An approach for gravity compensation of planetary rovers

Experimental investigation of planetary rovers´ behavior requires low gravity (LG) simulation. It is true because rovers may have insufficient power to move and sink much deeper into soft soil in 1-g gravity environment. Constant-tension suspension is considered the best possible way for gravity compensation (GC) of rovers. Constant-tension cable has to be kept vertical, so tension generator mounts an active planar position-servo system to follow the suspended subject. Traditional suspension system, such as that for space arms or satellite reflectors, applies counterbalance forces to the center of mass (CoM) of each moving object of the tested subject. However, this approach is inappropriate for rovers that usually contain multiple moving objects. Such GC system for rocker-bogie rovers contains five constant-tension generators, five active planar position servos, and multiple on-rover attitude sensors. It´s far too complicated and unnecessary. By analysis on gravitational effects on rovers, this paper brings forward the conclusion that keeping pressure of each wheel is sufficient and necessary to ensure all concerned low gravity behaviors of rovers. Applying counterbalance forces to CoM of all the moving objects is proven unnecessary. Compensation forces required to ensure wheel pressures are derived. Single constant-tension suspension system for rover is invented accordingly, the schematic diagram of which is shown. The system includes a novel passive force-distribution mechanism to distribute compensation force to wheels. Software simulation results are presented to validate the work of this paper.