2 CIM gearbox for drivetrain

Our team is working on transferring from a 6 CIM drivetrain to a 4 CIM drivetrain. we are looking for a fast 2 CIM gearbox for the 2020 game. Any recommendations? We are using the versa chassis from VEX with 8in wheels in a 3x3 fashion.

If you plan on/are able to make your own gearboxes, I highly encourage you to. There’s some great tutorials online, or I’d be happy to help. If you want to buy some, we ran these 2018.

We use 2 CIM ball shifters from VEXpro for our drive trains and they have been going strong for a while. They are not the best looking thing or the lightest but they have been very reliable for us

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This is the new 2-motor single-speed gearbox WCP released recently. Works with Falcons, NEOs, CIMs, MiniCIMS. And it’s suuuper compact. Just make sure to get a good gear ratio for 8 inch wheels (use JVN Calculator).
https://www.wcproducts.com/gearboxes/single-speed/wcp-ss-flipped-gearbox/wcpssflippedsinglereduction

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Almost any gearbox will do. What you’re more interested in would be the actual gear ratios. These are just something that you have to calculate. (Or use the JVN calc or the ILITE calc).

Does that work with CIMs? If you click on the little star with a question mark in it next to “stage 2”, the popup says it’s not compatible with CIMs or MiniCIMs. Why? It’s a ‘flipped’ gearbox and I think the motors are not high enough to clear the rail it would be sitting on.

I found that odd, because they allow an 8mm input shaft.

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CIMs and MiniCIMs will overhang the drive train rail and interfere with the wheel itself (even a 4" wheel).

Also keep in mind that a “flipped” gearbox is usually taller, which in some cases can complicate mounting for an intake (has happened to use the last couple of years).

This year we are using the VEX single speed double reduction gearbox as well but unfortunately with an 8" wheel that gearbox does not give enough reduction on its own. So you would need a chain/belt reduction after it.

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We second this

Consider taking a look at this excel based simulation:
FRC #1018 Robot speed simulation 2019?

Please locate the latest version at the bottom of the thread.
You can examine the performance characteristics of a number of motors with a number of gearboxes.