Martin Harris - Moderator Posted November 22 Share Posted November 22 Interesting behaviour from some servos yesterday. I had left my Durafly EFXtra racer on the grass in the pits for a couple of hours yesterday afternoon before deciding to fly it before too much of the light disappeared. After connecting the battery, it was immediately apparent that something was wrong with the ailerons…one was quite well deflected before powering up and it literally crept into position. Moving the stick revealed extremely slow movement so ideas of flying it were abandoned and I took it into the clubhouse to investigate. I then noticed that the elevators and rudder were less eager than usual. However, they speeded up noticeably after some stick wiggling so I applied similar activity to the ailerons - which still started more slowly than usual but steadily increased in speed as they were cycled - repeating this behaviour each time I repeated the exercise. After leaving the model in the vicinity of a heater for half an hour, performance returned to near normal but by this time the light had become less than suitable. The only conclusion I can come to is that the servo gear grease had stiffened up in the close to freezing temperature - affecting the wing mounted servos worse than those cosseted in the fuselage interior. I normally fly throughout the year, so it may be confined to the rather cheap servos fitted to foam ARTFs but it’s maybe something for the hardier flyers amongst us to be aware of. 1 Quote Link to comment Share on other sites More sharing options...
kc Posted November 22 Share Posted November 22 Could be just a poor connection at aileron extension lead - I had that happen when the plug & socket were perhaps a little loose or dirty. Could have been cold fingers with my model. Anyway inserting the plug a couple of times cleaned it up or made a proper connection. Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted November 22 Share Posted November 22 Interesting 'fault'........never came across this before, but then I'm not a lover of very cold weather for flying. If you have a spare servo of the same type or can easily remove one, perhaps leaving it in the freezer for a few minutes might recreate and explain the behaviour before looking elsewhere. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 22 Share Posted November 22 If it was anything like the cold we have had then there is a possibility of condensation in the servo. A 10 degree drop can create a layer of surface moisture even iside an enclosed space. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted November 22 Share Posted November 22 Its good to be wary of the cold! A tale from a few decades ago... (around 1975!) I was learning to fly helicopters, and could just about stagger round a circuit and land in one piece. It was so cold we lit a bonfire on the moor that were were flying from. I had just landed my heli, and was approaching it - hand outstretched to stop the rotors - when it suddenly went to full throttle, shot off over my head, and crashed behind me! The previously ultra-reliable receiver had gone berserk! Checking it with freezer spray, I discovered that the SCS devices (Silicon Controlled Switches - a form of transistor) that made up the decoder stopped working if the temperature dropped below zero. But not all stopped at the same temperature! This meant that only some channels stopped, with the result that the next channel in the chain got the previous channels output instead of its own! The next day I was down the transistor shop and came away with a bag full of SCSs, and proceeded to test both my six channel receivers, freezing the SCSs one at a time, and replacing them until I ended up with two receivers that would work reliably in the cold! Took me nearly all day, but I never had the problem again! Freezing temperatures can bite you in very unexpected ways! -- Pete 1 Quote Link to comment Share on other sites More sharing options...
Brian Cooper Posted November 22 Share Posted November 22 I have an EDF jet which has "temperature sensitive" electric retracts. They work fine in the warmer months. But when it's cold, one or two of the retracts won't come down. . . Curiously, they still go up, so it is still possible to do a wheels up landing. This particular model is my "Winter Detector". . When the undercarriage starts to play up, it's time to reach for the thermal socks.... lol. The model gets a rest until the weather warms up again. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 22 Author Share Posted November 22 1 hour ago, Simon Chaddock said: If it was anything like the cold we have had then there is a possibility of condensation in the servo. A 10 degree drop can create a layer of surface moisture even iside an enclosed space. I suppose condensation might have formed ice internally - the wings had a thin layer on them - but I still feel thickened grease might be more likely. I do remember buying special low freezing temperature “AeroShell” grease for glider maintenance back in the day. A different low temperature story was when I bought a Jeti Profi box which I used as a transmitter module on a Futaba transmitter. On a cold winter’s day, not long after fitting it, it refused to bind to any of my receivers until I was trying it in the clubhouse so after confirming that I could repeat the behaviour, I sent it back to the supplier for exchange. In the meantime, Jeti support replied to my query regarding the problem and sent me new software, stating that the original disabled binding at 0 degrees C. I forwarded this to the supplier and suggested he tried loading it - he did so and on return, testing in the freezer suggested that the new setting of -20 had completely cured the problem. Incidentally, it was reassuring that it only disabled binding and reducing temperature once bound, didn’t affect the operation so the logic must have been to limit the operating range well within safe limits. Quote Link to comment Share on other sites More sharing options...
john davidson 1 Posted November 22 Share Posted November 22 could it be the battery? Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 22 Author Share Posted November 22 No - it’s a BEC equipped model. Quote Link to comment Share on other sites More sharing options...
