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Old Jan 19, 2004, 12:13 PM
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galloping gimp's Avatar
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ronin8451 and Rad Racer-

If you are using a 9-pole stator, I believe the number of magnets needs to be an even number that is also a multiple of 3. For the typical small CD-ROM motor, most people are using 12 magnets.

You do not want an arrangement where all the magnets line up with the stator poles. This might seem logical, but it's not how these motors work. This means, for example, that a 9-pole stator with 3 magnets will not work.

One assumption is that you're using our typical 3-phase brushless controllers.

- Jeff
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Old Jan 19, 2004, 12:38 PM
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Weatherford, Tx.
Joined Oct 2003
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I will go to 12 magnets as it seems to be working best for most people. I machined a mount for mine that will clamp on to the brass "tube" on the back of the stator and has a .375" square cut at the top for mounting to a GWS style stick. I will post pictures later if it works as planned. Thanks to all with the help!
Rick
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Old Jan 19, 2004, 12:50 PM
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INDEPENDENTLY POOR in OHIO
Joined Dec 2001
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Depdog

The following applies to ANALOG meters that display several values on the meter face

R is the acronym for resistance measured in ohms and on larger volt/ohm meters where there is room for the extra graphics the range selections are displayed as R X 1 or R x 10 or times 100, 1000 or a 100,000 upto 1 meg ohm

For example, if you selected R x 1000 and the meter read 8, then you have just measured 8,000 ohms

It's funny but I did not realize ( until you asked the question ) that R times the reading on the meter = how many ohms does not apply to a DIGITAL meter.

You simply select the range and read it direct.

(use lowest range for checking for continuity of the wires ) and the highest range when checking for shorts to the stator

Sorry if I confused anyone and I hope my expanation didn't make matters worse!

Roger aka GIFLYRC
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Old Jan 19, 2004, 02:13 PM
Hi Wattage Electrics - Cool
Rad Racer's Avatar
Jordan, Minnesota
Joined Jan 2004
618 Posts
Quote:
You do not want an arrangement where all the magnets line up with the stator poles. This might seem logical, but it's not how these motors work. This means, for example, that a 9-pole stator with 3 magnets will not work.
Jeff,

Your exactly right, 3 magnets can not work...the stator would be magnetically locked in place. I also agree that you don't want all magnets lined up with all the stator poles.

What I have discovered is with a 9 pole stator and 12 magnets, 3 of the stator poles will be lined up with 3 magnets....the remaining 6 poles do not line up. The motor controller determines (syncronizes) which set of poles (3) should be energized, so it can pull itself to the next set of magnets.

I believe this syncronization happens when you first turn on your motor controller...it bumps the prop back and forth then spins forward. Thus sync'ing itself to the motor.

I know this same magnetic line up, happens with 6 magnets.... I'll look into 18, 24 and 30. (even multiples of 3)

Wow, who would have thought this stuff could be so technical.

Wayne
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Old Jan 19, 2004, 08:13 PM
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ni'ihau
Joined Nov 2003
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Here is a cool drive that I hacked from a Mac gizmo-drive. I am not computer savy enough to download the LRK Torque-man delux winding/wire size spread sheet.
Any one have a good starting place (19 winds of 34???) I don't mind winding these things over and over
jimbo
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Old Jan 19, 2004, 10:19 PM
Hi Wattage Electrics - Cool
Rad Racer's Avatar
Jordan, Minnesota
Joined Jan 2004
618 Posts
This is my latest CD motor, a direct drive version.

I mixed and matched CD rom parts to find a bell \ stator combination that would accept 5x5x2 mm N45 magnets.

I decided to build the motor backwards if you will...... heating is a problem when you start pushing lot's of amps....so I built it to self cool, like my ducted units. It work's, this motor stays cool even when pushing lot's of amps ~14 amps.

The motor mount won't work in all planes, this mount was I fabricated for my latest plane.

The complete motor weights 28gr just as pictured w/prop.

I have just started testing.....the motor is hot!! thrust is awesome, although the current draw is to high. I plan to try star winding as part of my testing.

