Hello Robin, I previously tuned a quadplane with 29’’ props, here’s some tips that was picked up:
If you want to be gentle on the motors during spool-up (given the high inertia from the large props), you can increase Q_M_SPOOL_TIME. Mine were doubled from the default values and it had no problems.
The spinning props responded quickly enough to handle gradual changes in roll and pitch, so long as the PIDs are tuned correctly.
Not able to answer this; but they were left as default on my quadplane and had no problems with tuning.
Tuning of parameters for QSTABILIZE
As the documentation states, the most important set of PIDs to tune are your Q_A_RAT parameters:
- Q_A_RAT_RLL_P/I/D
- Q_A_RAT_PIT_P/I/D
- Q_A_RAT_YAW_P/I/D
When you tune these params, perform the tuning in QSTABILIZE mode first. Doing it in QHOVER or QLOITER introduces additional layers of controls (height and position contollers) which will mess with your tuning.
What tuning method you use depends on the preference of each user. Personally, I like to use the following method:
- Zero the roll rate I and D params, and set the P param to a low value
- How low you want to set the starting P value depends on the thrust-weight ratio of your quadplane; the higher the ratio, the less aggressive your PIDs should be. Mine had a high thrust-weight ratio (for most quadplanes) of 2.41, so we decided on a conservative initial P value of 0.08. It turned out to be VERY conservative, but better to spend more time on tuning than to see the bird oscillating out of control!
- Takeoff in QSTABLIZE, and give it a few gentle rolls. Increase the P value in small increments (0.05 for me) until you start to see oscillations
- You can then add in a bit of D (Mine was added in increments of 0.0005) until the oscillations become less pronounced.
- For I tuning, if you see that the aircraft is consistently drifting in any one direction when your sticks are centred, add in some I value until the drift is minimized. Otherwise, we usually won’t touch it.
Repeat for pitch and yaw. You may find that the pitch and yaw rate PIDs may be higher than roll rate; the physical design of fixed-wing planes means they are more sluggish along the pitch axis, and multicopters have inherently poor yaw authority.
TLDR: For each axis, zero the I and D gains, start with a low P gain. Increment the P until you see oscillations, then add in some D to damp out the oscillations. Add in I if necessary to correct for drift/wind. This is a conservative method which we use for large quadplanes, to minimize chances of crashing due to over-aggressive PIDs.