cdrom motor with aluminum bell machined - RC Groups
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Oct 07, 2003, 10:05 AM
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cdrom motor with aluminum bell machined

can any one tell me if you can machine the bell out of aluminum to mount the n45 magnets or does the can have to made out of steel???? i have tried this and the performance dosent seem any better then the gray magnet matl. there is alot more magnetic cogging. but doest the metel effect the performance or is just cheeper to make them out of steel? thank you for any help. marke
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Oct 07, 2003, 10:45 AM
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mmormota's Avatar
The bell of the PJS motors is plastic with glued magnets... Maybe there is a iron ring under the glue, but if there is any iron it has to be very thin... I don't think so.

I am curious too about the real importance of a iron ring. In theory of course it is better, but how it affects the parameters, the efficiency etc.?
Oct 07, 2003, 11:13 AM
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these are photos of the motor. i have not run this one yet. this is number 2 the first one looks the same except this armature hade more room to wind the 18 turns of 26 awg wire.
Oct 07, 2003, 11:16 AM
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here is the winding
Oct 07, 2003, 11:44 AM
Grand Poobah of Nothing
Trizza's Avatar
Beautiful, beautiful work. Did you make this?

In theory the iron should increase efficiency, thus power.

The iron ring to be most effective should probably be soft iron. At this scale though losses shouldn't be too large, so it should run well without.
Oct 07, 2003, 11:51 AM
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thank you yes I did make this. The reason I did this was to allow more room for the 5x5x2 n45 magnets. I am using this in a micro heli. but i am not that impressed with the perfomance compared to the orig. gray ring style magnet . but ill try this one and let you know how it works. marke
Oct 07, 2003, 11:54 AM
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norbique's Avatar
Hey Marke,

What did you do with the aluminum to look pink/purple?
Also what type of CD drive did this stator and bearings come from?

Last edited by norbique; Oct 07, 2003 at 12:15 PM.
Oct 07, 2003, 11:57 AM
Registered User
The iron in the rotor provides a high permeability return path to allow the magnetic flux to travel from the back side of a magnet to its neighbors. This helps to increase the magnetic field strength in the motor gap - you will get more cogging and a lower Kv, and better efficiency. You can get similar effects by using bigger and/or better magnets, but steel is cheap so it is a good option. The steel doesn't need to be very thick to be quite effective; a millimeter should be thick enough even with very good magnets. Your windings are beautifully made, from an efficiency standpoint you will get better performance if you cram more copper in there (there appears to be space available).

Oct 07, 2003, 12:04 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Originally posted by Trizza
... In theory the iron should increase efficiency, thus power ...
No Trizza, in fact, efficiency will slightly decrease due to eddy current losses in the bell and increased fluxin the stator (higher eddy currents and hysteresis losses). But the motor can swing a bigger, more efficient prop thus increasing overall efficiency. Without steel the motor will probably not run at all.

The bell has to be steel: st37, st38 etc. Carbon, aluminium, wood, plastic will give a very high rpm and little torque. The iron will not give you more power.

Lovely job
Use thicker wire or two (slightly thinner) wires in parallel to use up as much slot-space as you can, the way tclark explained.
When will you start producing in quantities? (Using a steel bell)

Met vriendelijke groet Ron van Sommeren
diy outrunner brushless e-motor discussion.
Electric fly-in & lrk meet, June 27th, 2004, Nijmegen, the Netherlands.
Last edited by Ron van Sommeren; Oct 07, 2003 at 04:50 PM.
Oct 07, 2003, 12:09 PM
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corey's Avatar
How do I place an order!
Oct 07, 2003, 12:20 PM
Just an average RC'er
Jim McPherson's Avatar
Ron: I understand your argument about needing steel however the PJS motor run quite well with high torque and use a plastic bell. Any idea as to why they work so well?

Oct 07, 2003, 12:22 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Jim, I don't know how the PJS motors are build. Is the bell really plastic or plastic covered?
Oct 07, 2003, 01:07 PM
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finish on can

I do my own anodizing at home and the color is purple rit dye. as far as the iron ring i can try a strap around the out side of the aluminum but my concern is the gap made by the alum. may be to much to do any good. the other thing i could do is make a cut on the inside where the magnets are and place the ring inside. the metel i would use is called nickel/iron 50/50 this is what is used in torque motors for aircraft. I agree about the hysterisis. the iron will short out the flux. the first motor i made works and looks the same but dosent have the get up and go I would expect. as far as the windings the first motor was jammed full with 18 turns of 26awg. Thank you every one for the help Marke
Oct 07, 2003, 04:52 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Can you put up a picture of the inside of the bell? You only need steel (strips) between the magnets, not necesarrily behind the magnets.
Oct 07, 2003, 06:02 PM
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Ænima's Avatar
would you get the same effect if the magnets are touching??

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