Robin Kearney Posted March 31, 2013 Share Posted March 31, 2013 Hi all, I'm wondering if anybody has seen anything like this before. Today rigging my Phoenix 2000 for flight the left flap servo went slightly nuts. The two flap servos are wired (via multiplex connectors and wiring I soldered up myself) into two separate channels on the RX, with the TX configured to expect a 4 servo wing. I dont have any mixing at all, so both flap servos should behave identically, however while the right one stayed at neutral the left one went full down (90° which is far more than the travel I normally get), not content with that it started travelling up and down on its own. Best seen in the short video I took while up on the hill: Since getting home I've tried that servo in other channels directly wired into the RX. And have also tried other servos in the same wiring loom as that flap servo. It seems to be the servo itself. Plugged into any channel on the RX it behaves randomly like this. I guess its a duff and I just bin it, I'm just a bit surprised it has died so randomly and after maybe 20 flights and nothing I'd classify as a hard landing. Quote Link to comment Share on other sites More sharing options...
ERIC DODSWORTH Posted March 31, 2013 Share Posted March 31, 2013 Had it happen to me I was using cheap acoms servos all I could put it down to was condensation in the servo's causing a short they worked fine when indoors took them outside and they went crazy used better quality servo's and it never happened again Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted March 31, 2013 Share Posted March 31, 2013 If you suspect a servo, best remove it. It could fail at any time with obvious consequences. Problem is that ARTF aircraft fitted with servos are generally budget and normally not available seperately - due to the fact they are so cr.. rubbish. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 31, 2013 Share Posted March 31, 2013 Looks like a dodgy feedback pot or connection to same. Is this a pre-fitted no-name servo or do you know the type? It's not necessarily damage - I once had an SD200 which behaved similarly from new - it went straight back to the shop without being fitted... Edited By Martin Harris on 31/03/2013 22:24:17 Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 31, 2013 Share Posted March 31, 2013 I would temporarily plug the offending servo into a tester or even another channel on the receiver and see if it misbehaves. If it does, its goosed, and you should be bale to dig it out and replace it. The phoenix is a decent model, and I think it a litle unfair and not particularly helpful to describe it as rubbish. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 31, 2013 Share Posted March 31, 2013 oopps, just spotted that you say it behaves erratically in any channel - so....its goosed. Irrespective of age or landing technique....flap servos are very hard worked. Replace with a nice metal geared high torque jobby. Edited By Tim Mackey on 31/03/2013 22:27:18 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 31, 2013 Share Posted March 31, 2013 Wasn't it the cheap servos pre-fitted to ARTFs that Paul described as "not very wonderful"? I can only agree after encountering problems with those fitted to ST Models and Hobbyking examples... Edited By Martin Harris on 31/03/2013 22:29:39 Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted March 31, 2013 Share Posted March 31, 2013 ...I meant the servo is probably rubbish, not the model. Best replace both servos with the same type. Would be nasty if one worked faster than the other. Imagine full aileron (on flap when you don't want it). Quote Link to comment Share on other sites More sharing options...
Robin Kearney Posted March 31, 2013 Author Share Posted March 31, 2013 Martin that sounds likely, I was wondering what could have gone up the spout to give this sort of behaviour and that sounds like a possible answer. Paul it was a hxt900 fitted by me and not included in the original package that has gone bad. I've got several other of the same type all working fine and I believe the are commonly recommended. Servo is in the bin btw! Am I right in thinking a hxt900 ought to be up to the job of flaps on a Phoenix or should I be getting something beafier? Just wondering before I order a replacement. r. Quote Link to comment Share on other sites More sharing options...
