2.25 gram 6-pole and 3.5g LRK Outrunners - RC Groups
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Nov 16, 2004, 11:41 PM
in persuit of low wing loading
Gordon Johnson's Avatar

2.25 gram 6-pole and 3.5g LRK Outrunners

Here is a 2.25g outrunner that is a collaboration between Gail Graham and myself. It uses a 11.5mm diameter 6-tooth stator from a MiniDisc music player. Gail machined the front bell and flux ring. I did the final machining of the bell and also machined the bearing tube and motor mount, installed the magnets, and wound the stator. It's hard to appreciate the number of emails both ways planning and figuring out this motor. And, as usual, lots of machining advice flowed my way from Gail.

More details can be found on my MiniDisc Motor page.

Another motor that is a joint collaboration between Gail Graham, Mike Cross, and myself is a micro LRK. Pictures and details can be found on my Micro LRK page. Currently this motor weighs ~3.5g.

Neither motor has run yet. And, since I leave on vacation in two days, neither is likely to run till early December. At the present there is no light weight 1-cell BL controller. But, I know I have lots of testing and refining of the winds etc on both both motors. Since I do have a TMM controller that will operate on one cell I can develop winds for both one and two cell operation. I'm assuming if we build it they (1-cell controllers) will come.

Pictures shown below are of the 2.25g MiniDisc motor. But, the Micro LRK motor looks almost the same. That's a penny the motor is sitting on.

Last edited by Gordon Johnson; Nov 17, 2004 at 09:03 AM.
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Nov 17, 2004, 04:51 AM
My member is not
Zlatko's Avatar
Beautiful work again
I love the 12 pole LRK, that would be awsome fully wound
Nov 17, 2004, 05:24 AM
jmquetin's Avatar
Congratulations Gordon ! You deserve your holidays .
Nov 17, 2004, 05:49 AM
Registered User
billystiltner's Avatar
I agree with Jean-Michael.
It looks awesome. Someone needs to build you a controller.

Nov 17, 2004, 05:59 AM
Sticky Shepherd
Graham Stabler's Avatar
I thought you were quiet, well done!!

Very shiny too!!

Nov 17, 2004, 06:14 AM
Registered User
Quax is developeing a single Lipo controller , the cct and software is available and a PCB is being developed -it will be released after testing .
You can get details here :- http://home.versanet.de/~b-konze/blmc_flea/blmc_en.htm
Nov 17, 2004, 06:50 AM
in persuit of low wing loading
Gordon Johnson's Avatar
I'm counting on Quax and others to have 1-cell controllers relatively soon. I've been following his progress. I think it's just a matter of time till we have a couple of choices in this area.

Here is a weight breakdown for the MiniDisc motor. The portion of the weight from components starting with "glue" on down the list represents the portion of the motor that does nothing to create torque. Torque is created by the stator, windings, magnets, and flux ring. The proportion of total motor weight coming from non torque creating components is approximately 22%.

These non-torque creating components were the ones we attacked like building a micro plane to analyze each one and see how light it could be made and still be just barely strong enough for its function. To this end I machined a few different trial bearing tubes/mounts to see how light I could go. I also have one failed front bell that determined how thin was too thin in the persuit of lightness. Even the shaft size is important. Although a 1.5mm shaft might be more durable, it would weigh 2.25 times as much as the 1mm shaft, and thus weigh ~0.20g instead of 0.09g. It would also require heavier bearings.

Last edited by Gordon Johnson; Nov 17, 2004 at 01:03 PM.
Nov 17, 2004, 07:21 AM
Registered User
Looking great! Is it going to become a product soon, as a fully assembled motor or in a kit form ? or do we need to start searching for old mini discs to take appart ? In my mind I allready see sub micro 3D coaxial helicopters made with these motors... just what I was waiting for. Thanks for sharing all the info about it.
Nov 17, 2004, 08:00 AM
Registered User
@Gordon, Gail and Mike

Simply beauftiful. These designs line up directly with the interior of ancient watches
(those my grandfather repaired - me being a child.).


usually minidisc players are still expensive - at the other hand they contain other interesting motors. Only a few contain stators - lot more are discrunners.

Peter Maul
Nov 17, 2004, 08:11 AM
Frequent Poster
Pete P.'s Avatar
Gordon: Why N45's? Do N50 grade magnets not come in that size?

Very awesome! You're going to make me one too, right? HAHA
Nov 17, 2004, 08:17 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Sorry. No commercial product plans. Commercial choices relatively soon will be Uttam's and his dad's 3.5g outrunner and Gary Jones' 7g disc motor.

Peter Maul is right about disc player motors. He and I traded a number of emails about this. Essentially you have to take a chance on a disc player not knowing if it will have an outrunner or disc motor in it. I got very lucky and found one on Ebay that had these stators in it. I then bought the remaining 5 players from that source. My average cost with shipping is about $15 per disc player. Along the way I bought a iPod hard drive for $45 only to find out that it has an inrunner motor not an outrunner.

If you want to do the LRK motor Mike Cross may begin selling stators for people who want to experiment on their own as we have here.

Experimenting requires at least a lathe and some specialized items like collets in the 2 to 3mm diameter size, tiny boring bars, and reamers etc. I laid in about $300 in new tools for my lathe to work on these motors. But, I probably got more sizes of various tools than was required as I really didn't know what direction it was all going to go (e.g., reamers in 0.005 inch increments are about $20 each, small collets are about the same, and collet holder and adapter are about $100). Our front bell weighs 0.16g. I'm pretty sure one weighing about 0.25g can be machined without CNC cut pie-shaped openings by simply boring four holes in the front. So, if one has a lathe and reasonable set of companion tools this is all possible. Unfortunately people are probably not going to be able to work on stuff this small with just a 3-jaw chuck.

N45 magnets were used as that's what was available in the correct size. N50's are only recently available in fewer sizes. Check out the magnets at Engineering Concepts. Can't buy what isn't there without ordering 1,000 custom magnets.

One other thing. The theoretical lower limit in weight for the mini disc motor is about 1.8g. Winding weight can be reduced by almost half by winding every other tooth. And, magnet weight can be cut in half by going with 4-magnet poles rather than 8, resulting in a loss of torque. But, it's unknown how well the motor would run in either situation and are for further experiments. Also, 0.08g can be added by going to 10 magnet poles, winding the stator differently, and going from a 4:1 turnaround ratio to a 5:1, resulting in more torque.

Last edited by Gordon Johnson; Nov 17, 2004 at 09:01 AM.
Nov 17, 2004, 09:21 AM
Registered User
Amazing work.
Nov 17, 2004, 01:58 PM
Registered User
CA'ed fingers's Avatar

Can't wait for commercial versions for my conversion projects...

Nov 17, 2004, 03:01 PM
FASST flyer
KatManDEW's Avatar
Continually amazing Gordon.

I'm going to expose some of my ignorance here and ask what LRK means?
Nov 17, 2004, 04:21 PM
Team30 Micro EDF
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