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Old Sep 29, 2012, 01:49 PM
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Help!
Hextronic 5g 2000kv motor: advice needed

I bought a new Hextronic 5g 2000kv motor from HobbyKing and tested it with two ESCs :
-HK 6A with 2s, 3s LiPo battery
-HK Blue Series 30A with 3s LiPo battery
They both can run the motor without propeller but have difficulties starting the motor with GWS propellers: the bigger the propeller the more difficult the motor starts.

Suspecting that there is a problem with the motor, I measured the resistance of its windings and found:
-1.9, 2.8, 2.8 Ohm
Then, I stripped the isolation from windings terminals and cut and tinned the wires coming from the motor.
The resistance of its windings then was:
-0.9, 1.3, 1.8 Ohm (not in the same order)
The residual resistance of the multimeter is 0.5-0.6 Ohm.

1. Whoever prepared the terminals did a very poor job: he/she soldered poorly some wires to the windings, put on some shrink wrap and called it a day !
2. The motor windings have hugely different resistances which leads to me to believe the windings are bad.

To the people with some experience with motors: is there some other test I should do ?

Or should I write this motor off as bad and maybe send it back to HobbyKing and ask for a replacement ?
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Old Sep 29, 2012, 02:27 PM
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Check its unloaded rpm to see if the kv is way off.
Check the unloaded current.
Turn the motor with a drill press and look at the generated waveforms on an oscilloscope or measure (ac) with your meter.
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Old Sep 29, 2012, 02:52 PM
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San Jose, California
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have you tried different timing on the ESC?

I've seen winding jobs where some tooth were over by 3 turns and some were under by 3 turns...so 6 turns difference...But it still ran find. So, Unless they rewound really, really, bad, it would work fine.

I would try the timing thing...some motors just like mid or high timing...and some just don't like the particular ESC.
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Old Sep 29, 2012, 03:09 PM
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Originally Posted by Plantoflap View Post
Check its unloaded rpm to see if the kv is way off.
Check the unloaded current.
Turn the motor with a drill press and look at the generated waveforms on an oscilloscope or measure (ac) with your meter.
I'll try to measure the unloaded rpm. I got a rpm meter from Ebay, but it will be 2-3 weeks until it arrives.
Maybe I can measure it with a microphone connected to a computer or some other improvised way.
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Old Sep 29, 2012, 03:16 PM
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Originally Posted by rcalldaylong View Post
have you tried different timing on the ESC?

I've seen winding jobs where some tooth were over by 3 turns and some were under by 3 turns...so 6 turns difference...But it still ran find. So, Unless they rewound really, really, bad, it would work fine.

I would try the timing thing...some motors just like mid or high timing...and some just don't like the particular ESC.
With the HK 6A ESC, I tried all three timing settings: auto, low and high with no difference.
I'm thinking that the high resistance before I redid the terminals might have impeded the start. I'll try again with the lower resistance terminals.

Taking into account the residual resistance of the multimeter, the windings resistance is:
-0.3, 0.7, 1.2 Ohm
There is a factor of 4 between the first and the last !
I'm thinking that maybe there are shorts inside the windings or maybe the wires are nicked.
It wouldn't surprise me, given the abysmally poor job they did with the terminals.
What else could explain such differences ?

Did anyone measure the windings resistance for this motor ?
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Old Sep 29, 2012, 04:10 PM
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San Jose, California
Joined Dec 2007
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While shorts between wires and the wire itself is possible, it's not likely. More likely just a short from the phase wires to the stator.

To check that, take the motor apart and do a continuity test from the terminal to the stator. There should be 0 or no continuity at all.
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Old Sep 29, 2012, 04:49 PM
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Originally Posted by rcalldaylong View Post
While shorts between wires and the wire itself is possible, it's not likely. More likely just a short from the phase wires to the stator.

To check that, take the motor apart and do a continuity test from the terminal to the stator. There should be 0 or no continuity at all.
Good idea ! Now, how do I take the motor apart ? Sorry for the stupid question, this is the first time I need to disassemble a motor.
It's this motor:

http://www.hobbyking.com/hobbyking/s...idProduct=6312
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Old Sep 29, 2012, 05:09 PM
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Quote:
Originally Posted by flylowfast View Post
Good idea ! Now, how do I take the motor apart ? Sorry for the stupid question, this is the first time I need to disassemble a motor.
It's this motor:

http://www.hobbyking.com/hobbyking/s...idProduct=6312
pretty straightforward. on the back there's a 'c' clip. take that clip off. Make sure you don't lose it. When trying to pry it open, either do it in a white room, or pry it off in a ziploc bag. Once that comes out, the entire bell should slip off.
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Old Sep 30, 2012, 05:08 AM
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pretty straightforward. on the back there's a 'c' clip. take that clip off. Make sure you don't lose it. When trying to pry it open, either do it in a white room, or pry it off in a ziploc bag. Once that comes out, the entire bell should slip off.
Thanks, I did just that and there seems to be no shorts to the stator.
Of course, the windings can still be bad in other ways.
I'll do more tests.
Maybe I'll even unwind the windings to check them, but this would be a bit of work for me since I've never done that before.
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Old Sep 30, 2012, 10:41 AM
Jack
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When you check for the shorts to the stator, put both of the DMM probes (set it for Rx1) on the stator to make sure you have continuity across the probes. Then take one probe off and touch each of the motor connectors. If you see even a flicker or dancing numbers you have a short, it should read open for all three.

