A disclosed vehicle wheel assembly includes a plurality of wheels, a plurality of rotary drive modules each having a respective rotation axis, and a plurality of rotatable arms, wherein each arm is arranged to extend radially from a rotation axis of a respective rotary drive module to couple the respective rotary drive module to a respective wheel. Each rotary drive module is operable to drive rotation of a respective rotatable arm about the rotation axis of the drive module, to thereby rotate a respective wheel about the rotation axis. A control module can sense stepped terrain, and control each rotary drive module to enable a vehicle to travel over the stepped terrain.
