Obstacle Avoidance - Duino-Robotics

8/10/2019 Obstacle Avoidance - Duino-Robotics

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Obstacle Avoidance Tutorial

Obstacle avoidance is a means of a robot being able to move around in an unknown environment whil st not

coll iding with surrounding objects. Obstacle avoidance can be found on many different types of machines, big and

industrial robots, or even on newer cars. Knowing how to program obstacle avoidance into your robots can be a

very useful skil l to have, whether for a l it tle robot project, or a larger project where obstacle avoidance is just a

small pieceof the larger picture.

First of all check out the below video which runs you through the basics of obstacle avoidance, it runs for nearly

twenty minutes so be prepared to learn a lot. After you have watched this video you can scroll down to check out

further explanations of the examples shown and even some Arduino code.

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Alright, so fi rst of all let' s look at the flowchart. This flowchart is a li ttle different (not so Arduino specific) but the

idea behind it i s sti ll the same.

Another check occurs to see what direction is the best way to go. If left is the way to go it has to turn back to the

left and then go forward. If right is the way to go the robot simply moves forward as it is already facing in the right

direction.

So that was pretty easy wasn't it? All we have to do now is convert that diagram into Arduino code and that's it,

obstacle avoidance code done!

For thi s example I wil l be assuming that you already know how continuous rotat ion servos work and how to hook

them up to your Arduino. If you don't know how to do what I just mentioned make sure to go to the Arduino Tutorials

and watch the video on Servos and DC motors.

The fi rst thing that I always do when making robots is to make the robot move forward. Getti ng your robot to move

forward a) means that you have connected everything together properly and b) means that you have the orientation

and the signals you are sending to the servos correct. One I have done this I move those commands into a separate

void with the name something along the l ines of moveForward.

voidmoveForward(){

leftServo.write(0);

First of all we start off with the diamond shape, the

diamond shape represents a check. For this check we

are seeing if there is an object closer than 30 cm to our

robot. The check has two possible outcomes, yes or no.

Yes, meaning that there is indeed some object closer

than 30 cm. No, meaning that there is no objects

detected within 30 cm.

If there is nothing within 30 cm the robot can simply

move forward as the path is clear. If there is something

closer than 30 cm the robot must perform obstacle

avoidance maneuvers.

The first stage of obstacle avoidance is to stop the

robot! If you don't stop the robot immediately it will

crash!

Phew! That was dramatic.

After the robot has stopped it needs to see what way it

should go. It does this by looking both directions, much

li ke you should when you cross the road. First the robot

turns left, takes a reading, turns right, takes a reading.


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RightServo.write(180);

}

Once you have got your robot to move forward it is easy to add all the other movement commands. To get it to move

backwards, j ust reverse the values for the left and right motor. To get the robot to turn right you can make the left

motor go forward and the r ight motor to move backward. Left, right motor forward, left motor backward.

voidmoveBackward(){

rightServo.write(180);

leftServo.write(0);

}

voidmoveRight(){


leftServo.write(0);

}

voidmoveLeft(){


leftServo.write(180);

}

voidmoveStop(){


leftServo.write(90);

}

I put all these voids below the void loop so that they aren't in the way.

I al so l ike to put my scan routine in a void of its own as well . Depending on what sensor you are using and how you

are coding it this wi ll change, so I won't put in code for this part. I wil l simply say that I have a void routine for

scanning the di stance named void scan().

Now that all of that is done the rest of the coding is as easy as making two minute noodles. We will simply follow

the flowchart from before but write it in Arduino language. First comes the initial check to see if there is something

in front of the robot. Because I have a void named scan(); I can simply call to that void to take care of the distance

scanning

scan(); //Get the distance retrieved

Now because this void stores the distance retrieved from the sensor into a variable named 'distance' I have to

create variables for each direction; front, left and right. Remember these go above the void setup.




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intfDistance; //Variable to store the distance in front of the robot

intlDistance; //Variable to store the distance on the left side of the robot

intrDistance; //Variable to store the distance on the right side of the robot

Now because the scan function was called the distance in front of the robot is stored in the 'distance' variable.

Because the robot if facing forward I need to give the value the variable 'distance' has into the variable

'fDistance'.

fDistance = distance; //Set that distance to the front distance

Now we can perform the check to see if there is something in front of the robot. What I like to do is to create a

variable that is purely used as a trigger distance. The trigger distance should be set to the minimum distance you

want your robot to perform obstacle avoidance maneuvers. In this case my trigger distance i s 30 cm.

if(fDistance < triggerDistance){ //If there is something closer than 30cm in front of us

Remember that the curly bracket signifies the beginning of the block, this means everything inside this block will

happen when this if statement is true, or yes in flowchart terms. Everything that is in this block is everything that

stems from the 'yes' stem from the first check in the flowchart.

Now to begin the obstacle avoidance routine!

This may look like a jumble of code, but i t really isn't, OK i t i s, but we can understand i t by looking at i t bi t by bit .

1)

2)

3)

4)

5)

6)

7)

moveBackward(); //Move Backward for a second

delay(1000);

moveRight(); //Turn Right for half a second

delay(500);

moveStop(); //Stop

scan(); //Take a reading

rDistance = distance; //Store that to the distance on the right side

moveLeft();

delay(1000); //Turn left for a second

moveStop(); //Stop

scan(); //Take a reading

lDistance = distance; //Store that to the distance on the left side

if(lDistance < rDistance){ //Left distance smaller than right?

moveRight(); //Move right for a second

delay(1000);

moveForward(); //Then move forward

}

else{

moveForward(); //This happens if left is larger than right

}

}




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1) Once an object has been detected the robot then begins to move backward, i t does so for one second.

2) The robot then begins to turn right and does so for half a second, then coming to a hault.

3) The robot takes a reading and stores that to the 'rDistance' variable.

4) The robot begins to move left and does so for one second (to get half a second left relative to it's original

orientation).

5) The robot scans and stores the distance value to the variable 'lDistance'.

6) Another check happens seeing which direction is the better way to go. I f right is the better way to go the robot

turns right for one second and then continues on to move forward.

7) If however left is the better way to go the robot will end up moving forward because it is already facing the left

direction.

The last section of the code goes back to the first if statement at the top of the code checking to see if there is an

object i n front. Remember how we looked out how the curly brackets held al l the statements in for that check, well

this is at the end of that check. The else represents the 'no side' of the original fl owchart at the first check.

else{

moveForward(); //If there is nothing infront of the robot move forward

}

}

That' s i t! We have now learned how to add obstacle avoidance capabiliti es to our robots!

Download full Source Code (Same as Yogy)

Note: Code uses newping library which can be dowloaded here


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Obstacle Avoidance - Duino-Robotics