  Superparamagnetic colloidal particles can be reversibly assembled into
wheel-like structures called microwheels ($\mu$wheels) which roll on surfaces
due to friction and can be driven at user-controlled speeds and directions
using rotating magnetic fields. Here, we describe the hardware and software to
create and control the magnetic fields that assemble and direct wheel motion
and the optics to visualize them. Motivated by portability, adaptability and
low-cost, an extruded aluminum heat dissipating frame incorporating open optics
and audio speaker coils outfitted with high magnetic permeability cores was
constructed. Open-source software was developed to define the magnitude,
frequency, and orientation of the magnetic field, allowing for real time
joystick control of $\mu$wheels through two-dimensional (2D) and
three-dimensional (3D) fluidic environments. With this combination of hardware
and software, $\mu$wheels translate at speeds up to 50 $\mu$m/s through sample
sizes up to 5 cm x 5 cm x 5 cm using 0.75-2.5 mT magnetic fields with rotation
frequencies of 5-40 Hz. Heat dissipation by aluminum coil clamps maintained
sample temperatures within 3 C of ambient temperature, a range conducive for
biological applications. With this design, $\mu$wheels can be manipulated and
imaged in 2D and 3D networks at length scales of micrometers to centimeters

Applied Physics;Fluid Dynamics;Instrumentation and Detectors