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Old Sep 29, 2003, 09:55 PM
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Jefferson, GA
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Brushless terms..What does # of turns mean?

Could someone please explain what it meant by the "number of turns" in relation to brushless motors?

Please explain what this represents or measures, and what the result is of having a higher or lower number.

Thank you,
David J.
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Old Sep 29, 2003, 10:12 PM
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The number of turns affects the RPM per Volt of the motor. The fewer the turns the higher the RPM per Volt, more turns has fewer RPM per volt. The trade off is that the lower turn motor will have less torque, while the higher turn motor will have more torque. In general the difference in torque is not directly proprotional to the RPM/V. That means that lower turn motors will have more torque per RPM, but it's not a huge difference. Another difference is that lower turn motors usually have thicker wire and can handle a little more current, becuase of this they will also have a lower impedance and thus less heat generation at a given power level.

-Jim
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Old Sep 30, 2003, 12:17 AM
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Quote:
Originally posted by Jim McPherson
The number of turns affects the RPM per Volt of the motor. The fewer the turns the higher the RPM per Volt, more turns has fewer RPM per volt. The trade off is that the lower turn motor will have less torque, while the higher turn motor will have more torque. In general the difference in torque is not directly proprotional to the RPM/V. That means that lower turn motors will have more torque per RPM, but it's not a huge difference. Another difference is that lower turn motors usually have thicker wire and can handle a little more current, becuase of this they will also have a lower impedance and thus less heat generation at a given power level.

-Jim
Jim,

I think I understand the general usage of the number of turns in brushless motors. However, what does "turn" refer to? Also, in brushed motor, there is also a reference to "wind". What does "wind" refer to and what is the relationship to "turn"? Does "wind" apply to brushless motor too? Since I don't see "single wind", "triple wind" etc. being mentioned in the brushless world.
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Old Sep 30, 2003, 01:28 AM
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Turn is the number of times the wire goes around the stator tooth (assuming a stator exists). In the car world the term wind is synonymus with turns. Single wind, double wind etc. means that instead of one wire going around each stator tooth there are two (double) or three (triple). The two wires are effectively acting as one, except that because they are actually 2 wires you can fit more copper into a smaller place. Many brushless motors are wired in this manner(my AXI and Mega motors do this) they just are not advertised as such.

-Jim
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Old Sep 30, 2003, 01:32 AM
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Germany
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Turns and winds are the same. In brushless-world it means how many times the wire(s) is/are wound around ONE tooth .
If one won't handle one thick wire, he uses "double" or " triple" wires parallel (each with smaller diameter).
regards
Olaf
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Old Sep 30, 2003, 10:14 AM
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This is great information. DavidJ, I am sorry if it sounds like I hi-jacked your thread but you brought up a question that I never gave any deep thinking of unitl now. And here we go, more questions.

Is it not true that all brushless motors then are single wind? There are only 3 wires coming out of the motor. If they are double wind or triple wind, would you not see 3 sets of double wires or triple wires? If everything else is equal, what do you get or lose with more or less winds?
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Old Sep 30, 2003, 12:19 PM
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Disagree...

Contrary to Olaf's comment...


- "Turns" refers to how many times the wire(s) are wrapped around the armature (or stator in a brushless)

- "Wind" refers to the number of parallel wires that are used carry the current, usually one, sometimes more.


The reality of turn/wind combinations are a bit of voodoo science (particularly in 540-size car motors).

The general rule seems to be that multiple thinner wires (versus one thick one) makes a motor that offers more torque versus higher RPM capabilities.

But, the entire operating "premise" for R/C cars is a fixed-voltage world, utterly different than R/C aircraft.



Perhaps a BL expert can chime in and give us some details?
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Old Sep 30, 2003, 02:02 PM
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aau007: No, many brushless motors have multiple winds however they are all combined inside the wires that you solder to. I am looking at an AXI 2808/24 right now that is double wind.

