Gary is very much correct about full body spinners, they are very difficult to build I'm afraid and are extremely dangerous to boot. However if you take your time you may well be able to come up with something that still meets the criteria.

On the subject or motors, Deathroll from Australia competed in Battlebots and used Balance Board hub wheels for drive. They were surprisingly effective for their cost, but once damaged you would need an total replacement rather than being able to change single components in a normal drivetrain. Check out their Facebook page for more info - https://www.facebook.com/TeamDeathRoll/