Normally an Auto Pilot contains both software and engine/sensors. This is an alternative solution, where the software is running on a computer, and your GPS-receiver is used for sensor(s).
By following these steps, you can make an Auto Pilot. The program is free, but you need to buy some parts for the connection of the computer and the rudder engine. This will have a cost less than $50 (plus a computer and a GPS-receiver).
Many people say it is impossible to enable an auto pilot to work without a rudder sensor and an electronic compass. They are correct to some extent, but here is the proof of the opposite. This Auto Pilot will not be as accurate as a professional one, but in nice weather it is very close. Here you can see how the mathematic calculations work. Run the simulation, and drag the red needle to see how it behaves in bad weather.
The logics of the auto pilot will keep the boat as close as possible to the lines between the route points.
Shopping list: (All you need to make your own Auto Pilot)
1 computer with available com-port and GPS Map Explorer installed, enabled to run powered from the boat
1 GPS-receiver with data cable to connect to the computer
2 30-Amp relays (The kind of relays with 5 connectors that are used in cars)
1 double optic connector. Suggestion: MCT6. Use stock no 75-363-60 at ELFA
2 micro relays (12 mA on the coil at 12V, 200 mA load when active.) Suggestion: DSS-4 1A12B. Use stock no 37-462-52 at ELFA
2 small resistances of 220 ohm each
2 reverse biased diodes to set in parallell with the coils on the big relays. (They are painted black in the diagram.) This is to protect the connection surfaces of the Micro Relays from the big induced voltage that comes from the coil when the magnetic field suddenly disappears. The optic transistors do also need protection, but in the suggested DSS-4 1A12B relays, these diodes are included. (In the cheaper DSS-4 1A12, they are not included, and you would need to implement them yourself.) If using the DSS-4 1A12B-relays, make sure not to mix pin 3 and 5! Pin 5 should be connected to ground, and pin 3 to plus from the optic connector.
1 fuse, 10 Ampere (Up to 30 Ampere if desired, regarding rudder engine, stress and cables)
1 fuse, 500 mA
2 fuse holders, one for each fuse
1 On / Off switch
1 electrical bi-directional engine to move the rudder (For example a hydraulic pump, or an old wiper engine)
1 male 9-pin connector to connect to GPSR (may also use direct cable to GPSR with comm and power)
1 female connector to connect to your computer (usually a 9-pin connector)
Some cables and equipment to connect this as described below, plus equipment to connect the rudder engine to the rudder.
That's it.
Please note: No guarantee is given for this to work on your computer, and no responsibility is taken if your computer or other equipment is damaged because of your effort to do this yourself. You might need some professional help to make sure the connections are made correctly in a safe way. Everything you do regarding this is on your own risk. Anyway, it has been tested, and it seems to work fine.
Here is an overview of how to connect the rudder engine to the computer:
Click the diagram to view it in full size.
You might want to print this diagram. In that case, click it first, to get its large version. Then right-click and choose copy, to paste it into Word or similar before printing.
It is pretty easy to make these connections, but make sure you understand how and why this will work. Otherwise: Ask someone for help.
As you see, the optic connector is completely shielding the computer from the relays. Inside the optic connector there are two LEDs that controls the 12V current. That way there couldn't be any leakage from the 12V part. The optic connector is guaranteed for voltages up to 5000V.
IMPORTANT:
The rudder engine will have alternating positive and negative voltage on the cables dependant on what direction to turn. If the engine uses its own chassis for ground, the chassis will in half of the cases have a positive voltage. In that case it is important to shield the engine from ground voltage in the boat, or you will blow your fuse.
Another case where your fuse will (and should) blow is if the rudder engine is forced to stop when it has in-coming voltage. When the rudder comes to one of its outermost positions, this might happen, unless you have some kind of slip friction to let the rudder engine continue even if the rudder stops. If such a slip friction solution is difficult to make, you could also mount two outermost sensors on the rudder. They may easily be connected as follows: Take 12V from the 500 mA fuse to both sensors, and put their signal back to the signal cable between the micro relay and the 30 Amp relay. The sensor for LEFTMOST rudder position should give signal for the RIGHT relay, and opposite. You could place the sensors at the very outermost position, or closer to the center position of the rudder. If one of the rudder sensors hits, the rudder engine will stop because it gets 12V on both the cables.
In the simulation, the parameter "Max rudder" is used for the position of the sensors. One of the purposes of the parameter "Max Curve" is to avoid too much swing on the rudder.
Here you see how the rudder sensors may be connected:
Very important:
Always pay full attention to where you are driving when using an Auto Pilot. The Auto Pilot helps you take the shortest route, but it can't do the captain's work.
Use common sense!!!
