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GoBrushless.com Motor Question

Old 06-06-2014, 07:49 PM
  #51  
ron_van_sommeren
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Originally Posted by Ohm View Post
... But who really needs efficiency? ...
Efficiency governs power/weight ratio.
Higher efficiency does not only mean that the motor makes better use of the batteries' power, it also means the motor is able to handle a higher power input before hitting its maximum temperature mark, i.e. a the power/weight ratio will be higher.

An example
Say the motor has an efficiency of 70% and it can handle 50Watt input. That means it can get rid off 30%*50=15Watt excess heat. Now, by cramming in thicker wire (and/or using better stator-iron, segmented magnets), efficiency increases to say 75% (I'm a bit optimistic here). The motor's ability to loose those 15Watts has not changed (by radiation, convection and conduction). This means the motor now can handle 60Watt before it hits the 15Watt (25%*60Watt) losses mark. An efficiency increase of 5% gives an increase in the power to weight ratio of 20% (from 50Watt to 60Watt). That's why efficiency plays such an important role, in any motor design: efficiency governs maximum power. The motors weight may have increased a bit due to more copper.
A rather extreme example, just for calculation's sake/fun: going from 80% to 90% efficiency would increase the input power the motor can handle by a factor two (a.k.a. 2).

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Old 06-06-2014, 08:11 PM
  #52  
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Excellent explanation of the value of bigger windings. One of the characteristics of rewinding with fewer turns of larger wire is that the RPM per Volt (kV) goes up, which is not always desired for scale planes and noise.

So a smaller prop, with less pitch may be required to allow this higher RPM.

I like small props as they transmit less torque to the plane's body.

Last edited by DBacon; 06-06-2014 at 10:18 PM.
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Old 06-07-2014, 05:40 AM
  #53  
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Originally Posted by ron_van_sommeren View Post
Efficiency governs power/weight ratio.
Higher efficiency does not only mean that the motor makes better use of the batteries' power, it also means the motor is able to handle a higher power input before hitting its maximum temperature mark, i.e. a the power/weight ratio will be higher.

An example
Say the motor has an efficiency of 70% and it can handle 50Watt input. That means it can get rid off 30%*50=15Watt excess heat. Now, by cramming in thicker wire (and/or using better stator-iron, segmented magnets), efficiency increases to say 75% (I'm a bit optimistic here). The motor's ability to loose those 15Watts has not changed (by radiation, convection and conduction). This means the motor now can handle 60Watt before it hits the 15Watt (25%*60Watt) losses mark. An efficiency increase of 5% gives an increase in the power to weight ratio of 20% (from 50Watt to 60Watt). That's why efficiency plays such an important role, in any motor design: efficiency governs maximum power. The motors weight may have increased a bit due to more copper.
A rather extreme example, just for calculation's sake/fun: going from 80% to 90% efficiency would increase the input power the motor can handle by a factor two (a.k.a. 2).
Precisely!

Some of those name brand motors only fill 50-60% of the available winding space for the magnet wire. Even though they have the same exact KV rating, nearly the same total weight, the the motors that completely fill the available winding space can have 1/2 of the winding resistance.

Since maximum power capability is inversely proportional to the winding resistance, cutting the winding resistance in half results in a similar increase in maximum power capability.

Take the E-Flite Power 32 motor vs the Hacker A40-12S motor. Both are the same physical size, both have the same KV rating, but the Hacker motor has about half of the winding resistance. The E-Flite measures 0.023 Ohms, the Hacker is 0.012 Ohms. So, for the same current, the Hacker windings get half of the heat of the E-Flite Power 32.

Yup, those E-Flite motors do work well, and a lot of them are in use. The Power 32 is rated by the mfg to 800 Watts, the Hacker A40-12S is rated to 1000 Watts. Running the numbers through www.motocalc.com, the Power 32 will be pulling about 900 Watts on a 4S LiPo with a 12X8 Prop. It will be pulling 65 Amps, and gets about 73% efficiency. Prop is predicted to be 8050 RPM. Motocalc suggests this will fry the motor. Yup, this is above the Power 32 rating.

