P06004: Air Surveillance Platform for CIS
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AP50

Test RC Car fitted with AP50 for ground testing

Test RC Car fitted with AP50 for ground testing

The UAV Flight Systems AP50 board chosen for this project as an off-the-shelf autonomous flight controller. This controller controlled flight for the airframe aspect of the project. The AP50 featured a PID controller which required manual tuning based on emperical data.

PID Controller

The AP50 features a low-power RISC controller with integrated gyroscopes, accelerometers, sensors, and a global positioning system. A proportional-integral-derivative (PID) controller with user-specifiable gain and flight control modes was used by this system to govern flight. The PID Control loops are as follows:
PID Correction Equation

PID Correction Equation

Therefore, a Kp or Kd value of 10 is an equivalent proportional or derivative gain coefficient of 1, while a Ki of 0 sets the integral gain to zero.

The multiple control loops for elevator position and desired pitch enabled adjustment of constant airspeed versus constant altitude. According to the documentation, the aileron, elevator, and rudder PID loops execute at the rate of 30 times per second, the calculation of desired roll, desired pitch, and elevator execute at a rate of 4 times per second, and throttle executes once per second.

Trimming Procedure

Plot showing AP50 control outputs at each of the three flight speeds

Plot showing AP50 control outputs at each of the three flight speeds

After the HobbiStar MKIII airplane was purchased, straight, level flight was accomplished. This was the first prerequisite for autonomous flight controlled by the AP50 flight computer. With level flight and neutral RC inputs, test flights were conducted at loiter, cruise, and dash speeds. Data gathered from these flights was used as initial values for the PID controller's proportional input. From there, test flights were conducted to try to damp error in the PID controller by making changes to the PID controller to yield the most stable autonomous flight.