Discussion Turnigy 3020 22-mag 24-tooth Rewinds

[timocharis]

A few of us have started fussing with these motors lately so it's time to start a thread. The impetus seems to be a recent "sale" at UnitedHobbyCityKing which is still on at this moment. You can see the stock motor BS here:

http://www.hobbycity.com/hobbycity/s...idProduct=9378

It's obviously bogus specs as usual. If you put a 9x4.7 prop on this 2S it would probably draw about twice the recommended max. An 8040 draws way over their limit. Here's the numbers for the stock motor:

Rm = 0.168
Io = 0.61 @ 7.98 volts
Kv = 1966
With 8040 prop and 2-cell battery, it produced 9253 rpm @ 7.44 volts and 10.70 amps. Badcock calls that 435 grams (15.3 ounces) of thrust @ 62.9% efficiency. Drive calc gives it 477 grams (16.8 ounces) @ 65.4% efficiency. In other words, pretty poor compared to a typical blue wonder, which has almost exactly the same weight.

It was wound with groups of four teeth in each phase, 9-10-9-10 turns to get a 9.5 average. Since there are 22 magnets and 24 teeth, there is no option save to do groups of four. 22 cannot be divided by four, so two-tooth phase setups are simply not possible. The motor as designed gives less cogging, but at the cost of phase-angle error. I do not know if it's a wise decision, but I do know it's very limiting as regards winding methods.

The motor is notable for having some resemblance to the Neutrino, a smaller lighter weaker motor that also has 24 teeth. Some components may be from the same manufacturer. However, there is almost no technical resemblance beyond the tooth count and some superficial looks. This motor is bigger and has 22 magnets rather than 26 (I think it's an inferior decision). Curiously, this one has better build quality than the Neutrino I saw, but the Neu was a proto supposedly.

They both share the characteristic of being underproductive for their size and weight, and having poor efficiency -- only in part due to humdrum winding.

[timocharis]

After running the numbers I decided one more turn would calm the motor down and might move it into a more efficient range. Of course, using thicker wire would be good too. The stock wire is probably 29 gauge, but might be 30. It's hard to be sure when it gets that thin.

Having decided that, I needed to locate the wire and winding technique. I wanted to use 26 gauge, but it just wouldn't happen. So down one, and it was fairly easy to find a system that would allow 11 turns of 27-gauge.

Here's the first stage, where I wound the motor as a simple 8-turn on the first layer. This is done by going up the first tooth, down the second, up the third, and down the fourth. Early transits waste too much space, and there's none to spare in these tiny slots. If you look closely, you can see the wire running across the top of the slot on the outer transits.

[timocharis]

Then I work back to the original starting point, adding the final 2 or 3 turns. After some mulling, I decided the four-tooth blocks should be wound 10-11-11-10 so everything would even out between the adjacent phase groups:
[10-11-11-10][10-11-11-10]
... and it's all about two matching teeth all the way around the motor. I don't know how much or if this matters.

This uglifies things, but that's fairly normal when you have only a few wires on the last layer.

[timocharis]

So there it was. The motor sounds good and runs very smoothly. However, even with the wire upgrade, the running results were fairly poor from an efficiency standpoint. Using a slightly flabby 2S battery and the same GWS 8040 prop I got:

9222 rpm @ 7.34 volts and 9.72 amps.

I give up 32 rpm, but gain back an amp. I consider that a good trade, and Badcock agrees, allowing that as 432 grams (15.2 ounces -- 0.1 less) of thrust and 69.4% efficient, a 6-1/2% improvement. But still pretty bad.

Vitals: Kv=1805 Io=0.61@8.05v Rm=0.142

Overall, I suspect these motors have just about nothing going for them in the 25-or-so gram category. They simply can't keep up with even the old Blue Wonders. I suspect there's more to designing a good 24-tooth motor than meets the eye, and neither Turnigy nor Neu have managed it yet.

