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Old Jan 16, 2006, 03:05 PM
Registered User
Tel Aviv-Yafo Sde Dov, Israel
Joined Nov 2002
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18mm duct fan

Hi duct fun lovers

Just wanted to share with you a micro duct fan that I've made. It started with wanting to make a brushless motor to replace an N20 motor. I didn't have magnets for that but then I rememberd I had magnets that I've ordered long time ago for a motor - propelor cupling for a submarine. That magnet seemed to be a good candidat for a small inrunner brushless. Though I had no need for such a motor I decided to attempt making one. Very quickly came the first version which require 1A just to turn itself... The current motor is the third version which differs mainly in the windings and more efficient construction. This motor had such a high free rpm (over 100000 ) that it only made sence to build a duct fun for it


6mm homemade inrunner motor 1.35grams
1mm stainless ball bearings
motor has no metal can! any metal can reduces it's efficiency
Fan+motor 2.07 grams
outside fan diameter 18mm
rotor pitch about 16.9mm, 5 blades
4 stators
all parts are made from Policarbonat plastic and are cnc machined


V ....... A ........W ........RPM .......Thrust [grams]......Grams/Watt

2.8 --- 0.57 --- 1.5 ---- 41700 ----- 4.4 ------------ 2.93
3.0 --- 0.61 --- 1.83 --- 44444 ----- 4.9 ------------ 2.6
3.2 --- 0.66 --- 2.11 --- 47244 ----- 5.4 ------------ 2.55
3.4 --- 0.7 --- 2.38 --- 48000 ----- 6.0 ------------ 2.52
3.6 --- 0.76 ---2.74 --- 50847 ----- 6.6 ------------- 2.4
3.8 --- 0.8 --- 3.0 --- 54054 ----- 7.0 ------------- 2.33
4.0 --- 0.86 --- 3.44 ---55555 ----- 7.4 ------------- 2.15


I'm running the motor with YEG4 controller which is currently set to 0 timming. With an E-tech 90 for example voltatage drop quickly to 3.4 volts and then decay gradualy, so usable thrust start at 6gram down to 4.4grams.

Hope this will give some of you ( especially Chris, I love your jet ) a starting point for your next micro duct fan design.

Nachman
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Last edited by nachman; Jan 16, 2006 at 03:13 PM.
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Old Jan 16, 2006, 04:15 PM
pem
Registered User
Frankfurt Intl, Germany
Joined Feb 2004
293 Posts
Hi Nachman

your ducted fan is incredible ! What a beauty !!!


Your observations with the motor: I think they are completely
valid - especially the influence of a flux ring around.

I made a similar one some time ago based upon a acryl tube
reinforced with carbon and it had above 60000 rpm unloaded. Problem I experienced was a too wide airgap - until I removed the tube around the magnet in total. But I never could make the winding self stable enough
without this tube between the magnet and the winding.
How wide is your airgap at the moment ?

Peter Maul
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Old Jan 16, 2006, 04:40 PM
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Tel Aviv-Yafo Sde Dov, Israel
Joined Nov 2002
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Peter
The magnet is 3.7mm in diameter. The plastic tube is 4mm inside & 4.4mm outside. So airgap is 0.15mm up to the plastic tube. ( and 0.35mm up to the coils ). How did you menaged to wind the motor without a tube, sounds almost imposible to me. The tube in my case is the only thing that holds the motor together in one piece. Nice to see another motor of similar construction. The more windings you put the better. This motor has 1.8m wire long for each coil. The resistance of each coil is about 3 ohms and when connected in a triangle fasion the total motor resistance is about 2ohms between any two wires.
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Old Jan 16, 2006, 05:03 PM
Micro Jet Pilot
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Joined Jul 2005
2,091 Posts
Nachman,
this is incredible. I have started thinking about motors in this range for a fan around 15mm. Great to see, you have the complete solution ready!! What's the exact rotor diameter. What would be the weight without shroud? Looks like a perfect fit for my next project. A 4'' L-39.

I am sooo glad, somebody is coming up with such a nice and fascinating approach.


Keep it up

Chris
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Old Jan 16, 2006, 05:06 PM
pem
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Frankfurt Intl, Germany
Joined Feb 2004
293 Posts
hi nachman

as I removd the winding before we transferred to the new flat over
here I think I can take a better picture. (If I find it
But you see the carbon rod that connects two acryl rings (with the bearings)
and stabilizes the remaining acryl-bars from front of the motor to the rear.

The winding was not distributed like yours (6-slots) but only three and the three
hang at the open ends of the carbon bars. (There was allwas the danger whe the wire got hot - it would bend to the magnet - so didn't trust it for more then prototyping.
Otherwise I would have shown it over here earlier.)

I still think it is a valid concept.

BTW: My winding was lot hotter then yours but the magnets are more then 12mm.
Actually I'm looking into that concept again with a shorter magnet and higher
winding count may hold the rpms a little low.

Good luck for further improvement. I think airgap is one of the the crucial factors.

