Abstract:
The subject matter of this specification can be embodied in, among other things, a control apparatus includes a first mounting member, an elongate member having a first elongate portion, a second elongate portion, a first axis member between the first elongate portion and the second elongate portion, pivotally mounting the elongate member to the first mounting member and defining a first axis, a track configured as an arc defined about the first axis, and a first feedback assembly supported upon the second elongate portion and providing a first interface device configured to travel along the track in response to movement of the second elongate portion partly about the first axis, wherein the mass of the second elongate portion and the first feedback assembly substantially offsets the mass of the first elongate portion about the first axis member.

Description:
TECHNICAL FIELD 
       [0001]    This specification relates to mechanical input controls, and more particularly, aircraft flight controls. 
       BACKGROUND 
       [0002]    Joystick input devices have been employed in a wide range of applications, from aircraft control to video game inputs. Joysticks may be provided to supply directional input information related to a single rotational axis, or to multiple axes. More sophisticated joystick instruments may provide magnitude data as well. 
         [0003]    In operation, an operator will manually displace the joystick relative to one or more of its rotational axes in order to issue directional commands to other equipment. Sensors within the joystick will sense the angular displacement of the joystick and develop input signals accordingly, which may be transmitted to the equipment to be controlled. The sensors and the signals they produce may operate electronically, hydraulically, or otherwise. 
         [0004]    In many applications it is desirable that the joystick return to a center or neutral position after it has been released by the operator. Many joysticks are designed to be displaced about two perpendicular axes, so that directional information may be detected through 360 degrees. Thus, in order to return the joystick to a center position on one or both axes, certain designs have included springs to provide a centering force relative to each axis. While these mechanisms can provide the desired centering functions, these return mechanisms also tend to add weight, complexity, and cost to the design of the joystick, and cause the joystick to be mass unbalanced and therefore more susceptible to the effects of acceleration, e.g., to resist movement of the stick by gravity, g-forces. 
       SUMMARY 
       [0005]    In general, this document describes mechanical input controls, and more particularly, aircraft flight controls. 
         [0006]    In a first aspect, a control apparatus includes a first mounting member, an elongate member having a first elongate portion, a second elongate portion, a first axis member between the first elongate portion and the second elongate portion, pivotally mounting the elongate member to the first mounting member and defining a first axis, a track configured as an arc defined about the first axis, and a first feedback assembly supported upon the second elongate portion and providing a first interface device configured to travel along the track in response to movement of the second elongate portion partly about the first axis, wherein the mass of the second elongate portion and the first feedback assembly substantially offsets the mass of the first elongate portion about the first axis member. 
         [0007]    Various embodiments can include some, all, or none of the following features. The track can include a collection of gear teeth, and the first interface device can include a gear configured to engage the gear teeth such that the gear rotates in response to travel along the track. The gear can define a second axis that is radial to the first axis, the gear teeth can be arranged radial to the first axis, and the gear can engage the gear teeth perpendicular to the first axis. The gear can define a second axis that is parallel to the first axis, the track can have an outer surface radially distal from the first axis and an inner surface radially proximal to the first axis, and the collection of gear teeth can be arranged along the inner surface parallel to the first axis. The gear can define a second axis that is parallel to the first axis, the track can have an outer surface radially distal from the first axis and an inner surface radially proximal to the first axis, and the collection of gear teeth can be arranged along the outer surface parallel to the first axis. The feedback assembly can include a motor configured to drive the first interface device to modify travel of the actuator along the track to modify movement of the second elongate portion partly about the first axis. The first interface device can include a sensor configured to provide feedback in response to movement of the first interface device along the track. The upper elongate portion can include one or more user controls. The control apparatus can include a second mounting member, a second axis member between the first mounting member and the second mounting member, pivotally mounting the second mounting member to the first mounting member and defining a third axis perpendicular to and intersecting with the first axis, and a second feedback assembly having a second interface device and at least one of (1) a motor configured to drive the second interface device to modify travel of the actuator to modify movement of the second elongate portion partly about the third axis, and (2) a sensor configured to provide feedback in response to movement of the second elongate portion partly about the third axis. 
         [0008]    In a second aspect, a method of actuating a control apparatus includes providing a control apparatus having a first mounting member, an elongate member having a first elongate portion, a second elongate portion, a first axis member between the first elongate portion and the second elongate portion pivotally mounting the elongate member to the first mounting member and defining a first axis, a track configured as an arc defined about the first axis, and a first feedback assembly supported upon the second elongate portion and providing a first interface device and a motor configured to urge travel of the interface along the track. The mass of the second elongate portion and the feedback assembly substantially offsets the mass of the first elongate portion about the axis member. The method also includes urging, by the first motor, travel of the first interface device, modifying, by the first interface device, a movement of the second elongate portion along the track, and modifying, by the movement of the second elongate portion along the track, a first torque developed about the first axis. 
