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Flybarless Rotor Head Systems

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Ulitmate Trex 250 Flybarless !

marcw

Senior Heliman

Southern California

Thanks to all here who have helped and contributed to the various flybarless discussions. Without this collection of information, it would be a lot harder to take the plunge into flybarless.

I wanted to share my latest project – my new flybarless Trex 250!

I first tried adapting the Gaui 200 flybarless head and GU-365 3-axis gyro. Big mistake on both fronts. The head needed a lot of work to make it fit (different mainshaft diameter), and in the end I really did not like it. The GU-365 is just a tad too big to fit inside the Trex 250 frame, but I got it in there by using a couple of spacers to widen the gap between the frame sides. The unit works OK, but really is not on the same level as the SK-360 or V-bar.

I ditched the GU-365, and installed it on a big aerobatic nitro plank…should be interesting to see how that project goes.

The V-bar is the best unit out there right now in my humble opinion, but it’s way too big for the Trex 250. The SK360 is just a tad too big too. We did, however come up with a novel solution to make the SK360 fit perfectly in our little ‘Rex. We took the guts of it out of its enclosure, and shrink-wrapped it like an ESC! Take a look at the picture, this works perfectly!!

Next, we tried to use the stock Trex head and mixing arms to reduce throws like as suggested in the SK360 manual. It flew, but felt sloppy. We had to come up with an idea of how to do a direct link to the blade holders with blade grip extensions.

Our solution was to use Trex 450 aluminum mixing arms! If you take a look at the stock Trex 450 aluminum mixing arms, you will see that on the side normally facing the washout assembly, there is a CNC’ed slot down the middle. Well, it so happens that this slot, with a bit of touching-up, fits nicely around the Trex 250 blade grip arms. So, what we did was to make a version of the Mikado Trex 500 blade grip extensions, using these Trex 450 pieces (see picture). The only inelegant thing about this idea is that we had to use 450-size ball links on the grip extensions.

After some fine tuning with the SK360 software, we have a fantastic little flybarless machine!! Our final SK360 settings using the stock swash servos and Trex 450 aluminum mixing arms as grip extensions were as follows:

Control Rates 180/210
Bell 34/40
Hiller 34/28
Damping 20/16
Tail Drag -6/0
Hiller Decay 70

This is not (yet) a 3D setup…it’s very stable and has great control for flying around in the back yard.

Hope this helps for anyone considering going flybarless with this great little heli!!

Marc

01-17-2009 Over year old.
jyzoom

Senior Heliman

Singapore

Very Good

Cool.....
I would have to use your design onmy Trex 250 FBL. Hope you don't mind me copying your design.

Jonathan

Goblin 700, Furion 450, Synergy E6

01-17-2009 Over year old.
marcw

Senior Heliman

Southern California

Hey Jonathan...of course...feel free to copy. I wanted to share to give back a bit for all I have learned here and the hints Ive picked up in the past.

Marc

01-17-2009 Over year old.
ScotY

Senior Heliman

USA

Nice how-to...thanks! Would like to see how you did the blade grips...got any pics that are easier to see?

01-20-2009 Over year old.
marcw

Senior Heliman

Southern California

Here's a closer view. The parts are all black and so tiny. If I get the camera any closer than this, it cant focus correctly. Maybe ill try to do a sketch of how it goes together if you cant see from this pic how it goes. Let me know.

Marc

01-20-2009 Over year old.
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Flybarless Rotor Head Systems

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Ulitmate Trex 250 Flybarless !

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