May 1, 2015 -- BIT Magazine Maker Zoo Bangkok, a Thailand-based makerpace, has recently published a helpful tutorial on converting servos to continuously rotate. If you have ever used a servo you might notice they only rotate a total of 180 degrees, or, half a circle. To use servos to move robots around, turn augers, or move anything beyond this limited field of rotation, you must either buy servos especially made for continuous rotation, or covert your servo to continuously rotate.
There are already a lot of tutorials out there on this subject but this one is by far the easiest and requires the fewest tools.
Basically what the process entails is the removal of the topmost gear. It contains both a tab and a notch that fits in with the potentiometer to limit the servo's field of rotation. By removing the tab and turning the half-circle tab into a full circle, the top gear can move freely 360 degrees. By centering the potentiometer and supergluing the shaft at the base, you can prevent the electronics within the servo from disrupting continuous motion.
After the conversion process is complete, there is also some code you can use on your Arduino board to test the servo's new continuous function. Keep in mind that while the code indicates 90 degrees is center and therefore should cause the servo to remain at rest, it is very difficult to get it perfectly centered. So make sure you note where center is (maybe 87 degrees or 105?). The tutorial suggests you mark a 'C' on the servo to differentiate it from others. You might also want to note the actual center in degrees too.
Micro servos are cheap and plentiful at makerspaces and electronic stores. Now you can have regular and continuous servos whenever you want!