Aerospace Vehicle Motion Emulation Using Omni-Directional Mobile Platform

Testing and validation of flight hardware in ground-based facilities can result in significant cost savings and risk reduction. We designed a relative motion emulator for aerospace vehicles using omni-directional mobile bases which provide large 3 degree-offreedom motion, while Stewart platforms mounted atop these bases allow superposition of limited 6 degree-of-freedom motion. This paper addresses the design and implementation of the omni-directional mobile base. Each omni-directional base uses a trio of active split offset castor drive modules to provide smooth, holonomic, precise control of its motion. Three encoders on each castor, three optical mice sensors, and a 3-axis inertial measurement unit provide full feedback information to a kinematics based control law. We built a one-third scale prototype to demonstrate design feasibility and for use in testing and development of data fusion techniques, control laws, and a dynamics model of the full-scale platform. Results presented in the paper validate the feasibility of the design and the approach.