Konrad Posted November 22 Share Posted November 22 (edited) Thick grease is a real phenomenon as the temps drop. I often some times fly in -10°C temps in Denver (USA) and servo speed is an issue. I've traced this to battery chemistry and grease. Aviation grease often is rated to -50°C. Now if you don't have access to that I did a test using my refrigerator. I made up a few coupons with a dab of the test greases I had around the house and garage. To test the viscosity I put them in the freezer for 20 min and then ran a 300mm long 0.4mm dia. wire through dabs and notice the deflection. Of the house hold greases I think I found that the Sunbeam clipper grease would have the lowest viscosity at the temperatures that my fingers would tolerate. I have a few sets of Dynam retracts that appear to be temp sensitive (below 10°C). The fix was to change the servo pulse timing, move them from +100 to +120). Actually it was to change the timing of the adjacent channel. I think the timing circuit in the retract amp changed as a function of temps (this is a problem with simple (RC) circuits). The real issue was the length of time of the channel separation pulse. (FYI, simple 5 ch pulse trains don't seen to show this. But longer 6ch plus pulse trains do seem to be an issue for the Dynam retracts. I'm told that there are now newer Dynam retracts that aren't as sensitive to the cold Edited November 22 by Konrad Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted November 22 Share Posted November 22 Not looked into deeply, but generally it looks like some servos are rated down to -10C, but it is likely if the servos came with the budget price ARTF then perhaps their spec is less resilience to lower temperatures. If the model was sitting on the ground then damp and wind may have caused a wind chill effect + moisture entering the servo. Quote Link to comment Share on other sites More sharing options...
Konrad Posted November 22 Share Posted November 22 Wind chill? How does the rate of heat loss effect this? Are you thinking that the latent heat of transformation(evaporation) is lowering the effective/actual temp of the grease? Quote Link to comment Share on other sites More sharing options...
Don Fry Posted November 22 Share Posted November 22 All oils and greases have operating temperature ranges. Here we get a problem, does the maker of a servo know this, and a budget servo at that, who works in warmer climates, buying grease from a third party, ditto the provisos. I’m not knocking the servo. Mind, yet another reason to check, then fly. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 22 Author Share Posted November 22 Yes - the main reason for posting! So many people give a quick wiggle at best. As to wind chill, there was little or none. 1 Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted November 22 Share Posted November 22 Rub a dab of Vic on it. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 22 Author Share Posted November 22 Wot - not a quick waft of a handy blow lamp? Quote Link to comment Share on other sites More sharing options...
Geoff S Posted November 22 Share Posted November 22 4 hours ago, Peter Christy said: Its good to be wary of the cold! A tale from a few decades ago... (around 1975!) I was learning to fly helicopters, and could just about stagger round a circuit and land in one piece. It was so cold we lit a bonfire on the moor that were were flying from. I had just landed my heli, and was approaching it - hand outstretched to stop the rotors - when it suddenly went to full throttle, shot off over my head, and crashed behind me! The previously ultra-reliable receiver had gone berserk! Checking it with freezer spray, I discovered that the SCS devices (Silicon Controlled Switches - a form of transistor) that made up the decoder stopped working if the temperature dropped below zero. But not all stopped at the same temperature! This meant that only some channels stopped, with the result that the next channel in the chain got the previous channels output instead of its own! The next day I was down the transistor shop and came away with a bag full of SCSs, and proceeded to test both my six channel receivers, freezing the SCSs one at a time, and replacing them until I ended up with two receivers that would work reliably in the cold! Took me nearly all day, but I never had the problem again! Freezing temperatures can bite you in very unexpected ways! -- Pete I was working at Murphy Radio in the service department as a teenager in the late 50s. Transistor radios were a very new thing and the transistors were all germanium rather than silicon. The local oscillators wouldn't operate at low temperatures, not even on a cold morning in (say) a bedroom so the radio didn't work. Those holes and electrons were reluctant to move until they warmed up - rather like me now 🙂 Semi-conductor technology has moved on a lot since the transistor was invented in 1949. Quote Link to comment Share on other sites More sharing options...
Konrad Posted November 22 Share Posted November 22 55 minutes ago, Don Fry said: All oils and greases have operating temperature ranges. Here we get a problem, does the maker of a servo know this, and a budget servo at that, who works in warmer climates, buying grease from a third party, ditto the provisos. I’m not knocking the servo. Mind, yet another reason to check, then fly. Not just low end manufactures. I had these issues with Futaba servos way back in the 80's (I'm thinking the S133 and S132H servos). But yes this should be part of your radio check along with the range check one should be looking at servo (surface responce) speed. Looking at the surface can find issues with the hinges linkages and general rigging issues. Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted November 22 Share Posted November 22 You quite find that Mil Spec stuff is actually off the production line but tested to the required conditions to find the stuff that doesn't work and return that to commercial use! Meanwhile, having tested said component to the specified temperatures and found that it works, it gets a certificate and the price goes up by a factor of 10. Of course, infant mortality can also be eliminated by following similar routines and throwing away the stuff that doesn't work. Quite an important point raised by the OP and should also apply to Txs especially where a kill switch is relied on to keep you safe. I have to say, I always treat kill switches with great care and never assume that the model is safe once the drive battery is connected. I do see lots of folk who have undue faith in the ability of our complex electronics to perform perfectly despite weather and electromagnetic conditions. Take care! 2 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 22 Author Share Posted November 22 I thoroughly agree with that last point. The only safe EP model is one with its battery physically disconnected. 3 Quote Link to comment Share on other sites More sharing options...
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