-Jim
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Old Sep 30, 2003, 03:10 PM
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Does this terminology correlate to the voltage of a brushed motor? I see different voltages for the same size motor like s400 4.8v, s400 6v, s400 7.2v. I understand that a higher voltage motor can handle more cells, the lower voltage motors generate higher rpm per volt but don't know exactly why.
Thanks,
Howard
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Old Sep 30, 2003, 06:44 PM
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Food for thought... (actually very important!)

Here more than you want to know, from the guys at Aveox:

http://www.aveox.com/torque.html


What's very interesting is the statement:

"...Since the construction of the motors are identical, except for the number of turns on the armature, ALL of these motors can produce the same output torque!"



This kind of kills the common "understanding" that there is such a thing as a "hi-torque" or "low-torque" motor. (within a specific range of motors like the Mega 16/15/x, etc)

Really the difference in turns is where that maximum torque point occurs in relation to current (A) going in to the motor, in response to an applied load.

A low-turn motor can "use" (bad terminolgy!) more amps to attain maximum torque, a high-turn motor uses less to reach maximum torque.


It's the old "watts are watts" axiom, as long as you load the motor to the torque peak (current), the voltage you apply is really irrelevant, unless you reach the thermal or mechanical limits of the motor.

Bottom line: when choosing a particular number of turns, no one number of turns is more "powerful" than any other, that's strictly a function of voltage.


Very cool!
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Old Oct 01, 2003, 03:35 AM
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Torque is not power.

Hotter wound motors will do best power at lower voltages. Hotter wound motors may alos be more efficient - certainly at lower voltages.

There is a lot to consider, but best power out of a motor is at max RPM it doesn't disintegrate at, and max current that doesn't fry the windings. Hotter wind menas you can put more current through, and it will scream up to max RPM on small cell count. To get same power on 'cool' motor takes more cells. Then it will indeed have same RPM, and same toruue at less current.

In reality, taking something like MEGA motors, a 16/15/3 will approach max power at 8 cells or so, whereas teh cooler motors really need far more cells than people run em at to get to teh same power levels. In reality, those coooler motors run at less power (but excellent afficiency) to swing bigger props DD.

No one says you have to run a motor at max theorteical power before damage! However for best power-to-weight, sometimes you want to.
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Old Oct 01, 2003, 08:31 AM
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Efficiency?

We had a thread going on efficiency a while back, but it kinda never got resolved...

But, this thread is right on topic...


Like vintage1 observes, there's a common "understanding" that low-wind (hotter) motor are more efficient than their higher-wind cousins...

But, I think that there's a number of variables being read into the statement; "low winds are more efficient", which miss the point.


You have to keep in mind that although we in R/C aircraft are not slaves to fixed voltage like the R/C car guys (6-cells/7.2V), there is still a lot of bias towards mid-range cell counts (7-10), which is really derived from the capability and weight of the cells commonly available, not any particular power system requirement.

Also, most speed controls, and chargers in particular, are aimed at a less than 12V supply/output operating environment

Thus, there is a natural bias tends to favour battery packs, and the corresponding power systems, which emphasize amperage over voltage.

Li-Poly cells, and lightweight NiMh cells are slowly changing this landscape, but it'll still be a while.


What this environment tends to do is make people apply their experiences in ways that are not appropriate to the power system at hand.

For example, I have read of -numerous- examples of people consistently exceeding the maximum published amp rating of high-wind motors simply because it can be done, not through any system of empirical tests or observations.

These people are stuck in the mindset that "more amps must equal more power".

Nothing could be further from the truth!

(This is usually not an issue with low-wind motors as the maximum current for the windings usually exceed the practical limit of the batteries.)



As an example, lets take the Mega 16/15/x series, and make a few assumptions:

- the practical thermal limit is the same for all winds
- the max RPM is the same (40,000)


Let's pick the 16/15/3 and the 16/15/6:

Max amps on the /3 are 30A, and 18A on the /6, and let's arbitrarily say that max torque is at 25A and 14A.


Now assuming we had something like a dyno, which could load the motor to max torque (regardless of RPM), at a fixed maximum watts in, which motor would produce the most power at the shaft? ( Hp=(RPM x torque)/5252 )


As mentioned above, once you reach the max torque, adding more amps is just going to generate more heat!

