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Unintended motor restarts


Nick Jackson

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Nick Jackson

Just had the motor restarting unintentionally on landing one of my electric gliders - any thoughts, please?

Symptoms: in the air I got just a quick blip and then off again as I was landing under crow. I was able to replicate this on the ground by waggling the left stick (on which I have the brakes), especially when done in conjunction with a handful of right rudder.  I get the same result if I remove the wing tips. But not a peep out of the motor if I also remove the centre section.

Setup: this is an Xpro; Jeti radio; RC Multi 2 height limiter non-FAI software; high-C rating 2.2Ah battery; ESC in the attached picture (which came with the plane and doesn't seem to have a brand name on it).  I have the ESC on a slider but with a safety-switch to prevent accidental restarts. This was definitely in place and when testing afterwards the tx indication of fully closed throttle (-118%) did not move when the blip occurred.

Thoughts: I imagine this must be associated with voltage-drop with current demand when the flaps are used vigorously? I've occasionally had this with other big soarers with different ESCs but the consequence has been an audio warning triggered by telemetry rather than any change in the behaviour of the plane.

 

There's quite a lot more I can easily try to investigate further / hopefully solve the problem: different  ESC or separate receiver pack (surely the ESC is not deliberately set to blip the throttle as a low voltage warning is it?); slow the flap movement on the tx to drop the current demand; even try it with FAI software - which I was running till recently, without encountering this problem (but anxiety at having no restart available was probably just making me gentler than usual on the sticks). But thought I'd check first for any thoughts / guidance / lines of inquiry?

 

 

IMG_6164(1).JPG

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Regards voltage drop - I don't know enough about what happens to becs when they go past their maximum rated amp output. But i would think those ratings are more related to over heating than voltage drop off. But maybe the esc/bec has a safety cut out or something. As i say i don't know enough about it.

I'm struggling to believe a 2200mah lipo would struggle with the servos even when well discharged.  Even so the esc should not blip if the rx goes off.

 

Are you saying the glitch happens when you remove the wing tips? Or just that it's the flaps that cause it. 

Make sure any fail safe is set with the motor in the off postion not with the channel set to zero (which is half throttle). That being said failsafe doesn't do anything without power.

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As a first step, use the channel monitor on the tx to check that CH7 sits at -100 until and unless the motor is armed and commanded to run. If so, will confirm that it's an ESC issue. If not then please pm me the setup so I can verify its integrity.

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My first thought was it might be the failsafe, if you have set that for power off (and brakes on) then it's beyond me.

 

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PeteMitchell

Nick, could it be a tx setting?

Do you have Crow as a separate flight mode, or is it active in all flight modes ?

Either way It could be that your throttle end point is a borderline setting in the off position. Perhaps when you apply breaking, your flight mode changes and there your setting may be different to all other modes?

Do you use the Jeti throttle cut function or have you made your own programme? Again either way it could also be an end point problem.

Or it could be the esc :(:frantics:

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Nick Jackson

Thanks for the various thoughts. Will chew on it some more and report back.

I do normally set failsafe for zero throttle but wlil check that applies for this model. Presumably any voltage drop under load will relate to the output from the ESC rather than to what the battery is capable of delivering? (Hope the servos are not drawing >120A!)

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Nick Jackson

Thanks Pete - your message crossed with my previous reply just now. I will certainly look at end points. This was also mentioned in a useful PM response. But if I remember rightly the -118% was on Bernie's recommendation.

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How many amps is the SBEC?     If you can reproduce on the bench, can you put a multi-meter inline to check the amp draw when you operate the flaps  - ensure nothing binding.

I vaguely remember someone else raising a similar issue recently which turned out to be incorrectly set end points.

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1 hour ago, Nick Jackson said:

Thanks for the various thoughts. Will chew on it some more and report back.

I do normally set failsafe for zero throttle but wlil check that applies for this model. Presumably any voltage drop under load will relate to the output from the ESC rather than to what the battery is capable of delivering? (Hope the servos are not drawing >120A!)

My point was though that the max output of the bec might be what it is safe for it to deliver continuously. Not what it can deliver in short bursts without burning out. Otherwise it would have to have an electronic cut out of some sort.

the stall current of most servos wouldn't add up to 5 amps for 2 servos (e.g flaps).

