Multicopter from Scratch. Need guidance on how to tune PID controllers

Projects General Guidance
1

I'm building a small multicopter, and I'm trying to get it into the air.

I've got the hardware set up, and the program has PID controllers in, and is able to read and filter the 6DoF IMU data to give me orientation. But I'm not sure where to go from here.

The multirotor is completely independent of RC control. No transmitters, no recievers, no nothing. It is purely programmed with the Serial interface at the moment, so its still got a serial cable plugged into it every time I test it.

I need to tune the PID variables but I have no clue how to go about doing it. I've looked into a PID autotune library, but I dont think that will work for a multirotor since it plays with the values a bit. I know what the 3 PID constants are, and how they translate to performance of the copter, but again, I cant just randomly play with the variables since if the copter destabilizes it will crash.

I'm having second thoughts as to whether I should:
Set up a completely manual ('dumb') control system first, and have it hovering before attempting to tune the PID values
OR
tune the PID values first, then building a control system

Reasons I'm a bit apprehensive:

  1. I dont have a big budget. I really dont want to flip it and bust the components
  2. I've got 2 scars on my arm from where the propeller sliced it open when I tested it and it throttled up due to a mistake in my program. (I now bench test without the propellers on, but to do PID tuning it will have to be in the air, no?).

Any advice would be greatly appreciated.
I apologize for the convoluted post, but in summary:
I need advice on HOW TO APPROACH this process of achieving stable hovering flight using PID controllers.

StefL

2

I have tuned the PID by getting two chairs and putting them back to back with about 6ft in between. Then fasten a strong string from one chair through the airframe of the quad and into the opposing chair. Effectively, this creates a balance and restricted the quad to one degree of freedom because only the propellers off the axis of the string can rotate the quad. This way you can isolate and tune your x-axis and y-axis individually and in a controlled way.

I would recommend some manual control for tuning.

3

Thank you so much,
sounds like a wonderful method and i will try that today.