rngadam4 min read

First successful autonomous run of A.R.T.

Today was a day of many firsts for me: First time I made holes in a piece of wood with a Dremel First time I bought tie-wraps in China First time I blew up the fuse for Xindanwei putting everyone in…

Today was a day of many firsts for me:

It's neither very nice looking or very impressive when it runs, but I'm still very happy with the results.  I planned something electro-mechanical with a tiny bit of embedded software all by myself (with some help from Niko with the Dremel and Héqíchén / 何琪辰 to buy the tie-wraps!). I planned, executed and... got the results I wanted!
The simplistic code that I used:

const int FORWARD = 2;
const int REVERSE = 3;
const int LEFT = 4;
const int RIGHT = 5;
const int INFRARED_FORWARD = A0;
const int INFRARED_REVERSE = A1;
const int MINIMUM_INFRARED_READING = 500;
int current_reverse = LEFT;
int alt_forward = RIGHT;
char current_state;
void setup() {
pinMode(FORWARD, OUTPUT);
pinMode(REVERSE, OUTPUT);
pinMode(LEFT, OUTPUT);
pinMode(RIGHT, OUTPUT);
pinMode(INFRARED_FORWARD, INPUT);
pinMode(INFRARED_REVERSE, INPUT);
Serial.begin(9600);
}
char update_state(char state, int reason) {
char previous_state = current_state;
if(state != current_state) {
current_state = state;
Serial.print(current_state);
Serial.println(reason);
}
return previous_state;
}
void loop(){
// always check if we can go forward
int value = analogRead(INFRARED_FORWARD);
if(value >= MINIMUM_INFRARED_READING) {
// maybe we were correcting, so check that
char last_state = update_state('F', value);
digitalWrite(current_reverse, LOW);
digitalWrite(REVERSE, LOW);
if(last_state == 'R') {
// we just successfully exited a bad loop, turn for a bit for half a second
digitalWrite(alt_forward, HIGH);
digitalWrite(FORWARD, HIGH);
delay(1000);
digitalWrite(alt_forward, LOW);
}
digitalWrite(FORWARD, HIGH);
} else {
// otherwise, still correcting, keep off
digitalWrite(FORWARD, LOW);
// we want to try to find an alt path
int value = analogRead(INFRARED_REVERSE);
if(value >= MINIMUM_INFRARED_READING) {
//still have some ability to go backward
update_state('R', value);
digitalWrite(current_reverse, HIGH);
digitalWrite(REVERSE, HIGH);
} else {
// whooaah, even backward is not possible, we're stuck
digitalWrite(current_reverse, LOW);
digitalWrite(REVERSE, LOW);
update_state('S', value);
}
}
}
Wins:

  • Wooden board and tie-wraps work exceptionally well to prototype the physical arrangement
  • Using the breadboard to prototype the electronics also works well
  • The Arduino "Vin" to provide current in the board header works very well (and can seamlessy switch between USB and that without resetting!)
  • Sticking the RF transmitter board directly on the robot and controlling the motors with that from the Arduino works well
  • The LED that comes on when an obstacle is detected by the infrared sensors is very useful for debugging (need to keep that in mind when using other  sensors)
  • It works!

Losses:

  • Uses Alkaline AA batteries (I want to switch to the exact same Rechargeable NiCad as the car uses)
  • I spent too much time working with Sketchup instead of manually testing the mechanical design first (and then Sketchup)
  • There's not much around Xindanwei in terms of computer, electronic or small mechanical stores, so I should plan ahead to shop on Beijing road
  • The infrared sensors that I found in the pile of stuff in Xinchejian work, but more like "on/off" sensors (don't seem to have any linearity in the distance)
  • No bumper (the infrared sensor was crashing into the walls...)
  • Making an obstacle course big enough is annoying
  • I had forgotten to make the holes to attach the sensors (more holes == better)
  • No on/off switch so have to manually remove the connections to turn off power
  • You can never have enough tie-wraps... We only had four at Xinchejian before I bought a pack of 500 for 15RMB (but really, worth about 5RMB)
  • I need to learn how to solder... without blowing fuses...

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