  We report a closed-loop control system for paramagnetic catalytically
self-propelled Janus microrobots. We achieve this control by employing
electromagnetic coils that direct the magnetic field in a desired orientation
to steer the microrobots. The microrobots move due to the catalytic
decomposition of hydrogen peroxide, during which they align themselves to the
magnetic torques applied to them. Because the angle between their direction of
motion and their magnetic orientation is a priori unknown, an algorithm is used
to determine this angular offset and adjust the magnetic field appropriately.
The microrobots are located using real-time particle tracking that integrates
with a video camera. A target location or desired trajectory can be drawn by
the user for the microrobots to follow.
