I have a model with a large elevator and I am having problems using digital servos to control it. I have tried the JR 8411 and 8231. The elevator is balanced about the pivot shaft and the size is shown with respect to the servo in the picture. The elevator weighs 12 ounces. Most of that weight is lead to ballance it. When the servo tries to center itself, the weight of the elevator causes continous feedback oscillation (bouncing) with the elevator. It works fine with nondigital servos. Has anyone had similar experinces with large elevators?

at one point in time, JR could reduce the gain of some of their servos, that is your problem, too much gain.

If you add a bit of friction to the system it might stop it as well, with only a slight loss in centering accuracy.

BTW it the air I doubt it will do it.

I believe if you actually get it out of balance so that the center of weight is behind the pivot point, the oscillation will stop. This will achieve what Mr matt is basically saying up there and in flight you SHOULD have no problems!!!!, but I did not say that

I think Ehab has a good solution. A couple of questions, what voltage battery are you using, and was this using an extension lead to the servo?

This comes from the slight gear lash in the 8411. Under ANY kind of load this will not happen.

-Doug

Doug wrote:

<<This comes from the slight gear lash in the 8411. Under ANY kind of load this will not happen.>>

Mr Pylon,

What Doug describes is exactly what is happening. My AD Mirage elevon 8411`s have been doing it for 100flights. When they get a load on them the jitters stops. Don`t sweat it...

Vin...

Thank you gentlemen for responding. The battery I am using is a 4.8 volt nicad. At the time of the test it was freshly charged and the servo was plugged directly into the receiver. I also thought the gear backlash in the 8411 might be hurting me but the same condition happens with the 8231. Applying a small load does stop the oscillation but a small bump starts it going with increasing amplitude up to a point. I can try removing some of the balancing weight. Would it be better to have it balanced foward rather than aft?

Thanks,
Pete

If you set the TX to give max elevator throw, how many degrees will the stab move? If it's way more then you will need for adequate control, increase the length of the control horn on the stab. This will increase the mechanical advantage and reduce the effect of any slop in the linkage.

Most jets I have seen are very poor in this regard. If you have to reduce the electronic throw a lot to get the desired control surface throw, you are giving up a lot of power to the control surface and greatly reducing the resolution of the system.

Is that an F22 that your building?