Help with number of winds for cd-rom motor. - RC Groups
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Oct 07, 2002, 09:21 AM
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Frank B's Avatar

Help with number of winds for cd-rom motor.

I have got an old cd-rom drive, and would like to make my own brushless motor, but I need some help in determining the number of winds I will need.

The cd-rom motor has nine poles.
My power source will be 2 Li-ion cells (7.2V - 750mAh)
I would like to swing a 6.9 x 6.3 prop at max. 2A (full throttle).

I would prefer direct drive if possible.
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Oct 07, 2002, 10:01 AM
Registered User
Steve McBride's Avatar
9 pole CD ROM motor is fairly typical (in my experience). Swinging that size of a prop direct (that pitch is pretty steep), I would start with about 20 turns, measure current and then adjust accordingly (less winds = more current).

Others with more experience will probably be better able to zero in on the correct number.

Good luck!

Steve McBride
Oct 07, 2002, 10:10 AM
Registered User
senor_paco's Avatar
are there any tutorials on how t od othis? I have become quite fascinated lately over this, and when I was a boy, used ot make motors from paperclips, etc, so have some exerience in the matter.
Oct 07, 2002, 10:44 AM
rebmeM roineS
MrBungle's Avatar
Not a tutorial, but TONS of info if you read through every page(there are 54 of them to date) and pick out all the good bits.

Home made Brushless:
Oct 07, 2002, 02:32 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Originally posted by senor_paco
... are there any tutorials on how t od othis?...
E-mail discussion group on homebuilding brushless outrunners, lrk and cd-rom types:

Motor winding 'rules':

A winding diagram (star-Y configuration) for a 9-pole cd-rom motor:

A winding diagram for a 6-pole motor (4 or 8 magnetpoles, not a true lrk):
-> photos
-> winding diagram
The picture is for instruction purposes only, it's not a 'live' motor, too few windings and too thick insulation.

Please keep in mind, a rewound cd-rom motor and also the so called 'mini lrk' are *not* true lrk's, they are fundamentally different. CD-rom motors are classic 'synchronous self (ok.the controller does this ;-) commutating motors. LRK type motors use the lrk/sps winding diagram, only half the armature teeth are wound! Both use the standard brushless controllers.
See: (English and German)

So, the lrk winding calculation tools are not applicable for cd-rom motors. There are so many different cd-rom makes and types, it's impossible to come up with a 'catch all' formula. You have to experiment with the number of windings. Use a current limited power supply!

More cd-rom technical information and links here:

Threads on cd-rom motors:

And of course the lrk/cd-rom outrunner discussion, moderated by yours truly
You'll find a Frequently Asked Questions document on that site. I'm working on a newer version with more tricks and cd-rom links, just send me a message at ron-van-sommeren@hetnet-nl if you would like to receive a copy. Replace the '-' in my adres with '.'

More threads:

On the homepage you'll find the most important links, the FAQ has lots more. Check out the 'photos' section there.
Last edited by Ron van Sommeren; Oct 07, 2002 at 02:38 PM.
Oct 07, 2002, 02:45 PM
rpage53's Avatar
As Steve said, you have to experiment with your particular motor. Each one has different stator sizes and magnet strength. You could start with the windings it has now with that prop and check the current. It could be close to 2A already.
If it is a typical 52X CD-ROM somewhere around 30 winds would be typical. If you start with too few winds, you might overload the controller.