Chain/sprocket driven wheels of different diameters

FIRST General Forum
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We are looking at 10" diameter pneumatic wheels in the front and 6" omniwheels in the rear. We would like to run 4 wheel drive with a pair of CIMs running through a CIMple gearbox, output sprocket with a chain to the front 10" diameter wheels with a 60 tooth sprocket, and a chain to the rear 6" diameter omni’s with a 36 tooth sprocket.

Is the potential for the front and rear wheels to try to travel at slightly different speeds (due to the diameter change of the pneumatic tire, etc.) going to be a big problem? My first thought is that the omniwheels are pretty slick and should slip to relieve tension if/when it builds up.

We could potentially run 4 CIMple gearboxs (one for each wheel) and let the motors do the load balancing, but it would be nice to have both motors power to the front wheels, and we would like to keep things as simple as possible.

Has anyone successfully (or unsuccessfully) run powered wheels of different diameters off the same chain (or chained together)?

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Speaking from a position of never having done this before, I would suggest that you not do too much experimentation on a drive train during the build season, and instead save such prototyping for the off-season. There are simpler ways to get over the barrier, like extra off-set idler wheels in the front that are mounted higher so that they are not in contact with the ground.

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What Patrick said ^^

But a small amount of slip should not be a major issue. It does decrease your drivetrain efficiency, turning energy into heat from slip friction.

Also note that omni wheels will slip sideways easily, but not longitudinally. If someone decides to push you sideways, you’re sunk.

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We used 10" pneumatic and 8" omni-wheels in 2010 without any problems. http://www.chiefdelphi.com/media/photos/35118. We also used 12" pneumatic wheels and 8" wheelchair wheels in 2004. http://www.chiefdelphi.com/media/photos/18743

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330 ran a 6" solid Skyway (similar to an AM wheel) and a 12" pneumatic Skyway in 2004 to climb a 6" step. No problems with that, though most of the time the drivetrain wasn’t doing anything due to the game strategy that year.

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OP, that would work if you have some kind of load balancing system in place to avoid what DonRotolo mentioned. Unfortunately, we can’t do this easily in electronics due to the rules, but you might be able to explore some kind of differential or other mechanical load balancing system. This would preclude the use of a CIM on each wheel as the power would have to come from a unified source.

Of course, this is likely more trouble (or money) than its worth! Would be a great way to win an engineering award!

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For future reference for anyone searching for this subject matter, we had no problems running wheels of different sizes.

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Nice! Good of you to come back and post an update.

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