         [0009]    Various implementations can include some, all, or none of the following features. The method can include subjecting the elongate member to acceleration forces, wherein acceleration of the mass of the second elongate portion and the first feedback assembly substantially creates a torque about the first axis member that offsets a torque about the first axis member created by acceleration of the mass of the first elongate portion. The track can include a collection of gear teeth, and the first interface device can include a gear configured to engage the gear teeth such that the gear travels along the track in response to rotation of the motor. The gear can define a second axis that is radial to the first axis, the gear teeth can be arranged radial to the first axis, and the gear can engage the gear teeth perpendicular to the first axis. The gear can define a second axis that is parallel to the first axis, the track can have an outer surface radially distal from the first axis and an inner surface radially proximal to the first axis, and the collection of gear teeth can be arranged along the inner surface parallel to the first axis. The gear can define a second axis that is parallel to the first axis, the track can have an outer surface radially distal from the first axis and an inner surface radially proximal to the first axis, and the collection of gear teeth can be arranged along the outer surface parallel to the first axis. The control apparatus can include a second mounting member, a second axis member between the first mounting member and the second mounting member, pivotally mounting the second mounting member to the first mounting member and defining a third axis perpendicular to and intersecting with the first axis, and a second feedback assembly comprising a second interface device and a second motor configured to drive the second interface device to modify travel of the actuator to modify movement of the second elongate portion partly about the third axis, wherein the method can include urging, by the second motor, travel of the second interface device, modifying, by the second interface device, a movement of the second elongate portion about the third axis, and modifying a second torque developed about the third axis. 
         [0010]    In a third aspect, a method of actuating a control apparatus includes providing a control apparatus having a first mounting member, an elongate member having a first elongate portion, a second elongate portion, a first axis member between the first elongate portion and the second elongate portion, pivotally mounting the elongate member to the first mounting member and defining a first axis, a track configured as an arc defined about the first axis, and a first feedback assembly supported upon the second elongate portion and providing a first interface device and a first sensor. The mass of the second elongate portion and the feedback assembly substantially offsets the mass of the first elongate portion about the axis member. The method also includes sensing, by the first sensor, at least one of (1) a first movement of the second elongate portion along the track and (2) a first torque developed about the first axis, and providing, by the first interface device, information descriptive of at least one of the movement and the first torque. 
         [0011]    Various implementations can include some, all, or none of the following features. The method can include subjecting the elongate member to acceleration forces, wherein acceleration of the mass of the second elongate portion and the first feedback assembly substantially creates a torque about the first axis member that offsets a torque about the first axis member created by acceleration of the mass of the first elongate portion. The track can include a collection of gear teeth, and the first interface device can include a gear configured to engage the gear teeth such that the gear rotates sensor as the gear travels along the track in response to user movement of the first elongate member. The control apparatus can include a second mounting member, a second axis member between the first mounting member and the second mounting member, pivotally mounting the second mounting member to the first mounting member and defining a third axis perpendicular to and intersecting with the first axis, and a second feedback assembly comprising a second interface device and a second sensor, wherein the method can include sensing, by the second sensor, at least one of (1) a second movement of the second elongate portion about the third axis and (2) a second torque developed about the third axis, and providing, by the second sensor, information descriptive of at least one of the second movement and the second torque. 
         [0012]    The apparatus described herein may provide one or more of the following advantages. First, a control apparatus can provide a control stick having a self-centering capability. Second, the control apparatus can be substantially mass-balanced about an axis. Third, the control apparatus can be substantially neutral to forces of acceleration. Fourth, the control apparatus can be constructed with reduced size (e.g., envelope), weight, cost, and/or parts count. 
         [0013]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0014]      FIGS. 1-3  are plan views of example active control sticks. 
           [0015]      FIGS. 4 and 5  are plan and side views of an example feedback assembly. 
           [0016]      FIG. 6  is a plan view of another example feedback assembly. 
           [0017]      FIG. 7  is a perspective view of an example two-axis control stick. 
           [0018]      FIG. 8  is a perspective view of another example two-axis control stick. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    This document describes mechanical devices for accepting operator input, such as flight control sticks or side sticks used by aircraft pilots. In general, an aircraft or other machine may provide a “joystick” type side stick user control, and an operator may manipulate the stick to control the machine. For example, the operator may push, pull, move side to side, or otherwise manipulate a control stick to steer the machine. In general, some implementations may benefit from a control stick configuration that automatically returns to a default position after being displaced, or one that substantially maintains default position against gravity or other acceleration forces, e.g., g-forces. 
