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Old Dec 14, 2003, 03:41 AM
Registered User
Tokyo, Japan
Joined Nov 2002
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Re: Brushless mystery uncovered - part two

rysium,

It's called "synchronous motor"



Who said that?
ESC does not control driving with any motor rotation drive frequency.
I can not call it "synchronous motor".

Takao
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Old Dec 14, 2003, 10:40 AM
now that's a wattmeter...
simingx's Avatar
Singapore
Joined May 2002
1,136 Posts
Man, how do you guys remove the stator?? I hammered/twisted/plied at it for an hour and all I'm doing is deforming and generally totally maiming the bushing and metal mount... the brass bushing is NOT giving way anytime!
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Old Dec 14, 2003, 10:52 AM
M.Yutaka
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Gifu_Japan
Joined Dec 2003
2 Posts
Since I had care, please let me say.

There is the talk that a teacher of the university of an acquaintance said the other day.
[They are about brushless DC motor (it is also called DC brushless motor.)the following, "BLDCM", and a brief sketch.]
*Point out that with which the inverter and the permanent magnet form synchronous electric motor were united. A permanent magnet form synchronous electric motor is also called PM motor. PM is the initial of Permanent Magnet.
*When using BLDCM, input a direct-current power supply. It is changed into exchange by the inverter and a motor is driven by it. Since the input power supply of BLDCM is a direct current, although it is classified into the direct-current motor, it is classified into an exchange motor according to a motor simple substance.

With books that I read, the definition of a synchronous motor was what is depended on a rotation principle. I think that what Takao told about is that from which implications are a little different.

If I committed impoliteness, please allow.

Thanks.

Yutaka
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Old Dec 14, 2003, 11:10 AM
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mmormota's Avatar
Budapest
Joined Jul 2003
2,576 Posts
Re: CD-ROM motor RC Prop. torque meter

Quote:
Originally posted by Takao Shimizu
I hope that my torque meter has good accuracy.
The calculation(Torque x RPM) says that my CD-ROM motor's efficiency is 75%.
Wow, great results!
Really great for such a small motor.
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Old Dec 14, 2003, 11:13 AM
Why not Delta?
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Sacramento, CA
Joined Jun 2003
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Re: Re: Brushless mystery uncovered - part two

Quote:
Originally posted by Takao Shimizu
Who said that?
ESC does not control driving with any motor rotation drive frequency.
I can not call it "synchronous motor".
Takao [/B]
Please see the link http://members.chello.se/modellflyg/guide5.htm.
Scroll down to the end of the page to see the explanation how brushless motors work.

RysiuM
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Old Dec 14, 2003, 05:19 PM
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Dunlap, Illinois, United States
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Ok, what type of glue can be used on this motor that won't destroy the magnet wire? I know C/A is bad for the wires.
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Old Dec 14, 2003, 10:49 PM
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Tokyo, Japan
Joined Nov 2002
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Re: Re: Re: Brushless mystery uncovered - part two

rysium,

>Please see the link >http://members.chello.se/modellflyg/guide5.htm.
>Scroll down to the end of the page to see the explanation how brushless motors work.

RC airplane BL motor does not run with constant RPM.
As, slowdown with going Vertical, High up with dive flying same as brush motor.
Therefore, that is absolutely incorrect explanation.

http://www.rcgroups.com/forums/showt...threadid=70373

Takao
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Old Dec 15, 2003, 01:56 AM
Why not Delta?
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Sacramento, CA
Joined Jun 2003
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Re: Re: Re: Re: Brushless mystery uncovered - part two

Quote:
Originally posted by Takao Shimizu
RC airplane BL motor does not run with constant RPM.
As, slowdown with going Vertical, High up with dive flying same as brush motor.
Therefore, that is absolutely incorrect explanation.
Of course it's not running the same rpm. The examples I have given were to compare two identical motors (size, design etc.) under the same test conditions.
Going vertical = more load, Diving = less load. It;s true that under different load RC BL motor turns different rpm (on the same throttle position and the same input voltage). But it doesn't mean it's not a synchronous motor. It is. It still turns the same speed as the frequency give by ESC. It's the ESC who is addjusting controling frequency to the given load. If ESC wouldn't do that, the motor would fall out of the sync when the load is bigger than the max torque of the motor.

The deffinition for synchronous motor is, that the magnetic field of the rotor is all the time in sync with the rotating magnetic field of the stator. And that is exacly what happens in the RC BL motors.

The design of DC-ROM conversion allows us to turn rotor 6 times slower than the frequency of ESC but it's total different story, and it's been explained already a couple times.

