toetje

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Uncontrolled pitch movements
« on: June 04, 2017, 07:08:50 pm »
Hello All,

After a braek I picked up my old RC hobby again.
I used to fly planes a lot, and I started with a heli just before I had to quit flying due to time management issues (a.k.a. family stuff) :)
The planes are gone, but my heli is still here.

This is my currect flight gear:
Transmitter: Multiplex Cockpit MM
Receiver: MultiplexMicro IPD
Heli: Protech Zoom 425 CCPM (with flybar)
Flight Control Board: Mini CC3D

The transmitter/receiver combination is old, but still working flawless, but when I combine it with the CC3D I experience what could be described as uncontrolled servo fluttering on pitch. Not continuously, but not I cannot control when if happens too.
It is not completely random or uncontrolled. All three servo's work exactly together but with uncontrolled pitch as result. I'm pretty sure this is coming from the flight control board, since I never experienced this without it.

Only thing is, I have no clue what is causing this. Especially because pitch is completely manual controlled (as far as I can find)

Does anyone have similar experiences with the CC3D and maybe found a solution or has a clue where to look?

Maybe a hint for who is looking into the problem. Since I could not get the flight controller working from the start, I downloaded the file 1307Blackie.uav and started out from there.

Best regards
Joost

Re: Uncontrolled pitch movements
« Reply #1 on: June 04, 2017, 07:16:48 pm »
Sounds like PIDs too high.

Do you have a way to make it happen repeatedly?  You could turn down all the pitch PIDs by say multiply all by 0.75 and then try it again.  I bet it goes away.

I bet that it happens when you run the head speed a little high.  You could also just reduce your head speed.

toetje

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Re: Uncontrolled pitch movements
« Reply #2 on: June 04, 2017, 09:01:10 pm »
Wow, fast response  :) Thanks!

I assume you mean the PID banks under stabilisation?
To be honest this is a part of the setup which I considered for fine tuning later on. However I now realise how important it is.
I will reduce the values there a lot. Attitude is even set at it's maximum at the moment.

Now that you mention the head speed: I have seen the "fluttering" as well with 0 rmp, just by moving the stick for pitch. Especially with stick in lowest position pitch was coninuously moving. I played a bit with the minimum and maximum input values to get rid of that behaviour. But it appeared again during flight.

What I still don't understand is why it affects pitch, because as far as I can determine it is not being controlled by the CC3D.

Re: Uncontrolled pitch movements
« Reply #3 on: June 05, 2017, 05:40:26 am »
If you have a problem with the rotor stopped, then it is a different issue.

Is it nitro or electric?  Rotor stopped but nitro motor running, it could be vibration.  Anything else starts to sound like an FC issue, especially since it only happens in pitch.

Bad connection to pitch servo?  Is it a 120 swashplate?  Which servo(s) move when it glitches?
« Last Edit: June 05, 2017, 06:03:43 am by TheOtherCliff »

karla

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Re: Uncontrolled pitch movements
« Reply #4 on: June 05, 2017, 06:12:41 am »
Hello toetje, I think this jumpy behavior is caused by your neutral settings.
It can easily be fixed.

Have a look at this great little trouble shooting guide from Dave.

Troubleshooting Guide for LP/OP helicopters
...

Swash jumpy:
set the throttle neutral just a couple of points higher than throttle minimum
check throttle curves in System / Mixer Settings: Curve1 source is throttle and Curve2 source is COLLECTIVE. 0, 0.025, 0.50, 0.75, 1 == curve1 -1, -0.5, 0, 0.5, 1 == curve2 for a CP heli.

...

https://forum.librepilot.org/index.php?topic=1689.msg12284#msg12284

Hope it helps
Karl

Re: Uncontrolled pitch movements
« Reply #5 on: June 05, 2017, 02:00:39 pm »
That's probably it, but one more thing...  if you have a manual position on your Flight Mode Switch.  The issue produces a jump in one direction or another, not a flutter.

I have a fixed wing.  On the FMS I have a manual position where I take off and fly and also an attitude position for testing and finally some GPS flight mode that uses attitude.  After taking off, when I switch from manual to anything else, I get a large down pitch and a slight left (IIRC) roll for a couple seconds.  This is because the PID I term wound up when flying manual.

This is the same issue that quad fliers have if they sit on the ground at 1/4 throttle for 30 seconds.  It tries to adjust the level, but can't because it is on the ground.  It tries harder and harder (winds up).  When it breaks free from the ground, that wind-up makes it very un-level for a couple seconds.

toetje

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Re: Uncontrolled pitch movements
« Reply #6 on: June 06, 2017, 01:35:25 am »
It's an electric heli with a 120° swashplate. All three the servo's move the swashplate in the same direction, so it's really only pitch.

I'll check and try the options you both mentioned. Reading these solutions there are more than enough options for improvement :)
Unfortunately I'll have to wait for the new tail rotor parts (*) before I can test again, but I will give a feedback!

Thanks  :)

(*) small crash during the first test  :'(

Re: Uncontrolled pitch movements
« Reply #7 on: June 06, 2017, 02:36:50 am »
I'll have to wait for the new tail rotor parts (*) before I can test again, but I will give a feedback!

(*) small crash during the first test  :'(

And that is why quads are popular.  :)  Rugged, less likely to break, carrying a few extra quad props fixes crashes that would be a head rebuild and a new tail boom on a heli.  :(

karla

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Re: Uncontrolled pitch movements
« Reply #8 on: June 06, 2017, 02:58:52 am »
Thats one of the charming properties of Helis, need to be careful and precise with mechanics,
but they give you unlimited agility back :)

toetje

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Re: Uncontrolled pitch movements
« Reply #9 on: June 11, 2017, 10:54:37 pm »
Setting back the PID's turned out to be the solution :D
To be sure I also checked the link to the jumpy swashplate and made some improvements there as well.
Thanks for the suggestions.

Although the flightcontroller seems to be working I'm seriously thinking about removing the "damn thing", and go back to manual flying.
Even with the flight mode set to manual you can feel an enormous lag compared to flying without flight controller. Besides this the behaviour of the controller doesn't seem stable.  It seems to limit servo travel in some king of way after switching back and forward to manual or controlled flight.
And on the ground the controller pulls the rotorblades towards the ground on one side due to the drift of the MPU sensor.
I hooked up an MPU-9150 to an Arduino and you see the drift the in the same way as the CC3D drifts.

I'm not an experienced heli pilot (as a matter of fact I'm sill learing ;) ) and against all advise I just learn by doing it alone.
I still fly with my first helicpoter. appart from a landing gear all the parts on the heli were still Original.... untill the CC3D arrived....
The damn thing already costed me two landing gear sets and too many parts of the tailrotor mechanism within two minutes of flying.
I hope the CC3D to be an extra safety level in case of panic and with sudden strong wind, but the opposite seems to be the case  :o