         [0020]    Weight, cost, and size, are other considerations that may generally influence the selection of a control stick mechanism, especially for use in aircraft applications. Issues of weight, cost, and/or size considerations, however, may run counter to the inclusion of self-centering features which can add complexity to a control stick design, and still may not provide the aforementioned substantial neutrality to g-forces. 
         [0021]    This document describes a control stick design that is substantially mass balanced about its axis to provide increased resistance to movement under acceleration. In general, the balanced nature of the control stick is accomplished by incorporating mechanical components used for providing self-centering and other functions into the movable mechanisms of the control stick itself in a design that balances the amount of mass included on each control of the control stick&#39;s axis points. In some implementations, by incorporating the mass of such mechanisms into the balance of the control stick, the control stick can provide increased neutrality to acceleration without using additional counterweights, thereby providing increased neutrality without substantially increasing weight. 
         [0022]      FIG. 1  is a plan view of an example active control stick  100 . In some embodiments, the active control stick  100  can be provided as a side stick, a center stick, a control column, a control yoke, or any other appropriate adaptation of a lever control device. In the illustrated example, the active control stick  100  is shown in a substantially centered or default position. 
         [0023]    The active control stick  100  includes an upper elongate portion  102   a  extending above a base plate  114  of a housing  101  and a lower elongate portion  102   b  extending below the base plate  114 . In some embodiments, the housing  101  can be a mounting bracket or other mounting member, for example, for attachment of the active control stick  100  to an airframe, console, or other portion of an aircraft or other machine. The upper elongate portion  102   a  and the lower elongate portion  102   b  are two opposing radial sections of a rotary member  103 , which rotates about an axis  118  located near the base plate  114  and defining an x-axis  119 . Angular displacement of the upper elongate portion  102   a  causes a similar angular displacement in the lower elongate portion  102   b.    
         [0024]    The upper elongate member  102   a  includes a grip assembly  116 . The grip assembly  116  extends radially away from the axis  118 . In use, a user manipulates the grip assembly  116  to cause the example active control stick  100  to rotate about the x-axis  119 . In some embodiments, the grip assembly  116  may be formed for manipulation by a user. For example, the grip assembly  116  may be sized and contoured to fit the hand of a pilot or other machine operator. 
         [0025]    With regard to the example active control stick  100 , a track  108  is supported by the housing  101 . The track  108  is configured as an arc at least partly defined about the x-axis  119 . The lower elongate portion  102   b  includes a feedback assembly  106  and an interface device  104 . The interface device  104  is configured to travel along the track  108  in response to movement of the lower elongate portion  102   b  partly about the axis  118 . 
         [0026]    The interface device  104  is configured as a spur gear extending from the feedback assembly  106  parallel to the lower elongate portion  102   b . In this configuration, the interface device  104  defines an axis that remains substantially radial to the x-axis  119  as the lower elongate portion  102   b  moves. The interface device  104  includes a collection of radial gear teeth  105  with faces extending the axial length of the spur gear. 
         [0027]    The track  108  includes a collection of gear teeth  109 . The gear teeth  109  are arranged upon the track  108  such that the face of each tooth is oriented to be substantially radial to the x-axis  119 . The radial gear teeth  105  meshingly engage with the gear teeth  109 . In some implementations, the interface device  104  can be rotated to urge movement of the lower elongate portion  102   b  along the track  108  and urge the rotary member  103  to pivot about the axis  118  (e.g., force feedback). In some implementations, the interface device  104  can be held rotationally stationary to resist movement of the lower elongate portion  102   b  along the track  108  and resist pivotal movement of the rotary member  103  about the axis  118  in response to external forces acting upon the upper elongate portion  102   a  (e.g., position hold, clutching). For example, the feedback assembly  106  may include a motor and/or clutch configured to controllably spin the interface device  104  and/or prevent rotation of the interface device  104 , and provide force feedback to the user hand at the grip  116 . 
         [0028]    In some implementations, the interface device  104  can be rotated in response to the rotary member  103  pivoting about the axis  118 , causing movement of the lower elongate portion  102   b  along the track  108  (e.g., position sensing). For example, the feedback assembly  106  may include a rotary encoder or other sensor configured to measure rotation of the interface device  104  and provide position feedback to a controller or other receiving device as the user urges movement at the grip  116 . 
