Hi,
I've seen multiple threads about this topic and have tried most (if not all) documented fixes for this problem.
I build a quadcopter using these parts:
Pixhawk Advanced AutopilotUblox Neo-7M GPS with Compass (not connected)DT750 Hextronic Outrunner 750kvRotorBits QuadCopter Kit With Modular Assembly SystemProps 2pc CW 2 pc CCW Rotation 12" 4.5 pitchCompact 4000mAh 3S 25C Lipo PackAfro ESC 20Amp Multi-rotor Motor Speed ControllerPPM encoder for PWM signal from the 5ch RC controller
From the threads i've gone through, i have:
- Made sure that the proper motors are attached to pixhawk in the proper manner (shown in the picture).
- Made sure that the propellers were spinning in the right direction.
- Made sure that the clockwise and counter clockwise props are on the right motors (seen in the picture).
- calibrated the accelerometer in mission planner. Values given when on flat ground is
Pitch: (±0.01 - 0.2). Roll: (±0.01-0.4).
- Ran motor test to see if vibrations/battery affect accelerometer. They do not.
- tested over grass and flat concrete.
- Started with Arducopter 3.01, upgraded to 3.2 to see if the problem might be fixed.
- Radio gives proper outputs and was calibrated.
- ESC's are calibrated.
- Made sure it was in + configuration.
- Ran motor tests.
A couple of comments about the quad:
- The pixhawk is not centered on the base, its a little off (towards the back towards motor #4).
- The weight is pretty well distributed but not perfect.
- starts flipping at about 50% throttle.
- always flips towards the corner (between 2 arms, could this mean that there is extra pitch and roll?)
- using 5 channel controller and a ppm encoder for rc. All channels work (1-5) properly.
- I have logs, no idea how they work but i just downloaded them from the pixhawk using mavlink.
I've tried fixing this problem for 2 weeks but i cannot find anything wrong with the quad. I've looked at multiple forums and all the solutions were not applicable to my quad (usually configuration problem with props/motors). I'd love some help or any suggestions.
Thank you.
Replies
Liban_O,
After you check all of the above a couple of more thoughts
1. During the radio calibrations the pitch control when moved away from you or forward must cause the bar in Mission Planner calibration display to go down not UP.
2. It often takes a bold jump to get the quad off the ground say 5 feet up so that the FC can start to control the motors. If you are too cautious it starts to tilt 6" off the ground and the fc can't do anything about it.
3. Balance is very important. Make sure the aircraft is not heavy on one side or another. Tie four strings to the arms at the plate and lift it up and see if it balances.
It is frustrating but hang in there and you will figure it out.
I had a similar problem with my hex. It tilted over when I tried to lift it. If I did the "bold jump" as Mike says, it would lift off, but oscillate quite a bit.
I solved the problem by lowering the Stabilize Roll/Pitch quite a lot.
My experience too. Not getting off the ground made it difficult to see the problem. After I got it in the air I could easily see the issue. My rig only oscillated in the roll plane. So I unlinked pitch and roll in the rate P and lowered the roll p value only.
Best of Luck
Liban,
From my own experience, two suggestions:
1) I believe strong, consistent flipping during take-off is most likely to be due to mis-wiring the Power Distribution Board (PDB). Your controller is sending 4 signals to the PDB, and the PDB is distributing those signals to the ESCs.
If you get the match-up wrong, the controller re-acts to changes in orientation (wobbling during take-off - inevitble) by sending a corrective signal to the wrong motor/ESC, which amplifies the instability instead of off-setting it, which causes the controller to send a stronger signal, which makes the problem worse...resulting in a sudden, violent flip-over every time you start getting airborne. The controller thinks it's correcting the problem but just making it worse. 'Positive feedback loop'.
(The story of my first real-world flight, by the way. I think I'm not alone).
Check those PDB connections very carefully. Check them again.
You say 'proper motors connected to controller in proper manner- see picture', but it's not possible to see if you've soldered the Controller-to-PDB wires correctly.
2) Somewhere around the 3.0 firmware update (3.01?), Randy advised not to touch the pitch or roll controls on the transmitter during take-off, or you 'may experience flipping on take-off'. Just centre them, use only the throttle control until you're well airborne (10 feet?), and trust the controller (only if it's properly wired!) to keep the craft stable until then.
This also works (also from hard experience).
Caveat - I have no Pixhawk experience, but I don't think it changes the 'PDB mis-wiring' danger.
George
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