Low-cost lab rotator

I'm doing a lot of magnetic bead DNA purification protocols, and they frequently have a step that requires rotating the tube at a low speed for 5-10 minutes. Until now, I'd been taping the tubes to the rotator shaft of the forgotten hyb oven in the hood of the lab next door. Then I realized I had a set of spare parts laying around that could do the job for me!

This lab rotator is designed for light duty around the same DC gear motor and PWM board I used in my low-cost remix of the Adafruit Crickit lab shaker. It uses a USB charger as a power source, and two ball bearings to keep the motor shaft captive. I designed it with a modular, magnetically-attached tube holder so that I could swap it out for different tube sizes in the future. There are spaces for eight magnets, but in practice a pair of 1/8" x 3/8" magnets or four 1/16" x 3/8" magnets per side are more than sufficient.

The version the I built uses a 1:48 geared motor, but the 1:90 geared version would be more appropriate for this application.

Parts needed:

• 1:90 DC gear motor
• PWM board
• Panel mount micro USB connector
• 4x 45mm M3 screws, 2x 30mm M3 screws, 2x 6mm M3 screws, and 6 M3 nuts (all available in this set)
• 2x 10x15x4mm ball bearings
• 8x 1/16" x 3/8" neodymium magnets