         [0029]    With regard to the example active control stick  100 , the upper elongate portion  102   a  and the lower elongate portion  102   b  are formed so the mass of the upper elongate portion  102   a  and the mass of the lower elongate portion  102   b  are substantially balanced across the axis  118 . In some implementations, the mass of the upper elongate portion  102   a  may be equal to the mass of the lower elongate portion  102   b , with their respective masses being distributed substantially symmetrically about the x-axis  119 . In some implementations, the mass of the upper elongate portion  102   a  may be equal or unequal to the mass of the lower elongate portion  102   b , with their respective masses being distributed substantially asymmetrically about the x-axis  119 . For example, the upper elongate portion  102   a  may include relatively lightweight components located to create a relatively long lever arm, e.g., distance between the components and the fulcrum, and the lower elongate portion  102   b  may include relatively heavier components located to create a relatively shorter lever arm. As such, unequal masses and/or unequal lever lengths may be combined to substantially balance the distribution of the active control stick  100  about the x-axis  119 . 
         [0030]      FIG. 2  is a plan view of an example active control stick  200 . In some embodiments, the active control stick  200  can be provided as a side stick, a center stick, a control column, a control yoke, or any other appropriate adaptation of a lever control device. In the illustrated example, the active control stick  200  is shown in a substantially centered or default position. The active control stick  200  includes an upper elongate portion  202   a  extending above a base plate  214  of a housing  201  and a lower elongate portion  202   b  extending below the base plate  214 . The upper elongate portion  202   a  and the lower elongate portion  202   b  are two opposing radial sections of a rotary member  203 , which rotates about an axis  218  located near the base plate  214  and defining an x-axis  219 . Angular displacement of the upper elongate portion  202   a  causes a similar angular displacement in the lower elongate portion  202   b.    
         [0031]    The upper elongate member  202   a  includes a grip assembly  216 . The grip assembly  216  extends radially away from the axis  218 . In use, a user manipulates the grip assembly  216  to cause the example active control stick  200  to rotate about the x-axis  219 . In some embodiments, the grip assembly  216  may be formed for manipulation by a user. For example, the grip assembly  216  may be sized and contoured to fit the hand of a pilot or other machine operator. 
         [0032]    With regard to the example active control stick  200 , a track  208  is supported by the housing  201 . The track  208  is configured as an arc at least partly defined about the x-axis  219 . The lower elongate portion  202   b  includes a feedback assembly  206  and an interface device  204 . The interface device  204  is configured to travel along the track  208  in response to movement of the lower elongate portion  202   b  partly about the axis  218 . 
         [0033]    The interface device  204  is configured as a spur gear extending from the feedback assembly  206  perpendicular to the lower elongate portion  202   b . In this configuration, the interface device  204  defines an axis that remains substantially parallel to the x-axis  219  as the lower elongate portion  202   b  moves. The interface device  204  includes a collection of radial gear teeth  205  with faces extending the axial length of the spur gear. 
         [0034]    The track  208  includes a collection of gear teeth  209 . The gear teeth  209  are arranged upon an inner surface  210  of the track  208 , radially proximal to the axis  218  and opposite a radially outer surface  211 . The face of each tooth is oriented substantially parallel to the x-axis  219  and extends from the inner surface radially toward the axis  218 . The radial gear teeth  205  meshingly engage with the gear teeth  209 . In some implementations, the interface device  204  can be rotated to urge movement of the lower elongate portion  202   b  along the track  208  and urge the rotary member  203  to pivot about the axis  218  (e.g., force feedback). In some implementations, the interface device  204  can be held rotationally stationary to resist movement of the lower elongate portion  202   b  along the track  208  and resist pivotal movement of the rotary member  203  about the axis  218  in response to external forces acting upon the upper elongate portion  202   a  (e.g., position hold, clutching). For example, the feedback assembly  206  may include a motor and/or clutch configured to controllably spin the interface device  204  and/or prevent rotation of the interface device  204 , and provide force feedback to the user hand at the grip  216 . 
         [0035]    In some implementations, the interface device  204  can be rotated in response to the rotary member  203  pivoting about the axis  218 , causing movement of the lower elongate portion  202   b  along the track  208  (e.g., position sensing). For example, the feedback assembly  206  may include a rotary encoder or other sensor configured to measure rotation of the interface device  204  and provide position feedback to a controller or other receiving device as the user urges movement at the grip  216 . 
