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Unread 03-05-2012, 12:46
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FRC #1197 (Torbots)
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Re: Dual CIMs and #25 Chain

Quote:
Originally Posted by sst.thad View Post
When in the 1 CIM mode, the other CIM is set to coast mode via CAN, and receives a 0 output. so it is just freespinning.
Freespinning can have multiple meanings. A motor that is supplying no power to the drivetrain but is connected to it fits none of them, however.

In fact, it's acting as a brake. I know you've set it to coast mode and all, but here's an experiment for you to try. Grab one CIM with minimal gearing (none, ideally). Try to backdrive it with your hands. Takes a lot of torque, right? Now apply torque at the stage of your gearbox where the second (powered) CIM comes in (or an equivalent gear ratio). The torque should be a lot less, but still very noticeable. Now, try the rotating the wheels from the same point. That should be very little torque if you're up on blocks, more if you're on the floor.

My point is, your "live" motor has to backdrive your "freespinning" motor as well as driving the wheels. It's not trivial to do so. There isn't a way around it. Your better offseason fix would probably be to run #35 chain on just the run you're having trouble on while you try to solve the root problem. It's a matter of changing sprockets and chain. (Real bonus if you try using bicycle chain--359 has done that.)
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Past teams:
2003-2007: FRC0330 BeachBots
2008: FRC1135 Shmoebotics
2012: FRC4046 Schroedinger's Dragons

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