Current motor:

12 turns, 4mm wire
6 5x5x2mm N45 magnets
billet bearing housing
MP Jet 3mm prop adapter

More spec's to come.
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Old Jan 19, 2004, 10:23 PM
Hi Wattage Electrics - Cool
Rad Racer's Avatar
Jordan, Minnesota
Joined Jan 2004
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FYI, for more motor assembly pictures, you can check out the follow thread:


CD Rom motor assy. pictures
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Old Jan 20, 2004, 11:09 AM
homo ludens modellisticus
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The Netherlands, GE, Nijmegen
Joined Feb 2001
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Quote:
Originally posted by t-turley
After another evening in front of the TV. LRK winding, 18T of #20. Magnet ring was 2mm black rubberized compound. The friend who gave it to me thinks it's from a VCR ...
The big one, with the 'teething' teeth, looks like it's from a stepper motor.
Quote:
Originally posted by t-turley
What would be the advantages/disadvantages of 10 magnets vs. 14?...
14magnets for more torque/Amp (= Kt) and lower rpm/volt (=Kv). 10 magnets will give you a higher Kv and a lower Kt.
Quote:
Originally posted by t-turley
... Is 28 the correct number of magnets needed? I plan to go with the star configuration.
Or 26. 28 magnets will gave you a field/shaft ratio of 14:1, 26 magnets gives 13:1, 22 gives 11:1 and 20 gives 10:1.
Quote:
Originally posted by soundman
... Some people have been double winding.....what effect does double (or more) winding have, examples:
a 30 turn single wind motor vs a 30 turn double wind motor.
Hardly noticeble, if at all.
Quote:
Originally posted by soundman
... a 30 turn single wind motor vs a 15 turn double wind motor.
30 turn has lower Kv (roughly twice) and higher Kt than 15turn (roughly twice). Latter will have half the Ri.
Quote:
Originally posted by ROGER GANTZ
Quote:
Some say it is better to have more surface area and double wire does have more surface area. I am not sure of this effect.Satoru
TRUE.
and this is because electrons are lazy seeking the path of least resistance so that they avoid flowing through the center of the wire and prefer to flow near the outer surface----therefore a double wind increases the surface area about 33 % vs. / single wind.[/B]
Skin effect does not come into play at the frequencies (and their harmonics) in RC e-motors.
Quote:
Originally posted by ronin8451
... I have a problem which I believe is in my quantity of magnets. I have the large stator Toshiba drive with bearings that I rewound to 27 turn single with #26 wire (green Radio shack) "Star" config. and put 8 n45 magnets in the bell N-S-N-S-N-S-N-S at 45 degree increments.
Use either 12 for high torque/low rpm or 6 for higher rpm/lower torque.
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Last edited by Ron van Sommeren; Jan 20, 2004 at 03:27 PM.
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Old Jan 20, 2004, 11:28 AM
Why not Delta?
rysium's Avatar
Sacramento, CA
Joined Jun 2003
1,714 Posts
19 grams high static thrust motor

I have posted this question in 10g motor, but nobody bothered to answer it yet, so I figured out, I used the wrong place.
I think this place is much better for my question, so here it is:


I need a suggestions for direct drive with max static thrust system?

Here it is what I have:
- small 20mm diameter stator (5mmx5mm poles),
- rotor with 12 5x5x1 magnets

I want to run it from 2s1p 340LiPo (7.4V) drawing no more that 5A. I'm going to use GWS 9x4.7 prop direct drive and I want to turn it 4-5k rpm (or GWS 8x4.7 turning 5-6k rpm). As I said, no gearbox.

You guys played a lot with DD systems, but I used my CD-ROMS with gearboxes only. So give me some numbers (rough estimate) for the number of turns and wire thickness. Something for the first guess. In example what would be better for 7V: 20, 25 or maybe 30 turns? For Phoenix 10 shold I use delta or star connection? I can figure the wire thickness from the space I have and reasonable resistance. Just bring me your experience and say the number

So, anybody?

RysiuM
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Old Jan 20, 2004, 01:03 PM
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Quote:
Originally posted by Ron van Sommeren
(Lots of good stuff snipped...)
Thanks for the info Ron.

