Any ideas please

[fly-navy]

After bench setting new model up and everything workin fine went to set engine up today,all servos working correctly and to all tx inputs before I started engine,As soon as engine fired up throttle servo went to max open position,passed tx setting which was identified by bowden cable bending at carb end.el and rudd both dancing and throttle servo would not respond to tx to close it.Disconnected servo arm on throttle and engine worked fine but el/rudd still dancing.Stop engine and full control again.Tx is 35Mhz Cockpit SX and rx is DC Futaba with DC xtal freq 69 fitted.Engine is OS MAx 45FSR with metal servo arm on carb so i fitted plastic clevis to reduce any chance of metal-metal noise.Going to try another xtal tom then rx if that does not work.This rx and xtal combination has worked before,albeit with a Taba tx.

any help appreciated fellas

Cheers John

Edited By fly-navy on 07/08/2010 20:05:23

[Stephen Jones]

Hi .

 

It is most likely  metal-metal noise , but more info or picture needed , engine bolted to metal engine mount with metal bolts to firewall . wheels ect . as you only have a problem when engine is running has to be vibration induced .  

[fly-navy]

Hi Stephen,

Engine is bolted to nylon/plastic mount which is bolted to plywood firewall.Throttle cable is steel bowden cable running through a plastic sleeve and the clevis on the carb end is nylon/plastic with a nylon/plastic pin which goes through the hole in carb arm.That is what I was thinking about metal to metal noise,I suppose I could tryplastic Sullivan snake to see if that eliminates problem.

Thanks for help.

John

PS all bolts are metal,both to mount and firewall don't see a way around that though

[Peter Beeney]

  Fly-navy,
    Because you don’t mention the ailerons being affected I’m assuming this may be a high wing model and you are running the engine without the wing attached. But I might be completely wrong here. However if this is the case, and this does make it a bit easier, can I ask how the receiver is assembled in the fuselage? Is it wrapped loosely in a piece of foam? I would be inclined to suspect rx vibration in the first instance. To check this,with the model well restrained and standing behind it, lift the rx clear of the fuz so that it’s not touching anything, and see what happens. If this fails to make any difference, disconnect one servo at the time, and replace the lead before you disconnect the next. That might indicate that one servo has decided to play up. Failing this, I’d say it would be a case of putting a bit of a different thinking cap on. One other thing, how close is the battery to the engine? If it’s extremely close, it could be an answer, I have known this to cause a once-in-a-while type glitch, but certainly not on this scale. This sounds severe, by anyone’s standards.
    But before you do any of that, is this happening with the glow clip disconnected? This can also occasionally be a source of these little aggravations.
I know there have always been some discussions about metal-to-metal noise but I’ve never taken any particular precautions against this and I don’t think I’ve ever suffered from it. I don’t know anyone else that has experienced it either. So I don’t know how prevalent this is. It’s easy to cause a momentary twitch, but I’ve never been able to sustain it for a longer period of time. I think I only happens between metal surfaces that are touching and breaking, i.e. that jitter together, not ones that are solidly joined. What causes it? I don’t know, but thinking about it, could it be that with the tx transmitting so close to the model a small voltage is induced into say a metal end of a pushrod and then if this is coupled to a metal arm by a z bend the engine vibration causes a series of little makes-and-breaks which in turn generate some rf harmonics which then proceed to bother the rx? So does it happen with the tx ats some range? Again, I don’t know, but it’s maybe something else to play with.
   I have to say that the item that precipitated this reply was the magic letters FSR. Instant memories of the late ‘seventies, 27 megs AM radio and the brilliant little OS 25FSR!  Lovely Jubbly!  Thanks.        PB                 

[fly-navy]

Hi Peter,thank you for all that advice,the rx is wrapped in a Hi-Tec foam crash pad and is held in place by a tie wrap on the servo tray,1st ever ARTF and obeying instructions to the letter,even though it put rx next to servos but no prob with engine not running.Model is the Blackhorse Spacewalker SWMBO bought me and the wing was not fitted.I had fitted remote glow start but when this happened removed it from the plug post and it still persisted with the glow clip connected and disconnected.Afraid it has to go on the back burner ,invited to daughters for lunch today baby sitting tom & Tues,shopping wednesday will see if I can have a look one evening.Might well be something in what you say Peter about vibration,this is the first and only time I have installed a rx like this in 14 years so 1st job will be to release it and see if things improve.

Cheers

John

[fly-navy]

Peter nipped out the back gate into field when we got back with model etc,cut the tie wrap holding the rx put it in plastic bag(keep exhaust crap off it) checked response of controls and all working,fired the baby up and not a twitter from the servos,plane was restrained so went through full throttle range and all ok pushed rx back onto servo tray next to throttle servo,original pos.,and still all ok.Could see neighbour was going to have BBQ so let engine tick over to empty tank,purred for 10 mins at a steady 2250 rpm,lovely these engines are'nt they?I have put some more foam around rx and put it back with the wraps not pulled up so tight,just enough to retain it and hopefully will be ok for next test,hope I just had wrap too tight and not enough foam>

Cheers

John

[kc]

The clue might be in your comment ' Rx next to servos'  

 If the this means the aerial runs close to the servo it may be the problem, and was changed when you unwrapped the Rx.   I had a severe lack of range problem with a new Rx  and even changing to another new Rx still  did not cure it.  Advice from the BMFA's Technical person said some receivers are more prone to this than other older models, so move the aerial away from servos.   Cured the problem!

