Solved SOLVED: Major (Roll) Oscillations when arming quadcopter

[samtkeen]

sorry for the long delay, I have been in the process of exams and moving but now have more time to do some drone stuff.

even when having the multipliers down to 0.5 for master and P and D gain i am still getting a wobble. its very difficult as it is unable to fly at all for safety resons when wobbling this much. I even tried turning up the PD balance but it did not help. I have even changed to dual blade carbon fibre props ( was running through the plastic ones too quick) and the issues still persists.

Anyone have any suggestions?

 

[sprzout]

Sounds like your getting fly away, your P gain is probably to high. If your P gain is to high, it will over correct, then over correct the other way... and 'fly to the moon' as it tries to level itself out.

--- looking at your videos give s much clearer explanation..

when you don't have props on, you can't test anything related to the PID/etc. as it can't actually control anything.

it looks like your configuration is incorrect, when you had the props on it flipped over, which means one of 2 things ->
- the FC thinks it is upside down and is in angle mode - so it is trying to flip itself right side up.
- you have something related to the FC orientation or motors configured incorrectly, so that when it tries to correct itself, it is increasing the error instead of correcting it.

Make sure that 1) in the main window that when you move the quad, the image moves in sync and is upright the same way. 2) the correct motor relative to the positions on the quad spin up. At least one of these 2 are wrong.

One other thing, just to make sure of, since it happened to me - make sure you have the props spinning in the correct direction. I put counter clockwise props on motors spinning in the clockwise direction, and my quad kept flipping over when I'd throttle up. Stupid thing, but I corrected it and it's worked without an issue since.

 

[PsyBorg]

After a quick read thru this thread I am pretty sure this is frame resonance or excessive vibration issues. I see you are using 9 inch props so that means longer arms. The SLIGHTEST out of balance in the props will propagate back thru the arms and at the right frequency can multiply the strength.

Start by balancing the props. Then go thru and shut off as much of the filtering as you can. Then you can black box and get a more realistic idea what frequencies are causing your issues. I learned early when messing with the very basic KISS filters that too high filtering added to air mode equated to instant full throttle fly away conditions. Once I got the filtering knocked back I learned simple PID tuning and progressed from there. To this day I shut off all Betaflight bells n whistles and tune strictly by PIDS with minimal use of base filtering.

 

[samtkeen]

by massively lowering PID values i managed to get it what somewhat stable but my throttle control is almost non existent! when it bumps on the ground it still goes a bit out of control but i will try and fix that. i have attached images of the PID setup (almost 1/5th of original values!) not sure if I have just made the thing non responsive now but it was stable so i was happy. I have now switched to INavFlight but Im having a seperate issue with that but will now close this thread as solved.

Notes for fix:

• if the quad is increasingly wobbling oscillating it was a I term wind up so lower the I term until no more wobble in that axis
• if the quad would fall over or excessivly tilt on launch this was fixed by adjusting the P term in the tilt acis
• reduced rates to be 35% ( not sure if this helped much ) but for a cruiser the rates dont need to be that high

regarding airmode i didnt manage to find a fix but have switched to the Matek F722 PX which doesnt seem to have as bad of an issue. deep in some forums i found people commenting that there was issues with the F722 STD gyros, probably didnt help. I will try PsyBorg's airmode solution soon.

 

[Jase_MK]

by massively lowering PID values i managed to get it what somewhat stable but my throttle control is almost non existent! when it bumps on the ground it still goes a bit out of control but i will try and fix that. i have attached images of the PID setup (almost 1/5th of original values!) not sure if I have just made the thing non responsive now but it was stable so i was happy. I have now switched to INavFlight but Im having a seperate issue with that but will now close this thread as solved.

I know you've moved on from this, but I don't suppose you have any insights or hindsight on this whole thing now it's behind you? Did you get INAV working?

I've just built a 7" with large and powerful 2810 motors. I'm having exactly the same issues - shoots up in the air on arming on default PIDs. I brought all the sliders right down - master down to 0.5, P/D gain down to about 0.6. This stops the flyaway (at least at low hover throttle of 15% - I don't have to confidence to raise it much above that at the moment for fear of triggering a flyaway), but there are also lots of horrible looking oscillations on the logs. Frame seems sturdy and tight, I've tried 3 different sets of props, in case one was unbalanced. Don't know what else to do.

 

[PsyBorg]

I know you've moved on from this, but I don't suppose you have any insights or hindsight on this whole thing now it's behind you? Did you get INAV working?

I've just built a 7" with large and powerful 2810 motors. I'm having exactly the same issues - shoots up in the air on arming on default PIDs. I brought all the sliders right down - master down to 0.5, P/D gain down to about 0.6. This stops the flyaway (at least at low hover throttle of 15% - I don't have to confidence to raise it much above that at the moment for fear of triggering a flyaway), but there are also lots of horrible looking oscillations on the logs. Frame seems sturdy and tight, I've tried 3 different sets of props, in case one was unbalanced. Don't know what else to do.

These issues are exactly why I don't or use as little filtering as possible. Pid tuning will ALWAYS be the best way to get your craft to fly perfectly.

With large props you MUST balance them. They do not and will not come from any manufacturer fully balanced. It just would not be cost effective to mass produce them that way. There are many ways to balance props but the best way I have seen to date is to take a burnt out motor remove the magnets from the bell so the shaft spins freely and hard mount it with the shaft perfectly level and parallel to the floor. then do a proper balancing by standard methods posted on tons of RC websites.

Once that is done make sure your flight controller is soft mounted. I recommend using the bobbin style mounts for larger AP type aircraft. After that run the motors up at various speeds without props while black boxing to get a base reading on the frame resonance. Do this both stationary on the floor or table depending on craft size and room as well as suspended on string lines to remove any dampening effects of a hard surface being more close to what it will see in flight.

Also make sure there are no wires flopping around whackin the frame as they will transmit that impact back to the FC. Same thing with strain relief wires attached to the FC having too much play to wobble about and inject motion onto the FC.