I'm building a 3-Axis gimbal and have everything assembled but noticed that my pitch motor drastically effects the balance of my roll as the motor is much heavier than the other side (without motor). Should I add weight on the opposite arm to correct for this? Otherwise it seems like I have to slide the roll bar drastically toward the pitch motor to make up for the balance differential.
Which gimbal? What camera? What motors? Ideally, no you do not and should not need to add weight. Between sliding the camera rail away from the motor, and sliding the roll axis cross piece off center you should be close. I have a light camera with heavy motors on my gimbal and to help offset the weight, I mounted my battery on the opposite arm as the motor which helped a lot, almost enough that my camera is still centered.