Pixhawk wobbly & Unstable

[petronius]

Hello gurus of the drone world!
I have just finished building my Pixhawk drone and have so far taken it out for test flight several times, with no real luck.
I spent a long time checking and testing everything and calibrating, but here';s the problem, and the video says it all.
The drone is very wobbly in the sky! I don';t dare to take it higher than a meter or two as it just moves around wildly. I have tried recalibrating ESCs, compass, accelerometer, etc. even mounted the gps on a mast but to no avail.
when looking at the log file there seems to be a magnetic interference but I cannot understand what the source of it could be and whether or not it could cause such behaviour. I have loaded the video and it shows how it nods in pitch and drifts madly to the right...
Any idea what could be the problem?
the set up is a hexacopter on Tarot 680,
Pixhawk on ArduCopter Firmware Version V3.4.4
ESCs: Hobbywing Platinum-30A-OPTO
Motors: MT3510-600 kv with 10" props.
GPS UBLOX NEO M9N

video:
https://youtu.be/vFh-pZ-DBMw
https://youtu.be/DbsPH3SxZtk
https://youtu.be/xEJg89dyq1w

log files also uploaded

Appreciate your kind help and advise
Naeem

[Bajadre]

Looks drunk matey  looks like a prop could be on wrong way? my blade used to fall over if a prop direction or motor direction was wrong etc you';ve prob checked that but better to cover the simple things first 

[ched]

As said check props and motor directions. I also think your PID settings might need a bit of adjustment.

[orfordness]

I';m with everyone on this, check the props and motor direction:-

[petronius]

Ran back to the workshop wishing what you all suspected was true. but (unfortunately) all motors are spinning correctly and propellers are correct. sequence is also observed.
Here';s another interesting thing. when on Loiter, the throttle literally doesn';t do anything until it is midway. as soon as I switch to Stabilise, motors rev up, but the same dizziness still exists...
Could there be any other reason?

[petronius]

As said check props and motor directions. I also think your PID settings might need a bit of adjustment.

here';s the PIDs: Any suggestions? anything obviously out of order here?

[ched]

here';s the PIDs: Any suggestions? anything obviously out of order here?

I am not familiar with your FC so PIDs could be anything. One thing though, normal I think most peoples roll and pitch pids are the same as motors, props, esc etc are the same.

There are a couple of threads here that might give you some clues: http://www.multi-rotor.co.uk/index.php?topic=1385.0 & http://www.multi-rotor.co.uk/index.php?topic=4006.0
Good Luck and let us know how you get on.

[Fletch]

i know its a pain in the arse ... but start from scratch

Reflash pixhawk with a fresh flash, go through the setup again and redo stick and esc calibrations with the fresh flash.

In Loiter the throttle doesn';t work as a throttle it works as a height adjuster.

Centre Stick is Hold height, above centre is climb, below centre is drop.  The further you move the stick away from the centre, the faster it will climb or drop (up to the limits set in the pixhawk settings ... So this behaviour is expected

[petronius]

I guess I have to flash and rebuild.
while I';m doing this, what ground control do you suggest? QGC? or Mission Planner?

[Fletch]

I haven';t done much with a ground station but I use mission planner

[guest325]

Take a look at Peter King';s YouTube channel, there';s a lot of info there
http://youtu.be/Hdhn0E1hEYc
He uses Mission planner on most of his setups so you should be able to find out what you need to.

[orfordness]

You could also try peters pixhawk parameters here:-

https://drive.google.com/drive/folders/0B-B7PQy0joGrUjFmb2pSTFlqcWc

[petronius]

You could also try peters pixhawk parameters here:-

https://drive.google.com/drive/folders/0B-B7PQy0joGrUjFmb2pSTFlqcWc

Thanks. I';ve flushed the pixhawk and am going to load these params tonight. fingers crossed.

[ched]

Thanks. I';ve flushed the pixhawk and am going to load these params tonight. fingers crossed.

Good luck ';flushing'; the pixhawk  ::)
Let us know how it goes.

[petronius]

Good luck ';flushing'; the pixhawk  ::)
Let us know how it goes.

... yes nearly "flushed" it by reverse polarity! but luckily survived... but flashed ok 

[Hands0n]

I was going to say, as above, that your PID look a bit off.  I wouldn';t expect the Rate P and I to be the same, for example.  Did you run an Auto Tune?  How did you arrive at those values?

Normally the Lock Pitch and Roll is ticked unless you';ve deliberately done so through Manual or Auto Tune activity.

As regards Loiter - the Throttle behaviour you describe is quite normal.  It will spin up the motors to less than lift off power until you hit 50% throttle and then lift off.   

The behaviour you describe when switching from Loiter to Stabilise (for example) is an indication that your setting for Throttle Mid is not quite right.  It should continue to hover but then drift because the full lateral control is now in your hands. 

Some tuning work to be done methinks.   As a general rule, don';t try any of the auto modes until you get it lifting off and hovering in Stabilise.  The sequence is Stabilise, Alt Hold and then Loiter. 

There are some useful words here --> http://ardupilot.org/copter/docs/tuning.html

[petronius]

I was going to say, as above, that your PID look a bit off.  I wouldn';t expect the Rate P and I to be the same, for example.  Did you run an Auto Tune?  How did you arrive at those values?

