Study on Roller-Walker - Improvement of Locomotive Efficiency of Quadruped Robots by Passive Wheels

Roller-Walker is a leg-wheel hybrid mobile robot using a passive wheel equipped on the tip of each leg. The passive wheel can be transformed into sole mode by rotating the ankle roll joint when Roller-Walker walks on a rough terrain. This paper discusses energy efficiency of locomotion in wheeled mode. We define a leg trajectory to produce forward straight propulsion and discuss the relationships between the parameters of leg trajectory and energy efficiency of the propulsion using a dynamics simulator. We find optimum parameter sets where optimization criterion is specific resistance. The results indicate the faster locomotion achieves the higher energy efficiency. Then we carried out hardware experiments and empirically derived experimental specific resistance. We show that wheeled locomotion has 8 times higher energy efficiency than ordinary crawl gait. Finally we compare the specific resistance of Roller-Walker with other walking robots described in the literatures. keywords: leg-wheel hybrid robot, Roller-Walker, roller skating, energy efficiency, specific resistance