Studies on 4WD Mobile Robots Climbing Up a Step

In this paper, step climbing capabilities of wheeled mobile robots are studied in theory and experiments. For applying the mobile robot technologies to the actual applications such as personal scooters or wheelchairs, it is required that capability for overcoming rough terrains of conventional wheeled robots is improved. For enhancing the mobility of wheeled robots, new type of omnidirectional mobile platform with four-wheel drive (4WD) mechanism is introduced. The mobile platform includes a pair of normal wheels on the rear side of the platform and a pair of omni-wheels on the front side. The normal wheel in rear and the omni-wheel in front, mounted on the same side of the base, are interconnected by a chain or a belt transmission to rotate in unison with a drive motor, i.e. a synchro-drive transmission. To rotate the robot body at the center of the mobile base about vertical axis, the third motor is installed on the platform. To estimate and verify the enhanced mobility of the proposed 4WD system, statics of a wheel-and-step system is analyzed and surmountable capabilities are tested in experiments not only for 4WD but also for a conventional rear-drive configuration. For the experiments, a 4-wheeled small vehicle is designed and built which equips four normal wheels two or all of that are driven by two electric motors. In the experiments, the small vehicle with 4WD drive configuration overcomes a step more than three times of the conventional RD configuration in the step height.