Too powerful and highly unstable (CC3D)
« on: August 20, 2017, 08:00:20 pm »
Hey everyone,

So I built a 550mm quad from scratch with 30amp ESC 2300KV motors and a CC3D. I used to fly this with a 1300mAh 15-20C battery but that would only give me 4mins of flight time. It would fly well and be fairly stable with little to no wobbles. SO I upgraded to a 3500mAh 60C battery to get more flight time. As soon as I plug it in and give it a go, the quad shoots up with just a slight nudge to the stick. I tried bringing it down but the only way was to cut off the power and go on-off-on-off to bring it down. So to be safe I adjusted the throttle curve on the remote and made max power to 40%. even then, the quad would shoot up when you push the stick up and would show no signs of decelerating when you bring the stick down. its like power is binary with 1/0.
I used my initial battery with a normal throttle curve and it lifts off ok but after 5 seconds, it's started violently shaking. I've tried inputting different PID settings to try and stabilize but no effect.

any suggestions?

Re: Too powerful and highly unstable (CC3D)
« Reply #1 on: August 20, 2017, 08:46:58 pm »
You didn't say, but it sounds like you went from 3s to 4s too.  This is critical information to debug this.

Start by setting your PID, "D" terms to zero.  Especially for the yaw.

Since it used to work and you haven't changed ESC/motor/prop but you it sounds like you have "invisible oscillation".

Personally, I would start with setting ESC calibration and neutral, then zero D terms and retune PIDs.

Edit: And when you start with the correct props with 3s, and go to 4s, you must reduce the prop size or burn up stuff like motor and ESC.
« Last Edit: August 20, 2017, 09:03:22 pm by TheOtherCliff »

Re: Too powerful and highly unstable (CC3D)
« Reply #2 on: August 23, 2017, 03:46:43 am »
the battery is 3S (old and new). When i say unstable, I mean it wobbles violently just after lift off.
The quad used to run fairly well even with the pre-set PIDS and when i added my own PID based on OP tune, it made little to no difference. So i went back to the Pre-set PID's. But ill try your suggestions again.

Re: Too powerful and highly unstable (CC3D)
« Reply #3 on: August 23, 2017, 05:03:43 am »
Well then it maybe just needs PID tuning.  When you change the weight that much, the PIDs need to be tuned.

It's strange that it is so much more powerful with the new battery if new and old are both 3s.  Perhaps the old battery was weak and worn out.

What receiver signal type are you using and (Input page) what is min/neutral/max for throttle channel?
« Last Edit: August 23, 2017, 07:08:50 am by TheOtherCliff »

Re: Too powerful and highly unstable (CC3D)
« Reply #4 on: August 26, 2017, 04:05:52 am »
So before i even got to the PID's, i did a test of throttle without props. I re-calibrated my transmitter with the CC3D (attached image). The throttle curve is normal 0-100%.

I slightly push up on the throttle and it starts spinning fairly fast. I push it up a little higher, no difference in the sound.
i push it past 50%, same sound. Around 75% it sounds like it goes a little faster.

Re: Too powerful and highly unstable (CC3D)
« Reply #5 on: August 26, 2017, 04:35:07 am »
The problems you have don't sound like they are just because of a larger battery.

That picture is your input page and shows that the throttle is set up normally.

Try calibrating ESCs (again) and other stuff on ESC calibration page.  And do neutral settings.  And use default PIDs.  Then post your settings file (File -> Export UAV...) or a picture of your Output page.