Flight controller software
I spent 8 hours today writing the flight controller software. I have the sensor, navigation, guidance, and control routines completed. It will need much more development to fine-tune things, but almost all of the sophistication is there. I made it so the infrared sensors and pressure altitude are calibrated online. In the future I will add a feature to “lock” the altimeter calibration when the GPS is not working, and to trust the altitude value that indicates the lowest value if there is a significant disagreement.
Right now the navigation system relies mostly on the GPS. I will program 4 different target points to fly to, then the software uses a modified roll-command PN guidance to fly to each target in sequence, then start back at the beginning and repeat the process. A successful target intercept occurs when the airplane flies within a 200 foot horizontal radius centered on the target.
The altitude hold feature is a proportional-integral controller that commands pitch attitudes.
The pitch controller is proportional-derivative with elevator deflection being the control.
The roll controller is a P-D system similar to the pitch controller.
The throttle is currently open loop.
I put in a yaw rate controller to coordinate the banked turns. The output of the controller is proportional to the yaw rate error. The commanded yaw rate is based on the PN heading rate and the bank angle. I need to double-check the way I calculated the yaw rate for coordinated flight.
I don’t have enough time left in the semseter to make a SIMULINK model of the airplane to test controllers and gains, so I will have to do that by trial and error.
I need to calibrate the gyros. I also need to find the offset voltages for the IR sensors. Then I can install everything in the airplane and fly it.