[rich smith]

Thanks for doing that evaluation Dave. Saved me a few bucks. I'm losing my infatuation with high tooth count and going back to the RBW for now.

[timocharis]

Yer welcome. At least it was kind of fun in a self-torturing sort of way. I might even try a 3S version based on Lance's results, or not. Might be tolerable, though I doubt it will ever be competitive.

Here's a funny aspect of the whole thing: the Sinomotorherd have finally designed a motor with adequate clearance for the windings. The ironic aspect, of course, is they did it on a motor with such tiny slots that it's impossible to get a thick winding head. So it's just added weight for no reason at all.

Good to see that design and management are no better over there than they are here.


Dave

[rich smith]

In addition to poor stator design I'd like to see bells trimmed down too. For weight watchers like me they are a major disappointment. Instead of thick aluminum shells it would be nice if they'd go back to thin steel like on the old Gobrushless 12n 25mm CD-ROMs. I haven't been able to match those yet in terms of weight and efficiency.

As Rosanne Rosannadan used to say: It's always sumpthin'.

[timocharis]

Originally Posted by rich smith

12n 25mm CD-ROMs. I haven't been able to match those yet in terms of weight and efficiency.

They still win for weight, but not efficiency. The B&Rs do better power-to-weight (but then even larger motors have always done better, so no revelation there. Those grams add up though ...)


Dave

[rich smith]

Originally Posted by timocharis

They still win for weight, but not efficiency. The B&Rs do better power-to-weight (but then even larger motors have always done better, so no revelation there. Those grams add up though ...)
Dave

Sorry, what's a B&R?

[timocharis]

My bad. The new Turnigy Blue & Red Wonders. Same weight, more stator, thinner lams. You end up with 25-26 grams, depending on the weight of copper crammed on.


Dave

[rich smith]

Originally Posted by timocharis

My bad. The new Turnigy Blue & Red Wonders. Same weight, more stator, thinner lams. You end up with 25-26 grams, depending on the weight of copper crammed on.

Of course! I know them as RBW or maybe R&B. I've purchased dozens.

In my experience the GB 25mm result in 14 gram motors with significantly better thrust/watt than stock RBW. I haven't rewound the RBW but from reading your results still put my money (all $1.80 worth) on the GB. Only drawback is the GB has to be built and it's quite a pain what with the CF shaft and CF tube.

Even though stock RBW IMO has less thrust/watt and weighs twice as much I still use them as my main motor. Only for very critical long range flights of my solar UAV do I risk the GBs. RBW rulz!

[timocharis]

Hmm. That looks like a cut-down stator and bell, too. Not sure I've seen that variant and I'm positive I haven't built one! Looks like some serious wire smooshing.


Dave

[lance dalton]

A 3020 thread started by Dave....COOL!!!

Ramped up the 3020-1200. Used a Rhino 610 3s right off the charger. Slowly ramped the throttle on each run.

8x4 DD
9630 rpm
11.45 V
7.13 A
69.4% Effec.

Also tried a 9x5 but it was making a funny sound and only managed.

9x5 DD
7260 rpm
11.24 V
9.94A
Very Bad Effec. @ about 47%


Lance

[timocharis]

Starting to look like it's a 70% motor, huh? Oh well.


Dave

[mikebergy]

This may sound totally stupid, as I am no motor builder, but could you set this motor up as two dLRK windings that are offset 120 degrees to each other??? That probably doesn't make the least bit of sense to anyone that knows how the magnet counts and phases work with each other, but I was just kinda brainstorming as a way to wind this. I'd guess that inorder to do it the way I'm thinking of (if it could even work...), you have to have 28 magnets (14mag x 2)... I don't know. I still have to look at winding schemes for the normal 12 tooth dLRK windings, so please educate me as to what the most ideal mag setup with this stator would be - I also wonder how hard it would be to get the magnets reset. I have one of these motors, and would love to play around with it. Worst case scenario - I am out $14. LOL. At least I didn't pay for a neutrino. I'd spend my $$$ on a MicroDan long before then.