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Old Aug 06, 2009, 09:44 AM
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Excellent wind Dave; as usual, pushing the boundaries out one more turn. I think the extra 1.5oz thrust and a smooth ride is worth a few efficiency points.

Cheers,
Kev
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Old Aug 06, 2009, 02:51 PM
Dave North
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Yeah, but I wanted it all!

Oh well.



Dave
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Old Aug 15, 2009, 05:37 PM
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Quote:
Originally Posted by timocharis
It's fine! Especially when you consider that you're overdriving it hard with that battery. 76.5% efficiency with an 8040 at that power level is hunky-dory. Try a smaller battery (or the same one when it's a bit tired) and the watts are closer to 100 and I'll bet it snicks up a few points.

Dave
Sorry fot the newbie-ish question, but I don't understand the above post. I know, for any given aircraft, you need to pick a battery that will supply the appropriate voltage and current for the motor/prop combo, without adding "too much" weight, but I thought that keeping the battery as "small" as possible was for keeping the wing loading low.

You can put "too much" battery on a motor? I don't understand how "too many" mah can be bad for a motor.

Is it that you're pushing the motor to the thermal limit, and relying on voltage sag to keep the temps down?
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Old Aug 15, 2009, 06:40 PM
Dave North
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Quote:
Originally Posted by carlsoti
You can put "too much" battery on a motor? I don't understand how "too many" mah can be bad for a motor.

Is it that you're pushing the motor to the thermal limit, and relying on voltage sag to keep the temps down?
Not really. The battery's voltage will sag as the amp load comes up. If a motor runs well at, say 10.8 -> 11.2 volts (the amps will adjust accordingly; as your voltage goes down the amps go down too) you may well get that voltage range by using, let's say, a 610 3S.

So you think, "yeah, I can get more power if I can hold voltage higher" ... and you put on a 4400 MAH battery. Now the load is next to nothing on that triplet of cells and they hold 12 volts, which drives the amps up to (just guessing) about 1.6 where they were.

Now you're in a whole different power band, probably getting way over the .70 ideal of unloaded rpm. More power comes out, but efficiency drops. It's not that the windings are necessarily getting all that hot, it's just that you're out of the appropriate rpm/load range for the motor. You may or may not have serious thermal problems, but going too far over the ideal rpm will always cost you in terms of efficiency. For practical reasons, we always do, but moderation in all things!

Short answer: yes, you can overbattery a motor.

Heck, that's easy to figure in an absurd case: let's say you get an unloaded rpm of 100000 @ 12.3 volts. Now you put a battery on that is so huge it holds 12.3 volts and drives the motor almost up to 100000 rpm with a prop on it. You're way past the efficiency range, and probably getting to the point where you do have thermal problems. Zzzzzt!

Try hooking up a blue wonder to your car battery sometime and watch what happens. But don't watch for long. Well, you probably won't in any event, but if you want the motor to survive ...


Dave
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Old Aug 15, 2009, 07:13 PM
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Ok. That makes sense. Thanks, Dave!
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Old Aug 15, 2009, 10:13 PM
Dave North
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Design Parameters

Incidentally, that's why I don't use some standard big battery or a power supply to test. I use batteries that I think would be appropriate to the motor (for weight considerations; what's the point of getting a 24-gram motor and sticking it on a plane with a 3oz battery?)

That way we find out what the puppy will do as a power system rather than as a pure expression of motorness. The latter has its place and can be very useful, but just about everybody does that. So I do "real world" testing. Partly because, ya know? That's what I'm interested in.


Dave
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Old Aug 16, 2009, 09:41 PM
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Has anyone done a really "hot" wind on the 16 magnet ABCABC wound 2730?

I'm asking because I've wound one of mine to use as a replacement micro heli motor in a Eflight Blade CP with 15.6:1 gearing. I trying for a lighter motor\battery combo on this heli and I'm not sure if the BW can handle the RPM.

I've wound it with 6 turns of the heavy RS wire, which I think is 20 gauge? It's terminated wye for now as I was worried it might be too hot. I'm shooting for about 3800kV. It was one of most problematic winds I've done, I wasted a lot of the RS wire because it wouldn't pack in tightly without shorting, very fragile insulation.
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Old Aug 16, 2009, 10:46 PM
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Quote:
Originally Posted by Looooeeee!
Has anyone done a really "hot" wind on the 16 magnet ABCABC wound 2730?

I'm asking because I've wound one of mine to use as a replacement micro heli motor in a Eflight Blade CP with 15.6:1 gearing. I trying for a lighter motor\battery combo on this heli and I'm not sure if the BW can handle the RPM.

I've wound it with 6 turns of the heavy RS wire, which I think is 20 gauge? It's terminated wye for now as I was worried it might be too hot. I'm shooting for about 3800kV. It was one of most problematic winds I've done, I wasted a lot of the RS wire because it wouldn't pack in tightly without shorting, very fragile insulation.

These are the windings of interest, according to the turn calculator:

6T-Y : 2884 RPM/V
6T-D : 4995 RPM/V
8T-D : 3746 RPM/V

8T delta would probably be 22awg, which RS also carries. I agree with you about RS wire. It's not all bad, but it is fragile, and 20awg is some thick stuff. I like microdan wire, but my favorite was given to my by my local motor repair shop.