As I said, the ESC for BL motors is "smart enough" to sense the motor timing angle and when the motor is about jump out of sync, ESC lowers the frequency allowing the motor to draw more cureent, so the motor increases the torque loosing the rpm at the same time.

I hope this explanation helps.

RysiuM
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Old Dec 15, 2003, 06:22 AM
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Spring Valley. MN
Joined Jun 2000
4,458 Posts
I just got my CDR motor running Here are some quick specs

24.6mm stator
20t .42mm wire/ delta wind
no load current .4amps
7x6 prop I took it up to 10 amps about half throttle much higher than I wanted so I'm going to change it to star wind and see how it does. I ran it yesterday with 25t .27mm Star wind and was pulling 5 amps on the 7x6 prop which was right about where I wanted it but I wanted to do some more playing around before I finish it off and mount it on somthing If nothing else these little motors are fun to play with.
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Old Dec 15, 2003, 08:47 AM
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Tokyo, Japan
Joined Nov 2002
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Re: Re: Re: Re: Re: Brushless mystery uncovered - part two

rysium,
[/i]
And that is exacly what happens in the RC BL motors.
[/QUOTE]

Sorry, I miss understand. I could say "And that is exactly what happens in the RC BL motors and RC brush motor". And I do not want to call them "synchronous motor".

Every time, I write ESC software to adjust the timing condition to supply the next power feed timing, not for any synchronization.

Takao
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Old Dec 15, 2003, 09:05 AM
radar jammer
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Bradenton, Florida
Joined May 2003
563 Posts
You'll find that many of us will not be conviced these are not AC synchronous motors as they are functionally made the same. Most manufactures claim the same.

Just because a controller is used to vary the speed/timing means nothing to the motor in general. The two should not be confused.
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Old Dec 15, 2003, 09:52 AM
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mmormota's Avatar
Budapest
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Re: Re: Re: Re: Re: Re: Brushless mystery uncovered - part two

Very nice circuit diagram, thank you. Clean, simple, practical. With a good firmware it will be the best homemade brushless controller for sure, competitive to the production types. Congratulations!

This extremely simple sensing part is really enough for the firmware?
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Old Dec 15, 2003, 10:50 AM
Why not Delta?
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Sacramento, CA
Joined Jun 2003
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Re: Re: Re: Re: Re: Re: Brushless mystery uncovered - part two

Quote:
Every time, I write ESC software to adjust the timing condition to supply the next power feed timing, not for any synchronization.
Takao
Now I have a question:

As I mentioned before the most of the motor's losses are in the motor's core and magnets (Hysteresis losses, Eddy current losses). So to improve the motor efficency we can use coreless stator. It make peffect sense for outrunners where the magnetic field from the stator will not go outside the rottor, so we don't need the ferromagnetic core to direct the magnetic field.

At the same time magnets in the rotor have fixed and limited strength that limits the maximum torque provided by motor. To be able to increase the torque we would need the stronger magnetic field in the rotor. There are two possibilities:
1. Use electromagnets (like in the big scale synchronous motors), but then the motor will not be brushless any more - it will need brushes to deliver the power to the rottor.
2. Build 3-phase induction motor (the cage type). The good thing about this solution is, that it delivers the torque under the load (without "smart controler"). The ESC would be simple throttle to frequency converter, and the motor will do the rest.

So my bet for best RC BL motor is: Brushless, coreless, induction outrunner. It's light (no magnets or iron core), without energy losses except for the resistance of stator wire and resistance of rotor's cage. Low maintenance (just bearings), with very simple controler (variable frequency 3-phase inverter).

What do you guys think: will I get the Nobel Prize for that

RysiuM
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Old Dec 15, 2003, 02:20 PM
Boffin
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Victoria, BC, Canada
Joined Apr 2001
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Re: Re: Re: Re: Re: Re: Re: Brushless mystery uncovered - part two

Quote:
Originally posted by rysium
So my bet for best RC BL motor is: Brushless, coreless, induction outrunner.
Interesting ideas, but since this topic is about converting CD-ROM motors in one hour could you please start another thread. You may want to move these posts over there.

Thanks,
Rick.
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Old Dec 15, 2003, 07:12 PM
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Re: Re: Re: Re: Re: Re: Re: Re: Brushless mystery uncovered - part two

Quote:
Originally posted by rpage53
Interesting ideas, but since this topic is about converting CD-ROM motors in one hour could you please start another thread. You may want to move these posts over there.

Thanks,
Rick.
True enough, but maybe a better question is has anybody converted a cdrom motor to an inductance motor? Copper wire is definatelly cheaper than magnets and the controller would probably be cheaper also.
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