Clive Moore Posted April 7, 2008 Share Posted April 7, 2008 I need some help with a problem.The problem:I am building a Great Planes Hawk PT6E ARTF. I have fitted a Laser 150 engine, mounted inverted. Due to the tank position being much higher than the carb on the Laser I have fitted an on board glow system which I purchased from Just Engines. When I run the engine the throttle servo arm intermitently moves back and forward (glitches)as if it is receiving interference.All of the other servos are fine.The receiver is a brand new Futaba PCM 1024 duel conversion. The servo is a brand new Futaba 3001.Action taken so far: I have re run all of the cabling to the on board glow making sure that the cables are separated from the receiver and power supply cables. I have fitted a ferrite ring to the throttle servo lead.None of the above have solved the problem. If I switch off the on board glow then the problem goes away. Anyone got any ideas? Quote Link to comment Share on other sites More sharing options...
Andy Green Posted April 7, 2008 Share Posted April 7, 2008 Not sure why it should do it only when the glow is on but make sure you have no metal to metal contacts, its easy to achieve with flying surfaces as we tend to use plastic horns but if the engine has a metal horn on the carb barrel and you use a metal clevis, that could cause you problems, so that would be the first thing to check.Also check that the pushrod isn't rubbing against anything metal as this will have the same effect.Andy Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 7, 2008 Share Posted April 7, 2008 Is the Just Engines onboard glo optically isolated ? I would not fit any such unit if it was not. I take it the onboard glow is electrically linked to the throttle channel in order to provide proportional contrl of the glow? I have done several optically isolated units for friends and they never have a problem. PM me if you want more info. Quote Link to comment Share on other sites More sharing options...
Clive Moore Posted April 7, 2008 Author Share Posted April 7, 2008 I'm afraid when it comes to on board glow systems I'm a complete novice. I don't understand what "optically isolated" means. There is no mention of this in the instruction sheet. The installation is as follows:The throttle servo is plugged into the on board glow (obg) the obg is then plugged into the RX on channel 3 throttle.A lead then runs from the obg to the negative side of a 1.2v 1900 mah cell with and a lead from the positive side of the cell to the glow plug. A lead then runs from the obg to the negative side of the plug (engine chassis). The plug is only on at low throttle settings and then gradually reduces as the throttle is advanced until it goes out completely at around a third throttle.The obg is made by a company in the USA called C-Tronics IncThe horn on the carb is plastic and the clevis is metal. It is attached to a metal push rod with a thread on the end and the metal clevis is then screwed onto the thread. I suppose its just possible that the clevis is vibrating on the thread but it seems a pretty tight fit to me. I've checked that the push rod isn't rubbing on anything. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 7, 2008 Share Posted April 7, 2008 If it is not mentioned as being opto isolated...then it probably isnt. JE stuff ( including there OBG is usually pretty good, and the chances of this being caused by a metal clevis on a metal pushrod is remote IMO.Try another servo first first, and then if it persists, post agin here and we will have another go. Quote Link to comment Share on other sites More sharing options...
Former Member Posted April 7, 2008 Share Posted April 7, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 7, 2008 Share Posted April 7, 2008 it may be the throttle one because of its interconnection with the throttle channel - for proportional operation of the OBG Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted April 7, 2008 Share Posted April 7, 2008 Yes, as you say spurious emissions would effect all servos. There is a signal breakthrough either within the OBG unit itself (unlikely) or from the negative cable from the unit to the glow body.If a replacement servo fails to eliminate the fault then perhaps you could try shortening the above cable,adding another ferrite filter or even fitting a decoupling capacitor across the unit? Quote Link to comment Share on other sites More sharing options...
Tom Sharp Posted April 7, 2008 Share Posted April 7, 2008 Try soldering the red lead to the glowplug itself. The supplied connector is only lightly spring loaded and vibration and movement of the motor pulling at the wire can cause an intermittent connection. Quote Link to comment Share on other sites More sharing options...
Clive Moore Posted April 7, 2008 Author Share Posted April 7, 2008 UpdateI have now changed the servo for a brand new Futaba 3010 but the glitching still continues as before. I have spent this evening re locating the OBG nearer the front and have removed most of the extensions to the power and glow supply cables. I have also removed the switch that I wired into the circuit as someone told me that it maybe the cause. I have also talked to Just Engines who are baffled though they have said that once I have tried it in the new location minus switches and extended leads that if the glitching still persists the will exchange it. I'll let you know tomorrow how it goes (assuming the weather lets me get the aircraft in the garden t run the engine. Quote Link to comment Share on other sites More sharing options...