Cheers,
Kev

[edit: Sorry, the above numbers were for 14 magnet DLRK. Here's the correct numbers for 16 magnet ABCx4:

6T-Y : 2917 RPM/V
6T-D : 5053 RPM/V
8T-D : 3790 RPM/V

One thing to keep in mind is outrunners like to run more torque than inrunners, so for helicopters this usually means taller gearing and lower Kv. Lets see, you'll need a max headspeed of about 2,200RPM, and with 15.6 gearing the motor will need to spin about 34,320RPM. I've only run these motors to 22,000RPM, so I don't know if it can handle what you'll be asking of it. I run a Himax 2015-4100 with 8T on my BPC. The tail can't handle much more power, and it only draws 4A hovering, 6A @ 10+ collective.]
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Old Aug 16, 2009, 11:15 PM
Dave North
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Not bad, Kev! My Hex 6T Wye 22awg had a Kv of about 2850. Delta would doubtless be too hot. I'm not sure if 8T 22awg would work (I know 9T 23awg will). There's room in the stator, but the front clearance is getting really persnickety even with the 23 awg. Oversmooshing can lead to insulation cuts so ... it would be a tough one. My 6T is a single layer and looks tres kewl:

http://www.rcgroups.com/forums/attac...mentid=1946845

The balance on a good can is probably okay to hold high rpm, but I'd put a little thought to the bearings. I have no idea of the quality of the shipped units, and a little visit to Boca might be in order.

Dave
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Old Aug 17, 2009, 06:00 PM
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Quote:
Originally Posted by timocharis
Not bad, Kev! My Hex 6T Wye 22awg had a Kv of about 2850. Delta would doubtless be too hot. I'm not sure if 8T 22awg would work (I know 9T 23awg will). There's room in the stator, but the front clearance is getting really persnickety even with the 23 awg. Oversmooshing can lead to insulation cuts so ... it would be a tough one. My 6T is a single layer and looks tres kewl:

http://www.rcgroups.com/forums/attac...mentid=1946845

The balance on a good can is probably okay to hold high rpm, but I'd put a little thought to the bearings. I have no idea of the quality of the shipped units, and a little visit to Boca might be in order.

Dave
Well the motor seems to have hit it's RPM limit with the present gearing, I'm running it on a Castle Phoenix 10 guessing that I'm close to the 3000 KV rating for wye, the head speed won't go faster than about 1800, It runs a little warm, I should expect that considering it's a pretty hot wind.

The can is fairly straight on this and the bearings at speed are quiet. It's the damn ABC whine as it spools up, it hits a certain resonance just below where the Castle's light comes on for full speed. I'm going to look for some 12 and 13 tooth pinions to see if I can get the head spun up faster. It's drawing very little current with the present gearing, so I think I've got more head room for reserve power.
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Old Aug 18, 2009, 08:11 PM
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You're on the right track. Standard setup for BCP 3D is 4100 RPM/V and an 8 tooth pinion. Some quick and dirty math tells us: 4100*8/3000=11, so 11 tooth would give roughly equivalent headspeed with a 3000kV motor. FWIW, the 3mm ID 0.5M pinions you'll need are somewhat hard to find, but you're in luck with the 11 tooth. The Blade 400 uses 3mm ID 0.5M pinions, and Eflight makes an 11 tooth for it (helihobby has several to choose from). ***OOPS edit*** I just realized the B400 has a 2.3mm stepped 3mm shaft, and Eflight pinions are 2.3mm. I also found that helidirect has the 3mm 0.5M pinions you want:

http://www.helidirect.com/motor-pini...c-1_78_513.hdx

Overheating is a chronic problem with these little CP machines. My Himax 4100 with 8 tooth & 3s730 gets too hot to fly longer than about 4min before I need to land and cool off. I used to have a nice heatsink, but then I noticed how much weight counts with 3D. You're rewound motor should be nice and light compared to the standard setup, and should easily handle the ~80W you'll be asking of it. The only question I would have is how long will those cheap bearings last? I'd get some Boca's (3x7x3mm), since you'll probably need them in the near future.

Cheers,
Kev

[Edited to avoid confusion between turns and teeth when using "T".]
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Old Aug 21, 2009, 04:22 AM
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Trug

Keep it coming,, Im thinking along the line of a GWS, ducted fan for my Red Wonder

Im addicted to this one // I have to fly it all the time on 2 cells
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Old Sep 08, 2009, 10:27 PM
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Newbie question

I tried my first rewind this weekend, and I had a question about how to count turns. This is for a regular ABC wind with each start and transit on the bearing tube side. Winding clockwise with counterclockwise transit would seem to give an extra half-turn compared to winding clockwise with clockwise transit. Does this half-turn count? In other words, does the attached picture illustrate a 2 turn wind or a 3 turn wind?

Also, is one of the transit directions generally preferred for an ABC wind?

Sorry this is a bit off topic. At least it is a blue'n'red wonder :-)
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Old Sep 08, 2009, 10:50 PM
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I think you're right on topic actually. It is an R&B wonder, and you are rewinding it.

What you have there is a typical 3 turn ABC wind. The best way to count turns is look at the front; you should clearly see 3 wires up front with your wind.

I suppose you could wind the other direction and loose 1/4 turn (wraps 3 sides out of 4, so it's 1/4 vs 1/2, which would transit in the front), but I haven't done that before. As long as all poles are done the same it should work; the magnetic field would reverse direction, but simply swapping 2 esc wires should fix that like usual. I'd be willing to bet Dave, Manuel, Ron, or Vintage could illuminate this subject for you.

Cheers,
Kev
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Old Sep 08, 2009, 11:26 PM
Dave North
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Quote:
Originally Posted by Truglodite
I suppose you could wind the other direction and loose 1/4 turn... it should work
It does, sort of, and it's popular with manufacturers for some reason. However, it has a nasty downside: the start and end of the transit wire want to get closer to the adjacent tooth rather than the tooth you're winding. This puts a bit of electromagnetic goodness into the wrong tooth, which 1/2 the time is actually working counter to the motor's motion. The "real cost" I've measured in winding experiments is about 1/2-turn and one point of efficiency.

In other words, it works much the same way the common cold "works." Avoid it.


Dave
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