Lab 7: Servo Motors

DESCRIPTION
In this lab, we controlled the angle of a servo motor first with the serial monitor then with a pot. Next, we attempted to make crawlers with balsa wood and rubber bands.
 
For homework, I made a 3-legged crawler by attaching 2 “front legs” to a servo and dragging one “back leg” which was used for balance. The front legs consisted of balsa wood, paper clips, and rubber bands while the back leg was a toilet paper roll. The crawler’s “body” consisted of the base of the servo and a piece of balsa wood which was inserted into a slit in the toilet paper roll. I noticed in order to drive the crawler forward, I needed to decrease friction between the front legs and the table so I placed the front legs on a napkin.
 
I modified the code provided to oscillate the servo back-and-forth by about 30-degrees every 0.3 seconds. This small, compact motion seemed to work well in making the crawler move (slowly) in a straight line. Note that based on the code provided to us, I think my modifications should have resulted in a 70-degree rotation range, but my servo had been modified and at a certain point, it started spinning in circles, so I'm guessing the rotation range was also altered.
 
I originally tried using 2 servos to make my crawler, but the servos were different models/sizes and one servo didn’t have a firm area to attach “legs” to, so there was too much compliance in the system with that servo to get it to work. I also tried attaching my Arduino/breadboard to my crawler so that I could power it with a 9-volt battery and set it free to walk anywhere, but I couldn’t get the large Arduino board to balance properly on my crawler.
 

COMPONENTS USED
1- Arduino Uno (plus laptop and USB cable)
1- servo motor
building materials (balsa wood, paper clips, toilet paper roll, rubber bands, napkin)
22 gauge wire
1- breadboard
 
CODE
/*
 * Servo Control Serial
 * modified for crawler October 2013
 * modified for TUI October 2007
 * Servo Serial Better
 * -------------------
 *
 * Created 18 October 2006
 * copyleft 2006 Tod E. Kurt <tod@todbot.com>
 * http://todbot.com/
 *
 * adapted from "http://itp.nyu.edu/physcomp/Labs/Servo"
 */
 
int servoPin = 7;      // Control pin for servo motor
 
int pulseWidth = 600;    // Amount to pulse the servo
long lastPulse = 0;    // the time in millisecs of the last pulse
int refreshTime = 20;  // the time in millisecs needed in between pulses
int val;               // variable used to store data from serial port
 
void setup() {
  pinMode(servoPin, OUTPUT);  // Set servo pin as an output pin
  Serial.begin(9600);         // connect to the serial port
  Serial.println("Servo control program ready");
}
 
void loop() {
  if (val == 600) {
    val = 1300;
    pulseWidth = val;
    updateServo();
  }
  else {
    val = 600;
    pulseWidth = val;
    updateServo();
  }
}
 
void updateServo() {
  // pulse the servo again if rhe refresh time (20 ms) have passed:
  if (millis() - lastPulse >= refreshTime) {
    digitalWrite(servoPin, HIGH);   // Turn the motor on
    delayMicroseconds(pulseWidth);  // Length of the pulse sets the motor position
    digitalWrite(servoPin, LOW);    // Turn the motor off
    lastPulse = millis();           // save the time of the last pulse
    delay(300);
    Serial.println(pulseWidth,DEC); 
}
}
 
IMAGES
The attached image shows the crawler. Unfortunately, I wasn’t able to upload the video.