 

 

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Nick Jackson

I've had a further play with this. Not a lot of progress and some alarm:

  1. Found the manual for the ESC online (thanks for identifying the ESC, Jef). The manual doesn't mention blipping the motor to warn of low voltage (or, obviously therefore, any way to switch such a warning on or off). Does say that the BEC output is 5A, which I'd normally reckon is what is required.
     
  2. Tried putting back the FAI, no-restart, software. To my surprise, the unwanted restart blips still occurred with this software when I waggled the flap stick with the wing centre-section mounted. (Apologies if I was unclear about this previously - just popped the centre-section on so that the flap servos were actually operating and loading the system. Didn't bother adding the tips for this testing). More vigorous flap-waggling than with non-FAI software loaded seemed to be required before a restart was provoked. But the restart blip  did still happen.
     
  3. Tried putting a short 'delay' on the servo function menu on the transmitter. This seems to slow the speed of travel of the flaps rather than delay the initiation of the movement? I first thought this had cracked it - with a bit of delay in place it was harder to provoke a restart. But it could still happen on 0.5s and 0.7s delay and I didn't want to go beyond this since I do rather want the brakes to come on when I ask them to rather than when they get around to it.
     
  4. Tried resetting the throttle end-point from -118% (if I remember set on Bernie's recommendation) to -100% (as mentioned in some of the posts) but this seemed to make no difference.

I'm trying not to think too hard about the implications of no. 2 above - still getting a restart with FAI software running. I suppose there could be some silly error on my part but I have double-checked. And I've made sure both times that, before testing, I've opened the throttle in the normal way using the slider to which the function is allocated, closed it and checked that the motor will not restart on the slider so the FAI software is preventing (or trying to prevent) restarts. Hmm.

Next stage may be rummaging in the toy cupboard for a different ESC.

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Nick Jackson

Thanks Tom. Interference between what? (I'm an ignoramus about electronics).

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I think it would be a good idea to try and elimate the bec or any sort of voltage drop from the situtation.

If it no longer does it with a separate rx pack then that could well point you in the direction you need to go in.

If the blip still happens with an rx battery then that tells you something as well.

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Nick, as you have a Jeti radio, you can set up the telemetry to log control positions - you can then look at the graph and see if there any transients/spikes on your slider channel at the same time as you get unintended motor signal.  (you can also just look on the servo monitor, although you probably won't see a short spike if it occurs.)

Have you tried it without the height limiter in the circuit?

Have you checked all the signal wires (broken wire internal to insulation, pushed back contact, broken crimp etc.)  It may be a broken ground connection.  The broken ground could be anywhere in your whole electrical system - an obvious  failure point would be the wing connector either in fuz or wing

You definitely changed the end point on the slider output (you can see endpoint numbers reducing on the servo monitor for the throttle output channel?)

Failing that, as I'm only a short distance away I can pop in on the way home from work, as I also have Jeti and I can review the set up.  I also have a clip current meter that I can check the BEC current draw, to eliminate that.  I could even copy your model onto my Jeti Tx, although if it isn't endpoint settings or an unwanted mix, it is probably not a Tx problem

Simon

 

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Nick Jackson

Thanks for the really helpful further suggestions. I'll give these a go as soon as I get time and report back (and ask you to take a look, Simon, if I'm still stuck - very generous offer). 

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Nick Jackson

Before trying other suggestions I popped in a Castle Creations ESC which I was fortunate to have in the spares box doing nothing. I'm getting no unintended restarts with this, however vigorous my flap-stick-stirring. So I seem to be OK, subject to confirmation tomorrow, when I hope to give it a go in the air.

Assuming it's still OK with the CC when flight testing I'll leave it at that. I'm not thrilled about putting an expensive ESC in an elderly windy-weather model but I'm not inclined to take up my time and everyone else's trying to figure what was causing a problem for which I now seem to have a work-round.  Thanks again for all the help.

Update 10 March: problem - touch wood - did not recur when flown with the different ESC. (And I can't find any wiring problems with the original one.)

Edited by Nick Jackson
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Good news - worth a careful look around the old ESC though, to see if you can see any bad joints on any of the wires, and that the Rx connector lead doesn't have any strained wires or pushed back/damaged pins.  It might just need a new lead to be soldered on.

Simon

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Nick Jackson

I'll do that, Simon - but it will probably be relegated to a sports model anyway.

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