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Old Jul 23, 2013, 09:46 AM
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Joined Sep 2008
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trex 600 nitro shorter shaft FBL questions


I started to work again on my trex 600 nitro limited edition. i m not sure but i think i got the flybarless head separately (chrome version like the limited edition) and it has a shorter shaft. After reading online it says its suitable for the trex 600 n as well.

When doing the mecanical setup, when having my servos horns horizontal as well as the mixing arms, and zero pitch at midstick, i get 12 degres positive pitch and 15/16 negative which is bad. I cant change the swash AFR coz then i get 12 neg and 8 positive.

So i was wondering if i could use the pitch curve to limit the negative pitch instead of going to each servo and set the endpoints which would be a pain.

If changing the pitch curve is feasible, would i need to change the dampeners? i heard that its better to have harder ones. I have used all the parts from the flybarless head kit so i m assuming the ones in the kit are made for it but in doubt should i change them?

I only do sport flying, no harcore 3d so i dunno if i would really risk a boom strike.

Any help is gladly appreciated
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Old Jul 23, 2013, 08:04 PM
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Joined Sep 2008
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I did some more testing today and i managed to get closer as my mecanical setup wasnt perfect.

I managed to get 12deg pos and 12 deg neg with only 10 for the first point of the pitch curve. Before i was at 22,5 which was quite a lot i think.

i guess its not too bad, can anyone comfirm?
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Old Aug 25, 2013, 11:25 PM
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Joined Mar 2005
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Which FBL unit?
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Old Jan 20, 2014, 11:40 AM
just gotta mess with it!
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North West Louisiana
Joined Nov 2009
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Assuming you have good quality servos, the thing that makes the biggest difference is getting the servo arms dead level at 50% collective (zero pitch)

When you look at most FBL heads, the grip arms are longer than the inner swash radius, so the links between the grips and the swash angle inwards. This results in some differential pitch. With leading edge control, i.e. if the swash moves up for positive pitch, you will get slightly more positive pitch than negative - but it usually only amounts to about 0.3 degrees difference for a +12 to -12 pitch range. So you might see +12.0 to -11.7 and with trailing edge control, you will see the opposite - eg +11.7 to -12.0.

You can compensate for this differential by setting the servo arms a tad higher than horizontal at 50% for a leading edge control heli, or lower for a trailing edge control one. On a heli with direct to swash links, about 5 degrees of servo arm offset compensates for most head geometry.

You can compensate for differential collective by adjusting your pitch curves, as you've done, but if there is a large amount of differential in the setup, you will get unwanted collective interactions with cyclic inputs, so it's best to try to get things mechanically as good as possible to minimise the amount you have to alter the pitch curves.
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Old Feb 28, 2014, 09:36 PM View Post
Amiee Smith
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