Thanks for pointing out an obvious reason of why position control for DC motor requires the cascade topology. Always used it, never understood formally why is was required. Just curious : how have you come to this conclusion / explanation ? Do you have any resources on the subject ? I'm still struggling to find a (formal again) rule on what should be the ratio between the outer and inner loop rates.
> how have you come to this conclusion / explanation?
Through personal suffering while working on firmware for UAVs (PX4/Ardupilot), CNC controllers (grbl, Marlin), inverted pendulum balancing exercises, RC car control etc.
Sadly, no resources. I guess the best advice I could give on this subject is: increase the visibility of internal state of the system. I have lost track of number of times I've seen people trying to tune PID controller just by outside observation (hmm, looks a bit better than last time) instead of real-time plots of measured process error.
Add high-resolution logging, look at the plots of error and P/I/D terms, have a simulation where you can replay the sensor values and observe the system output.
