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        How To Reduce The Weight Of A 4mm Pager Motor... ALOT!

#1 TimayTheToolman Jan 11, 2004 10:21 PM

How To Reduce The Weight Of A 4mm Pager Motor... ALOT!
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Hey guys,

I've been playing around with 4mm pager motors for a while when I realised how thick there casing was,

So pretty much I cut it off.

The Result: A over half weight 4mm pager motor, well that a guess Because I have no scales sensitive enough.

Still seem to go just as good. Yeah I though some of you room fyer guys might be interested, Like the guy with the 4.5 gram plane...( you could get that weight down to 4.0grams by doing this)


#2 TimayTheToolman Jan 11, 2004 10:21 PM

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Another angle:


#3 billystiltner Jan 11, 2004 11:21 PM


I thought about doing something similar a while back and so did others. I reckon the case forms a magnetic circuit with the elctromagnetic feild. I guess it holds some of the magnetism in, sort of compresses the feild so there is more energy to turn. I'm not for sure if this is really the right explanation but someone that has more knopwledge about the subject should chime in to explain in more detail. I am not sure how much of a performance loss you will see but it may not outweigh the weight loss from removing the can. I have run motors outside the can just to listen to them and was going to do some tests now that I have a multimeter that reads frequency, I can determine how much slower the motor runs outside the can. This is not meant to discourage you by all means throw a prop on there and see how much thrust you can get out of it. I'm interested in the results.

You have done a good job of putting that thing back together.
More progress than I made when I was dabling with it.
I just got around to taking a motor apart and putting the magnet in a clamp then touching 2 wires to the commutator to see if it sounded like it ran as good.

Nice job keep us updated.


#4 billystiltner Jan 11, 2004 11:51 PM

I forgot I weighed a 6mm motor can. It comes in at about .66g.
I guess a 4mm would be around .3g to .5g. I don't have enough to take one apart yet. The first one I burn up I'll try it out if the windings are still good.


#5 TimayTheToolman Jan 11, 2004 11:56 PM

Thanks for the info Billy.

I was thinking the same thing with the case providing essential magnet feild.

If anyone wants this thing to play with they can have it for free, just pm me you address.


#6 Gordon Johnson Jan 12, 2004 05:24 AM

Matt Keennon says without the case the motor loses quite a bit of its power. Another approach has been to turn the case down thinner in a lathe, which also reduced power. Still, you've been inside the motor and know what it looks like inside. That's good.


#7 MGM Jan 12, 2004 11:21 AM

You lose torque moment and gain higher rpm by reducing (turn thinner with lathe) or removing the backiron.
You weaken the magnetic flux, but get a better eta, due to less ironlosses...

As long as the motor can still turn the needed prop-size, this seems ok for me.


#8 mmormota Jan 12, 2004 12:29 PM

I am interested in using a small converted motor (like a pager) as a stepper. Unfortunately I don't know well the pagers.
Is it possible to remove the brushes and just connect wires to the 3 poles of the windings? (a motor similar to a brushless can be driven as a stepper too)

- The inner magnet is the rotor or the windings?

- If the windings are rotating, is there an easy way to to convert it to a rotating magnet one?

#9 Gordon Johnson Jan 12, 2004 01:37 PM

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The magnet is normally permanently fixed to the front bell and does not turn. The windings rotate around it. Here's a picture.


#10 Allan Wright Jan 12, 2004 03:20 PM

The windings on these pager motors look a lot like larger R/C inrunner windings. It looks like these would make a good starting point for brushless conversion.

(edited to convey my thoughts more accurately)

#11 Gordon Johnson Jan 12, 2004 03:40 PM

If you think it's easy you should read Mike Cross' brushless thread. Also, if you make one of these brushless, what do you gain? What if it turns out that all you get is bragging rights that it's brushless?

The magnet is permanently fixed in the front of the bell. This one came out because I drilled it out. Mike machined new front and rear bells for his.


#12 mmormota Jan 12, 2004 03:59 PM

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Also, if you make one of these brushless, what do you gain? What if it turns out that all you get is bragging rights that it's brushless?
Thank you for the photo.

I am trying to make a very small servo. The converted "brushless" motor works as a stepper motor. There is no feedback in the servo, the conroller in the receiver counts the steps and finds the way back to the neutral point.
I already tried the idea with a bigger (converted) motor, it seems to work.

Do you think is it possible to convert it to a brushless inrunner (rotating magnet) or it is too difficult?

#13 Gordon Johnson Jan 12, 2004 06:25 PM

I was referring to using it as a brushless propulsion motor. A servo motor is a different story. Mike Cross would be the one to know if rotating inrunner is reasonable or not.


#14 derk Jan 12, 2004 08:02 PM

well if you do make it a brushless try contacting the smoovy company to get the driver for the motor. them or matt keenon

#15 Allan Wright Jan 12, 2004 10:32 PM

just thought those windings looked a lot like the ones in a Kontronik BL inrunner
that's all. Magnet fixed to the case does make it harder though. I guess the similaraties are not as close as I thought.

I wish they made brushed motors with pager-like windings a little larger.

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