Please buy an ESP32 and a motor driver. Hook it up and upload the firmware. Please see my GitHub for further instructions.

Settings are as follow:
-Heading source
choose between compass and GPS. Not all phones have a compass. When navigating in waypoint mode, GPS will always be used.
- Precision
how accurate should the app try to steer the boat. so if set to 2 degrees, the app won't make any correction when the heading is off by 2 degrees or less

- minimum motor speed
All motors have a minimum power input when they start to move to overcome interval frictions. When the control mechanism says the motors needs to run with a speed of 50 , it will perhaps barely move. So the minium motor speed is what defines it. You can set it higher to make the ap more aggressive
- gyro smoothing
The gyroscope is the main input for the control mechanism. Gyroscope's aren't stable so an average off X gyro readings is taken. you can set the sample size here. If D is fluctuating too much, increase this setting.

- Pulse mode
So when the motor command is less than the minimum motor speed, we pulse instead. So if the minimum motor speed is 50 and the command is 25. Then it will be 50% of the time on and then 50% off. It also allows the pilot to see the rudder effects in the 50% off time.
-pulse interval
the pulse interval in milliseconds. so 5000 milliseconds = 5 seconds. when it runs ay 50% pulse the motor is 2,5 seconds on and 2,5 seconds off.

- soft end switch
To prevent a motor from burning or still running when the rudder is at its end it will stop after a certain amount of time.

- GPS smoothing
Average of X samples of the GPS. The GPS accuracy can be very low, especially for headings.
- GPS Gyro fusion
The GPS updates are slow, 1 per second. If you take the average of 3 seconds. A course change would only be seen multiple seconds later. The gyroscope can be used to update the GPS heading faster.