor core  208 . 
       FIG. 13  depicts a perspective exploded view of the rotor  204 , according to another embodiment. In this embodiment, rotor core  208  includes a series of alignment rings  290 , forming annular grooves  292  therebetween. Annular grooves  292  may be, for example, 0.05 to 0.3 mm deep relative to the outer surface of the rotor core  208 . The adhesive (not shown) is applied within the grooves  292  for retaining the magnet ring  206 . Annular alignment rings  290  have approximately the same diameter as the inner diameter of the magnet ring  206  to ensure a tight fit and proper alignment between the magnet ring  206  and the rotor core  208 . Alternatively, in an embodiment, annular alignment rings  290  has a slightly smaller diameter than the inner diameter of the magnet ring  206  to allow the adhesive to spread over the outer surface of rotor core  208 , though this arrangement may require an additional equipment for proper alignment of the rotor core  208  and the magnet ring  206 . 
       FIG. 14  depicts a perspective exploded view of the rotor  204 , according to yet another embodiment. In this embodiment, rotor core  208  includes a series of axial pads  296  along its outer surface. Axial pads  296  project from the outer surface of the rotor core  208  by approximately 0.05 mm to 0.3 mm, forming a series of axial channels  298  in between. The adhesive (not shown) is applied within the axial channels  298  on the outer surface of the rotor core  208  for retaining the magnet ring  206 . The inner diameter of the magnet ring  206  is sized to be form-fittingly received in contact with the axial pads  296  to ensure a tight fit and proper alignment between the magnet ring  206  and the rotor core  208 . 
     Referring back to  FIGS. 7 and 8 , motor assembly  200  includes a circuit board (hereinafter referred to as Hall board)  400  is mounted on the stator assembly  210 . Hall board  400  includes a series of magnetic (Hall) sensors arranged to sense a magnetic flux of the magnet ring  206 . A series of signal wires  402  are coupled to a first connector  404  that is mounted on the Hall board  400  on one end and a second connector  406  that is coupled to the controller (not shown) on the other end. The signal wires  402  provide signals related to an angular position of the rotor  204  to the controller. 
     Use of Hall boards for detection of the angular position of the rotor is well known. Hall boards provide signals related to the magnetic position of the rotor to a controller, which uses the information for calculating the timing of commutation of the next phase of the motor. Conventionally, a Hall board is rectangular shaped with three Hall sensors positioned at predetermined angular positions to sense the rotor rotary position. Also, conventionally, a sense magnet ring is provided in addition to the rotor magnet and mounted on the rotor shaft adjacent the rotor lamination stack. The Hall sensors are axially aligned with the sense magnet ring, and the sense magnet ring has an axial magnetic flux that is sensed by the hall sensors. Disposition of the hall board adjacent the stator, and addition of the sense magnet ring, add to overall motor length and cost of manufacturing. 
     Hall board  400  is described herein in detail with reference to  FIGS. 15-22 , according to an embodiment. In an embodiment, as described here in detail, no sense magnet ring is provided, and the Hall board  400  is designed to directly sense the leakage flux of the rotor magnet ring  206 . In addition, the Hall board  400  is designed to add little or no length to the motor assembly  200 . Various embodiments for coupling the hall board  400  to the stator assembly  210  are described in detail with reference to  FIGS. 23-32 . 
       FIGS. 15 and 16  depict rear and front axial views of the stator assembly  210  and the Hall board  400 , according to another embodiment.  FIG. 17  depicts a side view of the stator assembly  210  and the Hall board  400 , according to another embodiment.  FIG. 18  depicts a cross-sectional side view of the stator assembly  210  and the Hall board  400  from a different angle, according to another embodiment.  FIG. 19  depicts a cut-off perspective front view of the stator assembly  210  and the Hall board  400 , according to another embodiment.  FIG. 20  depicts a rear perspective view of the stator assembly  210  and the Hall board  400 , according to another embodiment. 
     As shown in these figures, in an embodiment, the Hall board  400  includes a main body  410  that is arcuate shaped and overlays the rear surface of the end insulator  222  of the stator assembly  210 , three legs  412   a ,  412   b ,  412   c  that extend radially inwardly from the main body  410 . The legs  412   a - c  penetrate the stator slots formed between the ends of the stator windings  224  substantially radially in-line with the ends of the stator windings  224 . In an embodiment, the main body  410  covers approximately an angular range ‘θ’ of the stator assembly  210 , where θ is in the range of 120-140 degrees, preferably approximately 125-135 degrees, more preferably approximately 130 degrees. 
