Servo problem
 

I had a strange problem today. When I turned on my recever the right aileron would flutter up and down very fast for a few seconds after moving the aileron. It has two DS8411 servos connected together with a Y harness. I have been flying the plane since last year with this setup. It would not do this everytime you moved the aileron, but would do it fairly often. It would do it for 5-10 seconds or if you touched the aileron with your finger it would stop. I connected the Y harness to the left side and also disconnected each servo one at a time with the same results.

Anyone know what is going on???

Bobby

RE: Servo problem
 

Couple ides:

Y harness is failing. Thats why I don't use them in large planes. Plug each servo into it's own port and mix them with the TX or use a JR Matchbox.

The servos are fighting each other. Your running 2 very high precision servos on a single aileron with a Y harness to tie them both together. The linkages might not be perfect, or a control horn is a little off. The servos are fighting each other. Use a Matchbox or the TX to mix them.

Pots in the servos are starting to get bad. Seams funny that they would both fail at the same time. I've never even had a JR servo go bad. Been using and abusing them for yrs and have never had one go bad or need servicing.

RE: Servo problem
 

Sounds like you have a little bit of binding on one or both servos. It probably clears up after you work the ailerons a bit to "loosen" then up. JR servos seem to be twitchy anyhow.

I agree with RCPilet above as well... the servos have to be very carefully centered or they can draw huge currents as well.

RE: Servo problem
 

Remove the Y harness and use just an extension, one at a time. May isolate the problem a little furthur. Could be the Y, or the servo.

I was thinking you had one servo per aileron. If you have two on one aileron, you should use a matchbox.

RE: Servo problem
 

I think you will find that the answer is none of the above. If you pull the top off the servo and look at the gears with a magnifying glass, you'll probably note that the gear mesh has been forced or jammed to one side of the gear due to excessive loading from the servo arm. It will look like one gear is wedging it's teeth a little under the bottom of the teeth on another gear. Time for new gears.

I went through exactly the same thing with some 8611's a short time back and that's what was found by the repair folks. It's caused by having the linkage attach point too far out on a long servo arm when using large travels.

RE: Servo problem
 

I thought about that, but it seamed too obvious.

I really would NOT use a Y harness on a couple 8411 aileron servos. You've got 2 servos on EACH wing and your using a Y harness. Thats no good. You really need to use a seperate extension on each servo and plug them into DIFFERENT ports on the RX. Mix it with the TX.

Or use a single Matchbox located inside the fuse. Run a SEPERATE extension from EACH servo into the Matchbox. Use the Matchbox to dial in the center points of all 4 servos and adjust the travel on each servo indivually.

It could be the gears. I'll concede that. But, either way, you don't have that plane set up right. Look at the gears and replace them if needed. Then follow my instructions and get a Matchbox or plug them into different ports in the RX and mix it with the TX.

RE: Servo problem
 

I doubt if it is the gears, most probably a bad connection (may be corrosion taking place) or your battery is getting weak (developing a high internal resistance). I'd definately check any extensions and accompaning connectors first.

RE: Servo problem
 

I did not really think that it was a servo problem since I disconnected each servo one at a time and still had the problem with each servo. I picked up another Y harness to day; I'll know in a little while if that was the problem. Sounds like the conscience is that I need to use a Powerbox on each wing however. I do have a spare Powerbox I can try and see if the problem goes away. I'll just have to buy another one for the left wing.

RE: Servo problem
 

I think you will find Rodney to be on target. Your problem sounds like a power problem not a mechanical problem. I would lean toward a battery rather than a loose connection. What voltage and type pack are you using? There is a good possibility that you are building internal resistance in your battery pack. Try a fresh pack and plug direct into your reciever. I hope you post the answer.

Best Regards...

Mark

RE: Servo problem
 

Ok, here's the latest. First, regarding the batteries; I am using two 4,000mah lipos with two regulators. The batteries were fully charged and load tested prior to beginning all of this yesterday.

