These Planetary Gearboxes are nominally 32mm in diameter with permanent magnet reversible DC motors. We carry 12VDC and 24VDC motors and range from 8 to 265 RPM. Several right angle gearboxes. Several motors have encoders.
These brushed permanent magnet DC gearmotors have a rated speed of 191 RPM and a gear reduction of 1:27. They work great on our robots as well as your own applications. Former item number TD-014-195. These are excellent geared motors for robots.
The Dual Motor Shield is quite a practical Shield for Arduino with a library developed by GarageLab that simplifies using it, because with just one command, you can define the direction and the speed with up to 2 DC motors.