Hi! This instructable will show you how to modify car window lifting motors that you can salvage from old cars in order to use them in your robots. This kind of motors have a very high torque and you only need to make some adapter pieces to make them usable in your robots. It is a short version of the original post I made in my blog that can be seen here.
If you salvage this kind of motors from old cars, the first thing you have to do is to test them. Plug them into a 5V or 12V power supply and check if they spin. The motors have a worm gear that gives them a very high torque and stops them from rotating if any mechanical force is applied to them. They only rotate if current is flowing through the coils of the motor.