RoboCrane is a 20-foot high inverted Stewart platform built by the National Institute of Standards and Technology (NIST). Six cables stretched between a large triangular platform and six winch motors enable the platform to move freely with six degrees of freedom in a roughly ten foot cubed workspace. The winches are equipped with rotational encoders, which supply data to the control cabinet. The encoders are the crane's only sensors. The crane can handle payloads in excess of 855 kilograms, moving at speeds up to 3 centimeters per second.
Low level control loops for the crane winches are handled by an array of PIC-SERVO boards and one PIC-IO board, built by J. R. Kerr. Each winch is controlled by a PIC-SERVO, while the PIC-IO manages the RS-232 communications with an outside computer. The boards receive commands from that computer, as well as an encoder feedback signal. The boards provide full PID control of position or velocity, with built-in trapezoidal velocity profiling when in position mode. Their maximum servo rate is 1953.12 Hz, while their maximum command rate to the joint actuators is 1000 Hz. The actual command rate from the software controller to the PICs is in the neighborhood of 20 Hz.
Currently, RoboCrane is working at CMU's Field Robotics Center with the robots Xavier and Bullwinkle on a project for NASA's Space Solar Power Technology Advanced Research and Technology program on the TRESTLE project.