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Old Feb 11, 2008, 10:42 PM
Re-Kitting Expert :o
Bullhead City, Arizona
Joined Jan 2005
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Video
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.
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Last edited by GorillaBob; Feb 12, 2008 at 07:54 PM.
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Old Feb 12, 2008, 05:12 AM
Thatsright I drankthe rum
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USA, MN, Robbinsdale
Joined May 2006
1,343 Posts
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
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Old Feb 12, 2008, 08:17 AM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
3,659 Posts
Nice noise, I can now get rid of all my 2 stroke glow engines!

Andy.
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Old Feb 12, 2008, 09:22 AM
Mr. ExperiMENTAL
Joined Apr 2004
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Pretty neat!

Tips
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Old Feb 12, 2008, 11:47 AM
Crash n'glue!
Joined Jul 2006
46 Posts
ESC's

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.
Roger
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Old Feb 12, 2008, 01:09 PM
Gas Monkey Vic
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Snohomish, WA
Joined Jan 2005
1,500 Posts
Thant is cool! Now make the Convair XFY-1 Pogo and install your set up in it.

Vitter
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Old Feb 12, 2008, 01:27 PM
SlingWinger
San Bernardino, California, United States
Joined Oct 2004
1,632 Posts
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.
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Old Feb 12, 2008, 01:39 PM
SlingWinger
San Bernardino, California, United States
Joined Oct 2004
1,632 Posts
My post above has some errors.

http://www.bugattiaircraft.com/kalempa.htm
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Old Feb 12, 2008, 02:18 PM
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United States, SC, Simpsonville
Joined Jun 2001
437 Posts
Is there any cost / performance advantage in doing this, or just the COOL factor?
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Old Feb 12, 2008, 02:38 PM
Re-Kitting Expert :o
Bullhead City, Arizona
Joined Jan 2005
1,673 Posts
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.
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Old Feb 12, 2008, 06:59 PM
Prop me up
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New Mexico, USA
Joined Oct 2007
2,358 Posts
I'm totally confused. How can one motor spin in both directions?

Jim


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?

Jim
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Old Feb 13, 2008, 02:49 AM
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United Kingdom, England, Basingstoke
Joined Oct 2005
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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.

Roy
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Old Feb 13, 2008, 03:08 AM
Prop me up
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New Mexico, USA
Joined Oct 2007
2,358 Posts
Quote:
Originally Posted by Basingstoke Roy
Hi Jim

Hope these photo's and my video help.

http://uk.youtube.com/watch?v=md_99-WGSEA

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

Roy

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?

Jim



Jim
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Old Feb 13, 2008, 09:58 AM
Re-Kitting Expert :o
Bullhead City, Arizona
Joined Jan 2005
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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!!!
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Old Feb 13, 2008, 10:12 AM
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United States, SC, Simpsonville
Joined Jun 2001
437 Posts
This is very interesting - do you have any numbers?

Thrust, amp draw, etc...
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