David Davis Posted September 16, 2021 Share Posted September 16, 2021 Some of you may be familair with the Baron, a traditional French three channel trainer which looks vaguely like a Great War monoplane fighter. Every year I participate in a mad competition, La Coupe Des Barons in which a high percentage of the entry are wrecked! This weekend my model aeroplane club celebrates its twentieth birthday and we are going to host a much tamer contest for the Baron. I have two Barons, one finished in Russian colours, the other as an RAF aircraft, pictures below. I have started servicing the Russian version for the weekend's events. The rudder and elevator are actuated by Hitec HS 5085 MG servos and the throttle by some non-descript servo extracted from some long dead ARTF foamy. The transmitter and receiver are Spektrum and the 5 cell Nimh is showing 6.5 volts. While the rudder and throttle servos operate normally on switch on, the elevator servo oscilates thirteen times before settling down to the neutral position. Each oscilation is less severe than the previous one. If you then touch the elevator control on the transmitter, the oscilating cycle starts all over again. It makes no difference whether you move elevator control on the transmitter up or down or whether you use full or partial movement. This situation continues even when you have disconnected the other two servos and moving the elevator servo to the throttle or rudder port produces the same result. I have concluded that the servo is faulty or have I missed something? If the servo is faulty this is the first time that I've had a problem with a Hitec servo. It's quite an expensive one too! Finally, what can cause a servo to behave in that way? I suppose that I will have to burn the midnight oil to get the other one ready! Quote Link to comment Share on other sites More sharing options...
Kim Taylor Posted September 16, 2021 Share Posted September 16, 2021 I don't know specifically on that Hitec servo, but in the old days of analogue servos, what you describe would normally be due to the feedback potentiometer going faulty. These days not so sure, but I'm sure that an expert will be dropping in soon to either correct me or confirm! Kim Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted September 16, 2021 Share Posted September 16, 2021 Have you tried it on a 4-cell pack? It could be the extra speed conferred by the extra cell is making it unstable. Otherwise, you could try cleaning the feedback pot, if its accessible. Otherwise, ditch it! PS: Met with Tony up at our local site today! -- Pete Quote Link to comment Share on other sites More sharing options...
Shaun Walsh Posted September 16, 2021 Share Posted September 16, 2021 Have you tried swapping the elevator and rudder servo plugs around on the receiver, if it's still the elevator that oscillates then it's the servo that's the problem, if it's now the rudder that oscillates then the receiver or transmitter are the problem. In that case swap receivers to determine which is faulty. If nothing oscillates when you swap plugs over it was a dirty/poor connection. I had this problem and spraying the plugs and sockets with contact cleaner followed by plugging/unplugging the servo solved the problem. Quote Link to comment Share on other sites More sharing options...
Nigel R Posted September 17, 2021 Share Posted September 17, 2021 12 hours ago, David Davis said: This situation continues even when you have disconnected the other two servos and moving the elevator servo to the throttle or rudder port produces the same result. does it happen if you power on with just the elevator servo connected? does it happen with the elevator disconnected from the servo? does it happen with a 4 cell rx battery? does it happen with a servo tester in place of the rx? characterise, characterise, characterise at first glance I would suggest cleaning the servo plug with spray cleaner and opening up the servo case to give the feedback pot a squirt of cleaner too Quote Link to comment Share on other sites More sharing options...
David Davis Posted September 17, 2021 Author Share Posted September 17, 2021 Thank you for all the advice gentlemen. I have disconnected both of the other servos and the oscillation continues. I have connected the elevator servo to the aileron/rudder port and the oscillation continues. I have removed the servo from the model but have not tested the servo without it being connected to the elevator. I haven't tried it with a 4 cell battery nor with a sevo tester. I do not know what the potentiometer looks like! It's a variable resistor isn't it? I'll report back. Quote Link to comment Share on other sites More sharing options...
leccyflyer Posted September 17, 2021 Share Posted September 17, 2021 Given the time pressure that you have in order to be ready for the weekend, I'd be inclined to swap the elevator servo out entirely, put in another suitable servo and then troubleshoot the dodgy servo at your leisure. The last thing you want is to take to the air with an elevator servo that you are not 100% certain about. 1 Quote Link to comment Share on other sites More sharing options...
