One motor responding slower when armed

[whoelseisbored (LiamHowe89)]

Hi guys,

Bit of a strange one but yesterday after a slightly 'bouncy' airmode landing (resulting in a flip), one of my motors decided to behave a bit strange. As you'll see from the image below, the bottom left motor is slower to spin up when armed than the others. Now I've had to use my iPhone's slow-mo camera to record the difference but it seems to be accentuated when the props are on.

Any thoughts?

[ched]

I assume you have 'felt' the motors and they all feel the same, none more notchy than others, no grinding?
After that I assume that it wont fly?
Are you running dshot? If not try re-calibrating.
Check the power wires to esc and to pdb and the signal wires including the 0v signal wires if you have them. Also the motor to esc connections.


You need to determine if it's a motor or esc issue. Ideally you need to swap a diagonal motor. If the problem moves then its the motor if it stays on same arm its esc.
One thing you may be able to try, although it's not 100% reliable is to check the resistance between each pin of the xt60 and each of the 3 outputs from the esc to the motor. They should all be approximately the same resistance. If 1 is lower resistance then that is the esc that is dead!!!

I blew an esc on a Mobula6 yesterday! It was only about 6" high when it crashed and somehow that took out an esc!! Which is an all in one board, so esc, fc, rx and vtx all in one! At least it wasn't too expensive at £29.

Good job you have 4 separate esc as I guess it's an esc failure. Don't buy anything till you know for sure.

[whoelseisbored (LiamHowe89)]

Yeh they actually feel like the always have and I can't see any physical damage. The motor does actually look like it fully powers up. I'm going to try a test flight later on just to make sure it's stable.

Pretty sure it's Dshot300 but I'd have to double check that. I'm assuming you don't re-calibrate if it's running Dshot?

I was planning on redoing some of the soldering so I'll switch the motor diagonally before I touch anything else. I'm wondering if it might be a bad soldering joint tbh, size of this frame is a bit restrictive so some of the angles are a bit suspect.

[ched]

DShot is digital control so no need to calibrate. Unless you are on the latest BF (4.2) then I think you might be worth using DShot600 - I doubt it will make any differance but it allows the FC to 'talk' to the esc faster.
It might be worth checking solder joints, might be 1 of the phases on the motor lost connection - that would be an easy fix!

[whoelseisbored (LiamHowe89)]

Ok, just done another test and it looks like it's taking off ok but after a couple of seconds it cannonballs towards the rear left motor. Definitely something not right! 

I'll get it taken off tomorrow for testing. Really wish I'd bought a few spare ESCs and motors 

Ahh ok, got you. I have a feeling that my ESCs don't support DShot600 which was why it stayed at 300, or does that not sound right?

So say if it was one of the phases... that would imply a wire or joint right?

[ched]

Ahh ok, got you. I have a feeling that my ESCs don't support DShot600 which was why it stayed at 300, or does that not sound right?

So say if it was one of the phases... that would imply a wire or joint right?

It might be a bit too hopeful that it's a poor joint but it could be. If it's a 'dry joint' (looks rough not shiny) then that could be high resistance thus giving a lower voltage to the esc.
Lower voltage would mean less rpm and less thrust!!

If they are Dshot300 then they are quite old spec but nothing to worry about. I doubt many people could tell the difference. That said in BF4.2 on depending on loop timings sometimes it's actually advised to use a slower Dshot!!!

Check joints first, maybe esc supply with multimeter if you can, if nothing swap a motor.

[whoelseisbored (LiamHowe89)]

Ok just resoldered it and spins up ok. Not been able to check it off the bench though as the opposite (so front right) esc and motor got really hot! I've not even touched that one! Any thoughts?

This is confusing the hell out of me! I do have a multimeter but I wont pretend I'm any sort of expert in using it.

 

[ched]

First thing to check is that the motor bolts are not touching the motor windings as that will cause heat big time!!!

[whoelseisbored (LiamHowe89)]

Nah they're fine, a little bit short if anything! Haha. Base-piece is quite thick.

[whoelseisbored (LiamHowe89)]

Ok I've swapped the motor from rear left to front right. The motor that had the original issue with it cutting out is still having it but it's actually even more prominent now it has moved.

What's interesting is that the one that was getting hot before (front right) is now not getting hot at bottom left. So I'm thinking there my be some ESC configuration issue there that's actually separate to the apparent motor problem.
It looks like my ESCs will only allow me to use BLHELI_S by the name of them... these are the ones I have.

Anyone got any pointers on the motor issue or is it just dead you think? I'll try and post a video of it doing it when I get a second.

[ched]

Not sure if anyone has said don't power the quad with props on when working with it as it's all too easy to somehow arm it then it's 5" razor props spinning at your fingers and face !!     Always props OFF on bench.

Sounds like there is an issue with either the wires from the motor or the internal windings, as long as the solder joints are good? Double check the esc to power connections. The motor wires you might be able to look at. Basically the windings are enamelled copper wire. The enamel should be sanded off then they solder the multicore wire on and cover joint with heatshrink. If it's the motor windings then unless you have a great magnifier and steady hands you have to replace the motor but it does give you a spare motor bell.

BlHeli_S is fine if you have read about JESC type fw I wouldn't bother as it really only makes a difference on very small motors like 0802 size. You can use BlHeli configurator to connect to the esc through the FC and view the config. Check that they are all same FW version and settings are same (other than rotation). It's unusual to have to tweak BlHeli settings, think I only ever did it to change the startup beeps 

You might have had a poor solder joint on the hot esc/motor. Now you have resoldered it might be better joint? 

[Bad Raven]

I have had very similar, and in my case after tearing what's left of my hair out trying various swap around hardware fixes, I reloaded the FC firmware and the fault instantly went, there's a thread here somewhere on it.

[atomiclama]

I'd say you have probably damaged one of the wires on the windings.
Are they multicore windings? Maybe one of the cores has gone, that would allow the motor to spin but at reduced power.

[whoelseisbored (LiamHowe89)]

Thanks all for your replies. After further investigations I decided that it must be a power issue to one of the phases. I took the bell off to inspect, low and behold... literally one copper wire left on that one. Explains the heat as well.

Image (excuse the image quality... quite hard to get that close and keep focus haha)

New motor time!

@ched Don't worry not quite daft enough to leave the props on haha!

[ched]

It's difficult to see.
If you want to know how they are wired this shows how to rewind a motor.
https://www.instructables.com/id/Rewinding-a-Brushless-Motor/
The section 'Step 7: Winding Design' shows how the enameled wires are connected and wound.
All very intricate work, too delicate for my eyes these days.
About 30 years ago I was taught how to wind transformers etc but never done one since     
 
Always good to get to the bottom of the cause of the issue.

Good Luck.