Bizarre brushless motor behaviour!

[Reuben]

After taking my 13.5 out of the car Friday night and fitting my 17.5 for the weekend, I span my 13.5 (As i usually do) by hand, just to make sure it was still good.

However to my surprise the rotor did not spin freely and felt "Gooey".

Surprised by this I took the motor to the track today and let others have a feel.

Now I dont run the motors hot and the last time it was ran it temped at just over 50C, ive also been running the motor at RRC and STCC bashley this year with no issues at all.

Still confused about anyhting being wrong with it, I soldered it up to the Sphere just now and gave it a quick blip on the throttle.. We had power . So I gave it full throttle and it sounded fine.

Then I decided to spin the motor again by hand, and you would never guess what happened next!!! All was fine! the motor span nice and freely with no gooey sensation .

Now I am officially confused, but happy it still works.

[Reuben]

Quest over!!

I was able to reproduce this weird issue.

Put a bit of solder between the B and C tab, and try to spin the rotor. Goes all stiff and gooey, remove the connecting solder and instantly the rotor spins properly again!

Im sure someone can explain the electricity being generating somehow and going accross 2 phases?? anyone?

[mattsedgley]

wow - I'm impressed, I really wouldn't have thought about that - how did you find that was what it was?

[lesbaldry]

Oct 4, 2009 18:47:19 GMT Reuben said:

Quest over!!

I was able to reproduce this weird issue.

Put a bit of solder between the B and C tab, and try to spin the rotor. Goes all stiff and gooey, remove the connecting solder and instantly the rotor spins properly again!

Im sure someone can explain the electricity being generating somehow and going accross 2 phases?? anyone?

That ones worth remembering

[TryHard]

I can't tell you how (i'm no electrical engineer... keith?), but I would assume it has something to do with creating a resistive circuit.
Spinning the rotor by hand will make the motor act like a generator, i.e. pushing a current through the coils. Normally, with the phases not connected, there's no completed circuit for the current to flow. However, solder across the tabs joins up the two phases, and bingo, a ciruit to resist the turning of the motor... At a guess... I would reckon the faster you span it by hand, the more gooey it felt?

HiH
Ed

[Simon Crabb]

Yes, exactly that Ed. A solder bridge is a resistive circuit, causing a braking effect when the motor is spun.

That's how 'electronic' braking works, by applying a resistance across the motor - in our case by using speedo FETs.

It could also happen inside the motor, could have a short on the circuit board resulting in a gooey motor, and not knowing why?

[mattsedgley]

Oct 5, 2009 7:35:03 GMT TryHard said:

I can't tell you how (i'm no electrical engineer... keith?), but I would assume it has something to do with creating a resistive circuit.
Spinning the rotor by hand will make the motor act like a generator, i.e. pushing a current through the coils. Normally, with the phases not connected, there's no completed circuit for the current to flow. However, solder across the tabs joins up the two phases, and bingo, a ciruit to resist the turning of the motor... At a guess... I would reckon the faster you span it by hand, the more gooey it felt?

HiH
Ed

What you say is partially correct ed, however there's a few gaps...

for those desperatley interested you can't go far wrong with a good wiki

en.wikipedia.org/wiki/Brushless_DC_electric_motor

[lesbaldry]

Oct 5, 2009 12:03:33 GMT @mattsedgley said:

Oct 5, 2009 7:35:03 GMT TryHard said:

I can't tell you how (i'm no electrical engineer... keith?), but I would assume it has something to do with creating a resistive circuit.
Spinning the rotor by hand will make the motor act like a generator, i.e. pushing a current through the coils. Normally, with the phases not connected, there's no completed circuit for the current to flow. However, solder across the tabs joins up the two phases, and bingo, a ciruit to resist the turning of the motor... At a guess... I would reckon the faster you span it by hand, the more gooey it felt?

HiH
Ed

What you say is partially correct ed, however there's a few gaps...

for those desperatley interested you can't go far wrong with a good wiki

en.wikipedia.org/wiki/Brushless_DC_electric_motor

Who cares ;D....At least Reuben found it and now we know what to look for should we have the same problem

[mattsedgley]

Here here!

[TryHard]

True, but looking at the diagrams, I bet that it'd be a more noticeable affect on a Start/Wye wound motor than a delta wind (affect two phases rather than one)... bit of pointless posturing

[mattsedgley]

posturing

[oldtimeracer]

Ok I apologise for this but just could not stop laughing.....

Having purchased last week one of the "new" Trinity Duo EA Motorsports 10.5 brushless motors from Terry I was sitting in the shed reading the instructions and WOW what do I read.....the second paragraph states you should be careful not to allow solder to connect between the tabs as this will give the effect of the motor braking when spun by hand.!!!!

Sorry Reuben, guess you should RTFM.

[Reuben]

its a good job I was using one of these older Duo's, that didnt come with instructions ;D

but I still have read a set of these.... never picked up on that, probably read it and thought what idiot would do that, so promptly forgot about it.

[oldtimeracer]

It's OK reuben, we have all done it. Just made me smile.

[lesbaldry]

Oct 6, 2009 9:34:13 GMT Reuben said:

its a good job I was using one of these older Duo's, that didnt come with instructions ;D
.

Poor excuse Reuben ;D......mind you I never spotted it when I had a look ....lol

[keitheroonie]

Yea you're right Simon, Ed etc. a battery drill works in exactly the same way, let your finger off the trigger and it shorts the motor windings together, hey presto instant stop ;D

I've never heard the term wye winding, must be a yankee thing, we call it a star winding over here.