     In an embodiment, main body  410  of the Hall board  400  has a curvature that generally corresponds to the curvature of the stator assembly  210 . In an embodiment, main body  410  is shaped such that, when viewed along the axis direction of the motor assembly  200 , a first portion  414  of the main body  410  does not substantially extend beyond the periphery of the outer surface of the stator core  212 . In an embodiment, first portion  414  covers an angular distance  81  in the range of approximately 35 to 55 degrees, preferably approximately 40 to 50 degrees. In an embodiment, while a lip  411  of the first portion  414  along the leg  412   a  slightly protrudes beyond the periphery of the outer surface of the stator core  212 , the remainder of the first portion  414  is substantially contained within a peripheral envelope of the stator core  212 . 
     In an embodiment, a second portion  416  of the peripheral surface of the main body  410 , however, does extend beyond the periphery of the outer surface of the stator core  212  to provide a mounting area for the first connector  404  and receiving through-holes for fasteners  420 . In an embodiment, the second portion  416  covers an angular distance  82  in the range of approximately 60 to 90 degrees, preferably approximately 70 to 80 degrees. In an embodiment, the second portion  416  radially intersects legs  412   b  and  412   c.    
     In an embodiment, the two fasteners  420  are received through corresponding through-holes of the Hall board  400  and the rear end insulator  222  and received into threaded receptacles of the front end insulator  220  in order to secure the Hall board  400  is secured to the stator assembly  210 . 
     In an embodiment, front and rear end insulators  220  and  222  together form a mounting support structure  430  that project radially outwardly from the stator assembly  210  and securely supports the terminal block  221  on the outer surface of the stator core  212 . In an embodiment, the through holes of the end insulator  222  and threaded receptacles of the front end insulator  220  are provided on the mounting support structure  430 . In an embodiment, the terminal block  221  is thus provided adjacent the first connector  404  of the Hall board  400 . 
     In an embodiment, terminal block  221  includes a series of three motor terminals  432  provided parallel to the longitudinal axis of the motor and mounted on an insulating mount  434 . Each of the motor terminals  432  includes a folded tang portion  436  around which the magnet wires of the corresponding stator windings  224  are wrapped and fused, and a tab portion  438  to which the corresponding power wires are coupled. U.S. Pat. No. 9,819,241, which is incorporated herein by reference in its entirety, provides a full description of terminal block  221 . In an embodiment, second portion  416  of the main body  410  has a periphery that extends in line with the insulating mount  434  so as to position the first connector  404  substantially in line with the tab portions  438  of the motor terminals  432 . 
     In an embodiment, second portion  416  of the Hall board  400 , together with the terminal block  221 , may be received partially within the handle  13  of the power tool below the motor housing portion  23 . The orientation of the first portion  414  of the Hall board  400  within the circumferential envelope of the stator core  212  ensures that the Hall board  400  does not increase the overall girth of the motor assembly  200  within the motor housing portion  23 . 
     In an embodiment, legs  412   a - c  of the Hall board  400  penetrate in between the ends of the stator windings  224  and the main body  410  is mounted in contact with the end insulator  222 . As best shown in the side views of  FIGS. 17 and 18 , this arrangement allows the Hall board  400  to be positioned in the radial position approximately within motor envelope  240  (see  FIG. 5 ), with legs  412   a - 412   c  being contained fully within the motor envelope  240 . Motor envelope  240  in this embodiment is bound by rear plane  242  at a rearmost point of the stator windings  224 , front plane  244  at a frontmost point of the stator windings  224 , and generally cylindrical boundary  246  surrounding the radially outermost portion of the stator assembly  210  not including the terminal block  211 . In an embodiment, at least a portion of the Hall board  400  opposite the stator core  212  is positioned along approximately the rear plane  242 , which intersects the rear ends of the stator windings  224 . In an embodiment, the rear surface of the Hall board  400  opposite the stator core  212  is positioned along approximately the rear plane  242 . 
     This arrangement eliminates or substantially reduces any contribution by the Hall board  400  to the overall size and length of the motor assembly  200 . In compact motor applications such as cordless power tools, where significant research and development is dedicated to optimizing the power density of the motor, a reduction is length of even a few millimeters is significant. 
     In an embodiment, mounted on the front surface of the Hall board  400  facing the rotor  204  are a series of three Hall sensors  450  disposed near the inner ends  452  of the three legs  412   a - c . In an embodiment, the Hall sensors  450  are positioned circumferentially in-line with inner ends of the stator teeth  214  or inner ends of the stator windings  224  when viewed along the axis direction, as best seen in  FIGS. 15, 16, 19 and 20 . In an embodiment, the inner ends  452  of the legs  412   a - c  are circumferentially in-line with inner ends  215  of the stator teeth  214  and Hall sensors  450  are circumferentially in-line with inner portions  225  of the stator windings  224 . This arrangement positions the Hall sensors  450  sufficiently close to the rotor magnet ring  206  for direct sensing of the rotor magnet ring  206  without a need for an additional sense manet, thus further reducing the axial length of the motor assembly  200 . 
