Abstract
This paper presents analysis and experiments of a 4WD omnidirectional wheelchair for climbing a high step. The conventional 4WD system provides enhanced step climb capability however, the maximum step height is restricted by the rear wheel. Namely, front wheels can climb up higher step than the rear wheels. To clarify the difference between front and rear wheels in the step climb capability, the statics of the 4WD system is analyzed. It is suggested that reaction of the drive torque cause the front-rear differences which depends on a wheelbase and vehicle weight distribution ratio to front and rear wheel axes. To verify the analysis results, step climb capability of a 4WD wheelchair prototype is tested through experiments. For varying a vehicle weight distribution ratio between front and rear wheel axes, we develop a chair tilting mechanism for the 4WD wheelchair with a linear drive mechanism controlled by a stability algorithm using an inclination sensor. In the experiments, both front and rear wheels of the prototype wheelchair can successfully climb a 9cm step while the rear wheels fail when the chair tilting system is disabled.
