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Nov 13, 2006, 08:10 AM
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Thread OP

Brushless motors in the mg range?

Did you never wish to have an even smaller motor than the Shicoh?
Here is a general solution.
Take a small magnet/coil actuator. Put a small prop on it. Connect it to a microprocessor. Write a clever SW. Blow to the prop to start it and it will perfectly run. That's all you have to do for the simplest version.

The SW measures via an ADC the EMF as long as you blow on the prop and determines the switching points (zero voltage). At the switching points the polarity of the output will be changed. Just before the next switch point is reached the program changes to input and measures the EMF again, until it is zero.Then the process repeates.
For those, who are not familiar with programming it sounds awful. But this is a very short program.

You need more power?
Make a new coil with lower resistance and add two double fets to the processor (SC70 for electronic freaks, = 12mg).

You need better efficiency?
Reduce the diameter of the axle.
Make an additional coil. Place it 90 degress apart and modify the SW, i.e. switch close to every 90 degrees. As a further improvement make two out of a single coil and place them opposite of each other. Thus you avoid the forces you get in addition to the torque, which improves the efficiency.

Here some experiments: 200mg motor single phase = 1 coil, 16mm prop dummy, speed control from 2000 to 30000rpm. Processor Cygnal F330 (too large, others will do as well, e.g. PIC10F222 = 15mg).
About 200mg magnet operated at maximum speed via a Hall sensor switch, no load: 450000rpm! Then the magnet exploded like a bullet! I hardly survived!

I have some programs to analyze these motors and have some SW.It is not yet perfect, but good enough to start.If somebody is interested in building such a motor, let me now the application and we can design one together.
By the way I can test thrust levels with my smallest thrust rig to 5mg (scale has 1mg resolution). So if you built something very extreme it can be tested.

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Nov 13, 2006, 09:20 AM
Micro Jet Pilot
Chris T's Avatar
That sounds great. I have been thinking about this before. I was wondering, if efficiency could beat pagers though. On the other side, you might easily get more power/weight than from a pager...

Will you share your software? What about a tiny fan?

Last edited by Chris T; Nov 13, 2006 at 09:31 AM.
Nov 13, 2006, 10:20 AM
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rguillot's Avatar

little brushless


I(we) tried, but the controller business is out of my realm:

Hey Chris
Nov 13, 2006, 11:00 AM
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Thread OP

this is no problem for me. We only have to decide what we want. Shall we as a first step design a unit around 100mg, operating at 3.6V? I will make a proposal based on the magnet of the Shicoh motor, though shortened. We can start with a single phase motor (1coil) and a Hall sensor. Then you need no electronics experience. I will provide the electronics. Later we go to the processor.
I have not yet killed a Shicoh motor. Do you know the diameter of the magnet? I need thisfor the design.

Nov 13, 2006, 12:16 PM
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rguillot's Avatar
Don't know that dim. off the top of my head. The ID of magnet is 1mm, inside of can is 2.9mm. I'll get it today and post it in about 5 hours. Did you read through that whole thread? There were quite a few sharp minds at work. I did get good at making the coils, winding them and transfering them to a delrin former and binding it together with epoxy. Can you do this?

Why do you need to shorten the magnet? just weight reduction?

Nov 13, 2006, 01:07 PM
Registered User
Hi Helmut,

Do you have any pictures/schematics of your motor/controller ?

best reguards,Dennis

PS: verstehst/sprichst du Deutsch ? In deinem Profil konnte ich (leider) keine Angaben finden
Nov 13, 2006, 04:41 PM
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rguillot's Avatar
Shicoh magnet is 1.87mm OD, 1mmID. Length is 4.25mm.
coil is 2.15mm ID., 2.65mm OD. OAL 6.6mm
Case/carbon tube is 2.9 ID.

More info later.

Nov 13, 2006, 05:16 PM
Registered User
Thread OP
Thanks Robert for the Info.

I will explain the schematic and SW a little later. Too many things are just going on. Besides my hobby I do some work like developping a new IR Sytem: fast and more than 4 channels in parallel.
Yes, I speak fluently German after living 67 years in Germany. But how is my English? I just made a visit to the US.

Nov 13, 2006, 05:31 PM
Registered User
Finally something I can respond to! Your english is quite good, Helmut. Sometimes you use a word that is unnecessary because you have already established what you are trying to get across. Take the below quote:

"I will explain the schematic and SW a little later. Too many things are just going on."

This is completely understandable and is proper english. However, the word "just" in the second sentence is not needed. You use the present tense when you say "too many things ARE going on" and if something is going on in the present, it is by default "just" going on.

Sorry to go off topic but I dont know how to program a pic or wind an act. This is the area that I could add value to
Last edited by lightflight; Nov 13, 2006 at 06:01 PM.
Nov 13, 2006, 10:32 PM
Registered User
rguillot's Avatar
I don't think Helmut needs English lessons
Nov 13, 2006, 11:22 PM
No, but he did ask ;]

As far as this stuff is concerned though.. I'm pretty thrilled to see that you guys are still making awesome headway!

Imagine.. a brushless motor that small? I'm sure you'll be all over that like white on rice, Robert.

Nov 14, 2006, 05:48 AM
Registered User
Thread OP

here is how we shoud start/proceed.
- Take a magnet from the Shicoh motor and install a 0.3mm or smaller diameter axle.
- Make a coil from 37micron wire (I have some 80km!), such that the magnet fits inside. Inner dimensions: 4.5 by 2mm. 3m wire is ok, about 200 turns. The width of the winding tool should be 1 to 1.5mm. Put some resin on the coil. Wait until it is almost hardened. Take it out the winding tool. Press carefully a cylindrical rod with the OD of the bushing onto the coil, in order to form a bed for the bushing.
- Have 2 bushings ready for the axle. Slide them over the axle.
- Fix a prop dummy at the outer end of the axle, a small wooden bar.
- Lay this assembly on/in the coil and fix the bushings with a very tiny drop of glue.
The motor is ready.
Most probably the glue did also fix the axle. You have to loosen it by turning the prop dummy/magnet assembly. It takes some experience to fix the small bushings.
This motor weighs about 100mg. It is a single phase motor and needs to be switched every 180 degrees.
It will provide the same output as the Shicoh motor with less current, but higher speed.
If you have a function generator you may test this unit at a low frequency. You have to start the motor externaly. Next week I will provide the info on the electronics.

Nov 14, 2006, 05:54 AM
derk's Avatar
so the basic motor runs like an ac motor you would plug into the wall. those only use one coil but most use inductance rather than a magnet but the same in principle right?
Nov 14, 2006, 06:33 AM
Micro Jet Pilot
Chris T's Avatar
I think, if I find time I will try this with a 4mm or 6mm pager and its original axis. I don't think I can handle the real small stuff. And anyway, a 0.5g brushless is a big enough step forward for me. Do you think this will work as well?

Nov 14, 2006, 03:41 PM
Registered User
billystiltner's Avatar
Sounds like fun.


With the open loop smoovy controller I could get the motor to start by itself but Never got around to winding another motor with low enough resistance to spin up to more than around 13000RPMS if I remember correctly. I think My next step was to wind a motor with 5 ohm coils.


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