[lukevanoort]

You don't actually need four sprockets on the tranny to make a 4WD. We had a 4WD last year that was so effective, the first time we lost a pushing match was at nats by a tank treaded robot. (can't remember who) We mounted the tranny in the center of the bot than ran one chain around it and the two wheels, than had idlers (literally HDPE blocks) that performed double duty as tensioners and gave us enough contact on the tranny to avoid slippage.