I've been having some issues with my robot drifting to the left. It has mecanum wheels (installed properly), and the motors seem to be in order. One side seems to be moving slower than the other a tiny bit, enough to make it drift. What is the best way to approach this? I imagine the speed has to be regulated on both sides (I'm not using speed sensors).
you will need to measure something to ascertain the difference in your motor speeds in order to compensate for this. The usual way is to measure the distance travelled with rotary encoders. I give you a link to a nice video that explains this very well.