How would I go about calculating the resultant forces / torques on a system if it's previously spinning at a constant angular velocity, but then an external torque is applied to it? I would like to use this for some very basic analysis of a custom gear box used in a robotic joint. We attach gears to a shaft using a pin, and I just wanted to calculate the worst-case scenario, i.e. reversing directions or starting from rest, to see if / when it would fail. I can calculate the moment of inertia of the system about its rotating axis, and we have the torques. I am aware of angular momentum equations, but I do not know where to start as far as incorporating it into the model.