         [0036]    With regard to the example active control stick  200 , the upper elongate portion  202   a  and the lower elongate portion  202   b  are formed so the mass of the upper elongate portion  202   a  and the mass of the lower elongate portion  202   b  are substantially balanced across the axis  218 . In some implementations, the mass of the upper elongate portion  202   a  may be equal to the mass of the lower elongate portion  202   b , with their respective masses being distributed substantially symmetrically about the x-axis  219 . In some implementations, the mass of the upper elongate portion  202   a  may be equal or unequal to the mass of the lower elongate portion  202   b , with their respective masses being distributed substantially asymmetrically about the x-axis  219 . For example, the upper elongate portion  202   a  may include relatively lightweight components located to create a relatively long lever arm, e.g., distance between the components and the fulcrum, and the lower elongate portion  202   b  may include relatively heavier components located to create a relatively shorter lever arm. As such, unequal masses and/or unequal lever lengths may be combined to substantially balance the distribution of the active control stick  200  about the x-axis  219 . 
         [0037]    In some embodiments, the interface device  204  and the track  208  may be configured to engage frictionally (e.g., direct contact without gears). For example, the interface device  204  may be a wheel with a rubberized outer surface, and the track  208  may be mostly smooth but with sufficient roughness to engage with the wheel to allow the wheel to roll along the track  208  to drive movement of the rotary member  203 , or to allow movement of the rotary member  203  to drive rotation of the wheel as it is rolled along the track  208 . 
         [0038]      FIG. 3  is a plan view of an example active control stick  300 . In some embodiments, the active control stick  300  can be provided as a side stick, a center stick, a control column, a control yoke, or any other appropriate adaptation of a lever control device. In the illustrated example, the active control stick  300  is shown in a substantially centered or default position. The active control stick  300  includes an upper elongate portion  302   a  extending above a base plate  314  of a housing  301  and a lower elongate portion  302   b  extending below the base plate  314 . The upper elongate portion  302   a  and the lower elongate portion  302   b  are two opposing radial sections of a rotary member  303 , which rotates about an axis  318  located near the base plate  314  and defining an x-axis  319 . Angular displacement of the upper elongate portion  302   a  causes a similar angular displacement in the lower elongate portion  302   b.    
         [0039]    The upper elongate member  302   a  includes a grip assembly  316 . The grip assembly  316  extends radially away from the axis  318 . In use, a user manipulates the grip assembly  316  to cause the example active control stick  300  to rotate about the x-axis  319 . In some embodiments, the grip assembly  316  may be formed for manipulation by a user. For example, the grip assembly  316  may be sized and contoured to fit the hand of a pilot or other machine operator. 
         [0040]    With regard to the example active control stick  300 , a track  308  is supported by the housing  301 . The track  308  is configured as an arc at least partly defined about the x-axis  319 . The lower elongate portion  302   b  includes a feedback assembly  306  and an interface device  304 . The interface device  304  is configured to travel along the track  308  in response to movement of the lower elongate portion  302   b  partly about the axis  318 . 
         [0041]    The interface device  304  is configured as a spur gear extending from the feedback assembly  306  perpendicular to the lower elongate portion  302   b . In this configuration, the interface device  304  defines an axis that remains substantially parallel to the x-axis  319  as the lower elongate portion  302   b  moves. The interface device  304  includes a collection of radial gear teeth  305  with faces extending the axial length of the spur gear. 
         [0042]    The track  308  includes a collection of gear teeth  309 . The gear teeth  309  are arranged upon an outer surface  311  of the track  308 , radially distal from the axis  318  and opposite a radially outer surface  310 . The face of each tooth is oriented substantially parallel to the x-axis  319  and extends from the inner surface radially toward the axis  318 . The radial gear teeth  305  meshingly engage with the gear teeth  309 . In some implementations, the interface device  304  can be rotated to urge movement of the lower elongate portion  302   b  along the track  308  and urge the rotary member  303  to pivot about the axis  318  (e.g., force feedback). In some implementations, the interface device  304  can be held rotationally stationary to resist movement of the lower elongate portion  302   b  along the track  308  and resist pivotal movement of the rotary member  303  about the axis  318  in response to external forces acting upon the upper elongate portion  302   a  (e.g., position hold, clutching). For example, the feedback assembly  306  may include a motor and/or clutch configured to controllably spin the interface device  304  and/or prevent rotation of the interface device  304 , and provide force feedback to the user hand at the grip  316 . 
         [0043]    In some implementations, the interface device  304  can be rotated in response to the rotary member  303  pivoting about the axis  318 , causing movement of the lower elongate portion  302   b  along the track  308  (e.g., position sensing). For example, the feedback assembly  306  may include a rotary encoder or other sensor configured to measure rotation of the interface device  304  and provide position feedback to a controller or other receiving device as the user urges movement at the grip  316 . 
