How To Make an Obstacle Avoiding Arduino Robot

Hello all! In this Instructable I'll be showing you how to make a robot similar to the "Mobile Arduino Experimental Platform" (MAEP) that I made. It is equipped with two motors that can steer the robot and the ability to see obstacles in front of it with a PING))) ultrasonic sensor. 

With the attached breadboard, you can do more electronics experiments, fool around with different sensors, etc. This project can teach you about electronics, programming, and robotics. It is also a fun toy to entertain younger siblings and pets (just be sure they don't break it!).

Here is a video of what MAEP will do when it is done:

Step 1 Parts

Here's everything you need to make MAEP. I tried to provide links to where you can buy these parts from YourDuino.com, which is the official shop of letsmakerobots.com. EDIT: YourDuino and LMR are now separated and YourDuino is no longer giving money to LMR, however they still have pretty good prices so feel free to shop there.

- Arduino compatible microcontroller. I used an Arduino Uno, so I recommend one if you wish to follow closely along with this tutorial. There are also some Arduino based controllers that are designed specifically for robotics that may be helpful, but you’ll have to find your own method of mounting those. You can buy a copy of the Uno from YourDuino which I believe is completely compatible: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=5

-  Breadboard. Make sure it’s not too big, or else it won’t fit. However, we want it to be as big as possible so we have more room for electronics. This is good: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=168

- A standard old 9 volt alkaline battery (which you can probably find at home), as well as a barrel jack connector to hook it up to your Uno easily (not required, but again, easier):  http://arduino-direct.com/sunshop/index.php?l=product_detail&p=119

- A power supply for the motors. I don’t believe the power supply I chose is the cheapest or best option, so I’m not going to recommend it to you. I used a 4.8 volt rechargeable NiCad battery, but it’s probably easier to just use a 4 AA battery holder (no need to buy a charger that way)

- A bunch of Boe-Bot hardware for the chassis. Unfortunately, you can’t get this from YourDuino, so look at Parallax, the manufacturer’s website. You can choose either to buy this: http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/304/Default.aspx?txtSearch=boe+bot+chassis which comes with tons of extra components you don’t need (although may be useful someday), or you can buy all the components in the following list from Parallax and no, I’m not gonna provide a link for each one:



Stock # Quantity              Product Name

700-00002            8             Panhead screw, 4/40, 3/8

700-00003            8              4/40 x 3/8" Nut

700-00009            1             Tail Wheel Ball

700-00015            2              #4 Nylon Washer

700-00022            1              Boe-Bot Aluminum Chassis

700-00023            1              Cotter Pin-1/16" Diameter

700-00025            1              Rubber Grommet-13/32" Hole Diameter

700-00028            4              Panhead screw, 4/40, 1/4

700-00060            2              Standoff, threaded aluminum, round 4-40

721-00001            2              Wheel, Plastic, 2.58 Dia, .3 W

721-00002            2              Rubber Band Tire for 721-00001

900-00008            2              Continuous Rotation Servo



- Wire to hook things up will be necessary. Some male-to-male jumpers will do the trick: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=94

- Finally, the PING))) sensor and mounting bracket, so that your robot doesn't kill itself: http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/563/Default.aspx?txtSearch=ping+sensor+mount


As for tools, all you need is a phillips head screwdriver, a computer, and one of those standard USB printer cables. The Arduino Uno I provided a link for has a cable included. 

Now lets get building!

Comments

[faroos7]

hey what does centering the servos do exactly? because im getting the same thing user greentree89 is getting. robot goes in circles only and the sensor is jolting its not like doing full movements and if u manually turn it it keeps goin to the right n gets stuck n jolts there. i know im months late but u have an interesting project. any help would be appreciated

[biomech75]

I think you fogot to add on the materials list a non 360º servo for the Ping sensor ;) 

[generalgeek314]

Good catch, but the PING sensor mounting bracket kit from Parallax that I included in the parts list comes with a servo as well.

[greentree89]

Hey there i am back, i finally got all the parts and i have put my robot together, all that is left is to wire it up! :)
Just got a quick question, I am not entirely sure about the 5v power rail you mentioned.
So i got the 3 servo motors and the ping sensor that all need 5v.
should i be connecting them all to the battery 5v rail or the arduino 5v rail that you said to connect to the breadboard?
Thanks again !

[generalgeek314]

Hi, I'm glad that the robot build went successfully!
Wire up the 3 servo motors to power from the separate battery. Motors use up a lot of current, more than the regulator on the Arduino provides, and they can't be powered directly from the 9V battery because 9 volts is too much for them. That's why you have to hook them up to the other battery.
As for the sensor, hook that up to 5V power from the Arduino. It needs the same steady voltage the Arduino is getting in order to give accurate results.
Hope I helped. If things are still unclear, feel free to ask and I'll do my best to fix whatever comes up.

