Throttle servo interferance?
 

I have a Wild Hare Edge 540 that is my first gasser. I have it finished, and went out to run the engine today, and that is where the problem was. I have done range checks before without the engine running, but I know it really only matters with the engine running. The engine runs fine, but the throttle servo jumps a little no matter what throttle setting you are at. I know some about interferance, but none of the other servos are glitching. I did a range check with it running, and it did fine other than the throttle servo. And honestly it is barely doing it. The glitches are maybe 4-5 clicks of throttle setting, and then it goes right back to where it was. Any suggestions? I was thinking maybe it was a bad servo. Any help is appreciated.

RE: Throttle servo interferance?
 

I would replace the servo to see if it is bad. make sure you have no metal to metal contact between the carb arm and the throttle servo control rod. The next thing to look for is make sure the wires from the ignition are not near any thing that attaches to the RX

RE: Throttle servo interferance?
 

I agree with Air Wizard. I have had a throttle servo with a bad pot and would work with the engine off but jump with the engine running. I also had one throttle servo that jumped and on closer inspection I found the wires frayed going into the servo. I replaced and resolderd with new wires and all was well. I've also had the throttle servo jump from a bad ignition and actually go into fail safe. That was my fault for not doing a proper range check. I will never do that again. Almost lost the plane. I would not fly the plane until this problem is solved.... by the way that was 2 years ago with a Wild Hare Edge 540.... Bill

RE: Throttle servo interferance?
 

I agree with others that you need to check the servo. Also, where do you have it mounted. Is it up front with the engine? I never do this on Gas planes. I always mount it back with the rest of the radio (at least 12" from the engine) and use Precision Ny-rod (this type doesn't expand and contract) to connect it to the engine.

RE: Throttle servo interferance?
 

How old is the servo and how many planes has it been used in are key questions. Old servos can be twitchy due to worn internal parts, broken gears, and worn out or dirty plugs. So the servo is the first place I would look. Try using contact cleaner on the plug, and replace the extension if you are using one. Go from there.

RE: Throttle servo interferance?
 

Not often, but i now need a coffee break. This question has been asked about 20 times, and also has been duefully covered.
A bagle to go with the coffee would be nice!

FWIW,
separate the two as far as you can manage, do not rely on modern devellopments, test your stuff on low transmitter power with ample distance and engine running.
Do not believe those who say they never had a problem. They lie!

RE: Throttle servo interferance?
 

Thanks for the help. My first instinct was the servo. It is not that old, but is not new either. It just kind of threw me off that the throttle was the only one that jumped. I have the servo mounted about 10 inches behind the ignition, and the reciever is about 10 inches behind the servo. I will definitely try and swap out the servo. There is no metal to metal contact between the control rod and the throttle arm. And pe rievers, thanks for the sarcasm. It is definitely not appreciated. I just asked a simple question.

RE: Throttle servo interferance?
 

Is the servo a full size one or a mini? Gassers have a way of quickly destroying small servos. Just a thought.

RE: Throttle servo interferance?
 

And what is the throttle push rod made out of?????

RE: Throttle servo interferance?
 

10 inches may not be enough. I would move it back farther if you can, and then check it again before you change the servo. Also make sure not to use your Rx battery for ballast and put it up front. It can pick up RF also. If everything is well back from the engine, and you still have problems, I think you will have eliminated RF as a problem. Then you can look at the servo.

RE: Throttle servo interferance?
 

The throttle push rod is a cable actually with a plastic guide. I have a plastic ball link on the carb and a set screw on the throttle end. No, it is not a mini servo. It is full size, but it is just a standard servo. I have everything as far back as I can get it I think. The rx battery is at least 22 inches behind the ignition module, and probably at least a foot behind the throttle servo. I don't believe I can relocate the servo any further back. I will try a new servo tomorrow and see if I get any change. Thanks for the input!

RE: Throttle servo interferance?
 

One more question. This is probably a long shot, but you do have the engine hard mounted and not soft, right? Soft mounting can cause all sorts of problems including the throttle jumping around.

RE: Throttle servo interferance?
 

Try a plastic push-rod.

RE: Throttle servo interferance?
 

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If the cable inside of the throttle's plastic guide is metal, or other conductive material, it will act as an antenna and it will direct RF back to the receiver, whether there is a metal pushrod end or not. You need to go with a totally nonconductive throttle actuation system. Yes, sometimes folks get away with using conductive throttle linkages and sometimes they do not. Do not is more the norm.

A friend of mine who is also an electrical engineer, used to leave the return spring hooked up on his carb, a normal strong servo and a single piece of kevlar fishing line to pull the throttle open. The stock spring would return the butterfly in the carb back toidle. Should a knot come loose and the kevlar line unattach, the spring assures the engine's return to idle.


Ed Cregger

RE: Throttle servo interferance?
 

Did you by chance do a search on this subject before posting, simple question, simple search, it seems to me that I have read this a number of times on this forum and everyone just keeps on repeating themselves.

Mike

RE: Throttle servo interferance?
 