     In an embodiment, an overmold or glue material  460  on two sides of the legs  412   a - c  of the Hall board  400  near the inner ends  452  to secure the legs  412   a - c  to teeth portions  462  of the end insulator  222  of the stator assembly  210 . This ensures that the legs  412   a - c  of the Hall board  400  are protected against damage due to vibration. 
       FIG. 21  depicts a perspective view of the motor assembly  200  including the fan  218  and support plate  230 , according to an embodiment.  FIG. 22  includes a rear view of the motor assembly  200  including the fan  218 , according to an embodiment. 
     In an embodiment, connector  404  and fasteners  420  are provided on the second portion  416  of the Hall board  400 , outside the peripheral area of the motor fan  218 . Heads of the fasteners  420 , which may have a thickness of 1 mm or more, and the connector  404 , are elements associated with Hall board  400  that project slightly rearwardly of the Hall board  400  in the axial direction. However, since the connector  404  and fasteners  420  are positioned outside the peripheral area of the motor fan  218 , the motor fan  218  may be positioned in close axial proximity to the Hall board  400 , with fan blades  470  rotatably positioned in very close proximity to the rear surface of the Hall board  400 . In an embodiment, the distance between the fan blades  470  and the Hall board  400  is approximately 1.5 mm or less. This allows the Hall board  400  to be secured to the stator assembly  210  without increasing the relative distance between the motor fan  218  and the stator assembly  210 . 
     Referring back to  FIGS. 15 and 20 , while fasteners  420  sufficiently secure legs  412   b  and  412   c  of the Hall board  400  relative to the stator assembly  210 , leg  412   a  is provided at a distance from both fasteners  420  and is therefore prone to movement and breakage due to high vibration without an additional retention feature in its vicinity. To overcome this, in an embodiment, a slot  472  is provided on the main body  410  of the Hall board  400  radially outwardly of the leg  412   a  that receives a snap post  482  of the rear end insulator  222 . Moreover, a retention feature  480  is provided to mechanically secure the snap post  482  of the rear end insulator  222  to the Hall board  400  proximate the slot  472 . In an embodiment, retention feature  480  is designed to allow a snap connection or sliding connection between the Hall board  400  and the snap post  482  of the rear end insulator  222 , without adding the length of the motor assembly  200 . In an embodiment, retention feature  480  may be made as a detachable or inseparable snap-fit connection. 
       FIG. 23  depicts a partial perspective view of the rear end insulator  222 , according to an embodiment. In an embodiment, snap post  482  of the rear end insulator  222  that extends along the longitudinal axis of the motor assembly  200 . In an embodiment, snap post  482  includes a snap head  483  that is received within the slot  472  of the Hall sensor as the Hall board  400  is being mounted on the end insulator  222 , an entrance side  484  for sliding engagement with the retention feature  480  as the snap head  483  is being received within the slot  472 , and an undercut portion  486  that makes a snap-fit connection with the retention feature  480  once the snap head  483  is fully received within the slot  472  to secure the Hall board  400 . In an embodiment, retention feature  480  is designed to allow the snap-fit connection to be made at approximately the front surface of the Hall board  400  so as to avoid adding any length to the rear surface of the Hall board  400 . 
     In an embodiment, rear end insulator  222  further includes an inner post  487  disposed on one side of the snap post  482  having a flat end surface on which the front surface of the Hall board  400  rests when the retention feature  480  makes a snap connection with the snap post  482 . In addition, in an embodiment, rear end insulator  222  also includes an outer post  488  disposed on the other side of the snap post  482  to engage a radial end wall of the Hall board  400  next to the slot  427 . 
       FIG. 24A  depicts a partial perspective view of the Hall board  400 , depicting the retention feature  480  for making a snap-fit connection with the snap post  482 , according to a first embodiment.  FIG. 24B  depicts a partial side cross-sectional view of the Hall board  400  with retention feature  480  in engagement with snap post  482  of the end insulator  222 , according to the first embodiment. 
     In this embodiment, retention feature  480  further includes a molded structure  490  disposed on the front surface of the leg  412   a  of the Hall board  400 . In an embodiment, molded structure  490  may be made of resin or plastic-based material provided via overmolding, injection-molding, and similar processes. In an embodiment, molded structure  490  covers Hall sensor  450  on the front surface of the leg  412   a  of the Hall board  400 . In an embodiment, molded structure  490  is provided integrally with overmold layer  460  molded in a single step. In an embodiment, molded structure  490  includes a lip  492  arranged to engage the undercut portion  486  of the snap post  482 . In an embodiment, the lip  492  is arranged at a distance from the front surface of the Hall board  400 , with at least a portion of the lip  492  covering a portion of the slot  472  along the radial direction. In an embodiment, the lip  492  makes a snap-fit connection with the snap post  482  proximate the front surface of the Hall board  400 . In this manner, the snap post  482  is received within the slot  472 , but it does not project out of the slot  472  over the rear surface of the Hall board  400 . 
