Working Micro Brushless Outrunner Motors - RC Groups
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Sep 21, 2004, 03:33 PM
in persuit of low wing loading
Gordon Johnson's Avatar

Working Micro Brushless Outrunner Motors

There are several different threads with micro brushless outrunners that people have made. The "mother of all" these threads is the "Micro Brushless Outrunner Experiments" Thread, and is just too much for people to wade through to see examples of micro outrunners. See the Brushless section in the "Micro Thread Index" to find these individual threads. So, I'm starting this thread to catalog working micro outrunners.

I'd like to keep the thread free of discussion. It's ok to post short comments/questions. But, I will periodically clean up the thread and delete these posts like is done in the "Working Pager Planes" Thread.

If you have questions, it may be best to PM the person who posted, and ask that they consider adding that info to their post, and also to write you back with this information.

Here are the rules of engagement, as Graham always says:

(1) Motors must be brushless outrunners or disk motors weighing less than 10g and must run well.
(2) Post a close up of your motor and if you have it in a plane a picture of that too.
(3) Post weight, Stator size diameter and length in mm, magnet size. If you would like to share your stator source, that would be nice. Specify whether your weight is with or without motor mount.
(4) Post wind, e.g., star/delta, LRK/Not, wire guage and number of turns
(5) Post performance. At the very least you should tell what prop is used, what volts it is tested at, and how many amps it draws. Static thrust and prop rpm would be nice if possible.
(6) Any additional detail you would like to provide.

That's it. I know of a few motors in the "Experiments" thread that meet these criteria. And, I'm sure more will come up . I'll start with my 9.32g outrunner and hopefully others will post theirs soon. Post away.

Last edited by Gordon Johnson; Sep 21, 2004 at 08:06 PM.
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Sep 21, 2004, 03:33 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Weight: 9.32g with wires & plugs, motor mount, and screws and nuts (8.44g without)
Stator: 18.4x1.8mm from a Viper 340 laptop hard drive
Magnets: N45 5x2.5x2mm
Wind: Star pattern, 50 turns of #32 wire.
Performance: With a GWS 5x3 prop at 10.5V it pulls 2.2amps and generates 105g static thrust.

Completed in January 2003, but not flown in a plane till September 2003. More information on construction details and performance at other volts and with different winds can be found on my Micro Brushless page. This motor is really a collaboration with Gail Graham, who CNC machined the openings in flat plate ready for final machining by me for the front bell, and also machined the 0.3mm thick flux ring.

The motor is currently installed in a foamie Staggerwing Beech (picture to be posted later).

Last edited by Gordon Johnson; Oct 11, 2004 at 02:58 PM.
Oct 11, 2004, 02:52 PM
in persuit of low wing loading
Gordon Johnson's Avatar
This is Mike Cross' micro LRK, see his Small LRK Outrunner thread.

Weight: 3.9g
Stator: 12-tooth
Magnets: 14 magnets
Wind: LRK, every other tooth
Performance: N/A

Mike first posted about this motor in December 2003, but had problems with his Phoenix 10 controller. In October 2004 he posted that it ran well after solving a few small issues.

Mike, please jump in with any updates for this summary thread.
Oct 11, 2004, 03:06 PM
in persuit of low wing loading
Gordon Johnson's Avatar
This is Gail Graham's micro LRK.

Weight: 5.2g
Stator: 12-tooth 12mm diameter self machined plates,
Magnets: 14 N45 1x1.5x5mm
Wind: LRK, 26 turns AWG #34 (0.016mm) wire
Performance: Just a couple of preliminary test results show 21 grams static thrust with a GWS 3030 at 0.75A at 7.0V and 68 grams thrust wide open throttle at 4.1 A at 7.0V.

Ran fairly well, but was stuborn about starting smoothly. See post #240 in the Micro Brushless Outrunner Experiments thread.
Oct 11, 2004, 03:13 PM
in persuit of low wing loading
Gordon Johnson's Avatar
This is Peter Maul's 4.6g outrunner using a stator from a Mini Disc player.

Weight: 4.6g
Stator: 6-tooth 11.5x1.95mm mini disc stator
Magnets: N45 3x3x1mm, 8 poles, 0.25mm airgap
Wind: 30 turns, 0.236 CuL
Performance: high load spin: 13240 rpm at 2.61 amps at 4.91 V

Peter posted about this motor in February 2003. See post #259 in the Micro Brushless Outrunner Experiments thread.
Oct 11, 2004, 03:16 PM
in persuit of low wing loading
Gordon Johnson's Avatar
This is Peter's next smaller outrunner, also from a Mini Disc player stator. Weight is 3.0g.

Weight: 3.0g
Stator: 6-tooth from mini disc player
Magnets: 8 magnets
Wind: 0.18mm wire
Performance: 20g static thrust from an Graupner Easyfly-Prop direct drive at 7V and 1A and gets only warm (wound for 2 140 Lipo).

See post #265 from thread above.
Last edited by Gordon Johnson; Oct 11, 2004 at 03:26 PM.
Oct 11, 2004, 03:43 PM
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Last edited by pem; Oct 18, 2005 at 04:53 AM.
Oct 11, 2004, 03:56 PM
in persuit of low wing loading
Gordon Johnson's Avatar
This is Uttam and his father's micro outrunner, first posted about on October 2004.

