Datasheet

Chapter 2 • Shield, Lights, Servo Motors
68 • Robotics with the BOE Shield-Bot
Controlling Servo Speed and Direction
For BOE Shield-Bot navigation, we need to control both servos at once.
 Create and save ServosOppositeDirections, and run it on the Arduino.
 Verify that the servo connected to pin 13 turns counterclockwise and the one
connected to pin 12 turns clockwise.
Example Sketch: ServosOppositeDirections
/*
Robotics with the BOE Shield – ServosOppositeDirections
Generate a servo full speed counterclockwise signal with pin 13 and
full speed clockwise signal with pin 12.
*/
#include <Servo.h> // Include servo library
Servo servoLeft; // Declare left servo signal
Servo servoRight; // Declare right servo signal
void setup() // Built in initialization block
{
servoLeft.attach(13); // Attach left signal to pin 13
servoRight.attach(12); // Attach right signal to pin 12
servoLeft.writeMicroseconds(1700); // 1.7 ms -> counterclockwise
servoRight.writeMicroseconds(1300); // 1.3 ms -> clockwise
}
void loop() // Main loop auto-repeats
{ // Empty, nothing needs repeating
}
This opposite-direction control will be important soon. Think about it: when the servos are
mounted on either side of a chassis, one will have to rotate clockwise while the other rotates
counterclockwise to make the BOE Shield-Bot roll in a straight line. Does that seem odd? If
you can’t picture it, try this:
 Hold your servos together back-to-back while the sketch is running.
Different combinations of
writeMicroseconds us parameters will be used repeatedly for
programming your BOE Shield-Bot’s motion. By testing several possible combinations and
filling in the Description column of the table below, you will become familiar with them and
build a reference for yourself. You’ll fill in the Behavior column later on, when you see how
the combinations make your assembled BOE Shield-Bot move.