Putting the same 12X8 prop on the Hacker A40-12S, Motocalc indicates this motor will be pulling about 1100 watts on a 4S LiPo, while pulling 79 Amps, getting 88% efficiency. Prop is predicted to be 9100 RPM.Yup, this is also above the Hacker current rating. But Motocalc indicates no problems with the Hacker.

Check out the photo of the Tera Hobby motor. It's windings measure 0.046 Ohms, four times that of the Hacker. Interesting, the rotor and stator of the Tera Hobby motor and the Power 32 motor directly interchange with each other.
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Old 06-07-2014, 06:14 AM
  #54  
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Originally Posted by DBacon View Post
Excellent explanation of the value of bigger windings. One of the characteristics of rewinding with fewer turns of larger wire is that the RPM per Volt (kV) goes up, which is not always desired for scale planes and noise.

So a smaller prop, with less pitch may be required to allow this higher RPM.

I like small props as they transmit less torque to the plane's body.
Or, if the mfg completely fills the winding area of the motor winding slots with copper wire, a heavier gauge wire with the same exact number of turns (and same KV) can be used. Completely filling the winding area with copper wire is a lot more work.

Yeah, I've rewound a bunch of brush and brushless motors over the years. It was nice to have access to the shop winding area with their big spools of wire. The "End of the spool" magnet wire could easily provide enough copper wire to wind a dozen small brushless motors. The coil department had every size wire from #34 or so, to heavy flat copper strips two inches wide. Some of those spools were hundreds of pounds.
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Old 06-07-2014, 06:10 PM
  #55  
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The united hobby link goes to Hobby King? go figure.
Having wound many motor kits and OEM rewinds I find it cheaper more satisfactory to buy low cost motors and upgrade the winding, the bearings and sometimes magnets . IMHO the cost of motor kits is atrocious considering they did not do the hard work. They did not build the stator, they did not make the bearings or shaft. It doesn't take much to push the button on a CNC machine and load the stock. It takes little skill to draw a picture of a motor frame considering all the standards are in place. So I suppose the huge mark up in price is due to someone putting them in a box and marketing them. No complaint just observation, anything to make a buck. Buying high priced motor kits is no guarantee that your getting top quality parts. I have bought several high priced kits that the bell was not made correctly so it needed balancing after assembly or other problems from sloppy machining. It's a PITA step. In contrast I have bought HK motor kits that have been the cats meow. All that being said a technique to low cost, high performance motors has come to finding reasonable quality motors on sale and then upgrading the weak points. I have found .2mm laminate stators in dirt cheap motors, usually accompanied with crapy bearings (only because they are full of dirt) and a sloppy wind and mediocre magnets. Key there is the motor has a top notch stator. It's the parts the kit manufacture doesn't make (although they do source them, I suppose that's worth 300% markup) that are the key to a good motor. IMHO
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Old 06-07-2014, 09:47 PM
  #56  
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Originally Posted by kyleservicetech View Post
... Even though they have the same exact KV rating ...
Denny, keep in mind, and spread the word ...
The Kv constant (motors have just one Kv, not 180Kv), is not a rating, not a figure of merit. More windings will give lower Kv, less windings will give higher Kv, that's all there is to it, no big deal, anyone can do that.
Also
A motors Kv constant says nothing about a motors max.power, max.current and rpm.
Maar we weten wel dat motorstroom wil stijgen met kwadraat van spanning en derde macht van Kv.

Last edited by ron_van_sommeren; 06-10-2014 at 01:33 AM.
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Old 06-07-2014, 10:59 PM
  #57  
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Originally Posted by ron_van_sommeren View Post
Efficiency governs power/weight ratio.
... ...
An example ...Say the motor has an efficiency of 70% ....
On the other hand, it can be advantageous to keep some open space for cooling air to pass through, because better cooling is also good for power/weigth ratio. So there can be a trade off.