Tony Turley
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Old Jan 20, 2004, 01:58 PM
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Joined Mar 2002
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had trouble winding...

with the RS 26gauge wire last night. i am using a standard type of cdrom similar if not identical to the one used at the beginning of this thread (Part 1).

just to get a proof of concept going, is it ok if i use the thick 22 gauge wire? it will give me only 5 winds but i only want to see it run. however, i am afraid that it might smoke my new cc phx-10.

how do the number of turns affect the amp draw? isn't there a trade off between having a lower resistance wire like 22g versus higher turns with a 30g setup that would have higher wire resistance but also higher number of turns?

the 26gauge was giving me about 15 turns or so but i kept on scraping the wire and either breaking or shorting it.

i tried 3 times last night but won't give up yet.

any thoughts on the 22 gauge wire is appreciated.

thanks,

jeff
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Last edited by burgan; Jan 20, 2004 at 02:01 PM.
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Old Jan 20, 2004, 03:25 PM
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Jeff,

I found the #22 to be tough to get around the poles of a motor that was about 75% larger; I'd think you'd have a real tough time getting it around the poles of a standard CD-ROM motor. I wouldn't try that # turns with a 10A ESC, either. My 10T dual-wind with #26 pulls over 8A with the stock magnet - I bet 5T would pull quite a bit more.

I had a LOT of trouble with shorts when I first began winding the little outrunners. It took me a while before I developed some finesse. You want to pull just hard enough to get a snug fit around the poles. Keep at it - you'll eventually get the hang of it.

Tony Turley
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Old Jan 20, 2004, 03:52 PM
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tony, thanks for the info..

that's exactly the kind of info i needed.

i will trod on with the 26gauge with more finesse. the local radio shack said they had "plenty" of the magnetic wire on their shelf. i'll stop by and pick up some more.


thanks,

jeff
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Old Jan 20, 2004, 04:58 PM
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mmormota's Avatar
Budapest
Joined Jul 2003
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Re: 19 grams high static thrust motor

Quote:
Originally posted by rysium
[I]Here it is what I have:
- small 20mm diameter stator (5mmx5mm poles),
- rotor with 12 5x5x1 magnets

I want to run it from 2s1p 340LiPo (7.4V) drawing no more that 5A. I'm going to use GWS 9x4.7 prop direct drive and I want to turn it 4-5k rpm (or GWS 8x4.7 turning 5-6k rpm). As I said, no gearbox.

RysiuM
I am afraid this is too much for that small motor. For optimum efficiency at this prop diameter you need a lot of turns on the stator (more then 40), and the max rpm will be low, much lower then your requirement.

A 6*3 or maximum a 7*3,5 is a better choice. If the thrust is not enough with this smaller diameter and about 20 turns, you need a gearbox or a bigger motor.

I made careful measurements on a motor in delta and star configuration.
Kv_delta = 1,738 Kv_star //very close to sqrt3 from theory...
Io_delta = 1.6*Io_star
R_delta = 0,345 R_star // this is not the dc resistance, but the Motocalc constant! Close to 1/3 from theory

Seems, that the effect of star to delta modification is very similar to the effect of rewinding it with n_delta = n_star) * 1/sqrt3= n_star*0,577 turns, using thicker wire.

It is interesting, because the magnetic system is different, in star 1 of the 3 windings is without current, while in delta every winding is under current.
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Old Jan 20, 2004, 05:24 PM
Why not Delta?
rysium's Avatar
Sacramento, CA
Joined Jun 2003
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Re: Re: 19 grams high static thrust motor

Quote:
Originally posted by mmormota
A 6*3 or maximum a 7*3,5 is a better choice. If the thrust is not enough with this smaller diameter and about 20 turns, you need a gearbox or a bigger motor.
Thanks for the input. If I put GWS 7x3.5 direct drive, is it posssible to run it at 8k rpm having 20 turns at delta? Remember, I have N45 magnets - that helps.
I don't want a gearbox, because GWS gearbox weights 12 oz alone. I want it light.

RysiuM
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