Design of Compact Omnidirectional Wheel Modules with Internal Differential Kinematics

Compact omnidirectional undercarriages enable the design of highly manoeuvrable mobile robots for narrow environments in industry, public spaces, and private households. This paper describes the design of wheel modules with two orientable standard wheels which form an internal differential drive. The modules come with integrated electronics, a slip ring, and an individual suspension for each wheel. Special consideration has been put on a compact and highly integrated design which can be easily fit into a mobile robot platform. The two wheel motor controllers are coupled to control the steer angle of the wheel module by differential motion of the wheels with low latency, thus ensuring stability in case of external disturbances. Four prototypes of the wheel modules have recently been built up and tested on a test bench with different obstacles like ramps, steps, and grates. The results show that the wheel modules are well capable to operate in indoor environments with thresholds and wheelchair ramps. A comparison between wheel modules with two wheels and single-wheel designs shows that two-wheel systems have several advantages at the cost of a higher complexity.