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Old Nov 13, 2002, 05:33 PM
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
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single phase brushless motor?

For all the motor gurus out there - why hasn't anyone made a single phase brushless motor for models? By single phase, I mean it has a rotor with a north and south pole and just 2 coils diametrically opposed for the stator. For most uses it would not be suitable due to high torque ripple, but for high rpm (such as ducted fan or pylon) I would think it has a lot going for it:

1. All of the coils are energised nearly all of the time, they just reverse polarity as the rotors' pole passes, which means that there is no wasted weight in copper.
2. Stator construction would be a doddle, as there are just two independant coils to wind.
3. The controller only needs to be an H-bridge (two less fets, and correspondingly less gate drive circuitry).
4. One less connector as the motor will now only have two wires coming out of it.

For me, the tricky part would be a reliable starting algorithm in the controller to make sure the thing gets going in the right direction every time (that is if you run it sensorless). Any ideas guys?

regards, Stu.
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Old Nov 13, 2002, 05:54 PM
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Torrance, CA USA
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Quote:
the tricky part would be a reliable starting algorithm in the controller to make sure the thing gets going in the right direction every time (that is if you run it sensorless).
I believe you hit the nail on the head. With the symmetry of single phase, one must be very creative in the microcontroller / sensor methodology to figure where the magnet is and which coil to pulse and when... It’s probably easier (hence cheaper) to go three phase the way Nikola Tesla intended...

Jeff
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Old Nov 13, 2002, 08:07 PM
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
Joined Aug 2002
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Actually, thinking about the starting methods, you could put two hall effect sensors close to each other on the same radius, give the coils a kick and see from the hall sensors which direction the rotor is going (one of them will latch first, triggering an interrupt on the micro), the keep kicking it in the same direction or kick it out of phase to reverse it, then once it's up to speed just run it sensorless
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Old Nov 15, 2002, 09:13 PM
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Tokyo, Japan
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Re: single phase brushless motor?

Hi stumax,
This may be yours.
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Old Nov 15, 2002, 09:15 PM
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Tokyo, Japan
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Re: single phase brushless motor?

This is under development and already flying every Sunday.
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Last edited by Takao Shimizu; Nov 15, 2002 at 09:49 PM.
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Old Nov 15, 2002, 09:17 PM
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Re: single phase brushless motor?

My coil construction. But ....
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Last edited by Takao Shimizu; Nov 18, 2002 at 08:39 AM.
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Old Nov 15, 2002, 09:24 PM
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Tokyo, Japan
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Re: single phase brushless motor?

over 12kv motor brakes my motor!(80k rpm testing)
Also, the max rpm of my 2mm phi shield bearing is 60krpm.
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Last edited by Takao Shimizu; Nov 15, 2002 at 09:37 PM.
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Old Nov 15, 2002, 09:34 PM
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Tokyo, Japan
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Re: single phase brushless motor?

Basic driver circuit is here.

http://www.cityfujisawa.ne.jp/~iijima-p/BRA2.htm

shows everthing RC controller(sorry, only Japanese).

Mine is sensorless. But, cannot use folding prop.. Because, never start by itself.
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Old Nov 15, 2002, 09:36 PM
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Re: single phase brushless motor?

And Peak current is quite high to drive this.
I am testing Ni-Cd + Li+ hybrid battery since 2 weeks ago.
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Last edited by Takao Shimizu; Nov 18, 2002 at 09:01 AM.
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Old Nov 17, 2002, 07:15 PM
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
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Hi Takao,
great minds think alike! Do you have any test data you would like to share? I'm curious about the efficiency - I think at high speed we should be aiming for around 95% with a slotless stator. I think at high speeds the size of the air gap between rotor and stator may be critical (may have to open it up a bit). What do you use for a rotor magnet? I found a source of 12mm dia x 32 mm long with 5mm hole, polarised across the diameter, quite inexpensive, but not high temp grade NdFeB, and was going to cut the length down to suit. May even cut the magnet into slices and laminate the rotor as per Lehner rotors. I'm currently designing a motor to use in 55mm EDF (my own design, similar to Vasa), hoping to use 3 LiPoly cells and keep the current below 6A. I gather from your info that your motor needs to be pre spun to get running? I've thought of that as an easy way to get developing - hard to get fingers inside an EDF model, though! Keep up the great work, and keep us posted! cheers,
Stu.
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Old Nov 17, 2002, 09:57 PM
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zagisrule!'s Avatar
Edgewood, NM
Joined Jan 2002
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Takao,
What Hall Effect sensor, and transistors are you using ( I would like to know the company that makes them and the part number please)? I am thinking about trying this as well.

Thanks Alot!
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Old Nov 17, 2002, 11:59 PM
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Tokyo, Japan
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Hi stumax,
>curious about the efficiency
.
>we should be aiming for around 95%

As you know, the single pole motor needs very low internal resistance battery, because there is only two times to feed the energy in a round.
I am developing the new method for this motor to increase the efficiency(with same prop., 30% up!).
(But, I have no measuring system for output power?!)


>the air gap between rotor and stator

I used the kitchen wrapping rotor magnet for CA glue coil before wind. You can wind it in 5 min.

>What do you use for a rotor magnet?

I got it from broken small brush coreless motor, NdFeB.

>12mm dia x 32 mm long with 5mm hole, polarised across the
>diameter, quite inexpensive

Sounds great! Get it ASAP. You can enjoy your design.


>not high temp grade NdFeB

Open case makes no trouble for heat-up with prop.


>hard to get fingers inside an EDF model,

There are a lot of ideas for self-start 2-pole motor with hall dev., except sensor less type.
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Old Nov 18, 2002, 12:15 AM
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Tokyo, Japan
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Single pole motor driver schematic

zagisrule,

All hardware info. is here.
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Old Nov 18, 2002, 01:38 AM
S55
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Beaverton, OR, USA
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Takao,

Could you please explain in more details how the coil is done and secured to the stator? Pictures would help.

Thank you,

S55
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Old Nov 18, 2002, 08:56 AM
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Tokyo, Japan
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There are a lot of no-hows.

Quote:
Originally posted by Takao Shimizu
Do not ask me anymore to make this simple motor?!
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