Aileron interference

[Mick Simms]

I have a sessna 182 -50 CMPro  with a twitching in the ailerons,my radio gear is JR X2720  its only the wing that is the problem ,wing lay out is 3 servos per side one aileron  two flaps ,servos are noisy and aileron servos twitch like crazy can any one help with this problem Thanks   Mick Happy new year to all

[simon barr]

Hello Mick, happy New Year to you aswell .

I think all you can do is to try to eliminate the problem by trying your radio with the flaps disconnected, try a different extention lead etc, even try a different servo on the ailerons. With two flap, and one aileron servo in each wing panel, you may be getting interference from the flap servo wires as the aileron servo wire passes through them, try seperating them.

Hope this is of some help.

Simon.

[Mick Simms]

Good morning Simon thanks for the input ,I have tryed all the above exsept the last sugestion to separaet all wires  .Thanks  Mick

[Nigel Wyatt]

Hi Simon.

You could try disconnecting everythig from the receiver except the ailerons, then reconnect each function one at a time until you replicate the problem.  That may point you in the right direction.

have a good New Year..

Nigel

[simon barr]

Hello Nigel,

I know its still early (!), but if you re-read the thread, you will see that its Mick's problem, not mine, and that I have already suggested what you say...but thank you for your imput...

[Nigel Wyatt]

Hi Simon (correct this time)

That last glass of red was really good last night....

Still  I think a hare of the dog is what's needed.

Nigel

[simon barr]

Here's a tip...miss out the fifth glass of red and go straight to the sixth...

As for the hair of the dog, just get out into the fresh air...and fly...

[Former Member]

[This posting has been removed]

[Mick Simms]

Hi Eric thanks for the reply ,battery OK plus slight error on my part only two servos per wing ,one of the lads at the field sugested rapping servo cable round ferrite rings ?

[Tim Mackey]

sounds like excessive servo cable length is attracting interference - ferrite rings MAY help, as also may a top of range receiver such as  MPX D/C synth etc....

[Frank Skilbeck]

You don't say what the servo's are, I had a new digital servo on rudder which went mad once the engine was started. I had a similar servo on the elevator and that was fine, but I swapped them both out for regular Futaba 3001's and the problem went away, note the servo's were on long extension leads.

I've also done two 4 servo wing planes, one with 91 FS and the other electric, using regular servo's and no ferrite rings, no problems with either. Both planes were fitted with a Multiplex IPD Rx.

So it maybe that it's the servo's that are the problem.

[Brian Parker]

Do all the negative/0volt leads (usually the black or brown) form a common earth/ground? If so and the problem persists, then I’m with Timbo, try another receiver.

However if you want to try ferrite rings (to prevent any RF entering the servo) then you will need several turns round the Ferrite Ring close to the servo.

[Brief explanation if anyone is interested- This will create a high series impedance and will drop any RF voltage. Stray capacitance within the servo will form the low impedance shunt to ground. We have presented a potential divider to the RF currents.]

[Bob Cotsford]

Mike, I've got the same Cessna, and I've never had a problem with the wing servos because of the lead length, they just don't need to be excessively long in this plane, certainly not enough to generate interference. 

I'd suggest one of two things, if you are using digital servos, it could be the greater current drain causing a problem so try a larger capacity battery,  otherwise swap out the servos and extension leads in turn, it may just be a dodgy unit.

The only time I've experienced your symptoms it was down to a bad batch of servos - I had to replace all 4 servos with some from a different production batch and the problem went away.  That was with some of the early production Chinese clone servos.   I only worked that out by substituting each part of the setup in turn, switch  - battery - receiver - servos, and trying the removed units in another setup. Any of the 4 duff servos would cause a bench rig to twitch.

[Tim Mackey]

The only thing I didn't do regarding the use of ferrite rings, was fit them near the servo - I always fitted them as close as possible to the receiver, the theory being that the long cables can act as their own crude aerials, and induce unwanted signal into the receiver ports"

"Curing" this problem at the servo end of the lead, still allows RF interference to be picked up by the remaining cable length and then enter the receiver, so fitting them at the receiver end, "traps" the problem before it enters the Rx.

Of course, since I only nowadays use 2.4Ghz....such worries are completely eliminated.

[Brian Parker]

Timbo,

As only the aileron servo is affected, the problem, (if indeed RF induced), will be caused by common mode currents flowing in phase in the cables because of stray inductance at the servo. The wanted signal is differential and is flowing in one wire and in one direction.

