Good afternoon everyone. I have a problem with a VTOL aircraft that is heavier than the rest of our fleet. An important point is that this system has exactly the same parameters loaded as the other aircraft that operate without issues.
When trying to take off in QLOITER mode, the motors lose power, the system collapses, and it falls violently to the ground. However, if I take off and land in QLAND, the aircraft lifts off and transitions without problems.
The second issue occurs during the fixed-wing phase: the airplane exhibits oscillations and predominantly negative pitch.
Since we cloned the configuration from a lighter aircraft, we suspect that the weight is affecting the dynamic behavior. Has anyone experienced this loss of power in QLOITER associated with weight with inherited PID? Any suggestions on whether the fixed-wing pitch is due to a CG movement or lack of tuning?
Hello, I don’t quite understand what you mean by “if I take off and land in QLAND”. Did you take off as a fixed-wing plane or during a VTOL_TAKEOFF mission?
Since QLAND mode is working fine, I suspect the issue might be related to the hover throttle parameter. However, if this value is incorrect, other critical initial tuning parameters might also be misconfigured. I’d recommend starting with steps 1 to 4 on this page: VTOL Tuning Process.
Once you have configured all parameters according to the documentation, I suggest skipping steps 5 and 6 unless you are an experienced pilot and fully comfortable flying in QSTABILIZE mode.
Ensure that Q_A_THR_MIX_MAN is set to 0.1 and Q_M_THST_HOVER is configured lower than your expected hover throttle. I typically use 0.2 as a safe starting value.
Then, take off in QHOVER mode and proceed with step 7. If the aircraft flies well, you can let the Q_M_HOVER_LEARN parameter adjust Q_M_THST_HOVER automatically by keeping the sticks centered (avoiding attitude inputs) for a few seconds.
Tell me, what mode are you flying in the fixed-wing phase?
You shouldn’t blindly copy parameters. Ardupilot wiki describes the way of handling variable mass for copters, you should apply that at a minimum, preferably run copter and plane autotune on the veicle.
To better clarify the behavior I’m observing: when I carry out the mission completely in AUTO (including takeoff with VTOL_TAKEOFF and landing with VTOL_LAND), the heavier drone completes the whole operation without any issues. The problem arises specifically when switching to QLOITER, where this vector experiences a noticeable power loss.
I find it curious that it behaves so differently in this manual/assisted flight mode, especially since in automatic mode the acceleration management works correctly. As a technical detail of the fleet configuration:
Heavy vector: Q_M_THST_HOVER set to 0.50
Light vector: Q_M_THST_HOVER set to 0.39 (this one flies without problems)