Help with number of winds for cd-rom motor. - RC Groups
Oct 07, 2002, 09:21 AM
Registered User

# 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.
 Oct 07, 2002, 10:01 AM Registered User 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 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 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: https://www.rcgroups.com/forums/show...threadid=37545
Oct 07, 2002, 02:32 PM
homo ludens modellisticus
Quote:
 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:
www.yahoogroups.com/group/lrk-torquemax

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):
www.yahoogroups.com/group/lrk-torquemax
-> 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:
http://www.aerodesign.de/peter/ (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:
http://groups.yahoo.com/group/lrk-torquemax/message/842

And of course the lrk/cd-rom outrunner discussion, moderated by yours truly
www.yahoogroups.com/group/lrk-torquemax
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 '.'