Arduino and servo

Forum 2005-2010 (read only) Hardware Interfacing
#1

I’ve got a Mega in a SERB robot. I’m using the serb test program (below), but the servos don’t seem to stop when they’re getting a stop from the program. At first I thought it was my servo mod, but a test program:

#include <Servo.h>

Servo myservo;

void setup()
{
myservo.attach(9);
}

void loop()
{
myservo.write(1500);
}
Confirms they’re pretty well centered.
I’m pretty new to this, so any hints would be greatly appreciated.

Here’s the SERB program…
/*

  • Arduino Controlled Servo Robot (SERB) - Test Program
    • Behaviour: A simple test program which causes the SERB
  • to turn randomly either left or right for a
  • random time period between 0.1 and 1 second.
  • The SERB will then drive forward for a random
  • time period between 1 and 2 seconds. Finally
  • pausing for 2 seconds before starting again.
  • Wiring: Right Servo Signal - pin 9
  • Left Servo Signal - pin 10

*/

//---------------------------------------------------------------------------------
// START OF ARDUINO CONTROLLED SERVO ROBOT (SERB) PREAMBLE
#include <Servo.h>

#define LEFTSERVOPIN 10
#define RIGHTSERVOPIN 9

Servo leftServo;
Servo rightServo;

int speed = 100; //sets the speed of the robot (both servos) a percentage between 0 and 100

// END OF ARDUINO CONTROLLED SERVO ROBOT (SERB) PREAMBLE
//---------------------------------------------------------------------------------

/*

  • sets pins to appropriate states and attaches servos. Then pauses
  • for 1 second before the program starts
    */
    void setup()
    {
    serbSetup(); //sets the state of all neccesary pins and adds servos to your sketch
    randomSeed(analogRead(0)); //sets the random number seed with something mildly random
    delay(1000);
    }

/*

  • turns the robot either left or right (randomly) for a period between
  • 0.1 and 1 second. Before going forward for a random time period
  • between 1 and 4 seconds. Before pausing for two seconds then starting
  • again.
    */
    void loop()
    {
    turnRandom(100,1000); //Turns randomly left or right for a random time period between .1 second and one second
    goForwardRandom(1000,2000); //Goes forward for a random time period between 1 and 2 seconds
    goStop(); //Stops the robot
    delay(2000); //pauses for 2 seconds (whilst stopped)
    }

/*

  • turns the robot randomly left or right for a random time period between
  • minTime (milliseconds) and maxTime (milliseconds)
    */
    void turnRandom(int minTime, int maxTime){
    int choice = random(2); //Random number to decide between left (1) and right (0)
    int turnTime = random(minTime,maxTime); //Random number for the pause time
    if(choice == 1){ goLeft();} //If random number = 1 then turn left
    else {goRight();} //If random number = 0 then turn right
    delay(turnTime); //delay for random time
    }

/*

  • goes forward for a random time period between minTime (milliseconds)
  • and maxTime (milliseconds)
    */
    void goForwardRandom(int minTime, int maxTime){
    int forwardTime = random(minTime,maxTime); //determine a random time to go forward
    goForward(); //sets the SERB forward
    delay(forwardTime); //delays for random time period
    }

//------------------------------------------------------------------------------------------------------------
//START OF ARDUINO CONTROLLED SERVO ROBOT (SERB) ROUTINES

/*

  • sets up your arduino to address your SERB using the included routines
    */
    void serbSetup(){
    setSpeed(speed);
    pinMode(LEFTSERVOPIN, OUTPUT); //sets the left servo signal pin to output
    pinMode(RIGHTSERVOPIN, OUTPUT); //sets the right servo signal pin to output
    leftServo.attach(LEFTSERVOPIN); //attaches left servo
    rightServo.attach(RIGHTSERVOPIN); //attaches right servo
    goStop();
    }

/*

  • sets the speed of the robot between 0-(stopped) and 100-(full speed)
  • NOTE: speed will not change the current speed you must change speed
  • then call one of the go methods before changes occur.
    */
    void setSpeed(int newSpeed){
    if(newSpeed >= 100) {newSpeed = 100;} //if speed is greater than 100 make it 100
    if(newSpeed <= 0) {newSpeed = 0;} //if speed is less than 0 make it 0
    speed = newSpeed * 0.9; //scales the speed to be between 0 and 90
    }

/*

  • sends the robot forwards
    */
    void goForward(){
    leftServo.write(90 + speed);
    rightServo.write(90 - speed);
    }

/*

  • sends the robot backwards
    */
    void goBackward(){
    leftServo.write(90 - speed);
    rightServo.write(90 + speed);
    }

/*

  • sends the robot right
    */
    void goRight(){
    leftServo.write(90 + speed);
    rightServo.write(90 + speed);
    }

/*

  • sends the robot left
    */
    void goLeft(){
    leftServo.write(90 - speed);
    rightServo.write(90 - speed);
    }

/*

  • stops the robot
    */
    void goStop(){
    leftServo.write(90);
    rightServo.write(90);
    }
    //END OF ARDUINO CONTROLLED SERVO ROBOT (SERB) ROUTINES
    //------------------------------------------------------------------------------------------------------------

Thanks

Dave

#2

I've never heard of a SERB, but I'm guessing it uses modded servos to drive the wheels. Be aware that the "stop" condition may not be at exactly the "90 degree" mark. You may need to experiment. I suggest cutting down your program to control just one motor, and maybe use a pot to set the "angle", and print the "angle" so that you can note when the ex-servo stops rotating.

#3

Thanks Groove. I've got some reading to do to better understand servo control. Info on the SERB can be found here: http://www.oomlout.com/serb.html

Dave

#4

I've got some reading to do to better understand servo control.

Be aware that what you've got is not now a servo anymore, it's a geared motor. It's a fine distinction, but quite an important one.

#5