Back to tonight, I replaced the Y harness and the extension from the Y harness to the receiver...still the same problem. At that point I removed the Y harness and hooked up one servo to a Powerbox and began centering the servo. At that time the one servo began fluttering again. I repeated with the second servo connected and it fluttered also. I think I have two servos with problems. I took the top off of the servos and to my untrained eyes the gears look ok. I guess I'll be sending them in to be checked out.

Any other thoughts???

RE: Servo problem
 

Dude

Don't call it Flutter because it isn't that .............

Either the Pot is starting to go or ur Gears need replacing. Any Airload or stick movement stops it right?

Run the motor and move the controls U will find it works fine.

Just that Once a Year if U Fly often Servo Gear Train replacement.

Best of Luck

Ian

RE: Servo problem
 

Your right, it's not flutter. It just sounded like a good way to describe it. You are exactly right though, all you have to do is touch the aileron and it will stop. I assume that you don't want to fly with it doing it however. How hard is it to replace the gears?

RE: Servo problem
 

I had the same situation. When you touched the stick on mine one aileron would start a rapid, short travel, cyclying. When the engine was started it sometimes did the same thing. Turns out the gear mesh between two gears on one sevor in a pair had jammed themselves deeply into the mesh. I had four servo total that showed similar wear patterns, but only one was causing the problem on one wing at the time.

What was happening was that the servo was actually binding at the gear train without a load (at neutral) and seeking an illusive center. The other three would have done the same thing a bit later if I had waited longer to pull them.

No, you do not want to fly with those servos that way. They will fail completely very soon if neglected. Checking them now and changing the gears will save you a whole bunch of money later. If your issue is a servo or servos doing the mini flutter thing all by themselves when at rest I seriously doubt it's an electrical condition. The gears are worn out and need servicing. Or the pot or amplifier as noted by the Moderator. I'm holding with the gears, though.

Replacing gears is easy. Purchase a gear set for less than 20 bucks. Pop the top and carefully remove the gears, noting their positions as you remove them. Only one of them has a timing tab and it's always the first one out. Replace them in reverse order. Find out from the manufacturer what they suggest for the best gear lube product. You probably only need to replace two gears in each servo, but do them all while you have them opened up.

RE: Servo problem
 

Did you try any other servos connected to that channels you are using on your PowerBox? RX? Check those also!!!

RE: Servo problem
 

All of my JR DS8411 servos do this after some use. You have to send them in for service. Mine have always been worn out feedback pots. The service folks say the gears are OK, but the pots wear out. I have had some servos in for service three times in 5 years. They always send back the old pots in the box with the repaired servos. As a diagnostic, I remove the servo from the plane and hook one large servo arm (no linkage). I have a homemade servo arm which is really a stick attached to a standard arm. With this setup, the servos that are bad will jiggle if the pots are worn. I do this to make sure it is not batteries, "Y" connectors, linkage, receiver, etc. The servos, even when bad, do not jiggle with just a standard servo arm on them. You must have a little mass - just a couple ounces - on the servo arm. This is enough to set off the oscillation when the pots are worn.

RE: Servo problem
 

Well, I ordered two new servos today(with 2nd day delivery), got to be flying by the weekend you know. Also ordered two matchboxes. Might as well do it right while I am doing it. I plan to send the two old servos back for servicing; I figure I'll need them when the two on the left wing start acting up.

I purchased this plane used so I did not have anything to do with the servo selection. My question is why would you install 8411's when you can get 8611's(or 5955's) for the same price??? Am I missing something...

RE: Servo problem
 

AU

While some of these Guy's are right about the Gears I have seen band new ones do this very thing.

Right now the Tail on my GP Cap does this on initial power-up and I fly it with no problem.

My CARF Yak 3.3M which hasn't flown yet has JR8611 * 2 in each stab and one Elevator is doing it as well.

I own a Servo Tester that allows me to check Dead Band. When the Dead Band is 1 or less it's common to see this problem.

Ian