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Old Nov 27, 2007, 12:25 AM
Dave North
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hexTronik DT750 Brushless Outrunner 750kv

Okay, I laid out the big bucks and got one of these new big motors from HobbyCity DoNotSayUnitedHobbiesOrGetSuedByJerkCo. You can see their specs at:

http://www.hobbycity.com/hobbycity/s...idProduct=6247

First, I'll toss out some numbers at you. The Kv computed out to more like 800 than the 750 indicated, but this should not be a surprise. The stator was probably supposed to be wound with 18 Turns of 8-strand 34swg wire, and indeed five of the teeth were. However, those other three proved a little challenging for our overworked winding slave, so they settled for 17, 16 and in a fit of pique, a mere 15 turns on one tooth. So I got a little bit "hotter" wind than intended.

Nevertheless, here are the stock numbers with Rod Badcocks calculator giving the thrust and percentage figures. The thrust is very close to what I observed on the stand, so I'll concur with those numbers.

Hex DT750 Stock 8strand 34swg ~18 Turn

GWS 10x4.7sf TP 1320 3S:
7210 rpm @ 10.76v/13.96a 962 grams 34 oz/thrust 83.9% Efficient
APC 11x4.7sf TP 1320 3S:
6446 rpm @ 10.5v/17.3a 1218 grams 43 oz/thrust 81.6% Efficient

Make of that what you will, it's quite good compared to almost everything else I've tested with those props, but weighs about .7oz more, so that should be no big surprise. What is surprising is it does so well with random winding. Makes me curious what it will do if wound somewhat properly.
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Old Nov 27, 2007, 12:33 AM
Dave North
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It sounds a little like a bag of rocks -- well, not _that_ bad -- perhaps due to the curious idea of putting a 4mm shaft into an 8mm bearing tube. The bearings are a bit on the wimpy side, and there is a bit of play. I don't think you'd mistake this for a "hefty" bit of construction. Oh, and the 4mm shaft is threaded in a weird throwback to the GWS 400-series gearboxen.

Stator is about 34mm x 7mm, give or take a shade. Weight is about 2.7oz. The stator wiring had some goop at the outer edges, but unwinding it was not overly difficult.

Now I have to plan out a wind. The stock wind should be roughly equivalent to 18 turns of 22-gauge, which would be trivial except I'm almost out of 22awg wire.

I gave a tentative test to the idea of using 20-gauge, but it looks like that's a 14-to-15-turn variant, which might be okay since I'm interested in pumping up the Kv a bit. On the other hand, that might be more than I want (rpms tend to go up with thicker wire even if Kv stays the same). So I'll mull around the idea of going 21awg if it looks like I have enough left.

Another interesting thought is trying 30-some-odd turns of 24awg doing a parallel wind. But I'm not sure I have enough of that left either! Tons of 20g, pity that looks unpromising. Going Wye would work easily, but that's hardly any gain on the original wind. Maybe 19awg Wye 10-11 turns? I hate doing the Wye "common tail" with wire that thick...


Dave
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Old Nov 27, 2007, 06:17 AM
jj1
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Surprisingly good efficiency on that original wind..
Was the original wye or delta terminated?

If those are your magnet wires listed, would go to the parallel wind ...
but if thick wire is no problem why not that 11T,Y, 19awg.. hmm..choices are endless..

Really love to hear how it turns out, specially how much more copper you are able to squeeze in comparing that factory made multistrand.

-JJ
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Old Nov 27, 2007, 11:04 AM
Dave North
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Duh on me! Delta for the original wind. 11T 19awg would be a reasonable shot, wouldn't it? I'm pretty sure it would go, and sometimes I see improved efficiency from Wye (though usually on thinner wire. And that's kind of a random result that I find unconvincing).

Here's a shot of the stator. The black blob to the left is the nice mount, and in the back is a standard 2205 stator for reference. The scale is inches, alas. I really do need to get a mm scale sometime...


Dave
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Old Nov 27, 2007, 11:35 AM
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One economic remplacement for E flite 480-920.
http://www.rcgroups.com/forums/showt...ght=blue+motor

I like this motor.

I thing that one APC 12x6e is a good choice
and 6446 rpm is over rpm for APC 11 x 4.7

Manuel V.
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Old Nov 27, 2007, 02:16 PM
Dave North
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You're probably right, Manuel. But the only plane I've got that could even dream of using this motor is an old slimer Pitts I'm restoring for my wife. I think the biggest prop it can tolerate is 10" unless I want to rebuild the landing gear too. It will probably end up around two pounds, so saving some battery weight by driving the amp draw down and efficiency up is probably a win.

But I'll have to go 10x4.7 or maybe 10x7. I've never been able to get an APC "e" prop to balance. What's the trick?

I did get some 22awg from HSC (finally got some wire stock in) so I'll be able to start with a simple reference wind. Wonder how it will run with 18 turns on each tooth...?

Dave
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Old Nov 27, 2007, 03:21 PM
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Timocharis.

Anyway. This is a great engine for only 11 dlls.
With great power and weight.
A Blue wonder with steroid.

I need to buy the mine. Prior to the end after your data in in thsis. They will fly.


