Paul René Jørgensen

I just wanted to let you know about todays progress. The GPS module landed in the mailbox this morning, but I forced myself not to rush and wire it up to the Spot right away. I know that this GPS module is compatible with the Spot so there was no reason to rush it.

What I was more concerned with was the enable/disable switch and the rudder pass through signal. I started out wiring up the RC receiver to the spot and wrote some lines of code to get the pulse length of a signal connected to one of the Dx pins of the Spot.

    private int getRCPulse() {
        EDemoBoard edb = EDemoBoard.getInstance();
        IInputPin pin = edb.getIOPins()[EDemoBoard.D3];
        return edb.getPulse(pin, true, 30);
    }

These few lines of code should give me the length of the pulse coming in on the D3 pin every 30 ms measured in microseconds. And guess what happened when I connected the battery? It worked!!

Next up was to prototype the rudder servo pass through. I added some more wires to the Spot connecting the servo signal cable to one of the Hx pins and made sure the servo was powered by the RC receiver.

        Servo s = new Servo(EDemoBoard.getInstance().getOutputPins()[EDemoBoard.H1]);
        while(true) {
            int l = getRCPulse();
            s.setValue(l);
            System.out.println(l);
            Utils.sleep(1);
        }

This code reads the rudder RC channel and passes the value on to the connected servo. Amazing as it sounds, but it actually works!

I now have a spot decoding the RC receiver signal and later outputting it to a connected servo, passing it through the spot as if it was not there! This is what is supposed to happen when the autopilot is disabled. When I hit the gear switch on my transmitter the autopilot logics should kick in. But that is another story..

Crazy me have been thinking about this for some time now. Those who know me know that I’m trying to make a part time business taking photographs from the air using RC model aircrafts. I have a dedicated page for some of the videos I’ve been making at http://paulrene.no/index.php/aerial-photography/. I even set up a page for my business at http://settfraluften.no (Norwegian only).

Anyway; During spring this year I got hold of a Sun Spot development kit and I’ve been playing around with it for a while. When writing a program to control servos using the built in accelerometer the idea struck me that this would be a nice platform for an autopilot. I’ve never worked in this field before so this is all new to me and a bit of a challenge. But if I can pull this of it would be a nice project and maybe something that would inspire others to do the same and improve it.

One of the first things I did was to assemble a list of parts:

• Sun Spot - http://www.sunspotworld.com
• Pressure sensor - MPX5100AP pressure sensor 15-115kPa
• GPS module - GPS-module EM-406a
• Headers - Stiftlist 2×10poler rak Au
• Gyro - MKS 380 Aeroplane Gyro

Along with this I need servos, RC receiver, wires and connectors.

The feature list as I see it just now will include:

• Way point navigation using rudder control
• Altitude hold
• Autopilot enable/disable using separate RC channel (landing gear channel)

I’ll continue to write about this as the project evolves. Stay tuned, this will be fun!