Duncan and I built his first rover-type robot today - he decided that "Alpha Rex's" time had been and gone, and it was time to build something new. So we sat at the table and mucked about for a bit, knocking out a simple twin-servo skid-steer rover in about an hour.

We then sat down at the NXT software and with some encouragement and some guess work fleshed out a simple rover program. The NXT software isn't that great for things like this, so we smashed out a better version in NXC.

We then went back to the table and added a button on the backside of the rover, because sometimes the ultrasonic sensor wouldn't pick up an object (say, a curtain, or on the corner of a wall) and the robot would run up the wall and get stuck. We made it so when the button is pressed, it initiates a program of rolling backwards for 2.5 seconds, turning for 1 second, and then continuing the main routine.

We then also added a sound for fun, on Duncan's orders.

The code can be found below:

// Duncan Robot v1
// "explorer" - uses ultrasonic sensor to detect objects in front of it
// and will turn until it clears the object. detects "stuck" situation
// by a push button sensor on the backside of it, will reverse for
// 2.5 secs and then turn ~70 degrees.

task main() {

    while (true) {

        // wall in front
        if (SensorUS(IN_4) < 15) {
            while (SensorUS(IN_4) < 30) {
                OnFwd(OUT_B, 75);
                OnRev(OUT_C, 75);

            // this is a file we recorded, comment this out if you like
            PlayFileEx("beepboprobot.rso", 100, 0);

        // bump button detects, usually, a stuck robot.
        // initiate reverse for 2.5 seconds then turn.
        if (Sensor(IN_1) > 0) {
            OnFwd(OUT_BC, 75);
            OnFwd(OUT_B, 75);
            OnRev(OUT_C, 75);

        // Otherwise, go forward
        OnRev(OUT_BC, 75);


I then drew the whole thing up in Lego Digital Designer, partially because I wanted to play with that software, but also so we would keep the instructions of each robot he builds and see how he progresses as he gets older and cleverer.

Horsham VIC 3400, Australia fwaggle




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Horsham VIC 3400, Australia

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