The Case of the Wayward Y Lead!

[Peter Beeney]

        This is a tale of an errant Y lead which may be of some interest.
    My club colleague has recently described a chain of events which has caused him much muttering under his breath. He has a JR tx with a Spektrum module and an AR7000 rx. He also has a aerobatic model with 2 elevator servos, one on each half. Connected together with a Y lead, and then into the AR7000, they work together as intended. Except that one servo constantly moves about the centre point, it permanently jitters to and fro. Always the same one, lets say it’s on the left hand side. So we swap the two servos over, still it’s the left hand one chattering. So then we change the Y lead legs, from left to right, again the same left hand one continues to oscillate. This oscillation varies from a small movement about the centre up to a random and sudden full servo deflection, where it then stops and jams, which he can only correct by unplugging the servo and moving the arm back, or by switching the rx off and on when it then resets. And then resumes it’s constant chattering….. He’s taken all the gear out of the model, so the servos can be separated as much as possible, no difference, tried three different Y leads, including a short one, different voltage batteries, plus a UBEC, all to no avail. Plugging the lead into the rudder output position, or indeed any other control socket, alters things not one jot or tittle. Thus he would have the same problem if he used a Y lead on the ailerons. Making one Y leg longer with an extension lead, no joy is seen here, either. He’s tried moving the tx from close at hand to far, far away. He’s changed all the servos, in fact changed everything except the rx, and still the fluttering continues. The only thing that does make a difference is actually taking the ‘good’ servo out of the Y lead, then the ‘bad’ servo works normally. This effectively turns the Y lead into just an extension lead, but it does, on the face of it, appear to imply that there is some interaction between the servos.
    I’ve not actually seen this in the raw, so to speak, as yet, but it is now getting a trifle difficult to know what to suggest that is different to try and effect a cure.
    He has decided on the alternative way out, so that he might proceed to some flying, mixing ele/aux2 so that the two servos operate from two channels. I think that the ailerons are mixed on ail/aux1 so that he can meddle with the aileron differential. All the switches are disabled, to prevent any inadvertent operations, and the servos are synchronised. This works perfectly well, neither a quiver or nor a twitch, ever, does he see!
    It’s difficult to see how the rx is at fault here, and yet at the same time how it is not. He thinks Santa may dib up another AR7000, so maybe he can try a comparison test later.
    He may also try a quick substitute with his old 35 meg rx, I’m sure that will be fine.
    He probably will consider an email to Horizon Hobbies to be in order too, it certainly couldn’t do any harm.
  

    Another club mate had some problems with a petrol engined model, Futaba 2.4, two elevator servos on a Y lead, not the same fault though, just simply some erratic operations; previously it had been ok on 35. He cured it with a couple of digital servos. Something the JR man has been unable to try as yet, it may well be another answer!           

    At the end of the day, this persistent pesky problem only occurs when the Y lead is connected. So that appears to be at fault. But is it? When you switch on, one servo starts fluttering; and then, what ever you do, that servo is the only one to be affected. I’d have thought that at least you could do something to make a difference. From our previous experience of 2.4 and ignition battery interference it may be that the decoupling requires a coat of looking at. Some strategically placed capacitors might have some effect.    
    But, we may never know! Until he requires another two channels I feel that he might leave well alone! Thus it may forever remain an unsolved conundrum.           PB

[Myron Beaumont]

2nd attempt at a response -damned computer!

While back I had haphazard responses from various configurations on my Optic 6 gear .Different ball game but just could not work out (even being methodical like yourself) what was going on . To cut a long story short I cleaned all the terminals on the Rx with a small soft haired paint brush & WD 40 -Yes I know you shouldn't! It softens some plastics ,but I didn't possess  any switch cleaner at the time. .The aforementioned Rx had been moved from one model to another (the only one I had) & consequently had obviously gathered invisible debris during the transferral ops. from the new builds . It worked !. Now then, I reckon you should beg steal or borrow another Rx to complete your investigation .

Worth a try Eh?

[Myron Beaumont]

PS I forgot to mention the obvious -There was some sort of short intermittent circuit syndrome going on betwwen the power & the signal

[Tim Mackey]

Interesting Peter. I have a couple of models ( using ar7000 ) with Y leads - one on ailerons, and one on elevators - both appear to work fine.

I also had a model ( the flyfly hawk ) which used a mix, as the servos could not be positioned mechanically to get corrrect travel direction - aux 2 and elevator were the channels mixed I seem to recall. Again...all fine.

Only difference I can see here - and I am NOT suggesting this is the cause ) is that I make all my own extensions, or Y leads myself, and they are only ever done to the minimum length required.

[Doug Ireland]

Peter,

 

Do you know off the top of your head if the "Y" lead your mate used was a reguar one or if it has an amplifier, JR and Spectrum Rx's don't like them.