Hey everyone
Relatively new to the quadcopter world here, and I have a pretty generic question about PID theory and tuning, etc.
There are tons of great articles out there about how to tune PID loops, and I have a pretty good understanding of the process and the math behind control loops. However, I haven't been able to find anything that relates PID tuning to external factors like the physical characteristics of the quadcopter, the trim on the controller, etc.
Here are some specific questions:
- Intuition tells me that on an ideal copter (perfect motors, rotors, weight distribution) I should be able to turn all PIDs entirely off, simply react to thrust and divide power equally among the four motors, and achieve a SLIGHTLY stable hover. In other words, it'll drift all over the place and be unflyable, but it shouldn't simply invert itself and slam into the ground. True?
- Let's talk about RATE mode: What's the role of trim from the controller? It seems like on my current setup, one or more of my motors/props are unbalanced and my copter biases pretty heavily towards rolling left. I can fix this by trimming my controller. I've been completely unsuccessful in eliminating this bias via the Ki coefficient, and that makes since it's a pretty large amount of error. Is this an appropriate use of trim?
- Now, what's the role of trim in ANGLE mode? I'm thinking a well designed angle PID *should* be able to account for angle drift due to an unbalanced setup, without any trim at all. True
Any other insights into the relationship between PID tuning and other physical/external factors are welcomed!
Thanks
Sean
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