I haven';t done Autotune. well, it barely stays in the air a few seconds before crashing...
I tried playing with the PID numbers to see what effect it has... any suggestion on what numbers to begin with?

Also, I have noticed - from the log files -  that a huge magnetic interference emerges somewhere during the short fly. could this interference cause such unstability?
I have placed the ESCs and all DC wiring right under the Pixhawk mount but a good 1inch away. could that be the cause?

Thanks,

[Hands0n]

It is really difficult to give you a starting point for PID, which is why you seldom get an answer to that question (I recall doing the same when I started out a few years back).  Each model and build will be different from the next and so it doesn';t really work out.

I';d suggest defaulting the Pixhawk configuration (iirc its done in the Full Parameters section) to give you a starting point.  Then only using Stabilise try to get the hex to left off and hover under your control (no automation at this point other than self-levelling of Stabilise). 

The guidance in that article I linked you to should give you a good basis to work on the PID page. Keep the Rate Pitch/Roll linked for now.

As to the Magnetic interference ... Locating the ESC and high current wiring close to and under the FC is generally not a good idea but unavoidable at times.  You could try some hight shielding under the FC - copper tape if you have it, maybe kitchen foil if you dont - but make sure you don';t create any short circuits.  Just something to help limit the EMI coming from those devices. It might/should help somewhat. And you';ll be able to see any benefit in the logs I';d have thought.

[JeremyE]

Maybe some pictures of the hex and the ESC';s etc will help. What ESC';s are you using, and what are they flashed with?

[Baner]

Hi Start from her and you not go wrong
https://www.youtube.com/watch?v=uH2iCRA9G7k&list=PLYsWjANuAm4r4idFZY24pP6s1K6ABMU0p

[petronius]

Success at last! I did a series of things and the result was brilliant. perfect stability in all modes (Stabilize, Loiter, AltHold)
I moved the ESCs to the underside of the arms instead of right under the FC. simplified the DC wiring and twisted them together where I could. changed the props to 12". and mounted the GPS directly on the frame (no mast, so one less piece to break when crashed!)
but most importantly (I think) tweaked the PID values (to 7) and reverted the Gain values to Pixhawk defaults. It now works like magic!
Thank you all for your help and advises

[Hands0n]

 

Congrats, nice one  

Now you';ve got this far, and Loiter is working which is a good sign, it might be worth just making sure that your Mag (compass) is okay and not subject to any undue interference.   None of the auto modes (GPS) will work well unless the Mag is correctly reading. And remember with the Pixhawk there are two in play, unless you configure otherwise.  A bad or inconsistent Mag could cause a fly away!

[petronius]

Thanks!
Point taken. I still have some adjustments to do. when I switch from Loiter to Stabilize it rockets up in the sky...
I still get some Mag interference, but the figure is in WARN range. I';ll try adding a copper plate under the FC as you mentioned.
Cheers,

[Fletch]

A bad or inconsistent Mag could cause a fly away!

I';ve had this happen ... I found i had to switch off the mag inside the PIxhawk and rely on the one in the GPS

It doesn';t fly away it does drop into Stabilize, and if your throttle setup isn';t right (like you descirbed, and like mine is) it takes off up into the sky at a crazy speed!

Thankfully i kept the FPV signal and landed no problem, but it went from about 15m to 400m in the time it took me to realise what was going on and how to get it back!

[Hands0n]

Thanks!
Point taken. I still have some adjustments to do. when I switch from Loiter to Stabilize it rockets up in the sky...
I still get some Mag interference, but the figure is in WARN range. I';ll try adding a copper plate under the FC as you mentioned.
Cheers,

That is a classic symptom of an incorrect Throttle Mid setting.  More reading I';m afraid ::)

Full deets here --> http://ardupilot.org/copter/docs/ac_throttlemid.html 

Get that right and your switch from Loiter to Stabilize will be seamless if the throttle is at mid position. 

[petronius]

I have noticed that "Automatic Learning of Hover Throttle" has taken care of it after a couple of flies! I can now switch between the modes and no overshoot happens.
I';ve now noticed that every time I change yaw, the drone becomes wobbly for a few seconds before it stabilizes again... I think PIDs need another fine tuning.
Lots of work but definitely worth it...

[petronius]

I have been hesitating to ask this for a while:
ESCs beep every second when the battery is connected. at first they beep synchronously, but after awhile the beeping slowly goes out of sink. is that normal? I still have some yaw issues and I was wondering if this is a sign of one or a few of ESCs are slowly dying??

[Hands0n]

That ESC beeping - does it start after a short period of the multi-rotor standing idle?  Say 5 or 10 minutes?  And are the ESC BLHeli firmware?   I don';t think other firmware does this, I may be wrong.  But what you are witnessing is the "Lost Model" alert from the ESC to help you find it in the long grass if it ditches in a field.  You won';t hear them at much distance, but they could be the difference between finding or walking past it in a hedge ...

The out of sync beeping is just that their timers are not synchronised and so there will be a natural drift.

[petronius]

ESCs are hobbywing platinum pro opto.
the beepings get completely out of sync in about 5 minutes. should I be worried about these ESCs?
I have a set of Cicada BLHeli_S ESC as spare...

[Hands0n]

Nope, nothing to worry about just as long as the ESC work as they should.  The beeping is when they are powered up but not Armed.  So that seems like normal behavior to me.