       FIG. 25A  depicts a partial perspective view of the Hall board  400 , depicting retention feature  480 ′ according to a second embodiment.  FIG. 25B  depicts a partial side cross-sectional view of the Hall board  400  with retention feature  480 ′ in engagement with snap post  482  of the end insulator  222 , according to the second embodiment. 
     In this embodiment, retention feature  480 ′ includes a molded structure  500  similar to the first embodiment described above, but instead of a lip provided as a part of the molded structure  500 , the molded structure  500  supports a metal trap  502 . In an embodiment, metal trap  502  includes a U-shaped cross-sectional profile having a main body  504  and two legs  506 . The legs  506  of the metal trap  502  are mounted on the front surface of the Hall board  400  via the molded structure  500 . In an embodiment, the main body  504  is arranged at a distance from the front surface of the Hall board  400 , with at least a portion of the main body  504  covering a portion of the slot  472  along the radial direction. In an embodiment, the main body  504  makes a snap-fit connection with the snap post  482  proximate the front surface of the Hall board  400 . In this manner, the snap post  482  is received within the slot  472 , but it does not project out of the slot  472  over the rear surface of the Hall board  400 . 
       FIG. 26  depicts a partial perspective view of the Hall board  400 , depicting retention feature  480 ″ according to a third embodiment. In this embodiment, retention feature  480 ″ includes a molded structure  510  similar to the first two embodiments described above, but instead of a molded lip or a U-shaped metal trap, the molded structure  510  supports a planar place pad  512 . In an embodiment, place pad  512  engages a snap post  482 ″ that includes two laterally projecting side lips  520  on the top portion  482 ″ instead of a radially oriented retraction side. 
       FIG. 27  depicts a perspective view of the place pad  512 , according to an embodiment. In an embodiment, place pad  512  is made of sheet metal shaped to include a U-shaped planar body including an inner main body  514  and two outwardly projecting legs  516 . In an embodiment, the main body  514  is secured in contact with the front surface of the Hall board  400  along the leg  412   a . The main body  514  is secured against the Hall board  400  via the overmold structure  510 . In an embodiment, the legs  516  extend from the main body  514  around the slot  472 . Legs  516  include oppositely arranged snaps  518  that project laterally to cover a portion of the slot  472 . In an embodiment, snaps  518  are resiliently flexible and bendable relative to the legs  516 . 
       FIG. 28A  depicts a partial perspective view of the place pad  512  and snap post  482 ″, according to an embodiment. In an embodiment, as the snap post  482 ″ is moved in the direction of slot  472  of the Hall board  400 , the snaps  518  of the place pad  512  engage the side lips  520  of the snap post  482 ″ and bend upwardly into the slot  472 . This is illustrated in the perspective view of  FIG. 28B , where the place pad  512  is depicted without the snap post  482 ″. As the snap post  482 ″ is received within the slot  472 , the snaps  518  spring inside valleys  522  formed under the lips  520 , thus securely engaging the underside of the lips  520 . In this manner, the main body  504  makes a snap-fit connection with the snap post  482 ″ proximate the front surface of the Hall board  400 , allowing the snap post  482 ″ to be received within the slot  472  without projecting out of the slot  472  over the rear surface of the Hall board  400 . 
       FIG. 29  depicts a partial perspective view of the end insulator  222  including a clip post  494 , according to an embodiment. In this embodiment, placement post  493 , which is positioned to be received within the slot  472  of the Hall board  400 , does not include a snapping feature. Instead, clip post  494  provided adjacent the placement post  493 , with a recess  495  formed facing the placement post  493 . Recess  495  is designed to engage a clip  496  of the Hall board  400  described below. 
       FIG. 30  depicts a perspective frontal view of the Hall board  400  depicting a fourth embodiment of the retention feature  480 ′″ in the form of the clip  496 . In an embodiment, clip  496  includes a main planar body  497  mounted on the front surface of the Hall board  400  and having an opening  498  that aligns with the slot  472  of the Hall board  400 . A engagement edge  499  of the clip  496  extends beyond the radial end wall of the Hall board  400 . The clip  496  may be secured to the Hall board  400  by, for example, soldering, fastening, or other known method. 