         [0044]    With regard to the example active control stick  300 , the upper elongate portion  302   a  and the lower elongate portion  302   b  are formed so the mass of the upper elongate portion  302   a  and the mass of the lower elongate portion  302   b  are substantially balanced across the axis  318 . In some implementations, the mass of the upper elongate portion  302   a  may be equal to the mass of the lower elongate portion  302   b , with their respective masses being distributed substantially symmetrically about the x-axis  319 . In some implementations, the mass of the upper elongate portion  302   a  may be equal or unequal to the mass of the lower elongate portion  302   b , with their respective masses being distributed substantially asymmetrically about the x-axis  319 . For example, the upper elongate portion  302   a  may include relatively lightweight components located to create a relatively long lever arm, e.g., distance between the components and the fulcrum, and the lower elongate portion  302   b  may include relatively heavier components located to create a relatively shorter lever arm. As such, unequal masses and/or unequal lever lengths may be combined to substantially balance the distribution of the active control stick  300  about the x-axis  319 . 
         [0045]    In some embodiments, the mounting positions of the interface device  304  and the track  308  may be reversed. For example, the interface device  304  may be supported by the housing  301  and the track  308  may be supported by and move along with the lower elongate portion  302   b.    
         [0046]    In some embodiments, the interface device  304  and the track  308  may be configured to engage frictionally (e.g., direct contact without gears). For example, the interface device  304  may be a wheel with a rubberized outer surface, and the track  308  may be mostly smooth but with sufficient roughness to engage with the wheel to allow the wheel to roll along the track  308  to drive movement of the rotary member  303 , or to allow movement of the rotary member  303  to drive rotation of the wheel as it is rolled along the track  308 . 
         [0047]      FIGS. 4 and 5  are plan and side views of an example feedback assembly  400 . In some embodiments, the feedback assembly  400  can be used as the feedback assembly  106 ,  206 , and  306  of the example active control sticks  100 ,  200 , and  300 . 
         [0048]    The feedback assembly  400  includes an interface device  404 . The interface device  404  is configured as a straight bevel gear extending from the feedback assembly  400  parallel to a lower elongate portion  402   b . In this configuration, the interface device  404  defines an axis that remains substantially radial to the axis of rotation (e.g., the x-axis  119 ) of the lower elongate portion  402   b . The interface device  404  includes a collection of gear teeth  405  with faces extending substantially straight and substantially parallel to the generators of the cone of the straight bevel gear. 
         [0049]    The gear teeth  405  interface with a track  408 . In some embodiments, the track  408  can be supported by a housing. For example, the track  408  can be used in place of the track  108 , which is supported upon the housing  101  of the example active control stick  100 . The track  408  is configured as an arc at least partly defined about the axis of the lower elongate portion  402   b . The track  408  includes a collection of gear teeth  409 . The gear teeth  409  are arranged upon the track  408  such that the face of each tooth is oriented at an angle that is between 0 and 90 degrees relative to the axis of the lower elongate portion  402   b . The radial gear teeth  405  meshingly engage with the gear teeth  409 . In some embodiments, the track  408  may be a subsection of a straight bevel gear configured to matingly interface with the straight bevel gear configuration of the interface device  404 . 
         [0050]    The interface device  404  is configured to travel along the track  408  in response to movement of the lower elongate portion  402   b  partly about the axis of the lower elongate portion  402   b . In some implementations, the interface device  404  can be rotated to urge movement of the lower elongate portion  402   b  along the track  408  and urge pivotal motion of a rotary member (e.g., the rotary member  103 ). For example, the interface device  404  may be driven to provide force feedback to an operator. In some implementations, the interface device  404  can be held rotationally stationary to resist movement of the lower elongate portion  402   b  along the track  408  and resist pivotal movement of a rotary member in response to external forces acting upon an upper elongate portion (e.g., the upper elongate portion  102   a ). For example, rotation of the interface device  404  may be prevented in order to provide a position hold or clutching behavior for an active control stick, such as the example active control stick  100 . For example, the feedback assembly  106  may include a motor and/or clutch configured to controllably spin the interface device  104  and/or prevent rotation of the interface device  104 , and provide force feedback to the user hand at the grip  116 . 
         [0051]    In some implementations, the interface device  104  can be rotated in response to the rotary member  103  pivoting about the axis  118 , causing movement of the lower elongate portion  102   b  along the track  108  (e.g., position sensing). For example, the feedback assembly  106  may include a rotary encoder or other sensor configured to measure rotation of the interface device  104  and provide position feedback to a controller or other receiving device as the user urges movement at the grip  116 . 
         [0052]      FIG. 6  is a plan view of another example feedback assembly  600 . In some embodiments, the feedback assembly  600  can be used as the feedback assembly  106 ,  206 , and  306  of the example active control sticks  100 ,  200 , and  300 . 