Now, there are probably some vagaries which will make the number of amps need to generate max torque vary a little with the increasing RPM. (friction, timing, heat rejection)


Once you've got a consistent max torque, what you now need to do is add volts up to your pre-defined watt limit and see what RPM you get!

Assuming that we only have 250W to play with, and by definition our amps are determined by the motor, the voltage will simply be 250/amps.


Which motor will end up putting more power to the shaft?

It won't be an large margin between them, but the odds are on the high-wind motor.
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Old Oct 01, 2003, 02:14 PM
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Meteor has the right track on this. I’m new to electrics and just went through this learning curve with the help of some great folks at Aveox. I've flown fuel DF's and recently took the plunge into electric power ducted fans. Getting up to speed on electrics turned out to be a hefty learning process.

It is far better to use a higher torque motor (more turns) and then raise the cell count to achieve the desired RPMS. This should end up at a point where the total amp draw is at or near the maximum torque point of the motor (full throttle) which should meet up at the motor's continuous current rating, which meets at the desired RPM..

The DF folks using a Midi/Aveox combo are going to find this a surprise but the best motor/cell count for the Midi is:

20 cell Sanyo 4/5AUP 1800 or 1950
36/24/3 produces about 50oz thrust for a 5 minute duration.

Straight from Aveox, this is the best possible, maximized combination, and is contrary to many threads I’ve read.

The moral of the story is as meteor correctly points out, more amps is NOT more power. More torque at higher voltage IS.
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Old Oct 01, 2003, 07:06 PM
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MAN, I would really like to see more real-world examples of high turn, high volt, low amp aircraft. EDF systems on a Mega 5-turn motor running 6S1P packs at 18 amps ... as an off-the-cuff "for instance".

With 3.7 volts per cell and remarkably low voltage drop under load, it takes very few Lipoly cells to make a high voltage pack that is also LIGHT. But when higher amps are needed, it becomes expensive and heavy to parallel Lipos. So, enter the high-turn motor!

I've got a 2.8 meter ASW 22 just waiting for the right high-turn brushless/LiPoly precedent to follow. But at the present, most seem content to build expensive low volt, high amp LiPoly packs that mirror conventional NiMH/NiCAD thinking, and run low-turn motors on gearboxes. This thread (and others) show that the components for more LiPoly-favorable (High volt/low amp) systems are right under our noses.

I'm just not rich enough to be a guinea pig!
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Old Oct 01, 2003, 09:05 PM
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Thomas, I share your concern about being a guinea pig when it comes to buying all the goods needed for a complete, high performance electric system. This has been my approach; I went with two power plants:

Aveox 36/30/3 12 GP3300 using a 10-6 APC pusher prop installed on a Balsa USA Force one. The force one wing is at 600+ sqr inches which gives me great wing loading for a heavy battery pack, good high end speed (Delta wing), reasonable weight airframe, perfect for a e-power plane. This power plant gives me 52+ OZ thrust at 7+ minute duration. The motor and battery combo are well matched with the motor running at its best efficiency point (at full throttle) and just under its continuous amp rating.

Second power plant, Aveox 36/24/3 20 CPB 2100 NIMH cells from CheapBatteryPacks.com with a MIDI fan. Ducted fans, e power types lack the raw torque power of fuel power, however, e-power delivers a smoother, higher RPM ability. It s the RPMs that make a fan produce thrust. Second, fuel planes have a down side, they really shake rattle and roll. That means the airframes must be stronger, added weight. So the key to a great electric DF plane is really low weight airframes powered by high torque, high voltage motors. At this time I'm build a foam/glass canard with little or no body sections. The calculated weight is around 12 oz for the airframe. This should give me a 1 to 1 thrust to weight ratio at ready flight weight, I hope.

Just for kicks, I run a Mega 16/15/3 motor on my Corona heli using 8 RC2400 cells. I only have a few flights on this but the improvement was big when compared to the stock brushes system. Heli's love high torque geared motors because the required RPM's is around 2-3 thousand! Keeps the amps way down.

What’s important here is each power plant requirement requires good planning to maximize the performance while minimizing the amps, a very difficult thing to do
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