       FIG. 31A  depicts a perspective view of the Hall board  400  secured to the clip post  494  of the rear end insulator  222  via the clip  496 , according to an embodiment.  FIG. 31  B depicts a perspective view of the clip  496  secured to the clip post  494  of the rear end insulator  222  depicted without the Hall board  400 , according to an embodiment. In an embodiment, the Hall board  400  is mounted at an angle relative to the rear end insulator  222  as the engagement edge  499  of the clip  496  is positioned within the recess  495  of the clip post  494 . The Hall board  400  is pivoted around the engagement edge  499  as the placement post  493  is received within the opening  498  of the clip  496  and the slot  472  of the Hall board  400 . Once the fasteners  420  ( FIG. 21 ) are fastened to the rear end insulator  222 , the placement post  493  and the clip post  494  cooperate to structurally support and secure the Hall board  400  proximate the leg  412   a.    
     The above-described embodiments disclose a Hall board designed for sensed brushless DC motor control that does not increase the length of the motor. The Hall sensors  450  magnetically sense the magnetic flux of the rotor magnet ring  206  as the rotor  204  is rotated. That information is sent to the controller (not shown), which in turn measures the angular position of the rotor  204  based on the sensor information and controls the commutation of the motor according to the angular position. 
     It should be understood, however, that other aspects and embodiments of the invention may be utilized using a motor assembly without a Hall board, i.e., a BLDC motor that is sensorlessly controlled. Examples of sensorless motor commutation control are six-step trapezoidal commutation using the induced motor voltage signals, sinusoidal control, and field-orientated control. Reference is made to U.S. patent application Ser. No. 16/896,504 filed Jun. 9, 2020, for a description of sensorless sinusoidal and field-oriented motor control. Also, reference is made to U.S. application Ser. No. 16/530,090 filed Apr. 20, 2020, for a description of sensorless motor control using the motor induced voltage. An advantage of the Hall board design described in this disclosure is that it allows sensed trapezoidal control of a compact motor that is volumetrically equivalent to a sensorless motor capable of outputting the same power performance. However, other aspects of the invention, for example, the nested support plate, the rotor assembly, and the rear end cap design described below, may be implemented for use with a sensorless brushless motor. 
     Another aspect of the invention is described here with reference to FIGS.  32 - 39 . 
     In the embodiment of  FIG. 2  described above, proper alignment of the rear motor bearing  258 , the rear tool cap  54 , and the power tool housing  52  may be difficult to achieve. In one implementation, the rear motor bearing  258  is received within the rear tool cap  54 , the rotor  204  is mounted within the stator assembly  210 , and the motor assembly  200  and rear tool cap  54  sub-assembly is disposed within the clamshells that form the tool housing  52 . The rear tool cap  54  must be fastened to the clamshells of the tool housing  52  against the magnetic force of the magnet ring  206  interacting with stator windings  224 , which force the rear rotor bearing  54  to be offset with respect to the center axis of the motor assembly  200 . Moreover, since the housing  52  is often made of plastic, reliance on the housing  52  for location and alignment the motor assembly  200  relative to rear tool cap  54  and the rear motor bearing  258  adds to stack-up tolerances, increases the chance of stack rub, and limits nominal airgap. 
     According to an embodiment of the invention, as described below in detail, the rear tool cap of the power tool is designed to support the rear motor bearing directly with respect to the stator assembly, independently of the tool housing. In an embodiment, alignment features for piloting and alignment of the stator assembly are added to the rear tool cap, allowing the rear tool cap to directly interface with the stator assembly even prior to assembly into the tool housing. By tuning the rotor bearing pocket of the rear tool cap relative to the stator assembly rather than the housing, concentricity of the rotor outer diameter to stator inner diameter greatly improves, as the tool housing as well as some motor assembly components do not contribute to radial stack-up. 
       FIG. 32  depicts a side view of the power tool  70  including an improved rear tool cap  600  provided for interfacing with the motor assembly  200 , according to an embodiment. In an embodiment, power tool  70  includes a tool housing  72  that includes two clamshells that come together to house at least a portion of the motor assembly  200 , and rear tool cap  600  is mounted to the end of the housing  72  that also houses a portion of the motor assembly  200 . In an embodiment, power tool  70  is similar in many respects to power tools  10  and  50  of  FIGS. 1 and 2 , including a transmission assembly  20  and impact mechanism  50  forward of the motor assembly  200 , a handle, etc., the description of which are not repeated here. 
       FIG. 33  depicts a perspective partially exploded view an improved rear tool cap  600  provided for interfacing with the motor assembly  200 , according to an embodiment.  FIG. 34  depicts a perspective view of the rear tool cap  600 , according to an embodiment.  FIG. 35  depicts an axial view of the motor assembly  200  received within the rear tool cap  600 , according to an embodiment.  FIG. 36  depicts a side cross-sectional view of the motor assembly  200  received within the rear tool cap  600 , according to an embodiment.  FIGS. 37 and 38  depict two perspective views of the motor assembly  200  received within the rear tool cap  600 , according to an embodiment. 
