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HelicopterScale Model RC Helicopters Docs  Sport mechanics in scale helis
10-12-2015 11:09 PM  31 months agoPost 21
seahorse bob

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Arvada CO

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Here's my plan for using the Roban mechanics. I'm going to build a Cobra to use them because they're nice and narrow. It'll be 1/8 scale and will use 800 mm. blades. I've already flown these modified mechanics in a test bed configuration and I'm very pleased with it.
If you look closely, you'll see that I adapted the head of the Raptor 820 E to the Roban mast. The 15mm rotor shaft of the 820 had ony to be bored slightly with a 12mm. drill to fit right over the Roban shaft. Since the swash plate moves downward to achieve positive pitch on the Raptor, this further matched the configuration and there's no binding or interference anywhere.
You also might notice the modifications I made to the bellcranks going to the swash plate. I think the geometry that Roban used is far too aggressive for a scale heli and I therefore reduced this by about 33% by shortening the output arms to the swash plate. On the two front arms, I roughened the recesses milled into them and then filled them with JB weld. I then drilled and tapped a threaded hole closer to the pivot point and used a screw all the way through the ball and the arm. On the rear arm, I just drilled and tapped a new location the same distance as the front arms. I also used balls on the swash plate that were slightly shorter than stock to further reduce the throw.
Cheers,
Bob

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10-12-2015 11:20 PM  31 months agoPost 22
seahorse bob

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Arvada CO

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These two views show how the front bellcrank arms are moved outward to get better geometry to the swash plate. I used a spare hollow ball to get the spacing out just for simplicity.
I enjoy modifying and adapting mechanics and hopefully this has given some inspiration for others to try and see what they might be able to try.
Cheers,
Bob

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10-13-2015 01:18 AM  31 months agoPost 23
ICUR1-2

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Ottawa, Ontario

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looking at the last pictures ..
It doesn't look like there is much room left for + pitch or upward swash movement.
how much cyclic and pitch does a scale need?

spending time, paying attention

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10-13-2015 04:41 PM  31 months agoPost 24
seahorse bob

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Arvada CO

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Keeping in mind that the swash moves down for positive pitch, it is limited to about 15 degrees positive and 5 degrees negative mechanically. I use 0 degrees to 11 degrees positive on my scale helis, which is plenty.
Bob

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11-02-2015 10:06 PM  31 months agoPost 25
CopterDr

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West Plains, MO

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Excellent article Bob.....how's the H-34 doin' ? Love that ship.
Barry

To fly is Heavenly, to hover is divine!

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11-03-2015 03:57 PM  30 months agoPost 26
seahorse bob

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Arvada CO

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Hi and thanks, Barry. Always happy to give hopefully helpful info. Both H-34's are still flying and are improved with Bavarian Demon 3X SAS. The orange one gets the most flight time.
Bob

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11-03-2015 04:40 PM  30 months agoPost 27
CopterDr

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West Plains, MO

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Excellent Bob,

Yeah, she's my favorite ship alright....and yours does them justis.

Oh, a guy in Germany I think has added sound and a belch of smoke on start up to his....holy Johnson, that'll bring tears to your eyes..lol.

I'll see if I can find the vid and post it.

Take care my friend
Barry

To fly is Heavenly, to hover is divine!

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11-03-2015 04:42 PM  30 months agoPost 28
CopterDr

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West Plains, MO

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Ahhhh found it Bro. Enjoy!!

Watch at YouTube

To fly is Heavenly, to hover is divine!

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11-04-2015 04:05 PM  30 months agoPost 29
seahorse bob

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Arvada CO

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That's great, thanks for posting it.
Bob

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11-04-2015 05:58 PM  30 months agoPost 30
CopterDr

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West Plains, MO

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You betcha!! Man, to hear that round sound belching fire and smoke just does it for me...lol

To fly is Heavenly, to hover is divine!

