CDROM motor EDF unit working! - RC Groups
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Jun 30, 2004, 09:21 PM
Impossible? Hah!
KreAture's Avatar

CDROM motor EDF unit working!

Finally I got my 5x4x1mm N50 magnets so I could finish my EDF rebuild.
The EDF-unit came from a free-flight plane called "Blue Hunter Ducted Fighter" and was ran by something resembling a 150 motor.

After hacking off the back cone and pulling out the burned (obviously) motor I fashioned a new motor-mount on a cdrom motor that I could screw in place of the 150. I had to drill out the fan to fit my 3mm shaft and ofcource I did this wrong so it came out a tad crooked... But hey, nobody's perfect.

The motor is the groovey part. It's a 20.2mm stator wound with 24ga wite 15 turns pr pole, and with double ballbearings. The can is 24mm outer diameter and 5x5x1mm magnets would create an airgap of -0.003mm so that would be useless. Finally my supplier got ahold of 5x4x1mm mags and so my clearance now is 0.1mm !

On 8 cells it draws 4 amps, WOT. I tried taching it with my tach set to max number of blades (4) but it can't get a good reading. Finally I ended up reading a phase on the motor at WOT with my scope. I got a nice trapezoid with a period of 260 uS. From what I know of brushless motor commutation the phases are commutated 6 times for 1 electrical rev causing each phase to see a sinusoidal or in our case a trapezoidal wave once pr electrical rev.
The 6 magnets in my bell would then be pulled by one N/S pair pr such phase leaving 3 pairs "gearing" the motion down 3:1 so that the rotational period would become 780 uS. That would mean my motor is rotating at 76923 rpm... Isn't this very very fast for only 8 cells?

I found the error! Somehow I had hit the time-calibration on my scope and it was way off. After mopving it back to calibrated position I took new readings.
Now I get a period of 790 uS. This translates to 25316.5 rpm wich I think is more "normal".
Last edited by KreAture; Jun 30, 2004 at 09:34 PM.
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Jun 30, 2004, 09:51 PM
Impossible? Hah!
KreAture's Avatar
Here's some pictures...




The unit weighs 36g (1.3oz) and I'm very happy with the results so far. Now I just have to stuff it in something and fly...
Last edited by KreAture; Oct 18, 2005 at 10:13 AM.
Jul 15, 2004, 12:45 PM
Watts your motivation
roccobro's Avatar
That is sooo cute! Uh, I mean neat looking there Kreature! How much thrust does it put out compared to stock? Does the plane fly like it should? Good job! Lovew the plug/pins configuration

Jul 15, 2004, 01:28 PM
Impossible? Hah!
KreAture's Avatar
The unit has way too much power for it's size, but I have had a hard time measuring it as the pitch is very high. At 30k rpm you can hear it whine like if the blades are stalling.

Here's some failed attempts at using it back in it's original plane. My first mistake was using a Hitec Feather receiver wich glitched almost continously. My second mistake was trying to fly a 7oz plane in 25 mph winds.
My third mistake was not quitting... (Although I was kinda wanting to distroy it.)
(4.3 MB Mpeg)

As you can see, the power is there to stuff a 7oz plane about vertical and I did "hover" it when testing at home (supporting nose) so I cnow it has the power. Problem was total lack of conbtrol with all the glitching and lack of penetration.

Still, it was fun and the unit came though unharmed. I will be building something new for it later. Or maby rebuilding the old fuse to look more like a F-16 thing with low wings.
Jul 15, 2004, 01:33 PM
Registered User
Lynxman's Avatar
I have one of those fans. I have no idea where I got it. Tthe stock motor is a very low voltage unit and gets hot very fast even on 4 ni-cd. The wire on the stock motor is pretty thich so it's probably a very low number of turns. The inside diameter of the duct is 58 mm. I think I had a cone for the rear end too but I can't find it now.

I never thought the fan would be able to handle that kind of power. It loks so flimsy.
Last edited by Lynxman; Jul 15, 2004 at 01:35 PM.
Jul 15, 2004, 01:39 PM
Impossible? Hah!
KreAture's Avatar
Yeah, you need to make sure it is properly centered...

It runns true though and handles 30k rpm fine. (6 amps at 3s LiPo = over 60 watts! )
Oct 18, 2005, 06:37 AM
Fun is what matters!
Pmagall's Avatar

Can you post again those photos, I cannot see them. And do you have more photos of it?.
I bought that same model last year, but it's still in the box.
Oct 18, 2005, 10:13 AM
Impossible? Hah!
KreAture's Avatar
Updated post with correct links to pictures.
Oct 18, 2005, 01:08 PM
Fun is what matters!
Pmagall's Avatar
Thanks for the pictures, tell me what did you do to the old fuse? did you used it?
Last edited by Pmagall; Oct 18, 2005 at 01:19 PM.
Oct 18, 2005, 01:25 PM
Flying motor mount master
fly_boy99's Avatar
So effectively you build a 7.5T 24G EDF cdrom motor!!!

Looks like it should move out pretty fast!!!