[greentree89]

Hey thanks for your reply, i have now wired it and uploaded the code to my robot.
What happens however is that it rotates in a circle with the right motor moving forward and the left moving backward.
when i put my hand in front of the sensor it moves backwards untill all is clear and then continues to move in rotation, also the sensor servo does not operate at all.

I made sure i got all the wires in the right place and also tried swapping the motor wires around but just got more odd movements

here is the code i am using:
/*MAEP 2.0 Navigation
by Noah Moroze, aka GeneralGeek
This code has been released under a Attribution-NonCommercial-ShareAlike license, more info at http://creativecommons.org/licenses/
PING))) code by David A. Mellis and Tom Igoe http://www.arduino.cc/en/Tutorial/Ping
*/

#include //include Servo library
#include

Ultrasonic ultrasonic ( 4, 5);
const int RForward = 0;
const int RBackward = 180;
const int LForward = RBackward;
const int LBackward = RForward;
const int RNeutral = 90;
const int LNeutral = 90; //constants for motor speed
const int irPin = 0; //Sharp infrared sensor pin
const int dangerThresh = 4; //threshold for obstacles (in inches)
int leftDistance, rightDistance; //distances on either side
Servo panMotor;
Servo leftMotor;
Servo rightMotor; //declare motors

void setup()
{
rightMotor.attach(11);
leftMotor.attach(10);
panMotor.attach(6); //attach motors to proper pins
panMotor.write(90); //set PING))) pan to center
leftMotor.write(90);
rightMotor.write(90);
}

void loop()
{
int distanceFwd = ultrasonic.Ranging(INC);
if (distanceFwd>dangerThresh) //if path is clear
{
leftMotor.write(LForward);
rightMotor.write(RForward); //move forward
}
else //if path is blocked
{
leftMotor.write(LNeutral);
rightMotor.write(RNeutral);
panMotor.write(0);
delay(500);
rightDistance = ultrasonic.Ranging(INC); //scan to the right
delay(500);
panMotor.write(180);
delay(700);
leftDistance = ultrasonic.Ranging(INC); //scan to the left
delay(500);
panMotor.write(90); //return to center
delay(100);
compareDistance();
}
}

void compareDistance()
{
if (leftDistance>rightDistance) //if left is less obstructed
{
leftMotor.write(LBackward);
rightMotor.write(RForward); //turn left
delay(500);
}
else if (rightDistance>leftDistance) //if right is less obstructed
{
leftMotor.write(LForward);
rightMotor.write(RBackward); //turn right
delay(500);
}
else //if they are equally obstructed
{
leftMotor.write(LForward);
rightMotor.write(RBackward); //turn 180 degrees
delay(1000);
}
}

[generalgeek314]

For your servo direction problem, try changing this in the code:
const int LForward = RBackward;
const int LBackward = RForward;
To this:
const int LForward = 0;
const int LBackward = 180;

As for your sensor servo, I'm not sure what the problem is. Are you certain this servo works? Try using code from this tutorial to test it - http://arduino.cc/it/Tutorial/Sweep

[greentree89]

I fixed it! :D
I was reading up the reason for the odd behavior from all 3 servos and it turns out it was because the servos need to share the ground from both arduino and the battery, i must of missed that part on your tutorial, i just took a lead from from the arduino gnd and connected it to the breadbord gnd rail that you said to link from both sides.
now it responds perfectly! :)
I have now tested out the whole code as i was breaking it down to see how it responded.
everything seems fine except the panmotor still moves all the way to the right at the very start before it even detects an object.
i will do some more tests tomorrow to find out the problem.

[generalgeek314]

Great! Glad to see you were able to find a solution for that problem on your own :) For the problem with the panning servo, try do step 2 again with just that servo (after taking the servo "horn" with the ping sensor on it off). After you've centered the servo, put the ping sensor back on so that it's facing forward.

