A wheel assembly 10 for a golf trolley (30) comprises a wheel 12, a motor for driving the wheel, a battery 20 for powering the motor, detection means for detecting whether or not the wheel 12 is rotating, a control unit 22 for controlling the motor and releasable connection means 24 for releasably connecting the wheel assembly 10 to a golf trolley (30), the control unit 22 having at least a first mode of operation in which the motor can be activated only when the wheel 12 is already rotating.