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Old Jun 16, 2011, 03:30 PM
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Lee's Summit, MO USA
Joined Jan 2001
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Originally Posted by KC Flyer View Post
Speaking of smoking, my Radio Shack 26 ga wire finally gave out. I was flying in very strong winds yesterday way downwind above a forest of trees when the motor went quiet only a couple of minutes into flight. Luckily I was high enough to go into a dive and get back to field.

I probably had at least 60 flights on this rewound motor. But I had recently noticed that the green insulation had turned copper color in some places.

After I landed I gave it throttle and prop would turn and hesitate then turn some more. A few seconds later the magic smoke came out. When I tested with an ohm meter, one of the motor leads was shorted to the stator.

I had a little scare when I stuck an unmodified motor on last night and the ESC just kept beeping. I thought the ESC was toast too. But I just had to reset the throttle range and all was good. Flew a flight this morning and worked well - just not as much power with 12 winds.

I just put in an order for some Microdan 24 ga wire that is supposed to be good for up to 300 C (572 F). Will keep you posted.
The MicroDan rewind works great with 9 turns - maybe a little too good!

With fully charged batteries, I got 14k rpm with the HK 7x6 prop. But also 33 amps out of my HK SS 25-30a ESC. After the batteries drained down a little was still getting 13,200 rpm at 10.6v.

Was really windy this morning but took it to the field anyway. Great unlimited vertical and really quick rolls. Motor was cool even after a spirited run. Flight time shorter and ESC/battery a little warmer than usual.

I did notice that the motor stuttered at 11,500 rpm with prop on but not at any other speeds. Prop was balanced so I tried a different rotor (bell) and bearings but same problem. Then I changed the timing from medium to high and the problem went away.

Here are a few performance numbers below with HK 7x6 prop (the Kv values were calculated by putting 2 pieces of electrical tape on the rotor with no prop, then taching and dividing by voltage):

Stock: 1480 Kv, 11,400 rpm @ 11.2v & 16a
RS 26ga/10T: 1780 Kv, 12,400 rpm @ 11.2v & 21a
MD 24ga/9T: 1975 Kv, 13,200 rpm @ 10.6v & 27a

Here are a couple pics. The first is the stator with burned out RS 26 ga wire. The second is the same stator with MD 24 ga wire. It was hard to fit 9 turns on it. On the third tooth (out of 4) on each piece of wire, I used 8.5 turns which I later learned is equal to only 8 turns (only a full turn counts).

If you want to rewind a stator with 10 turns, I would use MD 25 ga wire to fit it all in and do 10.5 turns on the 3rd tooth. This should last much longer than 26 ga Radio Shack wire.
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