  We present a simple motorised rotation mount for a half-wave plate that can
be used to rapidly change the polarization of light. We use the device to
switch a high power laser beam between different optical dipole traps in an
ultracold atom experiment. The device uses a stepper motor with a hollow shaft,
which allows a beam to propagate along the axis of the motor shaft, minimising
inertia and mechanical complexity. A simple machined adapter is used to mount
the wave plate. We characterise the performance of the device, focusing on its
capability to switch a beam between the output ports of a polarizing
beamsplitter cube. We demonstrate a switching time of 15.9(3) ms, limited by
the torque of the motor. The mount has a reaction time of 0.52(3) ms, and a
rotational resolution of 0.45 degrees. The rotation is highly reproducible,
with the stepper motor not missing a step in 2000 repeated tests over 11 hours.
