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Old Feb 17, 2004, 10:19 AM
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LRK and other larger homemade brushless motors


This thread is for those who wish to post results from their experiments with building LRK and other brushless motors larger and/or different than the "standard" CD-ROM motors. I know there are several people on E-Zone who have mentioned - at least in passing - that they are working with mini-LRKs, VCR, FD, and other "unconventional" motors. So let's hear it, folks!

I'll start with this motor that many of you will recognize from the "One hour CD-ROM" thread. It began life as an unknown brand stepper motor. It had a heavy, rubber magnet ring, and all 24 poles were wound with 120+ winds of a very fine wire. I originally wound it with 18T of #20, as you see in the photo, and set it up with 14 magnet poles NN SS NN, etc. It didn't run, but only chattered and whined. Ron van Sommeren and his German friends correctly diagnosed my problem as being the magnet poles, which were covering more than one stator pole simultaneously, causing the motor to work against itself. I reconfigured the magnets (5x5x2 mm each) to 28 individual poles, and the motor ran. The winding was too hot, though, and it drew 5.5A no-load, so I rewound it last night with 22T of dual-strand #24, which packed a lot more wire onto the stator poles. I'll try it this evening when I get home, and post my results.

As you can see, the windings on this one are different than the standard CD-ROM rewind. The winding pattern is ABCabcABCabc, where ABC poles are wound CW, and abc poles are wound CCW. The speed of the motor is definitely slower, so I'm hoping it will swing a fairly large prop of 10-11". I just need to come up with a prop adapter; the shaft is 3.3 mm, and I had to grind it down to fit the 3x6 mm bearings - a nasty chore, at best.

Tony Turley
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Old Feb 17, 2004, 10:36 AM
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homo ludens modellisticus
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The other problem, apart from the magnet versus tooth size, was that for an 24 statorpole lrk motor you have to have 20, 22, 26 or 28 magnetpoles, not the original 14. !4 (or 10) magnets for 12 teeth lrk stators.

A better way to describe the winding pattern would be
A-B-C-a-b-c-A-B-C-a-b-c-
Where the '-' denotes an empty tooth.

Since you stator is not very heigh, it could be advantageous if you used the distributed lrk winding pattern, lower resistance, slighty higher Kv:
AaBbCcaAbBcCAaBbCcaAbBcC
Neighbouring teeth in one phase or wound the opposite way.

Groeten Ron
Last edited by Ron van Sommeren; Feb 17, 2004 at 10:40 AM.
Old Feb 17, 2004, 10:55 AM
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lrk formulae:
http://groups.yahoo.com/group/lrk-torquemax/message/574
http://groups.yahoo.com/group/lrk-torquemax/message/761

Met vriendelijke groet Ron van Sommeren
diy brushless e-motor homebuilders discussion.
Last edited by Ron van Sommeren; Feb 17, 2004 at 11:03 AM.
Old Feb 17, 2004, 11:23 AM
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Re: LRK and other larger homemade brushless motors


Quote:
Originally posted by t-turley
The speed of the motor is definitely slower, so I'm hoping it will swing a fairly large prop of 10-11".
Tony Turley
I just finished drawing up the "same" motor, I'm looking for a lower Kv, just like you, to turn a larger prop. I am axiously waiting for your post rewind results ...
Old Feb 17, 2004, 12:15 PM
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Here's mine, that I completed several months ago, it is basically a clone of the torcman motors, using the typical naming convention it would be a LRK 360-21-16 (36.0mm stator dia, 21mm stator length and 16 winds). Swings a 16x8 APC-e direct drive at roughly 6000rpm Pin is around 650W, Amps around 45+ static, batts are 4S2P Tanic 2200's, Castle Creations Phoenix 60, 16 winds of 18ga magnet wire, 5mm drill rod for the shaft, bearing are out of old harddrive. Truly an amazing motor to fly, so quiet and powerful.

Here's a link to the plane its in:

https://www.rcgroups.com/forums/show...hreadid=169750

If you go on Ron's torquemax Yahoo group http://groups.yahoo.com/group/lrk-torquemax/ I have a photo folder with lots of pictures under the name mykarmstrong.

Mike
Old Feb 17, 2004, 12:17 PM
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One more...
Old Feb 17, 2004, 12:20 PM
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Last one.
Old Feb 17, 2004, 12:53 PM
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cd brushless motors rule!
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Hi Tony!
Very nice motor, looks a lot like mine, except mine has 15 poles...
It works as a direct drive helimotor in a micro heli. It's really great, no gear noice.