E.g. several rewinds by Bert Dekker, notably the rewinds for helicopters
translate...www.modelbouwforum.nl/forums/model-elektronica/126944-scorpion-hk3026-hk4225-hk4020-hk4025-hk4035-buitenloper-wikkelen-35.html

Kontronik Pyro 850 5+5YY 1.6mm, Kv = 470rpm/V
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Old 06-08-2014, 03:00 AM
  #58  
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Default Automated Motor Winding Machine

Originally Posted by Ohm View Post
The united hobby link goes to Hobby King? go figure.
Having wound many motor kits and OEM rewinds I find it cheaper more satisfactory to buy low cost motors and upgrade the winding, the bearings and sometimes magnets . IMHO the cost of motor kits is atrocious considering they did not do the hard work. They did not build the stator, they did not make the bearings or shaft. It doesn't take much to push the button on a CNC machine and load the stock. It takes little skill to draw a picture of a motor frame considering all the standards are in place. So I suppose the huge mark up in price is due to someone putting them in a box and marketing them. No complaint just observation, anything to make a buck. Buying high priced motor kits is no guarantee that your getting top quality parts. I have bought several high priced kits that the bell was not made correctly so it needed balancing after assembly or other problems from sloppy machining. It's a PITA step. In contrast I have bought HK motor kits that have been the cats meow. All that being said a technique to low cost, high performance motors has come to finding reasonable quality motors on sale and then upgrading the weak points. I have found .2mm laminate stators in dirt cheap motors, usually accompanied with crapy bearings (only because they are full of dirt) and a sloppy wind and mediocre magnets. Key there is the motor has a top notch stator. It's the parts the kit manufacture doesn't make (although they do source them, I suppose that's worth 300% markup) that are the key to a good motor. IMHO
If you ever wondered how some of these motors are wound:
https://www.youtube.com/watch?v=2JsRYUTK5Pw

I'd guess those motors whose windings completely fill all available winding space are wound by hand.
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Old 06-08-2014, 12:07 PM
  #59  
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Good info here, should be required reading. Yes Kv is not a figure of merit, just a characteristic. But is it "Kv", "KV", "kV", or "kv"?
In my business (resistance welding) we use "kVA" for power handling ability of a transformer, and we capitalize the Volts and Amps out of respect for Count Alessandro Giuseppe Antonio Anastasio Volta and André-Marie Ampère.

That winding machine is amazing! Thanks
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Old 06-08-2014, 02:23 PM
  #60  
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Originally Posted by DBacon View Post
... But is it "Kv", "KV", "kV", or "kv"? ...
Kv, in rpm per volt, and Kt, in newton per ampère, voltage respectively torque Konstant.
Kt = 1 / Kv, in units for grown-ups, i.e.SI units, not imperial units.

See also Joachim Bergmeyer's excellent article about brushed motors. Since brushless motors are just brushed motors with electronic commutation (ESC) instead of mechanical commutation (brushes), all if it applies to brushless motors, mutatis mutandis:
www.rcgroups.com/forums/showthread.php?t=185271

Last edited by ron_van_sommeren; 06-10-2014 at 01:34 AM.
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Old 06-08-2014, 05:43 PM
  #61  
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Hmm...
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Old 06-08-2014, 10:35 PM
  #62  
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Originally Posted by kyleservicetech View Post
If you ever wondered how some of these motors are wound:
https://www.youtube.com/watch?v=2JsRYUTK5Pw

I'd guess those motors whose windings completely fill all available winding space are wound by hand.
The E-max motors of late are machine wound and they squeak by when tested against the advertised spec, consistently! But there is gobs of room for more wire. I think the big advantage to the OEM motor market is providing a consistent product. Which can be more valuable to the consumer instead of getting some good ones and bad ones that the hand wind market offers. The big advantage to folks who like to max-out their motors is that it provides a reliable base to work from.
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Old 06-09-2014, 02:09 AM
  #63  
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Originally Posted by ron_van_sommeren View Post
Since brushless motors are just brushed motors with electronic commutation (ESC) instead of mechanical commutation (brushes), all if it applies to brushless motors,
Yup
FYI, these brushless motors are actually three phase AC motors with a variable frequency three phase AC driver, namely the ESC itself.

