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PID help with a huge homemade octocopter

Posted: Sat May 19, 2012 6:49 pm
by oterpoter
Dear gentlemen!

http://youtu.be/8PS4F7YY4po

I have just finished the build of my Octocopter using ProFlyer.eu FC, MISIO OSD and VideoDownlink and a framedesign by me.
Today I had the my first liftoff, and it lifted streaight up, but just the minor movement of the sticks results in a very wobbly flight. I have not dared to lift it more than one metre up in the air because I am afraid it will wobble increasingly until it crashes...
The octocopter is fairly big; just more than 5kg, powered by 2 x 8400mAh Turnigy batteries.
Motors are Pulso 2820/14 860Kv, with himodel Pro 40A ESC.
AS seen in the video the whole octocopter feels like it is more at sea than in the air. I am new to PID tuning, and since this is a fairly expensive one of a kind octocopter, I want to be safe and not experiment if I can avoid it.
Please I am asking for your experience to get this octocopter up an flying.
PS. I have removed the landing legs/CameraGimbal, since this is a fragile part when it comes to crashing..

all help is more than welcome!
best regards
Mathias

Re: PID help with a huge homemade octocopter

Posted: Sat May 19, 2012 8:04 pm
by bill516
What are your settings in the GUI. If your like me when you install a new sketch you will have forgotten to drop the rc rate down to .60 or so to tame it down.

Re: PID help with a huge homemade octocopter

Posted: Sat May 19, 2012 10:14 pm
by oterpoter
I will post aettingsfile tomorrow
Yaw was 4.0, 0.030, 17..
I set expo in my transmitter but to no avail. I am pretty sure that I need to adjust PiDs, and not onky RC Rate.
So if anyone can suggest a procedure to find proper PID values without crashing my octocopter I would be a happy camper! :)

Re: PID help with a huge homemade octocopter

Posted: Mon May 21, 2012 11:41 am
by oterpoter
This is my settings for the octocopter.
I see that RC Rate is high, and will lower it to see if this helps.
But I got some instances of one of the motors speeding up for a very short time..
My quad has done some very strange flips the last 2 flights, resulting in crash, since it just starts to flip continously faster and faster..as if the Acc is flipped upside down or something.
I am afraid this could happen to the octocopter, resulting in a devastating crash.. and this is pretty expensive....
PIDs
ROLL: 4.0, 0.030, 17
Pitch: 4.0, 0.030, 17
Yaw: 8.5, 0.000, 0
Alt: 4.7, 0.000, 0
Vel: 0.0, 0.000, 0
Level: 9.0, 0.045
Mag: 4.0

RC Rate: 0.90
RC Expo: 0.65

Re: PID help with a huge homemade octocopter

Posted: Mon May 21, 2012 8:43 pm
by bill516
If your rc rate is .9 thats nearly at the max sensitivity, I think you will find it is less twitchy at .6/.65. Have you looked at the GUI trace to see what the gyro and acc are doing with about 50% throttle. You need props on to do this so be very careful, this is the best way to check for vibration from motors and props. A flat or almost flat trace you can rule out vibrations, if its dancing allover the place and the motor rpms are up and down you need to get it sorted before you can go any further. If you dont sort the vibrations it will be like trying to fill a bucket with a hole in it, you will never get far before you have to go back to the start.

Next step is to set up the trim on the Tx to get an hands off or almost hands off hover, an approx setting can be achieved using the GUI, with final setting by flight test, this is in gyro only mode, no acc, mag, baro or any other sensor. Once you've got that then you can get onto stick trimming again you can use the GUI to get an approximate setting, final setting by flight test, then start setting up pids for the different sensors, I'm at that stage myself and I'm concentrating on just one sensor till I get it right then I'll move on to the next.

The FAQ's have some good links in them on setting things up, there are no short cuts.

