When installing a servo or other actuator, I measure the force needed to perform whatever action is needed and find an actuator that can generate more than the necessary force. However, I recently wondered if there's a rule of thumb or guideline for how much overhead is useful, before it becomes a waste.
For a (perhaps oversimplified) example, say I have a lever to lift something, and the force needed is 100 Newtons. An actuator that can manage 100 N maximum will have problems with this and stall, with any sort of friction or other imperfections. I would use an actuator that can produce 150 or 200 N - whatever is available and fits the design and budget. After testing, it may become apparent that 200 is overkill, 120 is sluggish, but 150 is good. Other than trial and error, is there a way to measure this, or a rule of approximation?
I realize that variables in the mechanics and construction can significantly alter what force might is needed to be considered ideal, but is there a commonly accepted value for simple applications? Something like "If you need x force, install an actuator with x + 20% force."