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 Post subject: 700 size Coax Heli from Canada
PostPosted: Wed Nov 05, 2014 4:30 pm 
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Location: Houston, Texas
Hi Guys

Came across this today and thought it was worth sharing.

I dont know much about it but its very cool I love to see custom heli designs like these. It was built by Martin Renaud from Canada.
He basically took two 550 or 600 rotors, machined the coax setup and used two sets of pinion / main gear driven by two contra rotating motors. He made the side frames also. He used some kind of electronic mixer to get cyclic and tail. The most bizarre is that the two main gears and pinons are different in size but same ratio so that the two motors do not interfere one another. He also uses two different lenght/type main blades (on a budjet lol) and it apprently has no impact on his flying.
Pretty impressive that it works so well.

I dont remember my Coax Lama flying like that!



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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Wed Nov 05, 2014 9:27 pm 
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Location: Austin, TX aka BUDA
Im very confused.


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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Sat Nov 08, 2014 10:32 am 
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Joined: Sun Aug 21, 2011 7:22 pm
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Location: Tulsa Ok.
Cool stuff .
Thanks for posting Ben

Chuck


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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Thu Nov 13, 2014 2:20 pm 
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Location: Winston-Salem, NC
Wow...Thats an impressive display of ingenuity, for sure!

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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Mon Nov 17, 2014 8:34 am 
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Location: Houston, Texas
Hi Guys

Her is an update from the builder of this 700 Coax heli that was recently published on the sclaercheli forum where i found it.

Cheers

"Hi to all, and thanks Romeo for the link.

I don't know where to begin as there is a lot of programming involved in the twin motor coaxial, all the mixing available in my TX (futaba 8fg) are used, I also use an external gyro mixer that have its own lot of parameter to adjust, it can work with only a basic mixer and no mixing in the TX, but in some case it's dangerous and does not work very well.

The main gear size difference is to allow clearance for the pinion to not rub on the top main gear, another solution would have been to put the motor upside down but I'll have no room for the lipo pack, actually both ratio are the same, different ratio could have worked well of course, but not a good idea as one motor would came down hotter, and easier to bog down into hard maneuver.

The Yaw work with the inertia of the two rotor, and the more you have cyclic or collective involved, there is drag from the blade that come into play, hence the requirement of several mixing.

Both motor (rotor) RPM are varying, when one accelerate, the other proportionally decelerate.

The amount of RPM variation from the two motor are very different, the more pitch angle added to the blade, the smaller the RPM variation will be for the yaw, I can use as high as 60% to 70% gyro gain in just hovering but the gain must be lower for acrobatic, or climb up, as low as 25% to avoid ''wagging'' or in my case, motor pulsating, and this is acheived with mixing in the TX.

In the gyro mixer parameter I adjusted the parameter to avoid any of the two motor to completely stop with fast piro (yaw) command, if not, one ESC can fall into slow spool up mode, and I'll be in trouble.

There's other workaround in the TX for the gyro to avoid hot start of a motor when manipulating the heli on the field.

Other mix I've done, not required but i'm a big fan of Governor on all my other heli, that one don't have gov, I use throttle V curve and AiL-to-Throttle/ELEV-to-Throttle mixing.

The blade difference was not due to the budget, but for testing purpose, a light and an heavy set of 520mm. Now I use 550mm blade of the same weight (same brand of course).

As of now, I took appart the coaxial and I'm into rebuilding it with a two stage belted transmission (two sets of two stage) to make it even more quieter and to allow one motor on the front and the other at the rear, wich was impossible with the main gear and pinion due to servo clearance, and I'll put the frame in a speed fuselage."

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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Mon Nov 17, 2014 11:34 am 
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I followed a co-axial on RC Groups several years ago.

Both rotors driven by one motor. Extra servo for rudder.

http://www.rcgroups.com/forums/showthread.php?t=742847

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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Mon Nov 17, 2014 11:58 am 
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Interesting Rick

This Gif taken from that thread helps to explain how the Swash set up and linkages work

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My brain hurts now.....

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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Wed Nov 19, 2014 5:21 pm 
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Location: Round Rock, Tx
I suppose the burning question has to be "Why?". Maybe just because he could?

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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Wed Nov 19, 2014 5:35 pm 
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Location: McKinney, TX
I'm guessing that the top three servos are CCPM and the fourth is for yaw? Just thinking about the yaw mixing makes my head hurt.

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 Post subject: Re: 700 size Coax Heli from Canada
PostPosted: Wed Nov 19, 2014 7:33 pm 
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Joined: Thu Nov 10, 2011 10:35 pm
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Location: Winston-Salem, NC
TheBum wrote:
I'm guessing that the top three servos are CCPM and the fourth is for yaw? Just thinking about the yaw mixing makes my head hurt.



I am thinking you are on the correct path, TheBum. I imagine changing pitch of the top set of rotors would be more effective and have a beete feel than varying the motor speed...

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