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Electric Motor 'clunk' When Opening Throttle

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Richard Hayward 604/06/2019 15:55:00
41 forum posts

Recently decided to get back into the hobby after a 15yr break. Having got rid of all my old kit, started fresh with and Acrowot, Quantum 55 motor and quantum 60A ESC.

From day one, the motor makes a 'clunk' when opening the throttle from fully closed. Does the same thing if windmilling in flight. Mounts are tight, prop is tight, no sign of anything loose. Other flyers in the club have been unable to sort this. Wondering if anyone on the forums have come across this before please?

Martin Harris04/06/2019 16:10:27
9262 forum posts
245 photos

Could it be end float on the motor shaft?

Grab hold of the prop - battery NOT connected - and try to move it in and you hear a similar noise?

I don't know your motor but certain mounting configurations rely on either a circlip or grub screw retained collar to retain the thrust loads which pull against the magnets from their "home" position. If so, it might be possible to add shims to reduce its effect.

Edited By Martin Harris on 04/06/2019 16:11:16

Colin Carpenter04/06/2019 16:15:18
635 forum posts
35 photos

Got the same set up in a Wots Wot and I have noticed something similar . Got 70 flights on it and nothings happened yet ! Carry on regardless !! 😀😀

Richard Hayward 604/06/2019 16:21:43
41 forum posts

Martin - thanks. No end or side play. Colin. Thanks - do get strange looks from other modellers though!

Nigel R04/06/2019 16:42:26
3736 forum posts
585 photos

I have a couple of motors that visibly oscillate a little before they start rotating. As they do so, there is an audible clunk. Opening the throttle slowly fixes the issue for me.

Chris Walby04/06/2019 16:44:32
1196 forum posts
297 photos

From stationary you are asking the ESC to accelerate the motor shaft very quickly and it might just be a feature of that type of motor where it produces a "clunk" as it starts. Same sort of thing when its wind milling as you are asking the ESC to catch the motor shaft on the fly and accelerate it.

I have a motor/ESC combination that really does not like that if the throttle is picked up too quick and makes a right squeal.

Only other issue was a motor that would once in a while do a 1/4 back turn before rotating as normal...found the problem on the maiden at WOT when the manufacturers motor connector failed and dead stick on me. Not nice as it was a war bird twin at lowish level!

As previous post could just live with it or change the motor and or ESC out.

Richard Hayward 604/06/2019 17:15:21
41 forum posts

There's still some noise, even if I'm gentle with the throttle. This is all new to me having been a dyed-in-the-wool glow motor sort of person!

Tony Richardson04/06/2019 17:52:59
636 forum posts
25 photos

Richard, have you tried changing the timing? this can have an effect that you describe, sometimes the ESC may not be compatible with the motor even from the same manufacturers - had this with a Rimfire motor and Electrofly ESC both made by Great Planes - just a thought, you may want to try a different ESC and see if it changes.

Chris the problem I had with the Rimfire was exactly as you describe, a squeal when the throttle was opened rapidly or if the motor had been freewheeling - as in a down line after a stall turn or spin - Great planes actually recognized the problem with the 45amp ESC and re designed it.


Edited By Tony Richardson on 04/06/2019 18:00:09

Richard Hayward 604/06/2019 17:58:43
41 forum posts

Thanks Tony. The ESC has low, med and high (normally on med). On low it was the same. On high the clunck was minimal, but the motor was drawing far to much current. I've just ordered a Turnigy ESC to fit in a Phase 5e (if it ever gets delivered), so will swop to that when it arrives and report back.

Chris Walby04/06/2019 19:08:21
1196 forum posts
297 photos

Off topic, sorry. Thanks TR, I thought as much...just can't find the time to take to swap the ESC's over...better get back to the mass build or should I pop my Laser 80 in it wink

SIMON CRAGG04/06/2019 20:41:37
560 forum posts
5 photos

It might be worth altering the "Start" settings as well. "Soft" etc. Info should be with ESC instructions (sequence of beeps).

Richard Hayward 604/06/2019 22:06:57
41 forum posts

As I said, this is all new to me, but I understood that the soft start was intended for helps? I do have a programming card for the ESC, so easy to try

Dwain Dibley.04/06/2019 22:22:27
1384 forum posts
1388 photos

Hi Richard, you are correct, soft start is more common in Helis because of the bigger blades and the forces generated. However, I use the soft start option on my fixed wing models as well, stops them darting off like a nutter, and of course, looks more scale like.

Give it a go mate. also I always buy the associated programming card for the ESC, it makes life a lot easier.


Richard Hayward 604/06/2019 22:34:16
41 forum posts

Thanks Dwain. I’ll have a play tomorrow.

Nigel R05/06/2019 08:37:12
3736 forum posts
585 photos

Soft start might do it.

Just be mindful of coming in for a low pass with throttle completely closed - if you open up to go around, you have to suffer the start up delay.

Richard Hayward 605/06/2019 14:49:14
41 forum posts

Same with a different ESC, same on 'soft', so think I shall just put up with it!

Bob Cotsford05/06/2019 14:55:54
8383 forum posts
463 photos

Have you checked the grubscrews that hold the can onto the motor shaft? I doubt it would make much noise if there were play but it's the only other possibility that I can see for a noise maker.

PeterF05/06/2019 17:30:59
525 forum posts
724 photos

I had this on a Hyperion motor and changing ESC settings did not help and neither did it have any end float. I finally stripped the motor down and the stator coil could rotate a little on the mounting shaft. There was a small piece of about 1mm rod that fitted into a groove on the outside of the shaft and the inside of the stator to stop the stator from rotating. This rod was too small, so I removed and fitted a slightly larger bit of piano wire and the motor now starts up with much less clunking or hesitation.

Richard Hayward 605/06/2019 17:41:05
41 forum posts

Thank you Peter. The weather looks duff for the next few days, so I’ll have a go at stripping it down to see what’s what.

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