Edited By kc on 08/08/2010 19:57:11

[Peter Beeney]

   John,
          Many thanks for your replies, I’m very pleased you got a good result!
   I first met this situation many years back, when a lad at the patch had a problem. His model would get to a few hundred feet and then go berserk. I hadn’t a clue what was wrong, but looking inside, I asked where the receiver was. “ Under the servos” was the reply. It certainly was, I had to lever it out with a screwdriver!! When I queried as to why he’d done this, he said that the instructions advised - “Slide the receiver under the servo rails.” There is no answer to that. A quick wrap-up in a piece of foam, and all was well, and he was much pleased! Sometimes you have to slightly ‘adjust’ the instructions. I’m sure the vibration affects the crystal. Saying that, you have also put a turn of insulation around the crystal, haven’t you? If it’s the type without the little lid, they can come out. I once saw a very nice, very expensive i/c 90 powered ducted fan model fly at full speed into a concrete peri-track, because the crystal came out of the rx.
   I just wrap the rx in a fairly thick piece of foam rubber, just enough to stop it rattling around in the fuz.

 

   I must admit I’ve never seen an example of kc’s servos affecting the rx. In tests that I’ve done in the past I’ve never really managed to do anything very much to cause interference and certainly not a reduction in range. This would seem to be something of a retrograde step. Fortunately I’ve not bought any new radio kit for quite a while now. I’m also at a bit of a loss as to wondering why this happens, although it clearly does. Something else to remember for the future. Normally a severe lack of range is something that is quite difficult to arrange!

 

   Take care of the FSR! PB

[kc]

My comments were about a 'new' Rx when the ' Challenger' took over from the 5L as Futaba's basic set!   That is about 20 years ago!!   I was told then by Chris B of the BMFA  ( name obscured in case I mis-quoted him! )  that the Challenger was more critical than the old 5L when the aerial ran near / underneath the servos.  The model had flown well with the 5L but when tried with the brand new Challenger ( with the new aerial taped in the same place as old aerial and same set of old servos) it showed little range and crashed.   Moving the aerial an inch or two cured the problem

 

To me this sounds a similar cure to your removing the RX from being tightly wedged under the servos.  It might have been the aerial ran very close to the servos and was moved when you un-wedged the Rx and wrapped it in foam.  Of course wrapping the Rx in foam is essential anyway, but who is to say whether foam or moving the aerial was the cure.  As long as it cured it!  

 

 

Edited By kc on 09/08/2010 10:17:41

[Peter Beeney]

    kc,
         Yes, you may well be right, it’s just that I’ve never experienced any range problems associated with servos. I concluded that the servo mayhem was down to the vibration, it all seemed to be a good explanation. But, as you say, - whatever - it did the trick!
    The Challenger radio is a bit like the FSR engine, a nice warm blast from the past. As I remember, they were always good radios, except that some of the lower end of the price bracket models didn’t have a buddy box socket or switch.  So the ones that did were always eagerly sought after to borrow for a while for all the would-be aviators at that time.  

    Someone will be resurrecting nicads next, but I have noticed they are making something of a come-back, indeed that is if they ever really went right away!        

    Good Flying.            PB  

[fly-navy]

Peter & kc,thanks for help,I have not tried engine again since I put rx back in original position yesterday so cannot let you know the outcome yet.If you can visualise a servo tray with two pockets at rear for el & rudd servo then looking from tail to engine a third pocket hard on the l/h side is for the throttle servo,the gap created on r/h side is for rx which is where I placed it and the aerial was routed along this fuse.side through pieces of fuel tube to it's exit so basically the aerial cable was roughly in the same position through all the events.My dilemma now is do I trust the rx/xtal if it all seems ok on next engine run,take it to field and do vigorous range check with engine running,better check than normal, or change rx or xtal?

No falling out please

John

[Peter Beeney]

   John,
          I think if this were my model I might consider that I’d cracked the case of the insubordinate servos and I’d just go and fly it. However, I wouldn’t cable-tie the receiver down in the first instance, so if you do this I think it only needs to be just sufficiently tight enough to hold it in place and no more. Almost not tight at all! And plenty of foam!
   If it were someone else’s model I’d be a little less cavalier perhaps and do a range check. I’ve never been really strong on aerial down checks, sometimes the results seem to be a bit vague, and I’m trying not to dispatch a sermon here but this is what I might do. Ideally we’d need a couple of us for this one, but if not I would stand the tx in my folding chair with the aerial down, (the chair has a metal frame, but that doesn’t seem to have any adverse affect at all), and carry the model away to the point where the servos just begin to gently twitter. They are just starting to hunt for the centre, so you are approaching the limit. Sometimes this can be quite a long way, sometimes not so far. Then I’d really restrain the model, pull the aerial about halfway out, start the engine and I can now walk to that first point and a bit further maybe and still have full control of the engine. If the motor continues to throttle up and down ok for a few minutes without any signs of wanting to go off on it’s own, then there’s nothing left but to give it a go. In fact, if you just left the motor on a fast tick-over you would soon notice if it started speeding up on it’s own. If the motor’s ok, everything else will be all right too. I’d be very surprised if you do find any misdemeanours if you try this. I’m not sure that you have much of a range problem, anyway.

