Stabilisation on rudder/yaw
« on: October 22, 2016, 08:23:30 pm »
Hi Librepilots,

After a few flights with the CC3D on my Hobbyking Walrus (a foam powered glider) and trying to get the CC3D set up I am struggling with yaw.

I am trying to set my plane up so that the CC3D acts as a panic switch in attitude mode (or a good trainer mode by limiting bank and with self leveling) and then similar to a 3 axis gyro when in rate or axis lock. I want it to correct against wind and gusts when I fly as the wind here is always blowing.

Should yaw be used on a fixed wing?

I have tried using yaw in attitude, rate lock and axis lock but it never seems "right" when I bank and yank (I don't really use rudder when turning). If I fly with yaw on manual in all the modes the plane turns ok with an aileron bank and then gentle elevator up to "pull" the plane round.

As soon as I set the yaw stabilisation modes either as rates lock or axis lock I find that the plane banks but doesn't pull through the turn (if my description makes sense), the turns are a lot wider and the elevator now seems to make the plane climb rather than pull it through the turn.

I have used a 3 axis gyro before on my roll, pitch and yaw and this did not seem to affect my plane when turning like the CC3D does.

Is there some way to set yaw so it combats gusts but not when turning or am I best to leave yaw in manual?

Thanks,

HB

f5soh

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Re: Stabilisation on rudder/yaw
« Reply #1 on: October 23, 2016, 01:17:11 am »
Hi,
Try adding a value for Roll to the Mixer3 output (Yaw servo)
Go to the UAVOBrowser and search for Mixer3vector in MixerSettings uavo
Save using the small Hdd icon with a red arrow.


Test the behavior while moving roll stick and put a negative value if the rudder do not move the right way.
This should help for turns without use of Yaw stick

Re: Stabilisation on rudder/yaw
« Reply #2 on: October 23, 2016, 02:05:28 pm »
Thanks,

So I am fooling the CC3D into thinking that when I am banking with the ailerons, I am also applying rudder/yaw and it won't fight against me?

So I only need the rudder to deflect a tiny bit when I move the ailerons?

Regards,

HB

f5soh

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Re: Stabilisation on rudder/yaw
« Reply #3 on: October 23, 2016, 03:20:14 pm »
Sorry but the previous post should not work, too late :)
Roll command add command to the servo but Yaw axis still locked... the result is compensated.

The best option is set a mixer Roll > Yaw in your RC radio, this give automatically a heading deviation while banking on Roll.
This mixer should be disabled for Acro.

Re: Stabilisation on rudder/yaw
« Reply #4 on: October 23, 2016, 08:18:19 pm »
OK rodger that!

Fool the CC3D into thinking I am applying rudder (to stop it from applying corrections) by having my transmitter send a tiny bit of rudder when I use ailerons to bank in a turn.

Will see how it goes this weekend and report back.

Regards,

HB

Re: Stabilisation on rudder/yaw
« Reply #5 on: November 09, 2016, 05:22:08 pm »
For beginners flying fixed wing you should probably set aileron and elevator to Attitude mode and rudder to Manual mode.  Note that this will level the aircraft if you simply release the stick, but you will not be able to fly "bank and yank".  To make a turn, you will have to hold the bank while you also hold the yank.

IMPORTANT:  If you don't have ailerons (e.g. you have a rudder elevator throttle airplane), then you should set everything up as if the rudder is really an aileron control.  That includes putting it on the aileron stick on your transmitter.  Rudder does roll the aircraft, and this configures the FC to use the rudder to roll it back to level.

miker

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Re: Stabilisation on rudder/yaw
« Reply #6 on: June 13, 2017, 08:03:06 am »
IMPORTANT:  If you don't have ailerons (e.g. you have a rudder elevator throttle airplane), then you should set everything up as if the rudder is really an aileron control.  That includes putting it on the aileron stick on your transmitter.  Rudder does roll the aircraft, and this configures the FC to use the rudder to roll it back to level.

Can you use the CC3D mixer to output roll commands to the rudder?  Would that let you use yaw axis-lock as well as roll stabilisation, or will the system fight you every time you try to put in rudder (since it will undo your command from the roll stabiliser)?

Your proposal gives roll levelling with the rudder, but doesn't allow any sort of specific yaw stabilisation, right?

Re: Stabilisation on rudder/yaw
« Reply #7 on: June 13, 2017, 04:27:12 pm »
If you don't have ailerons, then you should connect rudder as if it were ailerons and think of it as doing a bank, not a yaw.

You can use Rate or Axislock on yaw with whatever on roll / pitch.  You will just have to coordinate your turns; hold rudder (in addition to everything else) during every turn, through the whole turn.

miker

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Re: Stabilisation on rudder/yaw
« Reply #8 on: June 14, 2017, 02:05:53 pm »
I'll give it a go.

