Espritmodel.com Telemetry Radio
Reply
Thread Tools
Old Sep 20, 2012, 11:03 PM
Registered User
Joined Apr 2012
144 Posts
Question
Is the flybar Necessary?

I'm trying to understand the control systems of a coaxial and I was wondering on the top rotor head the fixed pitch blades are connected to a flybar while the bottom rotor head has cyclic controls with a gyro system (in regards to 4 channel systems). If the bottom rotor head has a self stabilization system like the walkera lm130do1 then why is the top flybar system necessary? Don't they just fight each other or is it a case of redundancy?
gearwolf is offline Find More Posts by gearwolf
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 21, 2012, 12:16 AM
Fly Runaway Fans
United States, TX, Fort Worth
Joined Jan 2009
9,375 Posts
The gyro on a FB coax is for yaw only.

The A rotor FB does fight the swash B rotor. That's why coax doesn't have much motion authority.
arbilab is offline Find More Posts by arbilab
Reply With Quote
Old Sep 21, 2012, 07:15 AM
Registered User
Joined Apr 2012
144 Posts
Quote:
Originally Posted by arbilab View Post
The gyro on a FB coax is for yaw only.

The A rotor FB does fight the swash B rotor. That's why coax doesn't have much motion authority.
The walkera lm130 has a three axis gyro that tries to self stabilize. Its not fast and needs a lot of tuning but it will stabilize its attitude. If they fight each other couldn't we just have one set of permenantly fixed pitch with no flybar and the other with the same pitch but with the swash to control motion?
gearwolf is offline Find More Posts by gearwolf
Reply With Quote
Old Sep 21, 2012, 08:10 AM
Cranky old fart
Balr14's Avatar
Germantown, WI.
Joined Oct 2007
21,344 Posts
You could do that, but you would find movement authority is quite bad. You will observe that a coax has much more initial movement (such as it is) than it does after a few seconds of moving in the same direction, when the flybar gets a chance to catch up. You would be removing that window. Since the lower rotor is always moving through dirty air, any changes made to the lower rotor, to try to compensate, would have limited success.
Balr14 is online now Find More Posts by Balr14
Reply With Quote
Old Sep 21, 2012, 08:17 AM
Cranky old fart
Balr14's Avatar
Germantown, WI.
Joined Oct 2007
21,344 Posts
The concept has merit for 3 channels, since they don't rely on head movement. Their movement authority comes from a tail motor pushing up/down and you won't find anything with more movement authority than a quad, which uses the same principle.
Balr14 is online now Find More Posts by Balr14
Reply With Quote
Old Sep 21, 2012, 09:45 AM
Registered User
minbari's Avatar
Joined Jul 2012
379 Posts
Quote:
Originally Posted by Balr14 View Post
You could do that, but you would find movement authority is quite bad. You will observe that a coax has much more initial movement (such as it is) than it does after a few seconds of moving in the same direction, when the flybar gets a chance to catch up. You would be removing that window. Since the lower rotor is always moving through dirty air, any changes made to the lower rotor, to try to compensate, would have limited success.
wouldnt a shorter or lighter flybar do what he is suggesting? this would give some stability from the FB, but would have less influence than the standard one.

I know on the lama v4 they make a FB like this that is supposed to increase forward flight speed.
minbari is online now Find More Posts by minbari
Reply With Quote
Old Sep 21, 2012, 11:15 AM
Registered User
Joined Apr 2012
144 Posts
Hypotheically what about putting the swash plate on the upper rotor head where it would draw in 'clean' air and keeping the lower one fixed? Would there be a need for a flybar then?
gearwolf is offline Find More Posts by gearwolf
Reply With Quote
Old Sep 21, 2012, 11:34 AM
Registered User
minbari's Avatar
Joined Jul 2012
379 Posts
I bet it would be uncontrolable then. think about how much more leverage you have on the higher blade.
minbari is online now Find More Posts by minbari
Reply With Quote
Old Sep 21, 2012, 11:43 AM
Cranky old fart
Balr14's Avatar
Germantown, WI.
Joined Oct 2007
21,344 Posts
I think you answered your own question with your LM130 example. It needs a 3 axis gyro to stabilize the lower rotor, which has much less leverage. Out of curiosity, why is this meaningful to you?
Balr14 is online now Find More Posts by Balr14
Reply With Quote
Old Sep 21, 2012, 05:11 PM
Registered User
Joined Apr 2012
144 Posts
I wanted to improve a new design I was making. I wanted collective pitch too without using a double swash since my design has the motors facing each other and the blades are inside the frame. I tried it with parts from a walkera lm180 but the blade grips sheared off and blew through a card board box. The reason behind this design is I saw XXX2: state of the union the movie and had a small drone that I wanted to make, but I wanted it to be safe for all to use. The flybar would hit the other blades with my design so I'm trying to get outside the box on this. The walkera lm130 and lm180 is a "flybarless" system but their components are at their structural limits if I add more rpm.
gearwolf is offline Find More Posts by gearwolf
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Help! Necessary Upgrades for 120 SR? RCAddict16 Electric Heli Talk 4 Jun 22, 2012 04:25 PM
Discussion is it necessary to balance the motor jy0933 Multirotor Talk 1 May 27, 2012 07:57 AM
Discussion To Flybar or not to Flybar Bigfoot74 Micro Helis 16 Apr 17, 2012 06:56 PM
Question Component Update rate necessary for stability Gadgets_2012 Multirotor Talk 0 Mar 23, 2012 01:32 PM
Discussion computer radio necessary baldy1953 3D Flying 2 Feb 26, 2012 04:04 PM