Uncontrolled Oscillations
« on: October 31, 2017, 10:45:12 pm »
As I think I mentioned in a previous post I'm a long term fixed wing flyer but recently I've put together a DIY quadcopter.  Just to see if I could!  Despite my hamfisted efforts it does lift off and everything looks reasonably Ok.  However it them develops uncontrollable oscillations resulting in a rapid descent. The effect can be seen in the video at 50" and again at the end.  The FC is a CC3D.  As suggested in another post I've calibrated all the motors at the same time rather than individually.  Any suggestions for a resolution would be much appreciated.

« Last Edit: October 31, 2017, 10:49:33 pm by f5soh »

f5soh

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Re: Uncontrolled Oscillations
« Reply #1 on: October 31, 2017, 10:49:06 pm »
Please post your config file, may help.
File > Export UAV Settings...

Re: Uncontrolled Oscillations
« Reply #2 on: November 01, 2017, 05:41:45 am »
Oscillations are usually caused by PIDs that are too high for the current setup.

One frequent reason for a setup to respond slowly is using "PWM 50Hz" option for ESCs.

Make all the banks (1-3 for me, yours may be different) associated with all of your ESC output channels (1-4 for me) use the same thing and that it is PWM 490 or PWMSync.

For me, banks 4-6 are not used and they default to PWM 50Hz

Re: Uncontrolled Oscillations
« Reply #3 on: November 01, 2017, 06:55:25 pm »
f5soh, Config File attached.

Re: Uncontrolled Oscillations
« Reply #4 on: November 01, 2017, 06:59:23 pm »
TheOtherCliff, when I did the initial setup I selcected PWM490 as the ESC type.  However following your post I looked at the Output Channel Config page and found that the Update Rates were set to PWM 50Hz!!  I've changed them to PWM 490 and will let you know the result after a test.

Re: Uncontrolled Oscillations
« Reply #5 on: November 02, 2017, 07:43:20 pm »
After a quick test today it looks like flight is much more stable and there was no oscillating that I could see.  Thank you.
Now I need to try and do some fine tuning to try and stop the Quad creeping around on its own.  However some of that may be due to the FC not being secure I think.  Then I'd like to move on to altitude hold and RTH.  To quote Arni, "I'll be back"! 
Thanks again. 

mr_w

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Re: Uncontrolled Oscillations
« Reply #6 on: November 03, 2017, 01:03:14 pm »
If this is really cc3d (board id 402), there will be no alt-hold (no barometer sensor on that board) and no RTH (not enough program space in F1 processor for advanced GPS features).



Re: Uncontrolled Oscillations
« Reply #7 on: November 03, 2017, 02:55:45 pm »
I wasn't aware of that limitation on the cc3d mr_w. I can see an upgrade coming on. Can you suggest a replacement?

mr_w

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Re: Uncontrolled Oscillations
« Reply #8 on: November 03, 2017, 03:34:04 pm »
My current favourite is Omnibus F4 Pro, see comments here https://forum.librepilot.org/index.php?topic=3864.0


Re: Uncontrolled Oscillations
« Reply #9 on: November 03, 2017, 09:06:06 pm »
The Omnibus F4 Pro looks like a lot of work.  I was thinking of the Revo version of the cc3d.
« Last Edit: November 03, 2017, 09:31:44 pm by fun flyer »

mr_w

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Re: Uncontrolled Oscillations
« Reply #10 on: November 04, 2017, 10:17:21 am »
Yeah, using Omnibus right now does indeed require that you compile firmware yourself. Compared to Revo, Omnibus F4:

Pros:
- availability of high quality genuine hardware (if you buy directly from Airbot)
- integrated current and voltage sensors
- integrated LC filter for FPV gear
- integrated OSD

Cons:
- you don't get integrated oplink like with revo.

Although, there is Chinese Oplink AIR which could be connected to Omnibus F4 SPI connector. That is a thing I am considering checking out.

Re: Uncontrolled Oscillations
« Reply #11 on: November 04, 2017, 08:10:08 pm »
GPS setups make flight so easy that really anyone can fly it.  Release the sticks and it STOPS MOVING and stays where it is while you scratch your head and figure your next move.

Just to be clear, it is a good idea, call it "required" to be able to fly without the GPS.  You really should set it up and tune it without GPS and then enable GPS.  You get away with skipping this with DJI/Naza because Phantoms come designed pre-setup, and pre-tuned for GPS flight.

Although it may technically be possible to set LP up with a GPS from the beginning and not actually learn how to fly without GPS, it is so much better to learn to fly in Attitude mode without GPS.  Think of riding a bicycle before trying a motorcycle...  and for the same reasons, start small and learn from small mistakes.

So don't get a GPS setup just to avoid learning how to fly.  It isn't all that hard.

Re: Uncontrolled Oscillations
« Reply #12 on: November 14, 2017, 04:20:59 pm »
Thanks for that and I agree completly about learning to fly without stabilisation.  Many times I've seen fixed wing flyers learing on the modern trainers fitted with excellent stabilisation only to come to grief when trying to handle even a basic model without the assisting electronics.  I think my current problems are mainly with basic setup and tuning.  But I'm sure they're not impossible to master.