you could hack the gearbox out of a cheap cordless drill like a
harbor freight 900rpm with 3/8" chuck or the
ollies brand equivalent
they accept 550 size motors and the output shaft thread is 3/8-24
i wrote an instructable on the process of hacking the gearbox a while ago
http://www.instructables.com/id/Hack...rs-for-/#intro
hope it helps...