         [0053]    The feedback assembly  600  includes an interface device  604 . The interface device  604  is configured as a spiral bevel gear extending from the feedback assembly  600  parallel to a lower elongate portion  602   b . In this configuration, the interface device  604  defines an axis that remains substantially radial to the axis of rotation (e.g., the x-axis  119 ) of the lower elongate portion  602   b . The interface device  604  includes a collection of gear teeth  605  that are curved to the generators of the cone of the spiral bevel gear. 
         [0054]    The gear teeth  605  interface with a track  608 . In some embodiments, the track  608  can be supported by a housing. For example, the track  608  can be used in place of the track  108 , which is supported upon the housing  101  of the example active control stick  100 . The track  608  is configured as an arc at least partly defined about the axis of the lower elongate portion  602   b . The track  608  includes a collection of gear teeth  609 . The gear teeth  609  are arranged upon the track  608  such that the face of each tooth is oriented at an angle that is between 0 and 90 degrees relative to the axis of the lower elongate portion  602   b . The radial gear teeth  605  meshingly engage with the gear teeth  609 . In some embodiments, the track  608  may be a subsection of a spiral bevel gear configured to matingly interface with the straight bevel gear configuration of the interface device  604 . In some embodiments, the interface device  604  and the track  608  may be configured to interface as zerol bevel gears, hypoid bevel gears, mitre gears, or as any other appropriate form of gears. 
         [0055]      FIG. 7  is a perspective view of an example two-axis active control stick  700 . In some embodiments, the active control stick  700  can be provided as a side stick, a center stick, a control column, a control yoke, or any other appropriate adaptation of a lever control device. In the illustrated example, the two-axis active control stick  700  is shown in a substantially centered or default position. The two-axis active control stick  700  includes a one-axis active control stick assembly  701  having an upper elongate portion  702   a  extending above a base plate  714  and an axis  718  of an inner housing  707 , and a lower elongate portion  702   b  extending below the axis  718 . The upper elongate portion  702   a  and the lower elongate portion  702   b  are two opposing radial sections of a rotary member  703 , which rotates about the axis  718  and defines an x-axis  719 . Angular displacement of the upper elongate portion  702   a  causes a similar angular displacement in the lower elongate portion  702   b.    
         [0056]    The upper elongate member  702   a  includes a grip assembly  716 . The grip assembly  716  extends radially away from the axis  718 . In some embodiments, the grip assembly  716  may be formed for manipulation by a user. For example, the grip assembly  716  may be sized and contoured to fit the hand of a pilot or other machine operator. 
         [0057]    With regard to the example two-axis active control stick  700 , a track  708  is supported by the inner housing  707 . The track  708  is configured as an arc at least partly defined about the x-axis  719 . The lower elongate portion  702   b  includes a feedback assembly  706  and an interface device  704 . The interface device  704  is configured to travel along the track  708  in response to movement of the lower elongate portion  702   b  partly about the axis  718 . 
         [0058]    The rotary member  703  is substantially mass-balanced about the x-axis  719 . In some embodiments, the example one-axis active control stick  701  can be the example active control stick  100 , the example active control stick  200 , or the example active control stick  300 . In general, the two-axis control stick  700  extends the design of the active control sticks  100 ,  200 , and  300  to provide a second axis of motion (e.g., y-axis) while remaining substantially mass-balanced about both axes. 
         [0059]    The inner housing  707  is also configured as a mounting bracket for attachment to an outer housing  750 . The inner housing  707  is pivotally connected to the outer housing  750  by an axis  752  defining a y-axis  754 . The y-axis  754  is substantially perpendicular to the x-axis  719  and intersects with the x-axis  719  at an origin point  756 . In some embodiments, the outer housing  750  is configured as a mounting bracket or other mounting member, for example, for attachment of the example two-axis active control stick  700  to an airframe, console, or other portion of an aircraft or other machine. 
         [0060]    With regard to the example two-axis active control stick  700 , a track  768  is supported by the outer housing  750 . The track  768  is configured as an arc at least partly defined about the y-axis  754 . The inner housing  707  supports a feedback assembly  766  and an interface device  764 . The interface device  764  is configured to travel along the track  768  in response to movement of the lower elongate portion  702   b  partly about the axis  752 . In some embodiments, the track  768  may be supported by the inner housing  707  and the feedback assembly  766  can be supported by the outer housing  750 . 
         [0061]    The interface device  764  is configured as a spur gear extending from the feedback assembly  766  substantially parallel to the axis  752 . In this configuration, the interface device  764  defines an axis that remains substantially parallel to the y-axis  754  as the lower elongate portion  702   b  moves. The interface device  764  includes a collection of radial gear teeth  765  with faces extending the axial length of the spur gear. 
