[EricH]

I can think of one possible reason to use mecanums in a 4WD tank configuration. ONE.

And it's not even a good one--there are a number of other possible tricks to use to get the same result without loosing traction.

The reason? Better turning (this is on a 4WD long bot with a long wheelbase--say about 36" or so).

The other alternatives? Omnis on either one end or opposite corners. Play with the tread materials to get some better slippage. Use Lunacy wheels (). Stick a wheel in the middle with a slight drop (OK, so that's called a 6WD). Monkey with the wheelbase/trackwidth to get a shorter wheelbase and thus better turning (this is best done in the design stage, but if you're desperate...). Drop-down wheels. You get the picture. And guess how many of them are most likely better than the mecanum option?