NPC 2212 Motor
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.
$172.36
NPC-2212 NPC 2212 Motor <p align="left"><font color="00ff66" size="2" face="Arial, Helvetica, sans-serif">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.</font></p> <p align="left"><font color="00ff66" size="2" face="Arial, Helvetica, sans-serif">12V (can not be run higher)<br> Reversible, Permanent Magnet<br> 1/2" shaft diameter<br> 5.1 pounds<br> 285rpm / 21:1 gear ratio</font></p> <img src="http://www.robotmarketplace.com/images/store_2212results.gif">
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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
This looks like a very well constructed motor. it has two large ball bearings supporting the shaft, and has two lip seals protecting the bearings form the environment.
There is little to no backlash. It feels very solid.
The back drive torque is only about 21 in*lb. This could be a good thing or a bad thing depending on your application. It is not a self-locking gearbox like you might expect from a worm-drive gearbox.
10/28/2009
Champy
Fantastic little platform
Very versatile and well-put-together. Easy to mount due to the 4 1/4-20 threaded holes in the bottom of the gearbox. Comes with two keys (one for each shaft) and each shaft is also tapped with a 1/4-20 threaded hole. Very handy. I used mine to make a giant servo with a pololu controller.
5/19/2009
Dan Toborowski
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.
$172.36 
CAD Drawing 
Great motor, low back drive torque
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