         [0062]    The track  768  includes a collection of gear teeth  769 . The gear teeth  769  are arranged upon the track  768  such that the face of each tooth is oriented substantially radial to the y-axis  754 . The radial gear teeth  765  meshingly engage with the gear teeth  769 . In some implementations, the interface device  766  can be rotated to urge movement of the inner housing  707  along the track  7688  and urge the rotary member  703  to pivot about the axis  752  (e.g., force feedback). In some implementations, the interface device  766  can be held rotationally stationary to resist movement of the inner housing  707  along the track  768  and resist pivotal movement of the rotary member  103  about the axis  752  in response to external forces acting upon the upper elongate portion  702   a  (e.g., position hold, clutching). For example, the feedback assembly  766  may include a motor and/or clutch configured to controllably spin the interface device  764  and/or prevent rotation of the interface device  764 , and provide force feedback to the user hand at the grip  716 . 
         [0063]    With regard to the example two-axis active control stick  700 , the upper elongate portion  702   a  and the lower elongate portion  702   b  are configured so the mass of the upper elongate portion  702   a  and the mass of the lower elongate portion  702   b  are substantially balanced across the axis  718 . The inner housing  707  and the one-axis control stick  701  are configured to be substantially balanced across the axis  752 . In some implementations, the mass of inner housing  707  and the one-axis control stick  701  may be distributed substantially symmetrically about the origin  756 . In some implementations, the mass of the inner housing  707  and the one-axis control stick  701  may be distributed equally or unequally across the origin  756 , with their respective masses being distributed substantially asymmetrically about the origin  756 . For example, a portion of the inner housing  707  above the origin  756  may include relatively lightweight components located to create a relatively long lever arm, e.g., distance between the components and the fulcrum, and the portion of the inner housing  707  below the origin  756  may include relatively heavier components located to create a relatively shorter lever arm. As such, unequal masses and/or unequal lever lengths may be combined to substantially balance the distribution of the two-axis active control stick  700  about both the x-axis  719  and the y-axis  754 . 
         [0064]      FIG. 8  is a perspective view of another example two-axis active control stick  800 . In some embodiments, the two-axis active control stick  800  can be provided as a side stick, a center stick, a control column, a control yoke, or any other appropriate adaptation of a lever control device. In the illustrated example, the two-axis active control stick  800  is shown in a substantially centered or default position. The two-axis active control stick  800  includes a one-axis active control stick assembly  801 . In general, the two-axis control stick  800  is the example two-axis control stick  700  with the feedback assembly  706  and the track  708  in an alternate configuration. 
         [0065]    The one-axis control stick assembly  701  is substantially mass balanced about an axis  818  defining an x-axis  819 . The one-axis control stick assembly  801  includes an inner housing  807 , which supports a track  868  and is pivotally coupled to an outer housing  850  by an axis  852  defining a y-axis  854 . The y-axis  854  is substantially perpendicular to the x-axis  819  and intersects with the x-axis  819  at an origin point  856 . In some embodiments, the outer housing  850  is configured as a mounting bracket or other mounting member, for example, for attachment of the example two-axis active control stick  800  to an airframe, console, or other portion of an aircraft or other machine. 
         [0066]    In some embodiments, the track  868  can be the track  768  modified to be mounted upon the inner housing  807  instead of the outer housing  750 , and below the y-axis  854  instead of above the y-axis  754 . The outer housing  850  supports a feedback assembly  866 . In some embodiments the feedback assembly  866  can be the feedback assembly  766  modified to be supported by the outer housing  850  instead of the inner housing  707 , and below the y-axis  854  instead of above the y-axis  754 . 
         [0067]    The inner housing  807  and the one-axis control stick  801  are configured to be substantially balanced across the axis  852 . In some implementations, the mass of inner housing  807  and the one-axis control stick  801  may be distributed substantially symmetrically about the origin  856 . In some implementations, the mass of the inner housing  807  and the one-axis control stick  801  may be distributed equally or unequally across the origin  856 , with their respective masses being distributed substantially asymmetrically about the origin  856 . For example, a portion of the inner housing  807  above the origin  856  may include relatively lightweight components located to create a relatively long lever arm, e.g., distance between the components and the fulcrum, and the portion of the inner housing  807  below the origin  856  may include relatively heavier components located to create a relatively shorter lever arm. As such, unequal masses and/or unequal lever lengths may be combined to substantially balance the distribution of the two-axis active control stick  800  about both the x-axis  819  and the y-axis  854 . 
         [0068]    Although a few implementations have been described in detail above, other modifications are possible. For example, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. In addition, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.