Originally Posted by
Len Todd
To move a control surface with a given amount of air pressure on it, it takes a certain amount of watts to move the surface. If the voltage is lower, due to whatever reason, more current is required. (Watts = Voltage x Current.) To hold that surface in place on a flap, it takes that amount of current until the surface is returned to neutral position.
You seem to be saying that a servo is a constant wattage device, so that if the voltage falls the current will rise. In that case as voltage falls to near zero, the current will rise to near infinite. On the other hand according to you, if the voltage rises the current will fall!
That is not how things behave. A servo can not maintain a constant wattage, the wattage is whatever voltage is present and the current that can be driven by that voltage. The voltage drives the current, so as the voltage falls the current driven by it will also fall, and the total wattage at the servo will fall dramatically. A voltage sag means a current sag.