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Digital servos shake uncontrollably when radio testing.

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Old 06-16-2007, 04:32 PM
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jmehl
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Default Digital servos shake uncontrollably when radio testing.

With tx and rx on, fully charged batteries (4.8v 2500mah rx), five digital futaba servos , I can walk around the pits and when the radio antenna is postioned at exactly the right angle and elevation ALL the servos will flicker absolutely uncontrollably without my thumbs even on the sticks. This is not random...if I find the sweet spot usually standing 10 feet away with radio antenana pitched at 45 degree facing the plane I can make my servos spaz out....

Has to be something adjar...I do have several extensions and I am in the process of soldering all extensions and Y -harnesses just for good measure....


The question I have is could the battery be influencing this at all? I orignally had a Futaba 4.8 600 mah battery pack velcroed along side the rx and the glitches were sporatic but occured once in a while during flight just enough to keep me concerned....I built a 4.8V 2500MAH battery and used 20 guage speaker wire to install it in the rear of the plane since I had 1.5 ounces of lead in the back anyhow that I could replace with batteries. The battery wire runs inside the fuse along side the rudder extension, and 2 elevator servo extensions and parallel to the rx antenna which is inside of a tube about an inch higher than the rest of the servo wires and battery cable. Prob the most critical thing is the battery is installed right along side where the rudder and elevator servo wires are connected to the 12 inch extensions. Despite having this issue, I took the plane up and when angles were "right" I would momentarily loose control of the plane while the servos spaz out for a second or 2....it was really bad guys...only 5 seconds in and I already lost control. I mange to land in a field after takeoff without harm to anyonw or anything.

ANyone have a suggestion? Like I said I am soldering all my extensions and using shrink wrap around each solder. Hope that helps.
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Old 06-16-2007, 05:23 PM
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Default RE: Digital servos shake uncontrollably when radio testing.

G'day Mate,
First thing to try, is to get the end of your RX aerial away from the servos, extension leads, switch & any electrical wiring, & then test, bring the aerial out of the plane & tape it to the end of the tailplane, (horizontal stabilizer), or top of the rudder, I will almost guarantee, that the glitching will stop.
Give it a go, you have heaps to gain, & nothing to loose, by trying it.
Is the end of your RX aerial, in close proximity to your rudder & elevator servos?
If so, there is your problem, the servos, close to the end of the aerial will cause glitching, servos make RF noise, which will cause glitches in the servos through the RX.
I know it looks bad to have your aerial outside the plane, but it is the safest way.
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Old 06-16-2007, 06:04 PM
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Default RE: Digital servos shake uncontrollably when radio testing.

Hi Alan

Yea its interestesting you say that......the end of antenna sits almost right on top of battery with a few inches of servos.

Is that a problem?
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Old 06-16-2007, 07:47 PM
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Default RE: Digital servos shake uncontrollably when radio testing.

That could be the problem. Move the antenna and unplug the servos in the tail and try again. If this fixes the problem you know where to find a solution. If not, unplug all but one servo (at the RX) and see what happens. If that fixes things plug servos back in one at a time until you find the trouble maker. Hopefully this will find the problem.
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Old 06-16-2007, 08:56 PM
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Default RE: Digital servos shake uncontrollably when radio testing.

So after spending an hour soldering all the extensions and y harness.....moving the antenna to differnt locations, i can still walk around my garage and make those darn servos freak out...like i mean spas right out in all directions.....frustrating.

All the servos appear to be working alright when it sits idle and not twitching and I move the sticks.....but I will start disconnecting 1 by 1 and see what happens........
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Old 06-16-2007, 09:30 PM
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Default RE: Digital servos shake uncontrollably when radio testing.

Removing 1 servo at a time I was able to make that the remaining servos glitch...yesterday I tried a different receiver and no help. The antenna is away from all servos.

I am going to test my old futaba radio to see if it makes a difference.

I also tried hooking up the battery directly to rx and still did not stop the jitters.

I am really thinking my plane is posessed



has anyone had issues with batteries causing this? LIke I said before I installed a "new" home built battery pack. Could that be throwing off?
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Old 06-22-2007, 09:51 AM
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Default RE: Digital servos shake uncontrollably when radio testing.

It is unlikely that 4,8 volts DC will interfear with the servos, I have my reciever sitting right on top of my 4.8 volt battery pack and haven't had any related problems there, the problems with jitter I have had is the UK buying bulk amounts of crystals from abroard and passing them of as fit for use with a particular radio set the frequencies of which are slightly off set to the frequencies we use in the UK. finding British made crystals which are designed for use with british frequencies is very difficult these days. I wonder if you have been taken to the cleaners with some dodgey crystals to?

regards Nigel.
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Old 06-23-2007, 01:13 AM
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Default RE: Digital servos shake uncontrollably when radio testing.

I have seen this happen to a few planes as well...but when u touch the nervous jittery surface, they stop. Couldnt it just be that the digi servo is looking for its center??? I have been flying with nervous rudder servos for a while now, and while in the air, there is no problem at all? Should I stop?
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Old 06-23-2007, 09:59 AM
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Default RE: Digital servos shake uncontrollably when radio testing.

I had a similar problem with a Futaba digital on rudder. Tried troubleshooting from all possible angles and the final conclusion was to switch to an analog servo, or brand H. The analog worked well.
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Old 06-24-2007, 10:13 PM
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Default RE: Digital servos shake uncontrollably when radio testing.

Would the Rx happen to be a 127 Futaba? Getting my 86" Yak ready for flight the servos would have a twitch in them. Turns out I had to put in a new reciever for the digitals. Switched to a 319DPS and the problem stopped. Put the 127 back in and instantly twitched again.
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Old 06-24-2007, 10:26 PM
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Default RE: Digital servos shake uncontrollably when radio testing.

If the extension is too long and the wire is not heavy duty, this could happen. Try to use a 5-cell pack.
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