Hi Interested in the 591 debate. I've got a number of these in various aircraft, but I run them at 4.8v. I've had 5 fail on me, 1,in a Glens model extra 58" (gear train) on the elevator and 4 on the throttle of a a venture 50 heli.It seems the potentiometer fails on them , which is a bit worrying when its stuck flat out.It has caused a lot of head scratching to find a cure but without success,if there was excessiive vibration I could understand. Just wondered if any one else has had similar problems.