I've been searching all over for 24 pole of 12 pole stators, i would like to try a big diameter lrk in it, to shave some weight of maybe. Where did you find yours? I'd love to try LRK..

Mine's from a 3.5" floppy disk drive. Actually its a mix, the bell comes from another motor.

here are some pics of it mounted in the heli;




a pic to prove it flies


more here; https://www.rcgroups.com/forums/show...hreadid=197862

Niels
Old Feb 17, 2004, 01:59 PM
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Quote:
Originally posted by niels polfliet
I've been searching all over for 24 pole of 12 pole stators, i would like to try a big diameter lrk in it, to shave some weight of maybe. Where did you find yours? I'd love to try LRK..
Niels,

I don't know the source of the motor. A friend of mine knows that I like messing with homemade outrunners, so he gave me a box of old drives and motors. This motor had already been pulled from whatever device it was in. That's a great job you did with your motor.

Mike,

That is a great looking motor. Where did you get that stack of statorplates? I'd like to find a stator or statorplates with a 23 mm diameter. I did find an old Syquest cartridge drive that had a 23 mm stator, but the stack was only about 3 mm thick.

Tony Turley

PS: I'm hoping to get a mini lathe this summer, and begin some custom work.
Old Feb 17, 2004, 02:25 PM
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Quote:
Originally posted by t-turley

That is a great looking motor. Where did you get that stack of statorplates? I'd like to find a stator or statorplates with a 23 mm diameter. I did find an old Syquest cartridge drive that had a 23 mm stator, but the stack was only about 3 mm thick.

Tony Turley

PS: I'm hoping to get a mini lathe this summer, and begin some custom work.
Thanks Tony, I got the stator material from an old palm sander I had laying around. Alot of hand powertools that run on AC have 12 pole stators, I even looked at some new cheap sanders at sears for $19.00 that would make good donors. The only drawback is that the laminations are fairly thick which somewhat reduces the efficiency of the motor (eddy durrent losses) but I am totally satisfied with mine, it really goes like a bat out of you know what So go raid the shop, mommas kitchen (mixers, blenders, etc), local junk yard, electrical repair shops, you'll find a bunch of sources. Good Luck

Good looking heli motors guys, that is awesome a direct drive heli, never though I'd see that.

Mike
Old Feb 17, 2004, 04:26 PM
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Tony,
Take a look at www.batt-mann.de
they have 23 mm stator plates (22.8 actualy)

Hrvoje
Old Feb 17, 2004, 06:48 PM
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Thanks Hrvoje. For you or anyone else that speaks German, I have a few questions about that site. A screen capture follows. What does "paketlange" mean? Alta Vista translated it as "package for a long time", but I really doubt that is accurate, considering a dimension in mm is given. Also, what is "Elektroblech M270-50A"? And finally, I assume the prices on the right side are given in Euros?

Tony Turley
Old Feb 17, 2004, 06:56 PM
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Here are the promised results from my testing of the rewound LRK this evening. With 22T of dual-strand #24, the no-load current dropped to about 3A. With the 10x7 APC SF shown, it drew 9A from a 7-cell 600AE NiCd, but only turned the prop at 2600 rpm!! I took that measurement several times, to be sure. What next, guys? I doubt that 2600 rpm would do more than drag an airplane down the runway. I'd like to get the rpms up without drastically raising the current.

Tony Turley

PS: the line you see through the cooling hole was made by a Sharpie marker, when I was attempting to get the no-load rpms. It didn't work.

PS PS: Hey Ron, I looked at those links you posted above. Peter's 68.5 mm 24-pole motor sounds like it is a real stump puller. 60A & 1450W!! I'd like to limit mine to 15A or so, all the while getting around 5000 rpm or so on the prop.

Tony
Last edited by t-turley; Feb 17, 2004 at 07:25 PM.
Old Feb 17, 2004, 07:00 PM
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Old Feb 17, 2004, 07:59 PM
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mike, can you give some more detail about how the bell is attached to the shaft? also, I am working on a 50mm stator diameter, 12 pole motor... current stator height is 12.5mm, but I can double it up and make it 25mm (use two stators) by remaking the bell. I know not to exceed 2/3 length/stator diameter ratio, and that the same wiinds will turn faster on the double thick stator... but if I wind twice the winds on the thicker (using thinner wire), how will it compare to half the winds (with thicker wire) on the thinner stator? other than be able to absorb more heat, what would be the effect?

tony, how about testing with a popsicle stick for no-load rpms, and a larger prop or two fo some more data points? I'm guessing you're going to need fewer winds, for 12-pole I'd guess 10-14 for 8-cell, but for a 24-pole I'd guess much less...


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