Hence the suggestion of the high impedance ferrite choke at the servo end.

Getting technical and it’s late and the problem is probably not RF induced anyway.

[Mick Simms]

 Hi to all  .Well hopefully we should start to narrow it down ,the servos are standard JR and Rx is a synthesized RS77S  ,the wire length is as short as poss and have tried all swap overs of servos, i have 4 new  JR servos for my near complete Ta 152-H1 i will try them next.  Be back soon     MICK

[jimmac]

Hi Mick,

                   I would ditch the receiver I have one of these receivers which is going back to Macgregor,I had it in my first petrol plane first couple of flight no problem.The  last two the plane would range check perfectly then in the air would start doing it's own thing I have done one of my best bunts with no input from me at all and various other trouser filling gyrations.I removed the receiver and Y leads to my elevator servos suspecting that,I have just got back to the model and tried to set up the two elevators on seperate channels and the receiver refuses to link with either of my 2 JR transmitters.This receiver was removed from the plane and put aside and now it just doesn,t work.

                                               Jim.

[Mick Simms]

       Hi to all and a happy new year.       Well i am starting to think down the lines of  my JR RS77S synthesized receivers  not being good enough ,i have tried both RS77S receivers still the same,chatter and noise what would you recommend as a good receiver and servos to go with my JR X2720,budget now very low as the RS77S don't come cheap, and thanks again for the help and advice    MICK.

[Frank Skilbeck]

Mick the Multiplex IPD Rx's are about the best 35 mhz Rx I've come accross. I've used them in two planes with 4 servo wings and long extensions without a hint of problems.

[Tim Mackey]

I would second that, but they are not exactly "budget" items

Have you tried the ferrite rings, perhaps at each end of the cables - and what about trying twisted servo cables - Ashtek supply this stuff. Are you SURE of the integrity of all other installation EG: solid connnections, on switch harnesses, battery level, and conxn, etc......

When exactly does the problem exhibit itself - motor on and off / range checking / close to Tx etc?

How long ARE the leads?

I would not be looking at an expensive receiver change until ALL the suggestions given so far have been tried.

[Mick Simms]

                            Servo lead length for aileron is 760mm and 600mm for flaps,the interference starts soon as plane is switched on then settles down until ailerons are operated and sets it of again, first thing AM of to get some ferrite rings must solve problem before sat ' flying day ?

[Brian Parker]

Initially, before fitting the ferrite rings, double check (with a multimeter set at a low range) that all the negative voltage (zero volts) connections within the setup are in fact at zero volts with respect to the battery negative terminal (you may need to probe through the insulation if you can’t access the terminal, carefully, with a pin). Any reading on the meter will indicate a potential difference ie. A fault in the lead run.

[Tim Mackey]

As was suggested by you earlier Brian.... which is why I asked him, have you done all the other things that have been suggested earlier? - and obviously the answer is no , he hasnt. Mick...if you do follow Brians advice, then he means the MM set to a low DC voltage range incidentally, NOT resistance etc

76 cm is a pretty darn long servo lead, and I wonder if you may also be suffering a little voltage drop as hinted at by Eric earlier ? - are you using a 4 cell or 5 cell battery?

I would certainly try the following before spending out on a new Rx.

Heavy duty twisted servo cable - see here

Ferrite rings at each end of the relevant cables - try to get the cable through the rings and wrapped around as many times as possible - at least 4 turns if you can - I take it you actually know how to fit them correctly?

Decent capacity ( 1500maH + ) 6V battery pack 

PS I know you said you hope to fly it Saturday, but if it still glitches on the ground, then flying it would be irresponsible and NOT recommended - AT ALL !

[Brian Parker]

Timbo,

Yes, repeated because I’m convinced (well almost) that is the cause of the problem.

Leads of that length really need to be substantial and continuous (as per your Ashtek twisted cable (have used them…. a good Company)) from receiver to servo without any intermediate connections/plugs to reduce the possibility of introducing resistance/volt drop.

 

[Tim Mackey]

I use Ashtek stuff a lot - especially like the ashlok connector sytems, but I also never use extension cables as such at all.

If I need a longer lead than fitted to servos, I too fit a complete new twisted HD lead of the required length, and either cut and hard wire the joint near the case, or solder directly to the PCB within the servo.