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Basic Plane Autopilot (3x3)

A simple autopilot micro-controller designed to be easy to set up. Takes 2 inputs (preferably from a keyboard) for desired heading (in degrees) and altitude (in meters)

Installation instructions:

- Place this along with 3 numerical switch-boxes (for pitch, roll and yaw), a keyboard (or 2 keypads) and a toggle button of some kind. Also place a compass sensor, an altimeter and 2 tilt sensors (facing forward and left)

- Connect the 3 switch-box's outputs to the respective control surfaces (or controllers, such as gyros) Gyro Recomended for this

- Connect the 3 outputs of the micro-controller to their respective switch-box's ON inputs

- Connect the conventional controller (such as a pilot seat) to their respective switch-box's OFF inputs

- Connect the switch-box's toggle to the output of the button

- Connect the output of the keyboard/keypad to the respective "desired heading" and "desired altitude"

- Connect the tilt sensors to the respective "current pitch" and "current roll", also connect the altimeter to "current altitude"

Explanation

This should now act as a basic autopilot system. The altitude hold works by taking the difference between the target and current altitude and outputting that as a target pitch. The difference between the target and current pitch is then output to the control surfaces (if the autopilot button is on). This causes it to pitch (within set limits) to the current altitude and compensates for lack, or abundance, of lift.

The heading hold is a bit more complicated, but follows a similar principle. First, because the reading from the compass sensor a stupid (0 representing north, 0.25 representing east, + or - 0.5 representing south and -0.25 representing west), it corrects it so that north is 0 or 1, and south is 0.5. It then plugs that value into a tangential equation using the target heading as a set point: tan((target - current)/2), and outputs that as a desired roll (clamped by the roll limiter). This is also used to directly control the rudder, making turns faster. The desired roll is then output to a similar equation as the pitch, and then output to the control surfaces.

The roll and pitch are limited to 30 degrees, however this can be changed within the micro-controller

If the controls are inverted (pitching down when your below the target, turning left when you need to turn right etc.) then you need to go into the micro-controller and change the gain of the pitch and roll outputs to be positive or negative respectively. So far my control surface setup is as follows:

-Elevators have negative value at the top

-Rudder has negative value on the left

-Ailerons have negative value at the top on the left, and at the bottom on the right

This configuration shouldn't require any adjustment to the micro-controller (besides reducing gains and such)

This would actually work for land vehicles, if you just set the yaw output to steering