Servo Twitching

[Douglas Butterworth]

Hi all just set up two new GMS Mini STD servos in some new foam wings for the ailerons,three std Futaba 3003s for Rudder,Throttle and Elevator a Gws RX with new XTAL,6EXA TX all baterries new and charged,the wing servos are connected with new Y Lead.TX set up bog STD no mixing just EPA adjustment,RX aerial well away from servo and battery leads,when i move stick for ailerons left or right they start twitching a lot,i have tried another new XTAL (Futaba) another battery,another TX and another RX(Futaba) and it still does it,does anyone out there know of anything that might be the cause of this?if so please tell me how you solved it please,regards Doug. 

[Tim Mackey]

posssibly the Y lead or the total length of the leads are causing interference.If none of the other servos are a problem then it is unlikely to be the receiver or aerial etc.

Have you tried un plugging the wing servos from the Y lead, and just plugging one of them them directly into a receiver port - or are they already buried in foam

Ferrite rings on the servo leads near the receiver MAY help. 

[Doug Ireland]

Could be the servos struggling to find their centre point. I've had this with big digitals in the past. Try shifting it using "Sub Trim" then reposition the arms.

[David Martin 2]

You may have a duff servo Douglas. I had a similar problem with a model before Christmas, both of my ailerons and flaps were twitching when cold though.

I found it by process of illimination using another model on which everything worked fine. Leave the Y lead in place to the wing servos and unplug it from the Rx. Plug that into a good models aileron Rx channel and operate the wing now. You may find it still does it, unplug each servo in turn and see if the remaining one settles down.

I swapped the 2 wings to their partner fuselages to prove my wing was at fault and not the other electronics. My one noisey servo was feeding interference to the others.

Good luck     (keep us informed..!)

[RichB]

Check your aileron Y lead!

A fellow club member had a very lucky escape last Sunday when, two minutes into its maiden flight, his new 1/4 scale Extra performed two uncommanded rolls! luckily he was able to land it OK.

On checking the radio installation, he found that the new aileron Y lead was faulty. The center joint had been badly made (it was actually butt-jointed!) and was making intermittent contact.

Hope you find your problem.

[David Martin 2]

That was his lucky day Rich..!

One of my planes is 72" span and has a load of extensions and Y leads, one with a servo reverser incorporated for one of the flaps, nearly a grand relying on all those connectors being 100% flight after flight.. Imagine how he would have felt to bin a 1/4 scaler - first flight - through a badly made lead...!...

[John Pilkington]

I make my own now, after buying a Y connection that had the wires crossed over at the joint. John P.

[Clive Moore]

Douglas,

I had a very similar issue last year with a GWS RX. It turned out to be a faulty reciever which the retailer changed for me to another of the same type and I had no further problems.

However it did take me till turned midnight to discover that it was a faulty RX (its the last thing I decided to try) 

As advised earlier in this thread you just need to change one piece of the set up at a time to identify the offending item

good luck and let us know how you get on 

[Martin Shoebridge]

Where can you buy connectors and crimps at sensible prices for making your own leads?

[Tim Mackey]

This is the chap I use, and have done for many years - excellent products ( I use multiway ashloks on all my radio connections )

ASH

[Martin Shoebridge]

That's one really useful web site! Thanks. Just a tip.... unless you are truly proficient at crimping, I would sugggest soldering the cripms instead. But this has it's own problems- vibration.

Use hot melt after assembling the connector, then cover in 'sticky' heatshrink to about 30mm down the wire.Use 3:1 ratio shrink. 

[Tim Mackey]

I would NEVER recommend soldering. A well executed crimp connection is far better - military applications for instance always use crimped connections - wicking of the solder is the problem.

Part of the answer is to use a GOOD quality crimp tool....ASH does these on his site...I have one and its a great bit of kit. 

[Martin Shoebridge]

I agree with you , to a point. Which is worse? A badly done crimp or a soldered joint.? Mil spec/avionics, sure they use crimp, but there is a long line of training and ruthless QC behind the operations. The average modeller, I suggest, will come nowhere near that, hence my suggestion of soldering.

One of the problems with these moulded 3  wires is that you can't  do a 'pull test' so how are you going to know that what you have done is good?

[Tim Mackey]

Well each to their own...but I still maintain that a reasonably adept modeller,  using the correct tool, and decent components will be able to achieve perfectly acceptable results crimping.

I am unsure what you mean about not being able to do a pull test ? I simply ensure that the first couple of inches or so from the plug are seperate wires and pull away

[Martin Shoebridge]

A 'pull test' is a QC method for establising that a crimp connection has been done  correctly. This will specify the load that will be applied to the wire in an attempt to pull the wire out of the crimp. It is usually done on a random sample basis. Clearly, this can't be done with 3 core flat wire as used in servo systems. As you say, each to their own.

[Tim Mackey]

I know what the pull test is, I just dont see why it cant be done in our case ?

As I say....I just seperate the three cables near the plug and pull each one

[Martin Shoebridge]

One is supposed to hang a spring balance on the end of the wire and attach it to a pulling device ( winch type thing) and apply the test force.

[Tim Mackey]

oh - far too OTT for my needs !

[David Martin 2]

Any luck yet Douglas...?

[646su]

Hi Doug

Back to servo twitching, it could be as simple as your tranny being too close to your receiver when trying it out?

[John Pilkington]

Hi Doug, I know just how you feel, no matter what you try changing you still get the interference, twitching, glitches call it what you like , it is most frustrating. I started a forum a couple of weeks ago with the same problem with no definite answers, and this was also experienced by two other people with ARTF models, these were slightly different to your model as they are wood built up and not foam. The chap in this country has managed to reduce his "interference" by moving the Rx as far away from the ESC as possible and has flown many times since. I myself like you would still like to know WHY but I have completely got out of the problem by spending about £150 and bought a Futaba 2.4 set and put the 2.4 Rx in the model and all has settle down and not a single twitch etc., and I have even tried very hard to make it twitch but it just would not. I know this does not tell you WHY but at least I can fly with confidence that it will not do like my club mate's did, 3 very heavy noses into mother earth before he finally managed to get some less twitchy  flights.  The anoying thing is that my other models with the 35m Rx on top of the ESC are perfectly OK. I have just finished a twin motor model with 2 ESC's and the Rx is within an inch of the ESC's and this is OK. So it must be that some twitch and others do not. I wish you well with your model Doug, best wishes John P.

[Tim Mackey]

 quote

The anoying thing is that my other models with the 35m Rx on top of the ESC are perfectly OK. I have just finished a twin motor model with 2 ESC's and the Rx is within an inch of the ESC's and this is OK. So it must be that some twitch and others do not.

If the ESCs or recvrs are all different then that could easily explain why some are OK and others are not.