In the University of Paderborn, Germany, we have used PX4 in our designed quadcopter, and are about to go for the first flight test. However, although we have done the calibrations carefully, the drone is seriously unstable, and cannot take off /hover. It rolls to the side and crashes immediately like 10 cm above the ground.
I would appreciate it, if some one could let me know of the steps we are missing, or the reason why this happens.
@Kasra_Amini It sounds like a gain tuining issue
Thanks, could you also guide me on how to perform the tuning?
@Kasra_Amini This might be useful to you
Did you calibrate ESC as well? Sounds like ESCs are not synced.
Yes, sure. they are calibrated already.
Try fix your drone tightly on the floor with props attached, then slightly throttle up.
See if all props turning gently and does not make any vibrations.
That’s how it seems right to me. I have also done motor tests, and that is also accurate.
However the thing which is weird, is that when giving a sudden pitch, or roll disturbance signal (simply by rotating it for some small degrees), the motors create a response torque towards making the drone even more unstable, rather than opposing my disturbance torque, and trying to bring the drone back in the hovering status.
Does it help you understand what the issue could be?
What type of copter? quad?
In case of quad, when pitch down commanded(forward motion) front two motors should turn slower while rear motors turn faster and vise versa.
This is always checked everytime you start flying your drone as well.
yeah, that’s a quadcopter.
but if I run the motors and take the drone in my hands, and suddenly with it a manual nose down, the two front motors should revolve faster, create more thrust, to oppose my disturbance, shouldn’t it?
if you are running in stabilized mode then yes.
Is the pixhawk correctly placed in the quad? Maybe redo the sensor calibrations? that shouldn’t be happening. But maybe you are in manual mode and not in stabilized flight mode
Kasra. Going off of your flight description, PIDs or tuning is not likely the problem. If the mechanics of your build are sound and the components are functioning correctly, the default tune or PIDS will fly well. It sounds like you may have 1 motor spinning in the wrong direction or your CG might be way off…I would go back to the beginning and check the basics that you may be taking for granted. Sometimes a picture can help when consulting others.