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Host an ultralightweight robotwars competition.
Bannana - firecraker - remote car duels.
You could probably take the chassis of one and individual motors for another to make a 'proper' remote control robot -- and if you have solenoids and h-bridges, you could get a dedicated computer to remote control it, without having it on-board. There might be a question of how to get sensor readings back, though, since you'd need to do feedback with another mechanism.