324 internal cable spool is used to create a clock spring configuration with the cabl e that allows for the ±180  degree range of motion at each joint.     The cable harness is broken in to seven segments, where each segment terminates at the joint motor controller. Multiple cable segments allows for the ability to quickly se ver the limb at any joint. This is  extremely useful for both debugging and repair. A cust om board connects the appropriate power line from  the harness to the motor / controller and interfaces the controller to the CAN communications bus that  runs down the entire length of the limb. The cable itself consists of a 60V DC power bus, a 12-V DC auxiliary power line, CAN bus , and a CAT6 Ethernet line to transmit  video from a camera at the limb end  effector. Since the required current for all joint motors can be as large as 100 A, the power bus is implemented using 15 twisted and shielded 22-gauge wire  pairs, connected to the main power system in  parallel. These power lines are configured such that 5 pairs provide power the upper most actuators in  the kinematic chain (Hip Yaw, Hip Pitch, & Thigh Pi tch). The next five pairs of the 60-V bus power the  actuators in the lower portion of t he limb (Knee Pitch, Knee Roll, Ankle Pitch, & Ankle Roll). The last five  pairs power the wheel motor, which can consume 30 A continuous and 60 A peak current. In this way, the  power axes can be stripped away from the main harness as the cable progresses down the limb, incrementally shrinking the width of the cable. A cros s section of the cable harn ess is shown in Figure 8. 

Figure 8. Leg Harness Cross Section     Wheel Design 

The Tri-ATHLETE team is also collaborating with Michelin on the development of a non-pneumatic  compliant wheel design that is appropriate for the lunar environment. This 71-cm diameter by 23-cm wide wheel is sized to support both the Tri-ATHLETE an d NASA JSC Chariot rovers (2500-N nominal load,  4500-N max load, 10-kph top speed) and efficiently carries load by using Michelin Tweel® derived  mechanics [7]. One advantage of this approach is that t he wheel’s effective contact pressure is largely  independent of load and uniform across the ground contact area. A low and uniform ground contact  pressure greatly contributes to the overall mobility performance of Tr i-ATHLETE. In addition, this wheel  design, which contains no elastomers, exhibits low energy loss from obstacle impacts and allows for a  tunable vertical stiffness that is independent of contact pressure. Thes e features are important because  the wheel system is the only additional source of passive comp liance beyond actuator windup and  deflection of the major struct ural members on Tri-ATHLETE.   The most recent design iteration, sh own in Figure 9, of the so-called Michelin Lunar Wheel is comprised  of a proprietary composite that has a specific elastic strength (elastic strength/ density) that is 4.7 times  that of 7075-T6 aluminum and 7.2 times that of 36NiCrMo16 steel. This material was chosen primarily because of its excellent cryogenic res ilience such that the wheel may remain flexible at the lower end of  the lunar surface temperature regi me (40K, -233.15ºC). Paradoxically the mechanical properties of the  NASA/CP-2010-216272