[Justin M.]

If you up the gear ratio, and used four gearboxes on four wheels, it would be possible. Make sure you connect the wheels together with a chain to transfer even torque to the front or back of the bot (in the event of a pushing match). You'd also need to make or order a hub for whatever wheel you are using, as well as a pillow block to support the shaft.

Now - would I recommend it? Not really. Gear it down with chains, and if those are too heavy use belts and pullys. If space is an issue then use some type of slim-2nd stage output gearbox with the outputting shaft running directly to the wheels.