At the moment I'm trying assigning the "yaw" input to both roll and yaw, and mixing roll back in to the yaw output channel.

On the bench, this gives me normal control in manual, and also causes the rudder to respond to counter both roll and yaw.  Fingers crossed I'm getting the right balance with roll attitude and yaw axislock.  I've got a complete manual mode, so if it goes pear shaped I shoudl be OK. 

Re: Stabilisation on rudder/yaw
« Reply #9 on: July 03, 2017, 03:13:26 pm »
Hi Libre Pilots,

Since there have already been comments on my original post I thought I would carry on here.

Back to flying agian after a short break.

Has anybody succesfully enable yaw control on a throttle/aileron(2 servos)/elevator/rudder powered glider like the AXN or Bixler or Walrus? Should I give up and leave yaw on manual?

I have trimmed my HK Walrus so that it flies straight and level without any trim on the transmitter, all good.

I have Axis lock set up on pitch and roll and I am happy with how it flies (if I leave yaw control to manual).

However if I try and add yaw control on the FC I cannot get the plane to fly nice.

Today I had Axis lock on roll and elevator, yaw was manual (flight mode switch position 1), and axis lock on roll and elevator and rate mode on yaw (flight mode switch position one).

Plane flies nice when I am in position 1 (axis lock roll and elevator). But when I go to position 2 (roll and elevator axis lock, yaw now on rate) turning becomes a battle and plane just flies horrid.

Here are some quick observation (I doid fly long with yaw enable):

1. plane seems to fight when I try and turn - bank, slight rudder to stop the tail dropping and elevator to pull her round.

2. level flight into wind, give almost full rudder right for a couple of seconds, release rudder, it seems as if the plane tries to turn back to it's original heading, not the new heading that the plane is pointing at when I released the rudder.

3. same as 2 but when I release the rudder plane goes into oscillations on the yaw (maybe my yaw stabilisation set to high will drop it abit).

My next steps are to lower the yaw PI in the inner loop and try fly again.

What is the rate yaw in Responsiveness?

Any advice? Or does trying to use yaw stabilisation on a fixed wing just not provide any benefits?

Thank.

Hoenderb.

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Re: Stabilisation on rudder/yaw
« Reply #10 on: July 03, 2017, 03:41:33 pm »
Quote
Has anybody succesfully enable yaw control on a throttle/aileron(2 servos)/elevator/rudder powered glider like the AXN or Bixler or Walrus?
Here is a video doing knife-edge flight. Roll is Attitude (bank angle max = 90°) and all others axis are using Rate.



Yaw stabilization works the same as others axis stabilization and can give oscillations.
This oscillations can be removed by reducing the Yaw PID numbers according to the rudder response.

Quote
What is the rate yaw in Responsiveness?
This is the maximum allowed rotation speed around the Yaw axis, in deg/s.

Re: Stabilisation on rudder/yaw
« Reply #11 on: July 03, 2017, 07:03:12 pm »
If you stabilize yaw, you must use "coordinated turns" when you fly.  During a turn, you must constantly hold yaw just like you constantly hold elevator.

That is why it is better to leave yaw set to manual on a 4 channel fixed wing.

Re: Stabilisation on rudder/yaw
« Reply #12 on: July 03, 2017, 10:12:26 pm »
f5soh - that looks good and doesn't seem like yaw is making the plane act strange (although 3d is another type of flying that appears to defy the laws of physics).  ;)

TheOtherCliff - Yes I am busy working on co-ordinated turns to use rudder to lift the tail in turns instead of letting it drop/drag.

So then its back to fiddling with settings and see what I can do. Based on your comments it appears there are no tricks or anything special settings to get yaw to work on a fixed wing and if set up correctly should work like it does on the other axes.

Thanks.

miker

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Re: Stabilisation on rudder/yaw
« Reply #13 on: July 04, 2017, 03:40:54 am »
Going back a few posts, I've got my elevator/rudder plane set up with the "yaw" stick feeding the roll channel in the CC3D as advised.  This seems to be working pretty well - it's doing a nice job of stabilising. 

One problem I'm hitting is running out of yaw (roll) authority - with the engine off, the plane will NOT roll to the right, even with full stick.  I've tried ramping up the "Attitude" integral term, but it seems to have no effect. I would have expected that if I dial that up, then roll the aircraft while it's on the bench, that it should gradually feed in more and more rudder (since there's a continuing roll error).  However, even with it set to 100, there's no visible effect.

There is some margin left - the maximum output in stabilised mode is 100ms less than the maximum output in manual mode.

Thoughts?

Re: Stabilisation on rudder/yaw
« Reply #14 on: July 04, 2017, 04:44:46 am »
Don't use the transmitter trim.  Put it back where it was when you ran transmitter wizard.

First get it flying level and straight in Manual by adjusting mechanical trim.  Then use Attitude -> Rotate VIrtual to get it flying level in Attitude mode.