[Al Skierkiewicz]

Iam,
There doesn't seem to be any rule that would prevent this application. I would tender that answer with a caveat to insure that magnets do not come loose on the wheels. Traversing the barrier is going to put a lot of stress on wheels and typical plastic hubs will take the brunt of the shock causing deflection and breakage. Should your magnets find their way into a competitors robot during competition, there could be nasty results. While the hall effect sensors meant for the transmission are difficult to use, they do produce significant resolution when used on the high side of the reduction.