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Servo chatter

Old 08-16-2011, 05:56 PM
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EZ Fly
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Default Servo chatter

Open Question, I need help. Has anyone solved the problem of servo chatter. I have one aileron servo that does it most of the time. I can watch what it's doing by looking at the Volt Watch as well as hear it. On the Volt watch it will jump up and down 3-4 lights and uses up the receiver batt. very fast.

I have tried two different servos, three different receivers and two different xmitters. I used different brands. (Futaba and Hitec) for each test. It's driving me crazy! Anyone have suggestions to solve this?
Old 08-16-2011, 06:59 PM
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Campgems
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Default RE: Servo chatter

Sounds like a bind in the hinges or linkage.

Don
Old 08-17-2011, 03:34 AM
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JIMF14D
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Default RE: Servo chatter

Disconnect the linkage or take the arm off and see what the servo does then!
Old 08-17-2011, 05:07 AM
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BuschBarber
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Default RE: Servo chatter


ORIGINAL: EZ Fly

Open Question, I need help. Has anyone solved the problem of servo chatter. I have one aileron servo that does it most of the time. I can watch what it's doing by looking at the Volt Watch as well as hear it. On the Volt watch it will jump up and down 3-4 lights and uses up the receiver batt. very fast.

I have tried two different servos, three different receivers and two different xmitters. I used different brands. (Futaba and Hitec) for each test. It's driving me crazy! Anyone have suggestions to solve this?
Servos can be sensitive to voltage. I have a couple of JR 791 Retract servos that jitter when using 6v. Horizon advises that these servos are not 6v compatible, so I either use 4.8v or voltage regulators. I have also had Y Harnesses that caused one servo on the Y to jitter while the other servo was silent. There are other examples, as well.
Old 08-17-2011, 08:50 AM
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EZ Fly
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Default RE: Servo chatter

Thanks for the comeback, guys. Yes, I've disconnected everything. In fact, while doing all the switching around, the servo is just laying on the outside of the plane. No perceptible physical movement on it, just that electrical chatter. The servos I'm trying to use are the Hitec MS-85MG. They replaced Futaba S3115, which had stripped a gear set in one. However, they both had this chatter. I'm using 4.8v power, but sensitivity may be the issue, I don't know. Sometimes it will settle down at null, but the minute I try to move it the chatter starts very loudly and Volt Watch power monitor goes crazy. It's really pulling down some battery power.
Any other thoughts?
Old 08-17-2011, 11:50 AM
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Campgems
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Default RE: Servo chatter

Ihave a couple older Hitech servos that like to clatter at neutral. As soon as a slight load it put on them they quit the bad behavior. My theory is that no load conditions lets them overshoot neutral and when itcorrects, it overshoots in the opposite direction. Try putting your finger on the output shaft and see if the problem goes away. It doesn't take much, just a slight resistance. As for fixing it, you might try a thicker grease, but this will put a bit more load on the servo.If yours is like mine, the issue is just at center and the resistance of the surfaces in the air is enough to tame it down.

Don
Old 08-17-2011, 01:19 PM
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modeltronics
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Default RE: Servo chatter

There is a pot in the servo that feeds back the position of the servo to the rest of the electronics. Since the servo spends a lot of its life near center that is the area that gets worn out first. The resistor material on the pot has only been silk screened on to the plastic base. The process is called thick film resistors. The screening process is similar to silk screening logos on t-shirts. So the feedback pots in servos are not the most robust. And on top of all this it has a wiper trying to rub through this pot material a lot near center.

My guess is that the pot is showning some wear on the servo and the voltage at the wiper is not staying constant so the servo is moving around (chattering) trying to correct this.

Pete
Old 08-17-2011, 06:33 PM
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EZ Fly
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Default RE: Servo chatter

Again, I thank you guys for helping me think my way through this problem. Campgem- my problem is just the opposite from your experience. My chatter gets much worse when the output shaft is moving. As I said earlier, the Volt Watch lights will jitter back and forth 3-4 lights while operating. Normal, under load is 1 light down.

Pete, I like your theory. It makes sense. The servos in question, however, are brand new and haven't been flown yet. Of course, that doesn't exclude a bad servo, I realize. Thats why I tried the Futaba servo in place of the Hitec. Same results. Can I have two bad servos? Of course, but I just resist accepting that. Maybe I'll try talking with Hitec and see if I learn anything.
Thanks again for the repies, guys.
Old 08-18-2011, 06:15 AM
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modeltronics
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Default RE: Servo chatter

EZ Fly
OK, this gets me thinking it you have the same problem with 2 different servos. If you move those servos to another radio system does the problem follow? If the answer is no then I would begin to look at the radio. Could the pot on the stick of the transmitter be the problem? If you move the servo to another function on the radio does the problem follow? If you hold the stick on the TX in a different position does the servo chatter in the new fixed position?

Do you have a scope? It would be interesting to look at the pulse width going to the servo to see if that is changing. And to look at the modulation line in the TX.

I know most people do not have a scope. I'm just trying to look at this to see if the problem is in the servo or some other place in the system.

I hope this helps,
Pete

EDIT
I went back and re-read the first post, that you tried different transmitters and receivers. Next I would try plugging the servo directly into the receiver with the battery plugged into the receiver. This makes the most simple set up. If no chatter then put in the extentions. It could be as simple as the contacts on the extention being not quite good enough.
Old 08-18-2011, 09:41 AM
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EZ Fly
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Default RE: Servo chatter

Pete,
I did the 2nd Futaba Rcvr as you described as well as a Hitec Rcvr, directly using a seperate battery instead of the planes hook ups. Same results although the chatter doesn't seem as severe using the Futaba Xmitter vice the Hitec Xmitter. Hmmm. I haven't switched to other plane functions yet, except swapping ailerons. That would be interesting to try, but right now I need to get some charging done so I can continue this process. I'll let you know. ( nope, no scope available)
Jim

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