Peter Maul
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Old Jan 16, 2006, 06:08 PM
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Tel Aviv-Yafo Sde Dov, Israel
Joined Nov 2002
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Chris
The fan without the shroud is 1.7grams, but a smooth shroud is a must, so a balsa made shroud for example won't be any good and tolerances will be hard to get. Maybe a carbon shroud. The fan rotor is exactly 17mm diameter. The inner diameter of the shroud is 17.4mm. The rotor has to be perfactly balanced to spin at such high rpm without waisting motor power on vibrations. About making another one, it's just to hard and time consuming, and having little free time for hobby I ruther not get into making more fans then need. The main and important details are here, so it should give some directions about what can be expacted from a fan this size and what rpm, pitch and diameter seems to work ( at least as a starting point ).

Nachman
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Old Jan 17, 2006, 06:33 AM
Sticky Shepherd
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Oxford/England
Joined May 2001
4,017 Posts
Nachman, fantastic work as always.

On making ducts, these were made using clear crispy heatshrink as used over nicads. The former was made on a lathe, I added a flair to the front and a taper at the rear but if you don't have a lathe or don't think these things will help just form over a suitable tube. They are very light and pretty strong.

I also made a carbon version using carbon braid, it took less than 10min, just wet out with epoxy, slip over the former and wrap with tape or use heatshrink to compress. The former was teflon/ptfe which helped.

ignore the fan in the picture it was just a drinks can mock up.

Graham
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Old May 14, 2006, 01:45 AM
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United States, VA, Clintwood
Joined Nov 2002
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Hey
Nice motor.

I noticed similar thing with homemade 4mm inrunner.
Adding a metal can reduces motors ability to rotate.
I did mess with adding a psuedo flux ring that rotated with the shaft and and am not xertain of its benifits but think that if a proper flux ring can be made that rotates with the magnet, it might improve performance. I just used a peice of wire wrapped around the shaft and shaped it in a half moon shape around the magnet. Someday I'll get back to experimenting with the little 4mm inrunners.

Billy
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Old May 14, 2006, 09:52 AM
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Sterling Heights, Michigan, United States
Joined Nov 2003
500 Posts
Wow nice ducted fan project. Do you have the CNC or CAD files. I would like to attempt something similar, if you don't mind. Have you flown this in a jet yet. Would be great if you posted the files on the thread. Would love to see more people pursue this and show what is possible.

Did you CNC the blades separately and glue them on? I'm still trying to figure out how you built such a fan unit with a conventional CNC machine? Seems like a 4th rotary axis would be needed to make the fan.

Kin

http://www.embeddedtronics.com/
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Old May 14, 2006, 05:11 PM
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United States, VA, Clintwood
Joined Nov 2002
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Graham
Did you try the drinks can prop in the duct?
It is hard to ignore because I recently tried a drinks can prop trying to match one of Robert's carbon props that done so well. The drinks can prop done better than all the similar balsa props I had carved. It was quite a suprize becasue the aluminum prop was out of balance, not symetrical, the pitch was bent in like a F117 fuselage.
What does bent in like an F117 fuselage mean? Well I matched the blade angle at the hub, then in the middle I bent a diagonal line so the tip angle matched the carbon prop so it was what I guess you could call polygonal pitch.

Billy
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Old May 15, 2006, 03:08 AM
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Tel Aviv-Yafo Sde Dov, Israel
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Kin
I didn't get a chance to put it on an airplane. No time since then. I'm sure it will fly one. It does go verticaly carying it's own battery and controller if that counts...
I can send you ( and anyone else ) the files for making one as long as it's for personal use and not commercial use. You need only a three axis cnc machine for making it and a good CAM program . I can also send you the magnet for the motor, I got a few of them.

Regards

Nachman Zimet
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Old May 15, 2006, 05:42 AM
Sticky Shepherd
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Oxford/England
Joined May 2001
4,017 Posts
Billy, no I didn't you just can't bend the aluminium to the right angles and keep it strong. It either needs a press tool making or better just go to making individual blades glued into a hub, lithoplate is even better than drinks can for that although the thickness of drinks cans seems to go down everyday!

Graham
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Old May 15, 2006, 05:44 AM
Sticky Shepherd
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Joined May 2001
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Nachman, I'd love a copy. I have Rhino3D and can import most things. It would be great to mill a tiny version for a 4mm pager even if it was only for fun.

Graham
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Old May 15, 2006, 08:52 AM
foamanologist
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United States, FL, Sarasota
Joined Apr 2006
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I would love to see the file nachman! You can send them to me via email-----
customminatures@yahoo.com. Might help in my explorations!
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Old May 15, 2006, 09:47 AM
Registered User
Sterling Heights, Michigan, United States
Joined Nov 2003
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Wow, that is impressive. I sent you a pm. If you don't mind, could you describe some of the steps you did to CNC such an intricate part? I can see how only one side would be milled. I picture that you had to flip the fan unit around for the other side to finish it off, but I can't picture how you would get things aligned or how you would even hold such a small part. If you have any pictures of your setup, any CNC advice or techniques, I'm all ears. Didn't know it was possible to do what you did with only 3axis. Now to look for some polycarbinate blocks.

Thanks for the inspiration,

Kin

http://www.embeddedtronics.com/

Quote:
Originally Posted by nachman
Kin
I didn't get a chance to put it on an airplane. No time since then. I'm sure it will fly one. It does go verticaly carying it's own battery and controller if that counts...
I can send you ( and anyone else ) the files for making one as long as it's for personal use and not commercial use. You need only a three axis cnc machine for making it and a good CAM program . I can also send you the magnet for the motor, I got a few of them.

Regards

Nachman Zimet
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