Robonaut's arms are human scale manipulators designed to fit withinthe exterior volume of an Astronaut's suit (the EMU). Beyond its volume, designobjectives were human equivalent strength, human scale reach, thermal enduranceto match an 8 hour EVA, fine motion, high bandwidth dynamic response,redundancy, safety, and a range of motion that exceeds that of a human limb. Thearm has a dense packaging of joints and avionics developed with the mechatronicsphilosophy. The endoskeletal design of the arm houses thermal vacuum ratedmotors, harmonic drives, fail-safe brakes and 16 sensors in each joint.Customlubricants, strain gages, encoders and absolute angular position sensors weredeveloped in house to make the dense packaging possible. TheRoll-Pitch-Roll-Pitch-Roll-Pitch-Yaw kinematic tree is covered in a series ofsynthetic fabric layers, forming a skin that provides protection from contactand extreme thermal variations in the environment of space. Two of these armjoints have already been tested in a thermal vacuum chamber at JSC, where theyperformed well as the temperature was varied from -25C to 105C.
The arms were designed using software developed as part of Dr.Ambrose's Ph.D. dissertation at the University of Texas at Austin .This software was used to size  and select components ,evaluate strength requirements  and simulate thermal endurance for specific task timelines. The combined design ofthe arms, body and leg (tail) for the microgravity applications was alsoperformed using custom analysis techniques, where load sharing andcompliance require an understanding of serial, parallel and bifurcatingchain kinetics . Arm requirements for advanced applications suchas climbing in microgravity and integration with surface mobility systems(rovers) are now being explored.
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