     As shown in these figures, in an embodiment, the rear tool cap  600  includes a radial body  602  that includes a central bearing pocket  604  for supporting the rear motor bearing  260 , and a peripheral portion  606  that is secured to the tool housing  72 . Peripheral portion  606  includes a series of receptacles  608  arranged to receive fasteners (not shown) for fastening the rear tool cap  600  to the power tool housing  72 . In an embodiment, fan  218  is radially received within the peripheral portion  606 . 
     Additionally, in an embodiment, rear tool cap  600  includes one or more constraining walls  610  projecting from the peripheral portion  606  around the longitudinal axis around the outer surface of the stator core  212 . Constraining walls  610  are arcuately shaped along a circumference that has a slightly larger diameter than the outer surface of the stator core  212 . In an embodiment, constraining walls  610  are discretely provided and extend peripherally equidistant from the central bearing pocket  604  along the circumference at least partially over the outer surface of the stator core  212 . In an embodiment, the tuning pads  616  are circumferentially distanced from one another to define one or more circumferential gaps  612  in between. Alternatively, in an embodiment, a single cylindrical constraining wall  610  may be provided. 
     In an embodiment, each constraining wall  610  includes one or more tuning pads  616  on its inner surface in contact with the stator core  212 . Tuning pads  616  cooperate to form-fittingly and securely receive the stator assembly  210  into the body of the rear tool cap  600 . In an embodiment, inner surfaces of the tuning pads  616  are provided along a circumference that has a diameter substantially equal to the diameter of the outer surface of the stator core  212 . 
     In an embodiment, the rear motor bearing  260  may be secured within the central motor bearing pocket  604  prior to assembly of the rotor  204  within the stator assembly  210 . Since the tuning pads  616  secure the stator assembly  210  relative to the rear tool cap  600 , once the rear motor bearing  260  is securely received within the central motor bearing pocket  604 , the rear portion of the rotor shaft  202  is properly and accurately piloted relative to the stator assembly  210 . 
     In an embodiment, a series of exhaust vents  618  are provided within the rear end cap  600  rearward of the constraining walls  610 . Each exhaust vent  618  extends circumferentially along one side of the rear end cap  600  between the receptacles  608 . Exhaust vents  618  are positioned around the fan  218  in fluid communication with the airflow generated by the fan  218  through the motor assembly  200 . In an embodiment, fan  218  has a smaller diameter than the diameter of the stator core  212 . The airflow generated by the fan  218  travels through the motor assembly  200  along generally the longitudinal axis of the motor and is expelled radially through the exhaust vents  618 . In an embodiment, on a lower side of the rear end cap  600 , instead of an exhaust vent, a lower opening  614  is provided that aligns with and receives the first connector  404  of the motor assembly  200 . 
     In an embodiment, as best seen in  FIGS. 36-38 , the tuning pads  616  may extend along the outer surface of the stator assembly  210  from approximately half of the length of the stator core  212  up to nearly the full length of the stator assembly  210  to fully contain the stator assembly  210  within the rear tool cap  600 . This allows the motor assembly  200  to be secured within the rear tool cap  600  prior to assembly of the rear tool cap  600  to the tool housing  72 . In an embodiment, as shown in  FIG. 32 , the clamshells of the tool housing  72  may accordingly be sized to only cover less than half the length of the stator assembly  210 . 
     This arrangement significantly eases the manufacturing process, as all transmission assembly  20  components can be assembled into the tool housing  72  prior to assembly of the rear tool cap  600  together with the motor assembly  200  and the support plate  230  into the tool housing  72 . To complete this process, the motor assembly  200  may be coupled to the transmission assembly  20  by locating the cam carrier bearing  32  within the second bearing pocket  236  of the support plate  230  as the rear tool cap  600  is fastened to the clamshells of the tool housing  72 . This arrangement, in combination with the features of the motor assembly  200  and support plate  230  discussed above, contributes to reduction in the overall length of the power tool  50 . 
     Referring to  FIGS. 39-41 , an alternative rear tool cap  700  is described herein according to an embodiment. 
       FIG. 39  depicts a perspective view of rear tool cap  700 , according to an embodiment.  FIG. 40  depicts an axial view of the motor assembly  200  mounted on the rear tool cap  700 , according to an embodiment.  FIG. 41  depicts a side cross-sectional view of the motor assembly  200  mounted on the rear tool cap  700 , according to an embodiment. 
