Assignment: Servo Motor: Actuation Assignment 2

Collaborators: schluchter, drolnitzky

Description

For this assignment, Thomas and I built a crawler, which crawls in the forward direction, taking the scenic route.  Named the "Pub CraweWe used 2 servo motors to power a wheelbarrow style craft.  We used 2 pots to control the movement of the "arms" (sticks attached to the servos).  The main method of movement was by rotating one pot at a time -- one pot would prople the craft forward, the other would then raise the craft high enough so the first one could reset in a motion-forward position.  There were quite a few iterations to get it crawling forward -- we played with the position of the arms, the weight, and the position of the motors.  A big challenge was the 180 degree limit of motion for each servo.  In the end, we got it moving forward, though a bit in a circular path (see video).  Thus, the Pub Crawler was born -- representing the movement of many folks afer a long night out at the pub.

Components Used

• 2 servo motors
• 2 potentiometers
• wires, breadboard, more wires
• 3 wheels, some connects pieces, cardboard, electrical tape, wood sticks
• Love

The Pub Crawler from David R on Vimeo.

Arduino Code

We used the 2 potentiometer arduino code provided:

/*
* Two servos with two potentiometer control
* Theory and Practice of Tangible User Interfaces
* October 11 2007
*
*/

int servoPin1 = 7;      // Control pin for servo motor 1
int servoPin2 = 8;      // Control pin for servo motor 2
int potPin1   = 0;      // select the input pin for the potentiometer 1
int potPin2   = 1;      // select the input pin for the potentiometer 2

int pulseWidth1 = 0;    // Amount to pulse the servo 1
int pulseWidth2 = 0;    // Amount to pulse the servo 2
long lastPulse1 = 0;    // the time in millisecs of the last pulse of servo 1
long lastPulse2 = 0;    // the time in millisecs of the last pulse of servo 2
int val_1;              // variable used to store data from potentiometer 1
int val_2;              // variable used to store data from potentiometer 2

int refreshTime = 20;   // the time in millisecs needed in between pulses
int minPulse = 500;    // minimum pulse width

void setup() {
pinMode(servoPin1, OUTPUT);  // Set servo pin 1 as an output pin
pinMode(servoPin2, OUTPUT);  // Set servo pin 2 as an output pin
pulseWidth1 = minPulse;      // Set the motor position to the minimum
pulseWidth2 = minPulse;      // Set the motor position to the minimum
Serial.begin(9600);          // connect to the serial port
Serial.println("Two servos with two potentiometers ready");
}

void loop() {
val_1 = analogRead(potPin1);    // read the value from the sensor 1, between 0 - 1024
val_2 = analogRead(potPin2);    // read the value from the sensor 2, between 0 - 1024

if (val_1 > 0 && val_1 <= 999 ) {
pulseWidth1 = val_1*2 + minPulse;  // convert angle to microseconds
}
updateServo1();   // update servo 1 position

if (val_2 > 0 && val_2 <= 999 ) {
pulseWidth2 = val_2*2 + minPulse;  // convert angle to microseconds
}
updateServo2();   // update servo 2 position
}

void updateServo1() {
if (millis() - lastPulse1 >= refreshTime) {
digitalWrite(servoPin1, HIGH);
delayMicroseconds(pulseWidth1); 
digitalWrite(servoPin1, LOW);  
lastPulse1 = millis();         
}
}

void updateServo2() {
if (millis() - lastPulse2 >= refreshTime) {
digitalWrite(servoPin2, HIGH); 
delayMicroseconds(pulseWidth2); 
digitalWrite(servoPin2, LOW);  
lastPulse2 = millis();
}
}