   Crystals seem to be quite robust, much better than I originally gave them credit for. When I do a bit of instructing I always take the rock out of the slave tx. Beginners sometimes inadvertently turn the slave tx on, not a good idea on a crowded flightline with the crystal in; I often use my own transmitters and I’m in the habit of putting the crystal in the top pocket of my shirt. And then forgetting it! I still use one that has been through the washing machine, twice. It’s not noticed until it goes under the steam iron. It was with some intrepidation that I first tried it out, but it’s never missed a beat. And this was in the nineteen nineties. Can we now deduce from this that my radio should have a smooth response with a nice clean signal?

   Good Luck!      I’m sure it will be fine.             PB

[fly-navy]

Peter I have erred on the side of caution and replaced rx and xtal with another combination tonight but as yet not tried engine run.As I said earlier it is the first time I have fitted rx like this,and I did not want the wrapped rx proud of the fuse wing seating.The replacement is a smaller rx so has plenty of foam and is still below sides.You would not believe how I normally protect my rx,there is enough foam to captivate across the width of the fuselage and battery is always in front of rx wrapped in some foam.With plan/kit builds I leave everything loose unitl I have done balance check then move it all around till balance is correct and battery in front of everything then glue in servo tray.Old fashioned but it works for me and only on very few occassions have I had to add ballast.

John

[kc]

Might be worth checking for other metal to metal contacts.  Perhaps the silencer or its internals etc etc.   Also I found that a glow clip seemed to give some effect whilst still connected. 

But I still suspect the Rx aerial position.

 

No, we were not in danger of falling out! , it was just a Gentlemans Discussion to produce all the possible causes for the benefit of all.  Seems to have been productive

[Phil Claridge]

i had metal to metal interference due to a silencer rear half only being hand tight, there was no lock nut on the rear half. this was cured at the field with a spiked nut found in the dark depths of someones toolbox this proed very effective and stayed on till the model and engines demise 18 months later

[Peter Beeney]

   John,
        Yes, I can well understand your caution. Having total trust in your gear is all. I’d also go along one hundred percent with your technique of keeping the weight down. Years ago I remember reading a sage’s very succinct words - “ For success, add lightness!” I have always tried to obey this very simple rule, you can always add ballast if necessary, but it’s much more difficult to lose weight.
   Some models, (and owners), seem to be able to sling the gear in any-old-how and get away with it. Others spend a great deal of time trying to get the perfect machine and it can go spectacularly wrong. The Devil, as always, is in the Detail. Returning for a second to my club mate in an earlier post, the one with the deleted ducted fan, he’d tailor made a really nice foam ‘box’ to accommodate the rx; and he’d done a similar job with every thing else on the model, it was magnificent perfection. But if only he’d just put a piece of insulation tape on the rx to hold the crystal in…….. It’s happened to other people, too.
   Batteries, too, can be a bit suspect. The plug and socket to the switch harness is a case in point, they have definitely been known to part company, on more than one occasion. A bit of a weak area, so I always thread a piece of string between the wires and tie them together. Or, alternatively, I cut the plug and socket off and solder the wires together. You can loose any excess wire, and I stagger the joint by about five millimetres and then just slide a short piece of fuel tubing over it. Easier than heatshrink, and the whole jobby probably doesn’t take much longer than a piece of string. I will have given the pack a bit of a bashing first, to make sure it‘s up to my spec., if so, it will most likely last quite a long time. My batteries are years old. As I’ve said before, the tape and string are mandatory for my younger trainees, advisory for the more senior gentlemen.
   After pilot error, I reckon batteries are the next biggest source of hassle for the model pilot. So with that in mind I think the on-board battery state indicator is a useful piece of kit. Another peace of mind thing. An added luxury is to calibrate it with a voltmeter, so you know exactly what voltage each led extinguishing indicates. I’ve seen two cases, where, when they were installed, they instantly indicated faulty battery packs. In both cases the pilots were lucky!

   Model planes have always seemed to me to be able to crash very easily without any provocation at all, trying to eliminate as many known risks as possible is the least I can do.

   Fly Safely. PB

[fly-navy]

Well fired the FSR up this afternoon Peter,and all seemed well,not servo jitter through full throttle range so weather permitting tom off to field and do range checks with engine running,between flying of course.Re the battery s/w it happened to me once,thankfully not flying,so I ended up always putting insulation tape around this connection,these days I take the outer cover off thes/w battery connection and use those purpose made retaining clips and also on the rx extension for the aileron,tis all belt and braces with me on things like that now>

John