Stabilize mode doesn't work, but Alt Hold mode works just fine, why?

Hello,I built my quadcopter with APMcopter/Arducopter and I use Mission Planner on Windows to fly it. There are no extra external sensors such as compass or GPS or cameras - I have those but didn't install them just yet - and want to try out the basic functionality of the quadcopter.In Alt Hold mode the quadcopter flies perfectly well and when I first tried the Stabilize mode, the quadcopter also flew just fine with that. But after I landed it that first time in Stabilize mode, I can't fly it in that mode anymore.The front two motors spin up normally, but one of two rear motors doesn't spin up unless I add quite a bit of power, and the other one spins much slower than the front one. It still reacts to inputs, but when I try to lift off, it flips over since the front motors spin quicker.In the "RAW Sensor" window in Mission Planner I can see that the apmcopter software gives less power to the two rear motors than the two front motors. So the quadcopter does this on purpose, it's not a defective ESC or motor. Furthermore, the Alt Hold mode works just as well as it did before.I calibrated everything and it doesn't change the behaviour. Basically, the quadcopter behaves as if it was tilted forward (nose down), and counteracts that by giving more power to the front motors.But it's calibrated just fine and the Alt Hold mode confirms that. All inputs respond, there is nothing defective whatsoever. It seems like a bug to me, but I didn't find any other users reporting the same issue, and I can't update the software because I am out in nowhere and only have my phone with slow internet to post this question.Thanks for your help!

You seem to have misunderstood. The quadcopter is placed on a flat surface, set to Stabilize mode. I arm the quadcopter and add power. The two front motors spin normally, one of the motors in the back does not spin and the other one spins very slowly. Once I add enough power for it to take off, the quadcopter instantly flips backwards onto its back. It has to, since the two front motors produce much more thrust. But that is certainly not intended behaviour now, is it?

There is no wind involved or anything, calibration is done successfully and the Alt Hold mode works normally, as in, all four motors get power. The first time I tried the stabilize mode, it worked fine too, but now I tried more than a dozen times and there is no difference. Does this clarify it?

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David Garrett July 30, 2016 at 1:59pm

Yeah I know that the DJI esc's can't be calibrated... but what I did do was to alter the CH3 MIN to 1120, and that made the esc's and motors more responsive and in synch with one another..

But glad that your system is all working as it should... could have been a glitch all along....
Andreas Puchl July 30, 2016 at 12:17pm

I see. Well, for the DJI ESCs I have it is not possible to calibrate them (if you try, it won't go into the calibration mode), it's simply not necessary.

I tried flying the quadcopter again today after letting it sit for three days. Guess what - the Stabilize mode worked flawlessly now, just like it did the first time. It started to rain so I couldn't test it for more than five minutes, but during those five minutes it worked.

There has to be something that breaks the mode sometimes, but not always. I am out in nowhere, so there is nothing that could possibly interfere with anything...
David Garrett July 30, 2016 at 9:33am

just been told that because I am using DJI E300 esc's that I needed to adjust a setting in the FULL PARAMTER TREE..

I have attached a screenshot.... I was having probs with motors not all spinning up in sync... I adjusted the RC3 MIN to 1120 and wrote parameters back to the Pixhawk... took the craft outdoors and all motors were in sync...

rc3.jpg

https://storage.ning.com/topology/rest/1.0/file/get/3702275294?profile=original
David Garrett July 29, 2016 at 10:37am

no worries, hope you get things sorted out soon....
Andreas Puchl July 29, 2016 at 10:32am

It certainly can't hurt, but as I said: In Mission Planner I can see that the APMcopter software gives less power to the rear motors, so it's something that will have to be resolved via APMcopter, not with an ESC calibration. If there only was a troubleshooting guide for APMcopter that had anything remotely helpful. I have read through everything I found so far and there doesn't seem to be anything usable.
David Garrett July 29, 2016 at 10:15am

I use the DJI E300 on my Hexacopter... but I still performed an ESC calibration.... not saying that it will make any difference... but it can't hurt to try.. ;-)
Andreas Puchl July 29, 2016 at 9:59am

I did not perform an ESC calibration because I use the ESCs from the DJI Flame Wheel F450 set and those do not require calibration.
David Garrett July 29, 2016 at 8:36am

you said you calibrated everything... did you perform the ESC calibration as well???
Andreas Puchl July 28, 2016 at 12:43pm

You seem to have misunderstood. The quadcopter is placed on a flat surface, set to Stabilize mode. I arm the quadcopter and add power. The two front motors spin normally, one of the motors in the back does not spin and the other one spins very slowly. Once I add enough power for it to take off, the quadcopter instantly flips backwards onto its back. It has to, since the two front motors produce much more thrust. But that is certainly not intended behaviour now, is it?

There is no wind involved or anything, calibration is done successfully and the Alt Hold mode works normally, as in, all four motors get power. The first time I tried the stabilize mode, it worked fine too, but now I tried more than a dozen times and there is no difference. Does this clarify it?
Andre K. July 28, 2016 at 11:36am

Congratulations on your conclusion "ap does that on purpose"
Now ask yourself, what would happened if two motors actually produced more thrust, as commanded ?
As long you hover in insignificant wind, and CG is about center, and ESCs are calibrated, and motors produce thrust as commanded, then you should see all work about the same.

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Stabilize mode doesn't work, but Alt Hold mode works just fine, why?

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