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11-04-2015 07:23 PM  30 months agoPost 31
v22chap

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Granger, Indiana

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Wooooooo ... Hope he will share his smoke setup ... I know about the sound system ... and hopefully will soon have an H-34 of my own and want to put something like this in mine .

Larry C ----------Bergen R/C helicopters

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11-04-2015 07:32 PM  30 months agoPost 32
CopterDr

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West Plains, MO

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I'm sure he will.....he seems like a really nice guy. I does make the ol' gal come alive. :O)

To fly is Heavenly, to hover is divine!

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01-07-2016 05:38 PM  28 months agoPost 33
seahorse bob

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Arvada CO

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I decided that the modified Roban mechanics with the Raptor 820 head didn't look scale enough because they were too short on the mast. The Cobra has a very tall mast with just the pitch control rods along side of it. This helped me to rationalize buying the Roban Cobra!
I basically liked the stock kit, but it still had far too aggressive mechanics for a scale bird. So, I did the same modifications to the Cobra mechanics as previously described for the Roban mechanics. This helped some, but wasn't as good as the Raptor head with the transfer arms reducing the throws.
I also changed the motor I was using to the KDE 700 XF 455 kv. It runs cooler and flies longer. It's definitely the biggest motor that will fit the Roban mechanics.

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01-07-2016 05:52 PM  28 months agoPost 34
CopterDr

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West Plains, MO

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Aweome work Bob......may I ask where you got those beautiful drawings ?? And do they have 3 views and engineering drawings for the H-34/ S-58....just too nice. :O)

To fly is Heavenly, to hover is divine!

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01-07-2016 07:19 PM  28 months agoPost 35
seahorse bob

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Arvada CO

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Wanting to reduce the throws and response, I modified the Roban head and used some CNC Heli blade grips with much longer arms that I already had. I made a spacer to fit inside them and therefore mount the same as the Roban grips. I then used the Raptor "grip posts" to achieve the correct phasing position.
These mods finally tamed the responsiveness to what I consider scale like flight without having to lose servo resolution.
I like the almost infinite adjustment possibilities of the Bavarian Demon SAS and I'm playing with various gains to refine the flying charteristics of the Cobra.

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01-07-2016 07:24 PM  28 months agoPost 36
seahorse bob

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Arvada CO

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Hi Barry, if you mean the "art" on my workshop wall behind the heli, then as I remember, I found them among "Google Images" for the H-19. I just downloaded them and went to Office Depot to get a 16x20 print.
Bob

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01-07-2016 07:34 PM  28 months agoPost 37
seahorse bob

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Arvada CO

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Here are some views of the Cobra as I've modified it.
I didn't like the translational lift characteristics of the stock flat bottom airfoil blades. It was "zoomy" in windy conditions that we have a lot of here in Colorado.
I substituted some SAB 2D 800 mm. blades and they work much better. I also had to change the 105 mm. tail rotor blades to 115 mm. to get yaw control back. It was a little scary with the small stock blades when I first tried it.
I'll continue to refine the Cobra when we get more flying time in the spring even though it's already pretty good. I'm still getting used to it's 17 lbs. mass and the inertia effect it has.
Bob

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01-07-2016 07:45 PM  28 months agoPost 38
seahorse bob

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Arvada CO

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Hi again, Barry, I forgot about your question about the H-34 drawings. I haven't found the same type of drawing as the art work on my workshop wall.

This is the best one I've seen for the H-34. You can download it from here or Google Images, where I found it.
Bob

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01-07-2016 09:43 PM  28 months agoPost 39
ssmith512

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Indianapolis, IN USA

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Nice Bob!!!

Good to see another Roban Cobra on the forum! I absolutely love flying mine. It is a real pussy cat to fly! Thanks for sharing.

Steve

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01-08-2016 04:41 PM  28 months agoPost 40
seahorse bob

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Arvada CO

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Thanks, Steve.
Bob

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HelicopterScale Model RC Helicopters Docs  Sport mechanics in scale helis
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