David Payne 4 Posted December 27, 2024 Share Posted December 27, 2024 I have a max thrust trainer that on it's maiden flight suffered with roll axis osilation There is no gyro fitted The servos are new with no slop The receiver is new The motor was at a constant speed The conditions were windy Anybody have any ideas what to check? The aileron hinges are firm and good My wot 4 performed as normal on the same day Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted December 27, 2024 Share Posted December 27, 2024 If it's an over-control issue, check the aileron exponential is set adequately and in the correct direction, negative for Futaba and positive for all others. Quote Link to comment Share on other sites More sharing options...
David Payne 4 Posted December 27, 2024 Author Share Posted December 27, 2024 Yes the exponential is set up ok on my futaba radio It's something I've never come across before If it had a gyro installed I'd say the gain settings were too high At the moment the plane flies like a pig Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted December 27, 2024 Share Posted December 27, 2024 Flimsy foam ailerons springs to mind. Alternatively are the servos strong enough for the surface size / speed? We did have an issue like this recently at our field which was traced to a poor servo extension causing one aileron servo to "wave" after returning to centre. Only happened when full deflection was used and stick was allowed to spring back to the centre, other servo never did it. 1 Quote Link to comment Share on other sites More sharing options...
David Payne 4 Posted December 27, 2024 Author Share Posted December 27, 2024 It is a balsa model, so the foam issue isn't here The servo are savox full size digital one around 15kg of torque The issue is happening with little aileron applied If it was the wot 4 I'd have said a light foam model being blown around by turbulent wind Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 27, 2024 Share Posted December 27, 2024 If we assume the balsa structure is rigid enough then it could be some form of aerodynamic disturbance caused by a part of the aileron at small deflection creating a projection that has a disproportionate effect on the aileron function. At larger aileron angles the airflow will be turbulent and thus a small projection have little or no effect. Where possible for accurate control at small control deflections it pays to fully "shroud" the control surface gap to maintain a smooth as possible airflow over the surface. Just a thought. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted December 27, 2024 Share Posted December 27, 2024 (edited) I flew one of these a few years back and it flew fine, so check the control linkages, a loose rudder or flexible rudder control could possibly cause this issue. Edited December 27, 2024 by Frank Skilbeck Quote Link to comment Share on other sites More sharing options...
David Payne 4 Posted December 27, 2024 Author Share Posted December 27, 2024 That would make sense Before it commits to the air again I am to give it a good looking over Being a high wing trainer , it should fly well The kyosho trainer 40 I had 20 odd years ago, couldn't be faulted and the wasp trainer worked well Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted December 27, 2024 Share Posted December 27, 2024 (edited) 2 hours ago, Andy Gates said: Flimsy foam ailerons springs to mind. Alternatively are the servos strong enough for the surface size / speed? We did have an issue like this recently at our field which was traced to a poor servo extension causing one aileron servo to "wave" after returning to centre. Only happened when full deflection was used and stick was allowed to spring back to the centre, other servo never did it. Agree. Bad connection at an extension lead is the most likely cause of servo 'waving' at centre. Easily checked before digging deeper. Edited December 27, 2024 by Cuban8 1 Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted December 27, 2024 Share Posted December 27, 2024 Perhaps have another pilot give the model a whizz around and see what happens? Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted December 27, 2024 Share Posted December 27, 2024 I don’t know your experience level but one possibility that springs to mind is that Futaba uses the opposite settings for exponential from all the mainstream systems. If you - or someone helping - has set a positive value it would result in some rather challenging handling characteristics! Quote Link to comment Share on other sites More sharing options...
Brian Cooper Posted December 27, 2024 Share Posted December 27, 2024 Savox servos are excellent but it isn't beyond the bounds of probability that the aileron servo is faulty. Try changing it. Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted December 27, 2024 Share Posted December 27, 2024 I have often noticed the phenomenon of servo bounce when checking one out on the bench when either the battery I'm using is almost flat or when there's a bad connection. This limits the current the servo can draw and causes an oscillation between pulling the supply voltage down which slows its operation there by it draws less current and allows the voltage to recover speeding it up again leading to an overshoot. All this confuses the electronics in the servo, leading to spurious movements. Quote Link to comment Share on other sites More sharing options...
Konrad Posted December 27, 2024 Share Posted December 27, 2024 I've suffered this a few times. That is I couldn't find what was causing my flight instability through static inspection. 3 times I've been able to isolate the issue to the iron on film graphics of the the sunburst. That is the film would lift up spoiling the air flow over the wing. When on the ground the film laid down fine. But as the angle of attack got higher the film in spots lifted up. Try to clean the surface real well and seal all the film edges with a going over with an iron and/or seal the edges with a clear varnish. Quote Link to comment Share on other sites More sharing options...