One additional item - many people setup the throttle so that at full "cutoff" trim on the throttle stick, the butterfly in the carb is completely closed. This is important if you want to "kill" the engine using throttle. To do that, the "idle stop screw" on the carb must be removed completely; most engine manufacturers either do that for you, or back the screw out far enough so you can stop the engine with closing the butterfly.

Your servo could be jumping if it's binding on the lower idle setting due to that screw trying to hold the idle actuator open.

RE: Throttle servo interferance?
 

Thanks for all the advice. I have switched out the servo and will be trying that momentarily, but if that doesn't work, I will switch the pushrod out to a carbon fiber one. I just liked the simplicity of the cable.

Edited by Rcpilot

RE: Throttle servo interferance?
 

I am sorry for the sarcasm. I did however offer good advise.

If only your throttle servo acts up there may be reason for that.
Use a new servo, and check disturbance again. If so, check out why. Do you have a metal (or conductive ) pushrod or pull wire? Is your ignition some way sending out HF signals by loose wires, insufficient shielding etc?
Such disturbances, if only affecting the (hopefully healthy) throttle servo indicate strong fluctuating electric fields that influence the servo's electronics and make it act up. The other parts are probably too far away. A conductive steel or carbon rod, wire or anything else that can lead the HF signal from the ignition to your servo vicinity must be avoided.

RE: Throttle servo interferance?
 

it is very unlikely that rf noise effects only one channel ! my guess is the servo or something to do with that one single servo.

RE: Throttle servo interferance?
 

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Many carbon fiber compounds are also conductive, but it might be worth a try if you already have the carbon fiber material available.

In the old traditional encoding schemes, radios NOT on 2.4 GHz, the throttle or a seldom used auxiliary channel was usually assigned the last position in the pulse train. The thoughts were that the channels furthest away from the sync pulse were more likely to suffer degradation than those cloest. I don't know if there is a technical basis for this assumption or not - but that is how it was explained many, many years ago.

So, with the above stated, it is possible that those channel assignments furthest from the beginning of the fresh frame could suffer some degradation, while earlier channels may not suffer anything obvious to the operator. That was the old paradigm. I was never convinced that the theory held any water, but I felt obliged to repeat this R/C myth.

I would rectify the conductive throttle cable first. That isn't good no matter what other problems are present. Then, if the cable replacement fails, change out the servo to a different one. If the problem goes away, all the better. If not, then it is likely that something else is causing the problem. Sometimes, just reorienting the wiring in your model can cause or eliminate such a problem.

Good luck.


Ed Cregger

RE: Throttle servo interferance?
 

So, I tried out the new servo this morning, but it actually got worse. Now, all of them glitch some. The throttle is by far the worst, but they all are doing it now. I will switch the servo back out tomorrow (am currently at work) and change out the pushrod. Hopefully that will be the fix I am looking for. It also seemed to get worse the longer I ran it. Does that make sense?

RE: Throttle servo interferance?
 

If you have enough stray signals from your ignition to find it's way down a cable, through a servo arm and past all the gears to get to the servos electronics you might want to check out some other ignition units. I've flown my planes with less than an inch gap between the reciever, servos and wires with CH units as a test. No problems!
The glitching you are experiencing should be duplicateable if you place the reciever or antena wire up near/on top of the ignition, heck wrap it around the ignition to see if it is sending stray RF interferance. If all servos start glitching then suspect a ignition problem.
Sullivan makes the best flex rod for throttle control. It has a small amount of CF and slides super smooth. It doesn't expand and shrink with temp changes.
Your fix will most likely be a replacement servo. Go to Towers site to read the specs for the servos you are using. Sometimes they put a note in the specs, (not for airplane use) it generaly means people are having gittering problems with a servo and they don't want to have to replace them. The note usualy disappears when a new version of the servo comes out.

RE: Throttle servo interferance?
 

With a traditional R/C system, not on 2.4 GHz, and without a regulator between the Rx battery and the Rx, normal behavior would be for the system to stabilize as the peak charge of the battery was consumed while the voltage was dropping to the nominal range. Of course, using LiPo cells in place of traditional Nicads could aggravate this problem as well. While receivers are more sensitive and servos move faster with more voltage, the receiver also becomes more easily bothered by spurious signals in the aether and the servos are enabled to track these spurious signals more accurately. This is one reason that I don't mess with 5-cell receiver packs. Yeah, I'm an old fart with old ideas when it comes to electronics. If you're running PCM, forget all that I have said previously.


Ed Cregger

RE: Throttle servo interferance?
 

I was not talking of one channel, but the servo electronics closest to the high power HF source. Radiated HF power can act like a DC bias on transistors and thus cause all kinds of analog-like inputs.

RE: Throttle servo interferance?
 

No, I am not running PCM. I tried to keep it simple. The servo I have on it is a JR that came with my radio system. I don't remember what brand the ignition is, but it could definitely be the problem. I was looking, and noticed that it didnt' even have a ground wire. I will probably try and add one to see if it gets better. I can't believe I overlooked this for so long. The engine is a Peak 65CC that I got in a trade brand new. It runs great, but the ignition is probably pretty cheap.