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        Question What ohm-age should they be?

#1 FlyBoy20 Dec 06, 2012 06:13 PM

What ohm-age should they be?
 
I've got three small motors which I thought were faulty (after crashes), but now I'm not sure it wasn't due to a dodgy ESC?

I've checked the resistance between the wires on all of them, and they fall between 0.4 and 0.6 ohms-ish. Is this OK, and might the problem lie elsewhere e.g the ESC?

The symptoms are jittering oscillations and rapid heating up. I was thinking maybe an ESC has inadvertanly had the timing set wrong.

Motors in question are HK S-Line1612 3200Kv, HK Park250 2200 Kv, and I think a HXT 10g motor.

#2 Odysis Dec 07, 2012 11:04 PM

How are you checking the resistance? It should be in the thousanths of ohms - not something a multimeter can easily measure, so don't even try!

Have you tried with another ESC? It sounds like a broken phase wire, a dodgy solder joint, popped FET. Something with one phase not working. Given it's on all 3 motors, I'd suggest the ESC or joints are worth looking at.

#3 C₄H₁₀ Dec 07, 2012 11:29 PM

First, stop. Don't keep trying to run the motors or you'll fry the ESC. The jittering-not-spinning condition means that only two of the three phases are connected to the ESC, which is only about half a step shy of a dead short across the leads.

Next, go over any bullets and solder joints to make sure none are loose. Sometimes you can't actually detect a damaged joint, especially with bullet connectors covered in heat shrink, so you have to sort of get your hands dirty to find out. I generally just recommend resoldering them to be sure.

If all the motors have been crashed, then there IS the possibility that they have damaged connections somewhere, possibly in addition to the ESC. Again, check the bullets, and also check where the leads enter the motor to make sure they're not broken down there at all. The 10-gram HXT motor would be a particular suspect as the wiring in those motors is like cheese.

#4 FlyBoy20 Dec 08, 2012 10:00 AM

Quote:

Originally Posted by Odysis (Post 23471485)
How are you checking the resistance? It should be in the thousanths of ohms - not something a multimeter can easily measure, so don't even try!

Have you tried with another ESC? It sounds like a broken phase wire, a dodgy solder joint, popped FET. Something with one phase not working. Given it's on all 3 motors, I'd suggest the ESC or joints are worth looking at.

I did use a multimeter, don't know any other way...I also checked the resistance with another working motor, an 1850 Kv on the Radjet - with the same sort of readings?

Anyway, I did resolder the joints on the HK Park250 and now it seems fine. Probably will be the same with the other, but these tiiny wires are a nightmare.

#5 Odysis Dec 08, 2012 08:16 PM

A multimeter is really only good for 0.1ohm, and even then not all. My $5 cheapy measures a dead short as 0.6ohms!

A milliohmmeter is a special device, capable of measuring down around 0.001ohms.

Good to hear you found the issue with one, hopefully the rest are just as easy.

#6 flydiver Dec 08, 2012 08:58 PM

Those small motors break wires easily.
Broken, bad connections, or shorted leads show the symptoms you describe.
Attempting to run them for very long WILL fry your ESC.
Then you can't tell what is wrong.

#7 jackerbes Dec 09, 2012 07:26 AM

Quote:

Originally Posted by Odysis (Post 23478326)
A multimeter is really only good for 0.1ohm, and even then not all. My $5 cheapy measures a dead short as 0.6ohms!

A milliohmmeter is a special device, capable of measuring down around 0.001ohms.

Good to hear you found the issue with one, hopefully the rest are just as easy.

But it is better than nothing for checking motors.

I use a non-RMS old Fluke (79-II?) and it will do the same thing (showing the resistance in the test leads) but that can be a good thing. I see the 0.6 between the leads, then check a winding and it should be about the same, maybe a little higher. And if the readings are not the same and steady you can spot a bad or intermittent connection.

I can zero on the leads also and it will give me a 0.0 on shorted leads.

Jack

#8 FlyBoy20 Dec 09, 2012 08:32 AM

Quote:

Originally Posted by jackerbes (Post 23480993)
.I use a non-RMS old Fluke (79-II?) .

Mine's a 25-year old RS Fluke 75 digital (from Radio Shack?) which reads to 3 decimal places. Brilliant piece of kit, but a set of croc clips would be handy as well as the supplied probes.

#9 jackerbes Dec 09, 2012 09:09 AM

I've promised myself that someday I'll get me a RMS meter...

Jack


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