barry widley Posted December 28, 2024 Share Posted December 28, 2024 I have seen similar issues when the ESC Bec can not supply sufficient current especially to a digital servo causing it to suddenly oscillate with load change . Could this be the problem in the air with higher loads 1 Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted December 28, 2024 Share Posted December 28, 2024 If you have checked all the hinges, control horns, pushrods and clevises then it could be a servo. The foam RIOT has quite a coupled rudder so worth checking the rudder servo and the aileron ones. From experience not just check them for a few seconds, but for minutes. I have a model with brand new servos and everything checked out on the ground and it flies well, but would occasionally would do something rather odd. In the end it was sitting on the bench (with the prop off) and I just kept stirring the sticks and after a couple of minutes (nothing before that) a servo would make a un-commanded movement and then recover, then return to its usual duties for an other 30 seconds to a couple of minutes and then do it again. Just one faulty servo but it took a lot of finding. My son had a model that flow many time suddenly developed un-commanded aileron servo movement, that turned out to be a servo plug to Y lead connection. As the lead flexed the servo moved with no command input change, just unpluged it and plugged it back in and it was ok until we sold the model a few years later. Again with the the model restrained or the prop off run the motor and watch to see if either the aileron or rudder servos move when no commanded. Quote Link to comment Share on other sites More sharing options...
David Payne 4 Posted January 3 Author Share Posted January 3 Hi all thanks for the replies I've had the plane out again today and it's performed perfectly After checking everything suggested and found nothing that looks incorrect, I fitted one of the capacitors into a spare channel on the receiver and the only other difference was the wind was a lot less, I'm going to run a separate power feed to the receiver and not use the bec feed off the esc Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 4 Share Posted January 4 IMO I would just replace the ESC as if part of it is playing up/faulty then it might pack up completely. OK it will only give up with a dead stick to deal with, but from experience it never happens a convenient time. Although the RIOT is not weight critical (have flown some porkers due to repair glue!), what's the point of making it none standard and over complicated. There are hundred of RIOT's and thousands of models out there that use the ESC BEC to power the RX and they don't have a problem and a lot of them have the retracting UC off the same BEC. Unless its your RX....but that's an easy swap to test. Quote Link to comment Share on other sites More sharing options...
David Payne 4 Posted January 4 Author Share Posted January 4 It is the max trainer not the riot so it has an overlander 60A esc, and recommended motor to the build instructions The esc was used in my wot 4 without any issues, however the wot 4 has the standard ripmax mini servos and the max trainer has standard size digital servos with a higher power rating Dropping in a 2s 1000mah lipo won't add too much weight to the balsa model and will cost nothing as I already have them Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted January 4 Share Posted January 4 I missed the digital servo bit earlier. How many servos are there and what is the BEC current rated at? It might be the BEC is trying to supply more current than it can so the voltage is dropping out. Analogue mini servos to standard digital servos is quite a jump in power required 1 Quote Link to comment Share on other sites More sharing options...
Philip Lewis 3 Posted January 4 Share Posted January 4 1 hour ago, David Payne 4 said: Dropping in a 2s 1000mah lipo won't add too much weight to the balsa model and will cost nothing as I already have them You'll need to use a regulator if you want to use a 2 cell LiPo or you'll kill the servo's and possibly even the RX, use either a regulator or a 2 Cell LiFe or NiMh's to get the correct acceptable voltage. Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted January 4 Share Posted January 4 (edited) David, Should you be looking for a regulator to drive the receiver from your 2S Lipo this one maybe well worth a consideration. It seems to be aimed primarily at the drone industry but I'm sure it will be eminently suitable for a fixed wing setup as well. It's a switching device and I've recently obtained two to play with by paralleling them together just to see what happens. This is for another thread and so far they been as good as gold just idling together for a couple of days; but that's only as far as I've managed to get. They're very small, lightweight and compact, at a cursory glance so far look to be very well-made, a good list of protection features, reverse polarity input, thermal cut out, output short-circuit and over current. I'm wondering if the output short-circuit just might be a current fold back procedure, I intend to try this when I can eventually get there… 2 to 8S input, max 36V together with 3 voltage outputs, 5, 6 and 7.4V - all at 5A; and this is all for less than £8 for cash, can't be bad.. Being so small and light the one area I have slight reservations about is temperature rise, particularly at high output rates so I shall be keeping a close check on that, contact thermometers at the ready…. The output plug is standard receiver style…. Good luck PB Edited January 4 by Peter Beeney insert correct link Quote Link to comment Share on other sites More sharing options...
David Payne 4 Posted January 4 Author Share Posted January 4 Yes a regulator will be used Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted January 5 Share Posted January 5 I can recommend these https://sussex-model-centre.co.uk/products/etronix-li-po-regulator-4-8v-5a-w-casing-20x14x49mm?_pos=1&_psq=4.8v+regulator&_ss=e&_v=1.0 Have had a couple in use for years with no probs at all. I believe they also do 6V and 7.4V versions as well. Easy to find from other uk suppliers. Quote Link to comment Share on other sites More sharing options...
David Payne 4 Posted January 5 Author Share Posted January 5 I either use the one on the link or the Futaba regulator Quote Link to comment Share on other sites More sharing options...
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