Paper: Replacing COTS gear stages with chain or belt

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Replacing COTS gear stages with chain or belt
by: Nate Laverdure

A spreadsheet of belt/pulley or chain/sprocket combinations that may be swapped into common COTS gear spacings

Did you know you can use HTD pulleys instead of gears in the VexPro Single Reduction Clamping Gearbox, or in the 3rd stage of a Ball Shifter?

Click to embiggen

Here’s a spreadsheet of belt/pulley and chain/sprocket combinations that may be swapped into some common COTS 20DP gear spacings: 72, 78, 84, 90, 96, and 112 teeth.

Open the Google document to see the latest version of this spreadsheet. The attachments below may not be the latest version.

Note: does not consider the 24t #25 spocket, am-3623.

This is really cool info.

+1, I’ve always wondered about this. Great spreadsheet!

EDIT: One note, for the “too small/ too tight” boxes you should make FALSE green instead of TRUE. That way it’s more clear what works and what doesn’t.

Good suggestion, thanks. I made TRUEs red instead.

App writers among us:
This exhaustive/exhausting spreadsheet was built by following a pretty short series of simple rules. It could be totally replaced by a program. You should write it.

Also you might include a check to see if the belts exist commercially. Vex, SDP, AM, mcmaster-carr etc usually only stock a few sizes.

Strongly recommend belts and pulleys from ( They have a very good selection and for us parts shipped out of Chicago area and showed up in 2 days.

I implemented my own version of this with some changes; the user now inputs the gear tooth count total to replace, added support for 32 dp gears, 3mm belt and pulley options are reported, and it checks quite a few more combinations.

Here’s the current sheet.

Currently it’s only checking belts against Vex parts, I’ll update it with belts from other vendors when I get a chance.

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I’m confused. There are belt pulleys that press onto a CIM shaft?

This might be what they plan on using for this

It’s not what’s shown in the picture, but WCP does have a 12t 5mm HTD CIM pulley. (WCP-0076)

Buy plain bore or pulley stock from SPD or B&B and make your own. Key broach and bushing for that size is affordable and can be done with a small arbor press. You can even go to a GT3 profile belt.

Royal supply is a great source for belts.

The Versaplanetary fits the pictured single-redux clamping gearbox. Recall that the VP has a CIM mounting pattern and is available in all sorts of output shaft options.

Okay, the reductions possible with that make sense. Now I understand.

Add in the benefits of high efficiency, lower backlash, load tolerance, etc of the planetary gear. This is pretty neat.