If it is reading open you have still not ruled out that you have a bad soldering joint on one of the motor connectors. For that I clip one of the test probes to one of the motor connectors and then touch the other two one at a time. I push and pull a little and wiggle the solder joint (probably invisible under heat shrink). Any flickering or dancing numbers means I'll strip and resolder the connectors. Also wiggle the point where the enter or attach to the motor a little to see if there is a break there.

It is not uncommon to find poor solder joints. Sometimes they will have visible flux residue on them (a white or gray powery substance or maybe a brown shellac looking coating) and under that there may be a bad joint. So I clean all of the original solder off and re-solder all three.

As far as the unwinding, that would be the last thing after you don't find any other problems. If you are lucky the windings will not be glued together, just wound on. In that case you will have to unsolder or cut the terminated groups and sort them into the original six ends (or six groups of ends in a multiple strand wind).

When you get them to that point it is a good idea to check the end to end continuity on each of the three phases. A probe on any one end should find a low (fraction of an Ohm) resistance to one of the other five ends. Those two will be the start and end of a phase. And there should be three pairs all reading about the same with all the end separated from each other.

And if you are going to unwind it is a good idea to count the turns as you do it. I usually count them all if I can just to see if they did a good job on the original wind or miscounted some of them.

And with all the wire off you are ready to start over with new wire! And welcome to the motor rewinding addiction!

5 grams? Not me! Not yet anyway! I have done a 19 gram motor as my smallest so far...

Good luck with it!

Jack
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Old Sep 30, 2012, 11:27 AM
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My smallest has been the bigger brother of that 5gram...the 10gram hextronic. Nice thing is it wasn't glued, so easy taking it apart was a piece of cake and it was also an easy wind. Took me like 30mins to rewind.

If you're going to get the same KV, on that 5gram you're going to need some thin 32awg or thinner wire.


If I remember correctly, on mine I used 28awg and got somewhere around 3000kv.

testing of HobbyKing Hextronic 10g rewind motor (0 min 54 sec)
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Old Oct 01, 2012, 03:57 PM
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jackerbes and rcalldaylong,

Thanks for the advice.

Yesterday I resoldered all the terminals after I stripped the isolation and removed the badly soldered wires. I also added mechanical reinforcement using using a 5mm shrink wrap tube with a strip looped around the stator "leg" and glued with CA to itself.
I also added 0.8mm gold connectors.
Then, I measured the windings resistance and found:
-0.9, 1.3, 1.7 Ohm

Weight of the motor with 0.8mm bullet connectors and their shrink wrap: 8.8g.
Today I had to fix a problem with my transmitter.
Tomorrow I'll retest the motor and see if it can start normally.

If not, the only thing left is either rewinding it or trying to send it back to HobbyKing for a warranty claim.
Looking on the Internet and Ebay, the price of wire for rewinding is more than the price of a new motor (of course I would get enough wire for tens of motors).
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Old Oct 01, 2012, 04:06 PM
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Quote:
Originally Posted by flylowfast View Post
jackerbes and rcalldaylong,

Thanks for the advice.

Yesterday I resoldered all the terminals after I stripped the isolation and removed the badly soldered wires. I also added mechanical reinforcement using using a 5mm shrink wrap tube with a strip looped around the stator "leg" and glued with CA to itself.
I also added 0.8mm gold connectors.
Then, I measured the windings resistance and found:
-0.9, 1.3, 1.7 Ohm

Weight of the motor with 0.8mm bullet connectors and their shrink wrap: 8.8g.
Today I had to fix a problem with my transmitter.
Tomorrow I'll retest the motor and see if it can start normally.

If not, the only thing left is either rewinding it or trying to send it back to HobbyKing for a warranty claim.
Looking on the Internet and Ebay, the price of wire for rewinding is more than the price of a new motor (of course I would get enough wire for tens of motors).
The -0.9 reading makes me think there is a loose connection somewhere in your vom. Use a clip lead to firmly hold the vom electrodes together and twist, shake and poke the lead wires and case, maybe the battery terminals are shot.
George
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Old Oct 01, 2012, 04:47 PM
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I forgot to mention that the residual resistance of the multimeter is 0.6 Ohm.
I measured the windings resistance again and got:
1.7, 1.6, 1.0 Ohm (indicated)
or
1.1, 1.0, 0.4 Ohm (real).
The first two are close, the third one is much smaller.

Does anybody know what the specification resistance is for this motor ?
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Old Oct 01, 2012, 05:42 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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If you are measuring a ABC wind terminated Wye, you are measuring the lengths of the wire in two of the windings when you check any to motor leads. You can see that in the image. If you touch S1 abd S2 it goes in on one and back to you on the other through the Wye bundle. The third phase (S3 in this case) is not seen or measured by the meter, it is just hanging off to the side basically.

Were you able to put both probes on the stator and get continuity and then touch one probe to the connectors? The uncoated ends of the hammer heads is good are to put a probe for that test usually, and a scratch there won't hurt anything.

And as you do the 1-2, 1-3, 2-3 thing you are just checking each pair. If one of the pairs is shorted to the other or the stator it will change the readings on one or morer of the phases. But if one is bad two are bad and all are bad.

Jack
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