Multi-Vehicle Cooperation over Rough Terrain: Experiments with Passive Coupling

Abstract

This work presents a passive coupling and control architecture for multiple ground robots to distribute loads across multiple robots. Six types of couplings were tested for mobilizing loads over adversarial terrain and for their ability to transfer forces in tension and compression. Couplings investigated include: Pin Joints (PIJs), Spring Joints (SPJs), Universal Joints (UNJs), Double Universal Joint s (DUNJs), Ball Joints (BAJs) and String Joints (STJs). Experimentation showed that many joints fail under compression, leading to the robots jackknifing. The STJ performed the best in compression due to the push bar providing large flat surfaces which realigned discrepancies in robot trajectories. How ever, the STJ’s discontinuous force transfer delays switching between states of tension and compression. Of the couplings tested, the STJ offered the greatest mobility, al lowing for omnidirectional rotation and translation. To coordinate the robots, four controllers were evaluated, including Proportional Derivative Controller (PDC), the STJ with a Virtual Damper Controller (VDC), and the SPJ with a Forward Looking Compensator (FLC) and Adaptive Position Controller (APC). In simulation, the VDC reduced the STJ impulse forces, but was difficult to evaluate on the physical robots. The FLC offered the best trajectory tracking by mapping the terrain with the first robot. The APC had stability issues with long chains. The best coupling was found to be the STJ due to its mobility, but it requires a VDC to limit discontinuous force transfers. A simple PDC was robust in all scenarios and allowed for rapid load sharing without the need for complex control or communication.