Building a small Arduino powered robot

It's time to play Arduino and Motor Shield

I received many weeks ago enough part to build a small arduino robot, and I have nos the time. Let's build it...

For this project I have no real objective. I just want to asseble an autonomous robot, avoiding wall or other object.

The parts

• Arduino uno for control-command
• Seeed motor shield V2 for power and simplifaction of command
• An HC-SR04 ultra-sonic sensor for objects detection
• A 9g servo motor for ultra sonic sensor rotation
• battery  clip connector 9v to 2,1 power plug (see here to build or buy )
• a chassi 2wd motor, with bolts and nuts, wheel, two small DC motor, a four battery pack AAA some wires and an end wheel

 

The assembly

Nothing very important to say here. Try to assemble, see what goes wrong, re assemble , what goes wrong and so on.

The only thing to say is that I make parts work separately first :

• the HC-SR04 ultra-sonic sensor
• then the servo 
• then the motor shield

 And finally integrate. And at this point it does not work...  as usual ...

• Motor shield use pin 8 to  13 to work 
• AND servo (library) disable PWM for 9 and 10 pin

So it does not work. The solution is to change the pin mapping in motor shield libraries from 9,10 to 5,6 and connect them physicaly (not shown on this picture).
I saw this on a blog here. It works for me too ,but if you  try, you try at your own risks.

Servo

Library used : arduino  Servo

#include "Servo.h"
const int SERVO_CMD = 14;
void setup() {
     myServo.attach(SERVO_CMD);
}

and

myServo.write(angle);

MotorShield (Seeed v2)

Library used : seeed MotorDriver modified in  MotorDriver56 to use pwm 5,6 in place of 9 and 10

include "MotorDriver56.h"
void setup() {
      motordriver.init();
      motordriver.setSpeed(200,MOTORB);
      motordriver.setSpeed(200,MOTORA);
}

and

motordriver.goForward();
motordriver.goBackward();
motordriver.goLeft();
motordriver.goRight();
motordriver.stop();

typical use

motordriver.go${Action}();
delay(time);
motordriver.stop();

HC-SR04

use

   const int trigPin = 4;
   const int echoPin = 7;

and

   int calculateDistance(){ 
      digitalWrite(trigPin, LOW); 
      delayMicroseconds(2);
      // Sets the trigPin on HIGH state for 10 micro seconds
      digitalWrite(trigPin, HIGH);
      delayMicroseconds(10);
      digitalWrite(trigPin, LOW);

     // Reads the echoPin, returns the sound wave travel time in microseconds
      duration = pulseIn(echoPin, HIGH); 
      int distance = duration*0.034/2;
      return distance;
    }

The basic control / command

if (nothing front) {
   goFront()
} else if ( something left ) {
   goBackward()
   goRight()
} else {
   goBackward() 
   goLeft()
}

But ...

My small rover does not go straightaway.  The reasons ... motor are differents, the end wheel is not so good. Those two points cause deviations.

Next improvment 

• the tail whell cause trajectory deviation. Need to change to a round ball, or use chains
• add encoder measurement to have a better distance/movement  estimation
• there's no sensor at back (securing goBackward() ) 
• Use arduino interrupt

Ultimate goal

Transform this rover into sensor. I mean acquire distance measurement, send it via ESP8266 (wifi) to raspberry Pi.  And finally build a 3D map of the rover context.