Robonaut's arms, shown in the Figures, are human scale manipulators designed to fit within the exterior volume of an Astronaut's suit (the EMU). Beyond its volume and design objectives are human equivalent strength, human scale reach, thermal endurance to 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. The arm has a dense packaging of joints and avionics developed with the mechatronics philosophy. The endoskeletal design of the arm, houses thermal vacuum rated motors, harmonic drives, fail safe brakes and 16 sensors in each joint. Custom lubricants, strain gages, encoders and absolute angular position sensors are being developed in house to make the dense packaging possible for these advanced actuators.
The Roll-Pitch-Roll-Pitch-Roll-Pitch-Yaw kinematic tree are covered in a series of synthetic fabric layers, forming a skin that provides protection from contact and extreme thermal variations in the environment of space. Two of these arm joints have undergone early testing in a thermal vacuum chamber at JSC, where they performed well as the temperature was varied from -25C to 105C. The new lubricants developed for making this possible are a major breakthrough in Harmonic Drive technology. The two arms are mounted two a central junction, with a third limb, called the tail, and a fourth called the neck. This junction of four segments is described in the web page section labeled body. The tail is similar to the arm design, with a larger scale. The first three joints have already been assembled and integrated into Robonaut, serving as a hip or waist motion. Robonaut can be configured for many such lower body arrangements, with the tail ideally suited to operation in 0g.