I've taken several of those high quality brushless motors, such as the Hacker A60 line, and connected them to a low voltage three phase AC power supply. (12 VAC Three Phase) You guessed it. Those motors immediately started spinning, locked into an RPM determined by the frequency of the AC power supply. In fact, spinning up a brushless motor with a battery operated drill, you can display a three phase AC voltage across its windings with a four channel oscilloscope. (Also done that)

And, last but not least, I've taken a Hacker A60-5S motor, directly connected it to a Hacker A40-10L motor, using brass adapters. (Jumpers don't work, to much resistance) Spinning up the A60 motor results in the A40 turning over exactly double the RPM of the A60, due to the different number of poles in the two motors. Trying that with some of the bottom of the line motors is not as successful, due to the higher winding resistance of the motors windings, and who knows what else.

Interesting but somewhat useless information

Last edited by kyleservicetech; 06-09-2014 at 02:48 AM.
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Old 06-10-2014, 03:30 PM
  #64  
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More SLS videos
www.sinusleistungssteller.de/projekte.html

Originally Posted by kyleservicetech View Post
... FYI, these brushless motors are actually three phase AC motors with a variable frequency three phase AC driver, namely the ESC itself. ...
Although RC Permanent Magnet Brushless motors (PM BLDC) can be driven by AC and VFD's, RC ESC's are not variable frequency drives Denny (ignoring the SLS controllers). In a brushless ESC the PWM pulse width is controlled by the throttle stick. But it's the that motor 'tells' the controller when to switch/commutate, using zero-crossing detection. Motor and ESC are an iso-synchronous system.
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Old 06-10-2014, 06:14 PM
  #65  
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Originally Posted by ron_van_sommeren View Post
Although RC Permanent Magnet Brushless motors (PM BLDC) can be driven by AC and VFD's, RC ESC's are not variable frequency drives Denny
Hi Ron
You're right, should have been more precise on what an ESC consists of. Early on, our brushless motors had extra lead wires that sent information to the ESC that synced the ESC to the motor as it rotated. Modern electronics allowed those wires to be eliminated, using the three motor wires them selves for sending that required information to the ESC. And, as you indicate, these ESC's vary power input to the motor by "Chopping" the three phase waveshape to the motor. This is easily observed by anyone that has access to an oscilloscope. (I've got three Tektronixs scopes)

One company, www.microchip.com has a lot of information on just how this is accomplished. Reading through this is a lesson on why it's not a good idea to try building one your self

As for me, I've designed and built a whole variety of brush type ESC's that were controlled by one of those Microchip PicChips. The last one made was capable of handling an Astroflight 90 motor, pulling 35 Amps at 50 Volts DC. The software for that ESC was some 20 pages of machine code.

The software in these brushless ESC's are several orders of magnitude more complex than what I had in my Brush type ESC's. Attached is a photo of one that I'd made back in the mid 1990's. Those brushless motors made all of this stuff relegated to the "Old stuff in the drawer".

Also attached is three Microchip files on what's involved in designing your own brushless ESC using the Microchip "PicChip" line.

Now, you can buy a little tiny brushless motor driver for those computer fans. Take a look:
http://ww1.microchip.com/downloads/e...Doc/22263B.pdf

You can buy one for $1.30 each, quantity of one.
http://www.digikey.com/product-detai...HC1-ND/3131735
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Attached Files
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Brushless Fundamentals.pdf (717.6 KB, 59 views)
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Brushless Motor Software II.pdf (440.6 KB, 207 views)

Last edited by kyleservicetech; 06-10-2014 at 07:54 PM.
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Old 06-17-2014, 05:50 AM
  #66  
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Default Hacker A60-16M Motor Winding

I had occasion to bust off the motor shaft of my Hacker A60-16M motor last Saturday. That after some 400 flights on the motor. Problem was caused by a high speed pass over the field, and getting hit by a downdraft, 5 feet off the ground. Winds were 15 - 20 MPH. Stupid. One blade of the 19X12 APC-E wide blade unit has sod stains on it that shows that the blade cut into the sod 3 1/2 inches during the hard bounce and go. That bounce and go bent the landing gear.

