An autonomous mobile device may use a pair of main wheels and a caster assembly to provide mobility. The main wheels are driven by motors, providing steering and movement. Each main wheel may include a cover that conceals and protects a hub of the main wheel from the external environment. The covers may be held in place by elastomeric posts, allowing easy changeout. The caster assembly has a minimal overall height and a field replaceable caster wheel. The caster wheel may include a target that is detectable by a non-contact sensor to detect caster wheel rotation. The caster wheel may comprise an axle, caster wheel hub, and a pair of caster wheel endcaps on each end of the axle. A set of features on the caster wheel hub and each of the caster wheel endcaps provide a labyrinthian path that prevents debris from fouling around the axle.