On my Tam F-18 I have Jr 8711's one for each stab half. I have had the airplane for quite a while but haven't flown it much in the last year. I did make one flight about 10 days ago and everything worked fine. the elev servos have always been a little "bouncy" or jittery when centering which I always thought was not abnormal for servos with very tight centering and tight deadband. The bouncing and jittering seems to be getting worse however. During normal slow movements of the stick as would be normal during flight they have little or no bounce and jitter around neutral. But if allow the stick to center rapidly i.e let go of the stick they both have quite a bit of bounce and overshoot of neutral. It dampens out in maybe one to two tenths of a second. They may have always been this way and Im just getting paranoid. cant say for sure. Pretty sure they have gotten a little worse. I tried running the surface charge off the top of the batteries to see if this would help but it didn't.

I am running 5 cell nimhs 4200 mah with no regulator. I know this will cause a great debate regulator versus no regulator. I don't use a regulator on any of my 5 cell packs NiCad or nimh and never have.

Are these particular servos unhappy on this much voltage ? I tried to find a 4 cell pack in my shop to pug in instead but all of the loose ones I have need charging. That will be the next thing I check when I get one charged

Big Bri, its all good. Tam F-16 does it too - just a big surface and digi's centering. Regulator non-issue, I'm running A123's (6.6) no reg, on everything for the last 3 years. I would say everything functioning normal.

I had a couple of those on stabs and one just got worse and worse until I replaced them and sent them to JR to get fixed.

When you let go of the stick rapidly, the stick does not go to center and stop, it overshoots the center and will bounce back and forth. The servo is just following the stick movement.

You can put some piece of fuffy (the soft side) of velcro between the fuse and the stab, this will provide some resistance to the stab and and will help to keep it centered.

If you slowly move the stick from one extreme to the other and the servo tracks normally I think that is OK. It the servo jitters at any point I suspect the pot is dirty or worn.

Wow that's strange, I had the same think happen to my Hi-Tec rudder servo on my Flash this past Sunday, I was thinking that I should replace it

The first thing is to exercise the connectors . About a week ago my slats on my F100 were choppy and loud. I pulled the connector and pushed it in and out mutable times . Their must have been corrosion on the signal wire. It fixed the problem . Also My buddy has had problems with 8711 going bad.  Dan Avilla

i had already thought about the size and weight of the stabs ( since they are mass balanced or counter balanced) they reallally in effect arent that heavy and these are massivly powerfull servos. i also. took into account that the stick is bouncing a bit past nuetral when let go from full travel. there is no way the stick is bouncing more than a couple times around center but the servo is bouncing numerous times. i was able to quick charge a 4 cell pack. and plugged it in. servos way slower and littlr or no bounce. it is the fact that this seems to have gotten worse that concerns me a little. on the other hand i dont want to use a regulator and i dont want to spend big bucks to buy new servos if they will do the same thing and arent needed. doubt i can get two servos in time for this weekends fly in anyway. they are probably fine. i know i wont experiance it during notmal manipulation of the controls......unless ofcourse the servos are rapidly deteriorating. pardon the typos. did this on my phone.

I have 8711 on my stabs and they used to shake around center every now and then but got worse as time went on.

I ordered the gear sets for 8711 servos and they are perfect now.

+1
Have had this issue with even rudder servos on Bobcats and Kingcats, disconnecting and reconnecting the plugs a few times at each connector and that issue seems to go away. Interested to see what you fine as I have a Tam hornet to finish up.

BINGO. overshooting as you describe is becaus you have a bad connection on the signal wire. The connectors we use clean thenselves when they are connected and disconnected. Plug em in and disconnect them and it wil go away. That said 8711 have a crappy pot in them and will develop occilation over time..

I have to agree with Dan and Kelly. Check servo connections and any connections in extensions going to servo. I have seen this more than once with corrosion in the connector over time. Replace or at least clean up the connectors in the servo leads and extensions.

Good luck, don't lose an expensive airplane over a relatively inexpensive cable or connector.

Paul S

Wow, and I thought I had rusty tools.

LOL I live in Florida things rust over night here. All my nice snap on tools stay in my toolbox at work for the FS aircraft.

Brian, try this. Add 5-10% expo around the center and see if it improves. I had similar issues when I used to fly IMAC (on different servo brands) and doing this helped.

David

I can see where that might help on bounce back but how would adding expo help on a servo that is sitting there shaking at neutral?

The Velcro trick will help but the servos probably need to be serviced.

If it is a bad connection somewhere it won't, it would keep jittering. This is a great way of troubleshooting for that.

I am no jet pilot but I am an engineer that has worked in the engineering department that designed jets.(F15,F16)
In my opinion Jr servos are set up to tight in the deadband. This means they will be very sensitive and jittery. Anything slightly wrong will set them off. It will not interfere with your flying but can make you paranoid.
One thing I would do is get rid of the NIMH pack and go to A123's. The lower internal resistance might help. If that dont help send them to JR and get them refurbished.
A regulator would likely make things worse.

Might change out your servo extensions....I bet they are not gold plated or have started to corode at the
connections. Be sure to use a good AWG grade....20 if you can get em.
Theirs my 2 cents...good luck!!

i already have quite a bit of expo on elev.. besides if i truly have a servo problem that would only servo to mask i or hide it...sort of a band aide fix if u will.after some thought i think i need to watch the servo horn and not the elev itself.. while the control surface appears to be moving quite a bit the amount of servo out put movement may be pretty slight. im pretty sure my connectors are gold plated. i will try cleaning the connection and see if that helps.. i can also sub in an a123. pack temporarily and see if that helps. if it does i wil change over to life or a123. packs.. if none of these ideas work i think i will glue the stab in a fixed position....that will for solve it and seems more effective than binding up the surface with a velcro patch.. out of town till late this eve. will try tonight or in the morning.

The expo on elevator does not fix any problems. I'm assuming you have a perectly fine servo and the problem is that the linkeage on the Hornet is super sensitive, similar to a Tam F-16, where you don't need that sensitivity. Now if this thing is flopping up an down and the control surface deflections are clearly noticeable, then there is another problem somewhere.

Nothing wrong with using expo to overcome servo sensitivity, that is exactly what it is for. But now I think you have a another problem if you say you already have expo applied and it still jitters.

i had the exact same problem jittery servos near centre, seemed worse on fully charged nimhs, tried batteries servos, receiver, same problem, this was on my ailerons, changed the extension leads and problem solved, tested the extension leads on other servos and the problem came back, from memory they were the twisted wire extensions, hope this helps .
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Hi Turnnburn,

I have been told not to balance a stab like the F-18, F-15, F-14 , BAE Hawk, where it will stay level when the linkage is removed. This will cause the servo (digital ones) to hunt for a neutral position because of a no load condition. To see if this the problem, just lay a small weight on the leading edge at the root of the stab, next to the fuse. If the servo still jitters around center, then check you connections.....

Larry

+1 on the extensions, had similar problem on a prop airplane some time ago.

What Dan Avila said [&:]