     Similar to rear tool cap  600 , the rear tool cap  700  of this embodiment includes a radial body  702  that includes a central bearing pocket  704  for supporting the rear motor bearing  260 , and a peripheral portion  706  that is secured to the tool housing  72 . Peripheral portion  706  includes a series of receptacles  708  arranged to receive fasteners (not shown) for fastening the rear tool cap  700  to the power tool housing  72 . Unlike rear tool cap  600 , however, in an embodiment, instead of circumferential turning pads disposed around the outer surface of the stator assembly  210 , the rear tool cap  700  includes axial posts  702  projecting axially from the radial body  702  arranged to be received within the slots of the stator assembly  210  formed circumferentially between stator windings  224 . Axial posts  702  are designed to penetrate the slots of the stator assembly  210  in contact with a portion of the stator core  212  and/or the stator teeth  214  to provide radial support for the rear tool cap  700 , and therefore the central bearing pocket  704 , relative to the stator assembly  210 . In an embodiment, axial posts  720  extend through approximately the full length of the stator core  212 . 
     In an embodiment, each axial post  702  may include an outer edge  712  and an outer edge  714  that is radially inward of the inner edge  712 . In an embodiment, inner edges  712  are arranged to come into contact with the inner diameter of the stator core  212 . Additionally, and/or alternatively, outer edges  714  are arranged to come into contact with adjacent tips of stator teeth  214 . In this manner, the rear tool cap  700  is supported with respect to the stator assembly  210  independently of the power tool housing  72 . Reference is once again made to US Patent Publication No. 2017/0294819A1, which is incorporated herein by reference in its entirety, for a description of the axial posts  710  for piloting and support of a bearing support structure such as the rear tool cap  700 , and consequently the rotor  204 , relative to the stator assembly  210 . In an embodiment, a series of six axial posts  710  may be provided, though as little as three axial posts  710  can sufficiently support the rear tool cap  700  relative to the stator assembly  210 . 
     In an embodiment, to accommodate insertion of the axial posts  710  into the stator slots, Hall board  400  may also be provided forward of the motor assembly  200  opposite the rear tool cap  700 . Additionally, in an embodiment, the fan  218  is positioned forward of the motor assembly  200  between the Hall board  400  and the transmission assembly  20 . In an embodiment, annular recess  216  of the rotor  204  is provided facing the rear tool cap  700  to receive the rear motor bearing  260  and central bearing pocket  704  of the rear tool cap  700  therein. In this embodiment, a radial plane B intersects at least a portion of the central bearing pocket  704 , the magnet ring  206 , the stator windings  224 , and the axial posts  710 . 
     In an embodiment, the rear motor bearing  260  may be secured within the central bearing pocket  704  of the rear tool cap  700  prior to assembly of the rotor  204  within the stator assembly  210 . As the axial posts  710  are received relative to the stator slots, the rear portion of the rotor shaft  202 , and thus the rotor  204  as a whole, is piloted relative to the stator assembly  210 . 
     Each of the above described power tools is compact in both axial length and girth. For example, the impact power tools  10 ,  50  and  70  each may have an overall axial length L 5 , L 6 , L 7  from the rear end portion of the housing  12 ,  52 ,  72  to a front end of the tool holder  28  of less than or equal to approximately 110 mm (e.g., approximately 96 mm to 110 mm, such as approximately 106 mm for power tool  10  or approximately 101 mm for power tools  50  and  70 ). In addition, an axial distance L 2 , L 4  between the rear plate of the cam carrier  22  and the front plane  124 ,  244  of the motor envelope  120 ,  240  is less than approximately 10 mm (e.g., approximately 7 mm to 10 mm, such as approximately 9.1 mm for power tool  10 ) and may be less than approximately 4 mm (e.g., approximately 2 mm to 4 mm, such as approximately 3.1 mm for power tool  50 ). 
     At the same time, the above-described power tools  10 ,  50  and  70  are configured to produce a maximum power output (measured in Max Watts Out or MWO) of at least approximately 450 Watts (e.g., approximately 450 to 550 Watts, such as at least approximately 450 Watts or at least approximately 480 Watts). The above described power tools  10 ,  50  and  70  also can produce a maximum output torque of at least approximately 1800 inch-pounds (e.g., approximately 1800 to 2010 inch-pounds, such as at least approximately 1825 inch-pounds). 
     Thus, the above-described power tools  10 ,  50  and  70  produce much greater power and torque for their compact size than what is commercially available or has otherwise been achieved previously. For example, the above described power tools  10 ,  50  and  70  have a ratio of power output to tool length of at least approximately 4.5 Watts/mm (e.g., approximately 4.5 to 5.0 Watts/mm (e.g., approximately 4.5 Watts/mm (for power tool  10 ) or approximately 4.8 Watts/mm (for power tool  50 )). The above described power tools  10 ,  50  and  70  also have a ratio output torque to tool length of at least approximately 18.0 inch-pounds/mm (e.g., approximately 18.0 inch-pounds/mm to 18.9 inch-pounds/mm, such as approximately 18.0 inch-pounds/mm (for power tool  10 ) or approximately 18.1 inch-pounds/mm (for power tool  50 )). Other exemplary power tools within the scope of the above disclosure are set forth in the below table: 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
               
