Large COTS Gear

Does anybody know where you can get large (>10" diameter) gears? I checked McMaster, and they didn’t have any that were big enough. It would be preferable if they were either 20 DP or 32 DP so they’d be more easily compatible with common FRC gears. I’m expecting that we’ll have to machine them ourselves, but I thought it was worth asking before we go ahead with it.

Well that’s asking for a lot. You’d likely have to machine one yourself. I’m assuming this is for a turret and you could instead print out a big pulley in sections and attach the sections together.

In the past, my team has been able to source very large sprockets (10-12" diamater) but I don’t recall where. That may be the only way to get something COTS for very large reductions.

we uhhh… we made our own.


I know a very inexpensive source of large gears…they are used on cars, to start the engine. This is a 14" diameter steel ring gear, that costs less than $20. If you pay more, you can get a piece of steel welded into the center, and it’s then called a “flexplate”.


We’ve machined large sprockets from 2mm plate with 2mm or 3mm endmills. It didn’t really take anything special. We made the model using Solidworks’ built-in sprocket generator, followed our normal procedure to turn CAD models into CNC router-cut parts, and voila. There was no beveling, lathe-work, or other post-machining necessary; it meshed perfectly with the #​25 chain


We did a similar thing, but with pulleys. Make only one tooth out of every three, and you can easily make an HTD 5mm pulley from a thick PC plate using a 6mm endmill. Because you have so many teeth, it will be fine if you only have some of them.

Edit: Just like in the SDS Swerve module base pulley

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There are two things I can assume you are trying to do.

The first thing I’m assuming is that you’re trying to make a turret of some sort. For this I would suggest machining a very coarse gear profile into two large sheets. You can waterjet or mill. If you’re willing to use Delrin, you could even laser cut teeth.

The other application that comes to mind would be for a genuinely large reduction, like an arm joint. If you are doing this, I would highly recommend against using gears for the final stage as the entire load of the arm will be often applied to just one or two teeth, and after awhile the shock loads really add up.

Anyway, nobody sells gears this big in FRC tooth counts, because their applications are so niche. Consider alternatives.