My new uC project required a continuous rotation motor, knowing that a servo motor can be modified to allow it to rotate continuously, I performed the modification on a 9g servo.
Servos are cool because you can tell them to rotate to a specific angle (between 0 and 180 degrees), a modified servo doesn't know what angle it is, but it can rotate in either direction without limits.
The mod:
Inside a servo there are two things that need to be changed in order to make it spin all around: a mechanical stop on the gears, and a potentiometer that tells the servo where in the rotation it is.
The mechanical stop is removed by filing or cutting it away from the gear.
The pot needs to be disconnected from the circuit board, and replaced by two fixed resistors of equal value which add up to approximately the original pot's value. My pot was 5k so I used 2.2k smd resistors.
Once everything is put back together the result is a continuous rotation servo gear motor that can easily addressed by Arduino's sofware servo library, your projects are now free to move.
Links:
http://4volt.com/Blog/archive/2009/04/18/modifying-micro-servos-for-continuous-rotation.aspx
http://www.acroname.com/robotics/info/ideas/continuous/continuous.html
Fp2010.