Manuel V.
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Old Nov 27, 2007, 10:00 PM
Dave North
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Impervious to poor winding

18T 22awg is really easy; a coffee-break wind (see pic). The test results indicate I got their wire right, but they also indicate that a few missed turns make almost no difference at all. Check out these numbers:

Hex DT750 22awg 18 Turn
Kv 9504/12.11 = 785 i0=1.63a PeakEffCalc = 780

GWS 10x4.7sf TP 1320 3S:
7237 rpm @ 10.92v/13.9a 970 grams 34.2 oz/thrust 84.0% Efficient
APC 11x4.7sf TP 1320 3S:
6666 rpm @ 10.6v/17.4a 1227 grams 43.3 oz/thrust 81.0% Efficient

That's so close to yesterday's overall results it's ridiculous. Slight decrease in IO and Kv, as expected. But who cares?

Just for ducks I threw in an APC 11x3.8:

APC 11x3.8sf TP 1320 3S:
7122 rpm @ 10.86v/14.7a 1109 grams 39.1 oz/thrust 93% Efficient

How about that efficiency? I suspect it's time to look at that prop database again...

So, mostly a waste of time other than to learn that I had the winding and wire right. Fortunately it's so easy that very little time is involved.


Dave
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Old Nov 27, 2007, 10:25 PM
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Dave.

Beautiful motor.

Why not wound so the Chinese?

Manuel V.
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Old Nov 28, 2007, 12:29 AM
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Good Question Manuel

The air gap looks biggish , and the lamination thickness ?
Nice long poles
I suppose LRK is out of the question , oh I forgot that the magnets are too close together for that ,

nice winding
Only thing I dont like is that those bearings will have tiny balls,
wonder on the bearing quality,
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Old Nov 28, 2007, 03:45 AM
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Regarding APC, e Balance

Quote:
Originally Posted by timocharis
You're probably right, Manuel. But the only plane I've got that could even dream of using this motor is an old slimer Pitts I'm restoring for my wife. I think the biggest prop it can tolerate is 10" unless I want to rebuild the landing gear too. It will probably end up around two pounds, so saving some battery weight by driving the amp draw down and efficiency up is probably a win.

But I'll have to go 10x4.7 or maybe 10x7. I've never been able to get an APC "e" prop to balance. What's the trick?

I did get some 22awg from HSC (finally got some wire stock in) so I'll be able to start with a simple reference wind. Wonder how it will run with 18 turns on each tooth...?

Dave
I have found the hole to be crooked and way off on some , I have not checked for different blade thickness though , I just put the prop up on a milling machine and put in an enlarged hole in,,, on centre , then just make a bush to make the hole smaller , lot of work ,
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Old Nov 28, 2007, 04:08 AM
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Quote:
Originally Posted by timocharis
18T 22awg is really easy; a coffee-break wind (see pic). The test results indicate I got their wire right, but they also indicate that a few missed turns make almost no difference at all. Check out these numbers:

Hex DT750 22awg 18 Turn
Kv 9504/12.11 = 785 i0=1.63a PeakEffCalc = 780

GWS 10x4.7sf TP 1320 3S:
7237 rpm @ 10.92v/13.9a 970 grams 34.2 oz/thrust 84.0% Efficient
APC 11x4.7sf TP 1320 3S:
6666 rpm @ 10.6v/17.4a 1227 grams 43.3 oz/thrust 81.0% Efficient

That's so close to yesterday's overall results it's ridiculous. Slight decrease in IO and Kv, as expected. But who cares?

Just for ducks I threw in an APC 11x3.8:

APC 11x3.8sf TP 1320 3S:
7122 rpm @ 10.86v/14.7a 1109 grams 39.1 oz/thrust 93% Efficient

How about that efficiency? I suspect it's time to look at that prop database again...

So, mostly a waste of time other than to learn that I had the winding and wire right. Fortunately it's so easy that very little time is involved.


Dave
Dave
On the contrary , not a waste of time , from my point , one point is that amazing same result , data wise
Whats your opinion on heat shedding , will the birds nest shed heat better than the 22g or not , I would go for the 22G, someone will know this
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Old Nov 28, 2007, 11:08 AM
Dave North
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I guess my take is heat just isn't going to be much of an issue. PeakEff thinks the motor as it stands is fine to 18 amps and my impression is that's correct. I also suspect anyone who feels the need to push harder might want to consider blowing a little more than $11. I'd feel comfortable running in that range.

Hey, Manuel: I finally got an "e" prop to balance! All it took was patience and a hand drill. Wow that thing was wayyyy out.


Dave
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Old Dec 06, 2007, 03:11 PM
Dave North
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So far all I've learned is 15-turn Delta and 16-turn Delta (both 21 awg) show considerably less efficiency than the 18 Turn. Okay results, but nowhere near as good.

Weird. One more experiment (9 or 10 turns Wye to see if that makes any difference) and I'll just put it back to stock. Messing with this motor has been extremely unproductive!


Dave
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Old Dec 06, 2007, 03:55 PM
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Timocharis.
That data got these windings and propeller used.
I will dare to infer a bit about these windings. Only theory. Since I had come to test my motor.


It is clear that this motor in the area of 185Watts input gives us an efficiency above 80%.
If rewound to 15 o 16 turns delta. Give us a Kv. About 936 and 837.
To continue to sustain the level of efficiency, I think we should continue in the range of 185Watts input. And in that case for the 936kv, 15T. A propeller APC 10x5 and GWS 10x6 would be very small. And a APC 11x5.5 or APC 10x7 be very large. In this range of any type SF us serve as RPM exceeds limits. Since it be run around 8000rpm. In any case, insisting, only one APC 10x4.7.
With 16T delta and 837kv. A propeller APC 11x5.5 be run in rank. The GWS 11x7 be very large.

For more of this engine is needed to push a level of 70% efficiency.

Manuel V.L
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