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VTOL/Quad plane transition porpoising

For some time we have experienced intermittent porpoising (pitch oscillations) on our aircraft when transitioning from VTOL to fixed wing flight. Sometimes it will do it real bad (high amplitude), others not at all. Some things that seem to affect it include stiffness of the tail’s mounting (A-tail supported by the vtol booms), and stiffness of the fuselage to wing mount. Any slop in either of those seems to make the porpoise way worse. I notice that both the VTOL and plane controls are fighting to correct this and wonder if this has something to do with this, but I have a feeling the root is in poor plane pitch PIDs.

Has anyone else had this problem?

Can someone look at this log and tell me how you’d adjust the PIDs (specific attention to time 15:50:43) I am in need of someone who is good at PID analysis and am willing to pay for good help and instruction. Autotuning isn’t really an option.

IB Crazy once had a video about tuning. His recommendations are as follows:

P to low, slow oscillations, sluggish
P to high, stable but fast oscillations

I to low, very sloppy, hard to keep position
I to high, overshoot and oscillate, can be compensated by D up, but can go out of control
25% of P is good to start

D to low, overshoot only shortly
D to high, fast oscillations, but almost unnoticed

For me, the above is almost like the Bible on tuning.

I your case, I’d start lowering pitch P. I’ll give you my bank account later, hahaha.

Thanks, do you have a link to the video? Was this for quad or plane tuning?

I’ve done okay but not stellar for myself with quad tuning, which we have more ability to play with than plane tuning. I’d really like to know if there is a way to look at the logs and be able to sort out based on the desired, actual, and the PID components what should be changed and by about how much.

Also, how the heck does the angle differ from the rates? What should be tuned first?

I don’t know how to look at the logs and start from there. I do my tuning in real life. It’s really not that hard, once you get the hang of it. This is Alex 's (ibcrazy) his video:

And by the way, yes, the stiffness of the frame plays a very big role. We also once had an airframe where the tail was almost unnoticeable loose, but it led to very high oscillations.

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Servers by jDrones