Hacker has replacement shafts in stock, I'll be getting them later this week.

That gives an opportunity to take a photo of one of the windings in this motor with my USB microscope. Note how the windings occupy 100% of the available winding space. Sign of a quality motor.
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Old 06-17-2014, 04:20 PM
  #67  
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The next step for a higher quality motor is with a single strand wind that fills up the stator. SSW has better air to flow thru the coils. SSW also provides more copper in the provided space.
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Old 06-17-2014, 07:08 PM
  #68  
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Originally Posted by Ohm View Post
The next step for a higher quality motor is with a single strand wind that fills up the stator. SSW has better air to flow thru the coils. SSW also provides more copper in the provided space.
Agreed:
Problem is, that will usually involve non-standard wire sizes which might be a problem.

What I ran into though, is when using larger single strand wire, the sharp turns required resulted in the varnish type of insulation cracking. That might have been the result of using $$$$ wire from work though.
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Old 06-17-2014, 09:15 PM
  #69  
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Chamfer (bevel? what's the difference?) the edges with a file a bit before winding.
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Old 06-19-2014, 05:52 PM
  #70  
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Originally Posted by Ohm View Post
The next step for a higher quality motor is with a single strand wind that fills up the stator. SSW has better air to flow thru the coils. SSW also provides more copper in the provided space.
Yup
Doesn't take much work with a compass and a piece of paper to show that. Just draw a big circle for a single strand wire, then drawing perhaps 6 smaller circles inside the big circle to show six smaller strands of wire inside the big circle. You wind up with lots of air space.

On the other hand, if you've got a half filled winding area, that does provide more air cooling. But, at a cost of higher winding resistance for the same size motor.

Cases in point:
The Hacker A60-7S has ratings of 215KV, 90 Amp, 2400 Watts, 1.2 Amps no load current, 0.026 ohms winding resistance. It weighs 595 grams.
http://www.espritmodel.com/hacker-a6...-motor-v2.aspx

The E-Flite Power 180 has ratings of 195KV, 65 Amp, 3000 Watts, 1.5 Amps no load current, 0.042 Ohms winding resistance. It weighs 642 Grams.
http://www.e-fliterc.com/Products/De...odID=EFLM4180A

I've got the Hacker A60-5S motor, a real power house. Its windings completely fill all available area. You can actually run it at its rated power level of 2400 Watts.

I've also had a Power 180 in my hands, its windings filled perhaps 60% of available winding space. That shows up in the 0.042/0.026 or 60% higher winding resistance. That will show up in higher temperatures at the same ampere loading.

So, which motor is better? Per www.motocalc.com, actually running the Power 180 motor at 3KW will fry its windings. I've run my Hacker at 80 Amps with no problems what so ever. And, the Hacker is cheaper.
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Old 06-19-2014, 05:57 PM
  #71  
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Originally Posted by ron_van_sommeren View Post
Chamfer (bevel? what's the difference?) the edges with a file a bit before winding.
I was using wire from work, a type called heavy duty formvar wire. That formvar insulation might be a bit more susceptible to cracking. On the other hand, its made for transformers, and is high quality stuff.
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Old 06-19-2014, 06:24 PM
  #72  
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The solution to damaged stator coating
can also be used for custom coloring.
http://http://www.harborfreight.com/...ack-93306.html

I cook them in my toaster oven after piling up the powder where I want it on the stator. The sand castle building skill developed at the beach now has a real world use.
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Old 06-19-2014, 06:29 PM
  #73  
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http://http://www.techfixx.com/
I find the amber wire top notch stuff,very supple. The red and green insulation not as tuff, but good for making light weight servo extensions. Their service has been A-1 to date.
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