ORIGINAL: seanreit
Bob, how do you explain JR providing the heavy duty plastic with the 8711? IMO that's a broad statement from the manufacturer saying it's up to the task. I'm head scratching on this because a friend of mine had the heavy duty plastic do the same thing (spline problem) on a Euro last week. In his case, the airplane was landed safely.
In my case, I've been using them exclusive for years and thousand flights, no issue ever.
Sean,
Ever see that show "Engineering Disasters?" Its all about how engineers (I am one, BTW), and in some cases, the manufacturerswho produced their designs, were ultimately wrong. I'm sure you can setup a test on the bench that shows that the HD plastic arms will take all that the 8711 can throw at it, but it CAN FAIL, even in a correct installation where it was not subject to unsusal loads or obuse. We've both seen it, and many others have too.
Personally, I think it might have something to do with vibration of large control surfaces. - like the Euro's elevons, that may be caused by things as simple as vibrations coming from the wheels on takeoff or landing. With a lesser servo, the motion may be partially absorbed by the servo, but the 8611/8711's are so rock hard that it gets transmitted all to the nylon splines, and eventually, they let go. Either way, in both cases, I was left with a surface that was not "centered" like normal, and a slight amount of pressure was enough to make it move with the servo stationary. Removing the nylon servo arm produced a white powder that was once the splines. I've *never* had that happen with a metal arm, so that's what I use on elevators (especially), ailerons, rudders, and sometime flaps, with 8611/8711 servos...
Bob