Direct-drive rotational mounts for transmissive optics based on open-source, hollow-shaft PCB motors

<p dir="ltr">We describe two types of hollow-shaft, printed circuit board (PCB) motors suitable for use as rotatable mounts for small, transmissive optics. One type uses coils etched into the copper foils of a PCB, while the other uses a PCB populated with discrete surface-mount ferrite-core inductors. The etched coil motors offer weak, cogging-free output torque sufficient to drive small loads such as optics, while the discrete inductor-based motors provide higher torque with some cogging due to the ferrite cores. Both motors provide reliable closed-loop speed control in the range < 40 to 300 revolutions per minute, with the (non-cogging) etched coil motors also allowing for accurate position control to ±0.09⁰. Due to their simple design, both motors can be assembled in fifteen minutes or less from a small number of off-the-shelf components and easily made parts at a unit cost of ~USD$125. Designs for both motors and their associated drive electronics are released here as open hardware, with technical diagrams, bills of materials, explanatory videos, and source-code for the firmware included as Supporting Information.</p>