articulating arm help

[Da Kid]

We are making an articulating arm for our robot. we have a cim motor on a CIMple gearbox with a gear chained to a much larger gear which is connected to the arm itself.

our problem comes when we are running the arm. we would like to be able to move the arm to any spot we want and have it stay there when we let go of the joystick. currently when we let go of the joystick, gravity takes over and the arm falls down. I'm asking if there is a way to keep it in any place we stop at. do we use a brake to create resistance or do we use encoders? if we have to use encoders we would need help in figuring out what our distance per count is among other settings in the programming side of things.