Is there a simplified "Arducopter light"?

Hello, I am looking to test a simple PID program for a quadcopter. I do not require any flight modes or failsafes or any of the extra features in Arducopter. Is there a simplified version of it, that just has the barebones?

why not just use Arducopter as-is, but just ignore the fact that it’s got a bunch of useful features. Eg: put it in “stabilise” mode, which does not need GPS at all, and does no position or altitude holding. You can probably also disable a bunch of subsystems, such as turning off the pre-arm checks, disabling the EKF might be interesting to try too, and perhaps the radio failsafe and telemetry failsafe could be turned off too. You might also want to disable the crash-checker , and the safety switch too.

Hi, I would suggest a spracer board and inav firmware, works great and not as complicated

Thanks for your responses guys. Unfortunately, your solutions will not work for me, for the following reasons:

1- I require the use of Pixhawk2.1 because I need the latest sensors and redundant imu’s, hence I am locked-in to using some variant of ArduPilot firmware.

2- I cannot have any other modes, only one single test mode. The reason for this, is that the test is highly experimental, and I don’t want some failsafe accidently activated and the drone slipping into another mode automatically. Furthermore, I would like to load the firmware with a bunch of my own (processor-intensive) code later down the road, so I really need to remove all the “extra features”, I would like to start with a light and simple package.