CR28M Contra Rotating Brushless Motor - RC Groups
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Feb 11, 2008, 11:42 PM
Re-Kitting Expert :o

CR28M Contra Rotating Brushless Motor

CR28M Contra Rotating Brushless Motor running on 1 40 amp ESC.

Added the 2nd video. CR28M Contra Rotating Brushless Motor running on Two 40 amp ESCs. Packs weren't charged and really couldn't keep Up. Motors had a couple problems I had to work out but seem to be doing great now.
Last edited by GorillaBob; Feb 12, 2008 at 08:54 PM.
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Feb 12, 2008, 06:12 AM
Thatsright I drankthe rum
K9000wner's Avatar
So, just so I can understand it better ..
you are running (two) 200watt or better bl motors off (one)
40 amp brushless esc?
cool...I was told for 2 bl motors I needed 2 esc's
Feb 12, 2008, 09:17 AM
Oxford Panic
AndyOne's Avatar
Nice noise, I can now get rid of all my 2 stroke glow engines!

Feb 12, 2008, 10:22 AM
Mr. ExperiMENTAL
Pretty neat!

Feb 12, 2008, 12:47 PM
Crash n'glue!


I'm looking forward to trying a twin... I notice Bob's stay in perfect sych, which they would have to do to run on one ESC. Seperate esc's give that whaw-whaw-whaw beat frequency. Beat frequency Hz = difference in Hz between two motors.
Feb 12, 2008, 02:09 PM
Gas Monkey Vic
Vitter's Avatar
Thant is cool! Now make the Convair XFY-1 Pogo and install your set up in it.

Feb 12, 2008, 02:27 PM
The Bugatti racer used two V-8 engines driving counter-rotating co-axial mounted pros using a gear box. I think the gear box synchronized the prop speeds.
It would be a very interesting experience to see if having one of the props running faster than the other would be beneficial. Or even maybe one prop should be larger/smaller more/less pitch , etc.
Definitely a lot of food for thought here.

The Bugatti (beautiful plane!) used counter-rotating to reduce or eliminate torque/P-factor so as to allow for smaller tail surfaces to reduce drag.
It was designed to take the speed record back from the Germans, who had set it using a ME-209.
Then war came and the un-finished plane was hidden in a barn. It wasn't re-discovered until many years later.

So perhaps it would work well for a 3D plane for the same reasons Bugatti wanted to try it.
Anyway that's what I thought of upon seeing this.
Last edited by dayhead; Feb 12, 2008 at 02:38 PM.
Feb 12, 2008, 02:39 PM
My post above has some errors.
Feb 12, 2008, 03:18 PM
Registered User
ericdod's Avatar
Is there any cost / performance advantage in doing this, or just the COOL factor?
Feb 12, 2008, 03:38 PM
Re-Kitting Expert :o
Well there is definit COOL factor here and the sound is great. Being able to run the two motors on 1 ESC helps bring the cost down but this motor isn't cheap. But then again, two motors aren't exactly cheap either I ran the motor for a few minutes on 2 ESC's and the sound is very differant on the 2 ESCs because they aren't synched.
Feb 12, 2008, 07:59 PM
Prop me up
cloud-9's Avatar
I'm totally confused. How can one motor spin in both directions?


EDIT: OK, so I guess you are running two motors. How do their shafts have the same centerline? Could you provide some photos or something?

Last edited by cloud-9; Feb 12, 2008 at 10:32 PM.
Feb 13, 2008, 03:49 AM
Basingstoke Roy's Avatar
Hi Jim

Hope these photo's and my video help.

The Contra Motor Project (1 min 39 sec)

The shaft of the back motor runs though the centre of the front motor, which is mounted on bearing.

Feb 13, 2008, 04:08 AM
Prop me up
cloud-9's Avatar
Originally Posted by Basingstoke Roy
Hi Jim

Hope these photo's and my video help.

The shaft of the back motor runs though the centre of the front motor, which is mounted on bearing.


Thanks, that helps a lot.

So, are the propellers actually blowing against each other? Can you get a prop made to work in the reverse of the usual direction?


Feb 13, 2008, 10:58 AM
Re-Kitting Expert :o
Jim the rear prop is a pusher prop, it is designed to turn the opposite direction of a normal prop and still push air the same direction. So both props push air to the rear of the motors. With glow powered models, a pusher prop is used when mounting a glow power engine facing the rear, which makes it turn the wrong way with a normal propellor. And boy oh boy do those twin props push air!!!
Feb 13, 2008, 11:12 AM
Registered User
ericdod's Avatar
This is very interesting - do you have any numbers?

Thrust, amp draw, etc...

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