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A teacher wrote us and asked: I was wondering if you had any advice/hacks or a resource about how to attach gears to a little dc motor. The goal of the student is to increase the power and make it turn a propeller. We have a bunch of gears that seem compatible, so we can probably figure it out, but I thought I'd check if there was anything out there that would be helpful.
The easiest answer is to find gears (and propellers and pulleys and wheels and...) that already have a mounting hole sized for your motor. The shaft on a common project motor measures 2mm. Kelvin and other suppliers will carry some parts that will fit, you just might have to dig to find them.
I like TeacherGeek gears. They sell these great motor adapters (I call them “nubbins”) that tightly attach to the motor shaft and fit their gears, pulleys, and wheels. The nubbins are difficult to attach to the motors though – I found that many younger students couldn’t do it themselves. (pro tip: put a gear on the table, insert the nubbin in the gear first, then push on the motor from the back. Wiggle as needed.) All of their bulk stuff is great and cheap!
Another option is screen spline. Spline doesn’t fit quite as tight, but you can get a lot of it for cheap at your local hardware store. Once the motor shaft is stuck in a small piece of spline, it’s fairly easy to hot glue on gears and whatever else your students want to send spinning. Just spline on a motor shaft adds enough grip to make things move on hard surfaces.
If your goal with the gears is to just make a motor slower with more torque - like for a micro:bit robot or a remote-control car - you can get compact, inexpensive geared DC motor assemblies.
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