David Davis Posted September 17, 2021 Author Share Posted September 17, 2021 3 minutes ago, leccyflyer said: Given the time pressure that you have in order to be ready for the weekend, I'd be inclined to swap the elevator servo out entirely, put in another suitable servo and then troubleshoot the dodgy servo at your leisure. The last thing you want is to take to the air with an elevator servo that you are not 100% certain about. Quite so Leccyflyer. Fact is, I do not have another servo of the same size to replace it with. I'm going to have to repair the other Baron. ☹️, Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted September 17, 2021 Share Posted September 17, 2021 (edited) I've seen this quite a bit on a couple my models that have not been used for while and found the problem to be a poor connection at a servo extension lead connector. Sometimes just disturbing the wiring would stop the problem - rather like bashing your TV remote because of poor battery connectors. My Goldberg Chippy would always play up in this way and the cure was to remove and replace a couple of cheapy (with non gold flashed crimps) leads for better quality ones. The plain tinned connectors must have been oxidising and giving high resistance. You'll find that the torque from a servo thus affected will be greatly reduced if you try a finger test on the output horn and the hunting will gradually decrease in amplitude to nothing - noisy servo pots in my experience will quickly and consistently hunt around centre but still retain much of their holding power. At least eliminate this potential issue before swapping out servos and possibly masking another fault. Hope this helps. Edited September 17, 2021 by Cuban8 Quote Link to comment Share on other sites More sharing options...
Nigel R Posted September 17, 2021 Share Posted September 17, 2021 DD, the feedback pot is indeed a variable resistor, it is found buried inside the servo, so it will require dismantling to clean - if that is the problem. I'd suspect the connectors are more likely to cause the slow oscillation though, gut feel that is more of a "low power at servo" sort of problem, a dicky pot would result in any unwanted movement being at full speed (I would think). Anyway, as for feedback pots, there is a pictorial on this page: http://www.uscoles.com/kapcontinuous.html Where a HS85 is dismantled (and modified for continual rotation) - the photos of the servo inside are useful. Look for "How the Servo Turns the Pot" you can see the main gear with the slot, the slot goes over the feedback pot itself. Quote Link to comment Share on other sites More sharing options...
RottenRow Posted September 17, 2021 Share Posted September 17, 2021 I've experienced exactly the same as Cuban8 describes above, as have a couple of other members of my club that I know about. It's nearly always one of the servo connectors or extension leads. Wriggling or unplugging and reconnecting the connectors and cleaning with contact cleaner is a good way of proving the point but any dodgy connectors or leads should be replaced before flying in my opinion. If it's the plug on the lead fitted to the servo itself that is at fault, this could be cut off and either a new plug fitted or a short lead soldered on, if you didn't want to open up the servo itself. Brian. 1 Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted September 17, 2021 Share Posted September 17, 2021 (edited) 30 minutes ago, RottenRow said: I've experienced exactly the same as Cuban8 describes above, as have a couple of other members of my club that I know about. It's nearly always one of the servo connectors or extension leads. Wriggling or unplugging and reconnecting the connectors and cleaning with contact cleaner is a good way of proving the point but any dodgy connectors or leads should be replaced before flying in my opinion. If it's the plug on the lead fitted to the servo itself that is at fault, this could be cut off and either a new plug fitted or a short lead soldered on, if you didn't want to open up the servo itself. Brian. Yes, it's an annoying fault because as you say, the problem will often clear by unplugging/plugging the suspect connector. Model is then put away for a while and hey presto at the next flying session it's at it again. A variation in the quality of crimp terminals I suppose, not helped by storing models in unheated, maybe slightly damp sheds and garages over winter. Edited September 17, 2021 by Cuban8 Quote Link to comment Share on other sites More sharing options...
David Davis Posted September 17, 2021 Author Share Posted September 17, 2021 OK gentlemen, this is the status quo. Tried the servo in the servo tester with a 5 cell feed. It continued to oscilalate. Cleaned the plug with contact cleaner and tried again. Same result. Tried the servo in the servo tester with a 4 cell feed. Same result. It all points to the servo being faulty. There are no extension leeds in this application, the servos plug directly into the receiver. I don't have the time to dismantle the servo so have started to repair my other Baron for tomorrow's event. Quote Link to comment Share on other sites More sharing options...
leccyflyer Posted September 17, 2021 Share Posted September 17, 2021 Well, I think that you've looked at All The Reasons, so if you really want to get Down Down to the field tomorrow, don;t want to be Accident Prone or Break The Rules you know What To Do. Fixing the other model as a substitute should Ease Your Mind, don't ask Is There A better Way, don;t let it Hold You Back, and just tell the organisers Let Me Fly. ? Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted September 17, 2021 Share Posted September 17, 2021 (edited) If the servo tester reproduces the problem then QED. However, do beware the bad connection syndrome it does turn up from time to time. Edited September 17, 2021 by Cuban8 Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted September 17, 2021 Share Posted September 17, 2021 David, what i would do.......................bin the servo and forget about it after all the faffing on you have done,not worth losing a model.☠️ ken anderson...ne..1...bin job dept. Quote Link to comment Share on other sites More sharing options...
David Davis Posted September 17, 2021 Author Share Posted September 17, 2021 I've been grafting all afternoon erecting the marquee so I'm not going to bother with the servo. I still have to repair the other model so I'd best get on with it! Quote Link to comment Share on other sites More sharing options...
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