This
is a great mid-size motor. The 2212 has a dual shaft design so you can run
it with two wheels for dual traction, or cut off one side shaft for single
wheel drive.
12V (can
not be run higher)
Reversible, Permanent Magnet
1/2" shaft diameter
5.1 pounds
285rpm / 21:1 gear ratio
I've used these motors for a 120lb robot built for an academic competition. Using one motor for each side of the drive system (2 motors total), our robot was able to manuever around the course quickly and climbed 23 degree ramps without any fuss.
They're very easy to mount thanks to the tapped holes. The dual shaft design makes it easy to power multiple wheels and the shaft features a key slot to make mounting wheels, sprockets, or pulleys simple.
CAD Drawing 
