Autopilot

First some basics

So there are 3 axis, A full autopilot will control all axis..

-Axis Autopilot - this phrase is often misused in talking about autopilot capabilities.
Some use it to mean “roll, heading hold and altitude hold.”
Since the first two functions are both roll axis functions and altitude hold is a pitch function, most autopilots are infact 2 axis systems.

GPS computer processes information into right and left steering commands. These are then sent to the autopilot that flies the airplane in response to these commands.
Most autopilots typically track a course using heading data and course deviation

Single Axis Autopilot, with Roll Axis Computer~US$ 3,756.00 ;-((

This type of autopilot is Also called WING LEVELER.
You are now flying on autopilot with the gyro keeping your wings level.
It's steering your ailerons. (roll-axis)roll, heading hold


Navaid can deliver the best value for money autopilot, assembled, tested, and delivered in U.S. or Canada: For $1,300.00 US ;-))
http://www.navaid-devices.com/index.htm

Two Axis Autopilots - Roll and Pitch ~US$ 5,836.00 ;-((

Additional to the above feature, there is altitude hold.

You can search and find in the RC corner an autopilot it will still cost $5000,- ;-((
; This isn't the right place to look, you must have some confidence in the parts. (I don't)

GPSS Roll Steering Converter
GPSS interprets left/right commands and fly multiple waypoint courses and steering maneuvers defined by waypoints automatically.
You need a GPS navigator that outputs composite roll steering commands through the 429 Buss

This needs time, In a year there will be cheaper avionics outputting this.
( Just wait, or pay $$$)

OziExplorer outputs the Standard NMEA 0183 sentences which can control an Autopilot. The sentences output are $GPRMC, $GPRMB and $GPAPB.
The sentences are output each time a sentence is received from the GPS

$GPRMB - Recommended minimum navigation info
$GPRMC - Recommended minimum specific GPS/Transit data
$GPAPB - Autopilot Sentence "B"

examples.
$GPAPB,A,A,0.10,R,N,V,V,011,M,DEST,011,M,011,M*82

APB -This sentence is commonly used by autopilots and contains navigation receiver warning flag status, cross-track-error, waypoint arrival status, initial bearing from origin waypoint to the destination, continuous bearing from present position to destination and recommended heading-to-steer to destination waypoint for the active navigation leg of the journey

You need a pushing or pulling a distance of 1.5 to 2.4 inches.
Then find a place to mount the servo nearby to accomplish this by means of the push rod.

The servo box is not very small LxWxH 4.75"x3.25"x3"

Crank Arm, 1" radius 30lb and 1.25"