Re: PID help with a huge homemade octocopter

Posted: Mon May 21, 2012 10:25 pm
by chilled
Watching your video, it's hard to determine what's going on because you are so close to the ground. As with any heli, you are going to have to get at least a metre or more off the ground to reduce it's influence on how the heli hovers/flies. I wouldn't have said however that the heli is overly-twitchy, though perfectly understand you concern about crashing that beast into the floor! :shock:

I would do more hand-held testing with it to see how it wants to manoeveur itself. With a *firm* grip, hold the centre about waist level, arm the motors, tentatively push the throttle up until you feel the octo taking it's own weight (still keeping a good grip of it mind!) then gently try forcing the octo into a roll to see how it counteracts your physical input...

Re: PID help with a huge homemade octocopter

Posted: Mon May 21, 2012 11:02 pm
by oterpoter
Thx for the fedback gentlemen!
I will definately try some more! I have read that one should not use both USB and LiPos at the same time. But to be able to test with notors using GUi i need to use LiPos.. Is that safe?
Usb, then LiPo?
I know I am not "flying" high enough, but the dancing movement makes me reluctant to fly higher..
My quad has performed some nasty 360++++ flips that just gets faster and faster until it smacks into the ground..
I do not want that to happen to this baby.. I am a chicken.. I know..
That said; it lifts off straight up..and seems very well balanced. I will drop the rc rate to 0.65 for starters. Only peoblem now is that the motos allof a sudden will not arm..
Uploading 2.0v of firmware fixed it, but camera Gimbal and OsD is not compatible with 2.0 as of yet...

Re: PID help with a huge homemade octocopter

Posted: Tue May 22, 2012 1:20 pm
by hexjump
oterpoter wrote:Thx for the fedback gentlemen!
I will definately try some more! I have read that one should not use both USB and LiPos at the same time. But to be able to test with notors using GUi i need to use LiPos.. Is that safe?
Usb, then LiPo?
I know I am not "flying" high enough, but the dancing movement makes me reluctant to fly higher..
My quad has performed some nasty 360++++ flips that just gets faster and faster until it smacks into the ground..
I do not want that to happen to this baby.. I am a chicken.. I know..
That said; it lifts off straight up..and seems very well balanced. I will drop the rc rate to 0.65 for starters. Only peoblem now is that the motos allof a sudden will not arm..
Uploading 2.0v of firmware fixed it, but camera Gimbal and OsD is not compatible with 2.0 as of yet...

After connecting to GUI by a USB cable, you could turn on your motors with lipo batteries without propellers. It will be safe enough. Post a screenshot of the GUI here if you want so that we can see the curves of the IMU's data reading at a 50% throttle level.
PS: I like your big monster.

Re: PID help with a huge homemade octocopter

Posted: Tue May 22, 2012 2:19 pm
by Pyrofer
I blew up my uBEC by connecting it at the same time as USB, which fed voltage back into it.
To be safe, remove any 5v feeds from the quad to the control board. Keep ground and signal wires connected.
The control board will then be powered from 5v and the rest from the liPo, as long as grounds are all connected this is as far as I can see the best way and is how I do it now.

Re: PID help with a huge homemade octocopter

Posted: Tue May 22, 2012 10:20 pm
by sismeiro
oterpoter wrote:I have read that one should not use both USB and LiPos at the same time. But to be able to test with notors using GUi i need to use LiPos.. Is that safe? Usb, then LiPo?

To be on the safe side I bought a BT Serial adapter and this way I can see the information on the GUI and have the LiPo connected. The bonus is that I can configure the MultiWii on the "field" using my Android.

Re: PID help with a huge homemade octocopter

Posted: Mon May 28, 2012 10:25 am
by oterpoter
Another video
I still feel it is a bit like a boat floating.. It dubbes back and forth when I adjust using the sticks.. As if it is too slow on stable mode.. Maybe it should be a bit more agressive? I just want to get rid of the minor rocking back and forth .. And I believe that adjusting PIDs will help, but I am unsure whether to increase or decrease the values.
Apart from that it flies fairly stable indeed!
Proflyer.eu FC card inside.
MISIO OSD as well, but have yet to hook up the camera gimbal and landing legs.
Connected everything yesterday, and will have my first testflight with all up later today!

Video of the complete copter assembled, with wings/arms folded
http://www.youtube.com/watch?v=vrAX80zD ... ata_player