A Stewart Platform Lunar Rover

A lunar version of the Robocrane is being developed at the Robot Systems Division of the National Institute of Standards and Technology (NIST) to address the needs of NASA researchers. The NIST robot, called ROBOCRANE, has three-pairs of rigged legs instead of actuators to create a gantry. The legs are joined in a Stewart Platform configuration providing a means for canceling out rotations normally present in gantry structures. Therefore, the frame can be made lightweight and yet, withstand high forces and torques limited mainly by the compression/tension strength of each leg. Each of three six foot legs rotates about an upper triangle to provide stable, yet flexible three-point ground contact. This makes an ideal configuration for attaching vehicles to the gantry for mobilization. The unique structure of the NIST Robocrane provides a powerful platform which can accommodate the execution of diversified tasks due to its exceptionally high payload to vehicle mass ratio, ease of payload manipulation, outstanding mobility characteristics (tested on a smooth surface), and compact packaging for transport. A 2-meter and a 6-meter version of the Robocrane have been built and critical performance characteristics and control methods analyzed. This robot, being able to rotate the legs independently about the upper triangle, is well suited for traveling over rough terrain and doing work such as construction or soil sampling on other planets. In 1992, the 2-meter Robocrane was exhibited at the Lunar Rover Expo, at the National Air and Space Museum, Washington, D. C. Introduction A new crane design utilizing six cables to suspend a load platform was first developed by the National Institute of Standards and Technology (NIST) in the early 1980's. A NIST program on robot crane technology, sponsored by Advanced Research Projects Agency (ARPA), produced the design, development and testing of three different sized prototypes to determine the performance characteristics of this proposed robot crane design. A description of the overall ARPA program and the results of this research are presented in [Dagalakis, 1989]. Initial testing of these prototypes showed that this design results in a stiff load platform [Dagalakis, 1989; Unger, 1988]. This platform (see figure 1) can be used in typical crane operations, or 1 Electronics Engineer, Robot Systems Division, National Institute of Standards and Technology, Bldg. 220, Rm. B127, Gaithersburg, MD 20899