My lab has been in need of a compact centrifuge for 1.7 mL Eppendorf tubes.
From the work by KemFic on a DIY Arudino powered centrifuge from old hard drive spindles, I modified the design for a more secure structure and fit on a standard 3.5" hard drive (molded to the spindle shape and screw-hole locations). The resulting structure is more stable at higher RPMs.
The code has also been modified (https://github.com/ekurt1/Hard-Drive-Centrifuge), with automated and manual speed calibration options, with work being done on RPM vs G-force readings and an emergency shutdown mode. The code has also been modified for our purpose in using a server hard drive, with speeds of up to 15,000 RPM.
The remaining tasks for the build are a secure, weighted enclosure (since vibrates heavily during use).
At least 50% infill is required for speeds higher than 7000 RPM, or else the structure may collapse while centrifuging (happened to one prototype). Also printed out of hardened PLA, although standard PLA prototypes held up just as well. ABS and nGen collapsed under load past 5000 RPM at 30% infill.