So you have a robotics application where you need a motor that can continuously rotate. One good option that still allows you some speed control is to modify a conventional servo into what’s commonly known as a continuous rotation servo. This works pretty well for most applications, but in reality what you’ve created is more like a conventional DC motor than an actual servo since there is no positional feedback.
When doing a continuous rotation mod, what you normally do is replace a potentiometer with resistors to trick the unit into thinking it still needs to move. If, however, you had a tiny encoder that could replace this potentiometer, you could have both continuous rotation and position feedback; in other words, it could act as an actual servo.
Mocoder is just such a tiny (magnetic) encoder, and can be dropped into a hobby servo for this kind of enhanced control. Naturally, there will be some modification and programming work to do, as well as the added expense of the encoder itself, but it seems like a great solution when you absolutely need to know how far a motor has traveled.
For that matter, though it’s designed around a hobby servo, there’s no reason this couldn’t be used in other applications needing positional feedback. Its tiny form factor certainly would open up many possibilities. Be sure to check out the Mocoder Hackaday.io page for more details on the build. There are also a few use cases, including the one below: