I used an ammeter to measure system draw without the motor on. That seemed to work well. With a 6-channel micro receiver, two HXT900s, and an 18 amp ESC, I measured about 40ma with the servos at rest. The total load would increase to about 150ma when one servo was exercised. However, I didn't load the control surfaces during this measurement, so the numbers should probably be bit higher in flight. That said, I don't think my servos are straining much to power the elevator or ailerons. They are technological marvels.