Clive Moore Posted April 8, 2008 Author Share Posted April 8, 2008 I'm afraid when it comes to on board glow systems I'm a complete novice. I don't understand what "optically isolated" means. There is no mention of this in the instruction sheet. The installation is as follows:The throttle servo is plugged into the on board glow (obg) the obg is then plugged into the RX on channel 3 throttle.A lead then runs from the obg to the negative side of a 1.2v 1900 mah cell with and a lead from the positive side of the cell to the glow plug. A lead then runs from the obg to the negative side of the plug (engine chassis). The plug is only on at low throttle settings and then gradually reduces as the throttle is advanced until it goes out completely at around a third throttle.The obg is made by a company in the USA called C-Tronics IncThe horn on the carb is plastic and the clevis is metal. It is attached to a metal push rod with a thread on the end and the metal clevis is then screwed onto the thread. I suppose its just possible that the clevis is vibrating on the thread but it seems a pretty tight fit to me. I've checked that the push rod isn't rubbing on anything. Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 8, 2008 Share Posted April 8, 2008 Would moving the input to the onboard glow to another channel work?The glow system I have (made by Timbo) has three connection options. I chose to mix the throttle to "AUX2", works perfectly! Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted April 8, 2008 Share Posted April 8, 2008 An optoisolator is a device (solid state) that allows one circuit to influence another yet maintains total electrical isolation between the two, achieved to opto-coupling a light source and a light detector within the device.Hope all goes well with the testing! Quote Link to comment Share on other sites More sharing options...
Clive Moore Posted April 8, 2008 Author Share Posted April 8, 2008 I have now run the engine with the OBG re located and re wired without switch and extension leads.I still get glitching on the throttle. I then completely removed the OBG and ran the engine and absolutely rock steady with no glitching.So the OBG unit is now on its way back to Just Engines for replacement. I'll update you when I have received and fitted it and run the engine (fingers crossed) Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted April 8, 2008 Share Posted April 8, 2008 Fingers crossed it is then! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 8, 2008 Share Posted April 8, 2008 Never did like the "fingers crosssed" method of pre-flight safety checking Sorry, but If these units are potentially causing interference, then they would not get fittted in any airframe of mine, even with everything crossed. What happened to the old saying once bitten twice shy? Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted April 8, 2008 Share Posted April 8, 2008 Yes perhaps a fair point!But how many units have Just Engines (and others) sold and how many are in use with no problems at all?It could be one isolated unit at fault. Lets wait and see how the replacement performs. Quote Link to comment Share on other sites More sharing options...
Former Member Posted April 9, 2008 Share Posted April 9, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 10, 2008 Share Posted April 10, 2008 Gents, we may be getting away from the main point here. Onboard glow systems are nice but by no means essential! If they were then the various engine manufacturers would specify them. Why didn't the guy that was having trouble with his set-up just switch it off? I really doubt if it would have affected his engine either way.The only application I can think of where a dedicated onboard glow system would be an advantage would be a multi cylinder four-stroke. In this instance it is very likely that a cylinder could cool down to a point where the glow could go out; especially on finals when the trhottle is reduced. Mine is mixed to a switch on the tx.I remember during my full-size training a simillar situation while practicing "forced landings". These were carried out at a starting altitude of 3,000' and the instructor would tell you to "warm" the engine every 500' during the descent so that it wouldn't die when you needed it! Quote Link to comment Share on other sites More sharing options...
Brian Parker Posted April 10, 2008 Share Posted April 10, 2008 I thought the main point of this thread was to help with Clives problem.The effectiveness of onboard glow systems on single cylinder engines is an extension to the thread. Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 10, 2008 Share Posted April 10, 2008 Hi Brian,Yes, I thought that too. If you look back through the thread no one actually suggested turning off the system and seeing how the engine set-up would behave. I did mention swapping the input to another channel but it seemed to fall on deaf ears. If he has managed to get a working system from his original suppliers then so be it. If not, then its up to him whether he heeds advice or not. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 10, 2008 Share Posted April 10, 2008 And of course they also make starting an engine a bit safer as well as more convenient...even single cylinder Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 10, 2008 Share Posted April 10, 2008 Couldn't agree more Timbo, especially if it a brand new engine! What we do need is consistancy from Glow Plug manufacturers; no two are the same! On a single cylinder donk its no problem but multi... well Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 10, 2008 Share Posted April 10, 2008 Yeh tell me about it. When setting up your multi cylinder glo unit, I actually went out and bought 5 new OS F type plugs for setting up purposes ( dont use a lot of glow plugs these days ) and no two were the same ! The current draw varied from around 2.6A up to 3.3A .... and all on supposedly identical plugs Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted April 10, 2008 Share Posted April 10, 2008 Tim,Haven't tried it yet in anger, still trying to find a 13.4mm reamer for the prop!!! Promise will let you know how it goes!All I've done so far is set up the throttle mix on the test stand! Quote Link to comment Share on other sites More sharing options...
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