Weight: 3.1g
Stator: 9-tooth self made
Magnets: 12
Wind: NA
1) 25gms thrust 520ma, 11V ( Close to a 3 cell Lipo pack ), GWS 2.5*1 prop
2) 32 gms thrust at 7.4V, about 800ma, on a Union U-80 prop.
3) 45gms thrust at 1.2A 11V.
Oct 13, 2004, 11:27 AM
Registered User

GWJ Micro Bl


Here are a few pictures of my brushless disc motor. It has 6 coils and 8 magnets. Depending on the plane I have it on I run it with a 2 cell 170 or a 2 cell 250 lith-poly pack.

The motor is 0.687 inches in diameter and 0.375 inches from the face of the disc to the back of the mounting plate.

Here are a few specs. More will come in the near future.

Weight /w wires and mounting plate that I am using is 7.6 grams

GWS 4x4 prop - 8500 rpm @ 8 volts @ 1.22 amps
" 5x3 prop - 8250 rpm @ 8 volts @ 1.26 amps
" 6x3 prop - 6800 rpm @ 8 volts @ 1.42 amps

Static thrust for the 5x3 and the 6x3 for the rpms listed is as follows.

5x3 - 55 grams
6x3 - 62 grams

I don't have a static thrust value for the 4x4 prop. Also remember these are peak values and will go down as the battery voltage drops.


[edit, Gordon: Note that this motor will soon be commercially available from]
Last edited by Gordon Johnson; Oct 15, 2004 at 07:52 AM.
Oct 14, 2004, 05:24 PM
Registered User
quax's Avatar

my college lent me his special brushless construction for the development of the Flea-BLMC. I think it's an outrunner, so it matches the thread conditions.

In a short while I will add some data here.

added ++++++++++++++++
edited: 2004/10/21 power consumption corrected ++++

Weight: 8 g
Stator: 6 coils on ferrit, 3.3x6 mm
Wind: 32 turns, 0.3 CuL
Magnets: 8 neodym, 5x2 mm
Diameter: 22 mm
Performance: 50 g static thrust from an 9x6 Prop with 1:6 gear at 7.2V and 0.66A
This motor is tested on the bench so far.

Last edited by quax; Oct 21, 2004 at 10:42 AM.
Oct 19, 2004, 02:45 PM
Registered User
Here is some pictures of a wind tunnel test I just completed on my BL motor. I am thinking of making more of the motor parts out of plastic and since it gets quite warm in a static test I wanted to see what the tempature was at different air speeds. This will help me to determine what type of plastic would be best to use. The reason for this change would make for far less maching.

Before anyone asks I did not check motor rpm at the different air speeds to see how it was unloading. The reason is because I have no way to do it in the tunnel. I did check the amp draw though just for the heck of it. I know and understand that the results of the amp draw readings don't really mean anything but it helps me to draw kind of a comparsion between air speed, motor tempature and amps. Measuring all of this when doing a thrust test with air frame drag mounted on a stinger would give me more valided results.

Oct 20, 2004, 04:23 PM
Registered User

Micro LRK

Micro LRK - design study with magnet array - thanks to Mike (mcross) and Gordon (there will come more !) . Weights 7,9 g but does not fulfill fully the criteria of this thread - Way to hot wound and a mechanical prob has to be fixed.

Update of data if available

Peter Maul

Feb 13, 2005, 07:48 PM
Registered User
Harri Pihl's Avatar
Here is so far my best attempt to make a under 10g outrunner.

Stator (9 tooth) diameter is 18mm and 4mm wide. Magnets (12) are 5x4x1mm N45. Winding is 32 turns 0,2mm (star). Weight is about 9g with mount.
The stator is splitted from about 6mm cdrom stator. Other picture shows size of the original stator and the orietation of the magnets. Beauty of this stator/magnet/ring combination is that 5mm wide and 1mm thick magnets fit exactly; actually magnets are not glued but simply pushed to the ring (ring is made made from steel tube with lathe), fitting the last magnet needs quite bit force! Inner diameter of the bell (with magnets) is 18,7mm so the air gap is 0,35mm.

I have just a simple stand for testing and I have no idea how accurate my measurements are but with the YGE 4 BL (timing 3) and 2x145mAh Kokam (voltage around 7V):

GWS 6x3 HD: 55-60g thrust 0,83-0,86A
GWS 7x3,5 HD: 65-70g thrust 1-1,02A

No load current is 0,16A

Last edited by Harri Pihl; Feb 15, 2005 at 05:34 AM. Reason: Suggestion by moderator
Feb 14, 2005, 10:05 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Nice work. If you want a way to make a lighter motor with your current work, you might check out taking that CD-ROM stator size and splitting the stack in half, for a 2mm long stator. I don't know which direction your 5x4 magnets are oriented, but you may find a size that is a direct replacement for your half-length stator, and there you have it, an even lighter motor. Here's a link.
My guess is you can get it down around 6.5 to 7.5g with a half-length stator. And, with its relatively large diameter it would still be able to turn a 5-inch prop and maybe more. Keep up the good work. It's a good feeling when a tiny motor this small made by you actually runs.

Your performance numbers look about right to me. I think because of your large diameter stator you get a nice low amp draw but still very good thrust. I think the key to these motors is to trade stator length for diameter. In other words, for the same stator mass, we prefer a short diameter stack with a large diameter.

Last edited by Gordon Johnson; Feb 14, 2005 at 10:08 AM.
Feb 14, 2005, 05:00 PM
Team30 Micro EDF
NitroCharged's Avatar
Gordon, Would this be why the A drive (3-1/2" floppy) motor in computers have such a flat motor but with a really large diameter?

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