Robin Kearney Posted March 31, 2013 Author Share Posted March 31, 2013 Aha, Tim I just spotted you suggest a MG/High Torque servo for flaps, anything you could recommend? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 31, 2013 Share Posted March 31, 2013 this maybe? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted March 31, 2013 Share Posted March 31, 2013 Posted by Martin Harris on 31/03/2013 22:28:41: Wasn't it the cheap servos pre-fitted to ARTFs that Paul described as "not very wonderful"? I can only agree after encountering problems with those fitted to ST Models and Hobbyking examples... Edited By Martin Harris on 31/03/2013 22:29:39 Well it didnt quite read like that TBH As for prefitted servos, I have to disagree. From experience, I must say that I have ( albeit surprisingly I admit ) been pleasantly surprised. I have several ARTF, fitted out models and have never suffered a servo failure, including a hobbyking very fast modified ( 800 Watt plus ) EDF F18 which is still flying after many flights and 2 years+ on the original servos, an Eflite P47, and Escale electraglide - all flown a lot and hard. Maybe Im just lucky ? Edited By Tim Mackey on 31/03/2013 23:53:27 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 1, 2013 Share Posted April 1, 2013 I have experienced this sort of thing twice before - both times on HS81 mini servos. In fact the second time it happened I found I was not alone! There are a number of threads on other forums about HS81 displaying this behaviour. Our own Steve Hargreaves tells me he's experienced it too! Now I know your servo isn't an HS81, but the is no reason I guess the effect has to be be limited to one type! I tried everything - changing extension leads, channels, mix, no mix. I couldn't cure it. The servo went in the bin! Its as if the servo thinks it has a command - but can't find the set point. Unless you can be sure that you find and isolate the problem - the servo really has to come out! BEB Quote Link to comment Share on other sites More sharing options...
Tim A Posted April 1, 2013 Share Posted April 1, 2013 Yep had similar behaviour from a couple of HXT900 even with low miles. Four days ago flying my E-flite Sea Fury it started twitching in flight just managed to keep control, then it suddenly did a rapid roll to the right, caught it and landed. On the ground it was fine, until I reconnected ESC again the right aileron servo went to full up, wiggled the stick and it settled again. Dirt or moisture in the pot apparently. So I replaced both aileron servos with Turnigy XDG-9 digitals problem solved. You could dismantle them and blow out the pots but at US $2.69 not worth it plus the risk of a busted plane. Quote Link to comment Share on other sites More sharing options...
cymaz Posted April 1, 2013 Share Posted April 1, 2013 There must be millions of servos built each day - you have my sympathies. It's annoying I know rigging up a plane only to have a sick servo. I had an HS 635 do that straight out of a packet!!!!! Shows the importance of pre flight checks. Well done on taking it home in one piece as you can always fly it another day.Edited By cymaz on 01/04/2013 06:19:42 Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted April 1, 2013 Share Posted April 1, 2013 Usually on flaps I don't use digital servos, as the Flap surface is under constant pressure when in use. Digital servos use loads of power when stalled - flattening your battery pack in double quick time and possible burning the pcb out. Probably what happened as these servos might not be upto the job of fighting virtual stall. Normally on my aircraft, I use digitals on the main controls, but normal analogue on flaps and throttle. I reckon other people use the same method... Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted April 1, 2013 Share Posted April 1, 2013 Thats a good point Paul, never thought about that before. Quote Link to comment Share on other sites More sharing options...
Olly P Posted April 1, 2013 Share Posted April 1, 2013 Oh, and on the pheonix 2k, the flap servos are NOT pre-installed, flaps are moulded into the wing and cut/servo'd if you want them. the servo is whatever the user fits - no influence of the aircraft! Quote Link to comment Share on other sites More sharing options...
Robin Kearney Posted April 1, 2013 Author Share Posted April 1, 2013 Now I've got home (was away at the MILs) I have managed to test it again, this time on my servo tester. And yep, sure enough same behavior. So in the bin it has gone and I've ordered a pair of these Turnigy metal gear jobs. I'll replace both left and right flap servos and see how I get on. Quote Link to comment Share on other sites More sharing options...
Glasshopper Posted April 1, 2013 Share Posted April 1, 2013 The splines on the drive shaft appear to be brass. I usually associate brass with a brittle tendency to shear easily. In fact I recently installed a metal geared (brass) servo and inadvertently obstructed the travel of the servo arm, the splines sheared on the shaft and the plastic spline on the arm remained intact. Is it common for metal gears in servos to be made from brass? I wonder whether there are better alternatives? Quote Link to comment Share on other sites More sharing options...
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