Roll and pitch behave differently

[kallaspriit]

Hey, I'm rather new in the multirotor field and just completed building my first quad using the Multiwii PRO flight controller



I've gotten the quad to actually fly a bit but not so good. The problem seems to be that the pitch axis is much less responsive than the roll axis even though the copter is in symmetrical plus configuration and the PID values are exactly the same so I should expect the axes to behave similarly?

When I run the quad at low power in my hand and try to roll the copter, it counteracts quickly and strongly. When I do the same with pitch, it does affect it a bit but not nearly as much. When I put the copter on an USB cable and arm it without actual battery connected (so the props dont run), I have observed that the power given to roll axis motors (left, right) is stronger than pitch axis ones at the same roll/pitch angle:



Sensors have been calibrated and looking at the graphs, they make sense and seem to be of equal magnitude for the different axes.

My config file: https://dl.dropboxusercontent.com/u/885 ... d/Config.h
The flight controller: http://www.hobbyking.com/hobbyking/stor ... odule.html

I'm probably missing something simple here, any ideas?

[Hamburger]

start tests in acro mode (angle off)
Does yaw work,
each motor spinning in correct direction?

[kallaspriit]

Yeah, the copter is capable of flight so the setup can't be entirely off. As shown in the GUI image, the values seem wierd even if not actually running the motors. Is this to be expected given the setup is symmetrical and the PID values are the same?

[Sebbi]

1402 pitch
1501 roll

Those transmitted values could be the cause. I think you are using a Turnigy 9X with the included receiver? I had similar problem with it when using no deadband and untrimmed sticks. 1500 should be the center value, but sometimes the 9X doesn't go back to the center when you let the stick go and will send 1495 or 1504 or something ... that will cause problems in angle mode without deadband active (config.h).

[kallaspriit]

Trimmed the pitch to a maximum reading of 1482 centered (cheapo hobbyking transmitter, still waiting for the new 9XR to arrive) and configured a deadband of 25 (#define DEADBAND 25) but it doesn't seem to make a difference.

Even if the pitch TX value is off by a little, I would expect the quad to drift a bit but still have the same responsiveness as on the roll axis?