               
                   
                 Motor 
                   
                   
                 Max  
                   
                   
                   
               
               
                   
                 Dia- 
                 Motor 
                 Max 
                 Torque 
                 Tool 
                 Power 
                 Torque 
               
               
                   
                 meter 
                 Length 
                 Power 
                 (inch- 
                 Length 
                 Tool 
                 Tool 
               
               
                   
                 (mm) 
                 (mm) 
                 (Watts) 
                 pounds) 
                 (mm) 
                 Length 
                 Length 
               
               
                   
               
             
            
               
                 Exam- 
                 46 
                 17 
                 450 
                 1825 
                  96 
                 4.7 
                 19.0 
               
               
                 ple 1 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Exam- 
                 51 
                 18 
                 480 
                 1910 
                 106 
                 4.5 
                 18.0 
               
               
                 ple 2 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Exam- 
                 51 
                 18 
                 480 
                 1825 
                 101 
                 4.8 
                 18.1 
               
               
                 ple 3 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Exam- 
                 56 
                 20 
                 528 
                 2008 
                 110 
                 4.8 
                 18.3 
               
               
                 ple 4 
               
               
                   
               
            
           
         
       
     
     Example embodiments have been provided so that this disclosure will be thorough, and to fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Terms of degree such as “generally,” “substantially,” “approximately,” and “about” may be used herein when describing the relative positions, sizes, dimensions, or values of various elements, components, regions, layers and/or sections. These terms mean that such relative positions, sizes, dimensions, or values are within the defined range or comparison (e.g., equal or close to equal) with sufficient precision as would be understood by one of ordinary skill in the art in the context of the various elements, components, regions, layers and/or sections being described. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.