[greentree89]

Hey i tried everything to get the panmotor servo working correctly but it will not respond other than go clockwise then it starts shaking, very odd i can only say it must be faulty.
i will order a new servo but in the mean time i have simplified the code for a fixed sensor so it simply turns left on detection of obstacles, i have also added a piezo and led to the code, i will make a video to show you my robot :)
it is very simple compared to your robot but for my first robot i am very proud :D
i also had to increase the speed of the right servo as it seems to turn left, i must of designed the balance of the chassis badly.
i also find that when it is heading towards obstacles at an angle it does not pick up on the obstacle and completely gets stuck, but i do have a spare sensor, perhaps i can use 2 on the robot to help this.
well theres plenty of ideas to upgrade my robot :)
I will make the video of my robot very soon, thankyou so much for all your help, you've been amazing and so very helpful :)

[generalgeek314]

It's too bad your servo isn't working, but I'm glad you've got your robot working anyways! I look forward to seeing it, and I like that you've added your own custom additions with the LED and piezo. Maybe to give it a more interesting behavior you could have it turn randomly when it detects an obstacle? Try looking here: http://arduino.cc/en/Reference/random

I hope you continue with this hobby, it's very fun and I'm incredibly happy to have helped you enter the world of robotics. I recommend you check out letsmakerobots.com, they have a great community of robot builders that give great advice and feedback, and also there are lots of robots there to get inspiration from.

[greentree89]

Hey there! :)
Thankyou so much for all your encouragement and it is because of you i have built my first robot.
I built up a random code from the link you sent me, it works great!
And to add to that i combined the code with something else i found which solves a problem my robot had,

from my last post, simply when the robot came in at an obstacle from an angle it would not detect it and then try and turn too late and it must move forward to make a turn, but when it gets too close to an obstacle it moves backwards then turns.
I have tested the random turning which i really like but i noticed a problem i had not thought of before,

lets say it comes to a corner, and chooses to turn left, it will then immediately meet the other wall and by chance the random code makes it turn right it hit the previous wall again, i have watched it do this quite a few times, but its still quite fun to watch it like this as you said because you never know which turn it will take making things interesting, it always gets it's self out of areas sooner or later anyway hahah

I have bought a new servo for the sensor which should arrive shortly.
Video coming soon! :)
Thanks again!
here is my code if you are interested in seeing it at the moment:


#include //include Servo library
#include

Ultrasonic ultrasonic ( 4, 5);


const int numOfReadings = 1; // number of readings to take/ items in the array
int readings[numOfReadings]; // stores the distance readings in an array
int arrayIndex = 0; // arrayIndex of the current item in the array
int total = 0; // stores the cumlative total
int averageDistance = 0; // stores the average value
int echoPin = 5; // SRF05 echo pin (digital 2)
int initPin = 4; // SRF05 trigger pin (digital 3)
unsigned long pulseTime = 0; // stores the pulse in Micro Seconds
unsigned long distance = 0; // variable for storing the distance (cm
int pinSpeaker = 13;
const int RForward = 0;
const int RBackward = 180;
const int LForward = RBackward;
const int LBackward = RForward;
const int RNeutral = 90;
const int LNeutral = 90; //constants for motor speed
int leftDistance, rightDistance; //distances on either side
Servo leftMotor;
Servo rightMotor; //declare motors
int randNumberSpeed; // variable to store the random speed value
int randNumberDir; // variable to store the random direction value
int x = randNumberDir;
void setup()
{
Serial.begin(9600);
rightMotor.attach(11);
leftMotor.attach(8);
pinMode(2, OUTPUT);
pinMode(3, OUTPUT);
pinMode(pinSpeaker, OUTPUT);
pinMode(4, OUTPUT); // trig init
pinMode(5, INPUT); //echo
// create array loop to iterate over every item in the array

for (int thisReading = 0; thisReading < numOfReadings; thisReading++) {
readings[thisReading] = 0;

randomSeed(millis());
}

}

void loop() {
digitalWrite(initPin, HIGH); // send 10 microsecond pulse
delayMicroseconds(10); // wait 10 microseconds before turning off
digitalWrite(initPin, LOW); // stop sending the pulse
pulseTime = pulseIn(echoPin, HIGH); // Look for a return pulse, it should be high as the pulse goes low-high-low
distance = pulseTime/58; // Distance = pulse time / 58 to convert to cm.
total= total - readings[arrayIndex]; // subtract the last distance
readings[arrayIndex] = distance; // add distance reading to array
total= total + readings[arrayIndex]; // add the reading to the total
arrayIndex = arrayIndex + 1; // go to the next item in the array

// At the end of the array (10 items) then start again
if (arrayIndex >= numOfReadings) {
arrayIndex = 0;
}

averageDistance = total / numOfReadings; // calculate the average distance
delay(10);

// Check the average distance and move accordingly

if (averageDistance <= 10) {
// go backwards
leftMotor.writeMicroseconds(1000);
rightMotor.writeMicroseconds(2000);
digitalWrite(2, HIGH);
digitalWrite(3, LOW);
{
playTone(750, 500);
delay(350);
}
}


if (averageDistance <= 25 && averageDistance > 10 ) {

//turn left
randomSeed(millis());
randNumberDir = random(300); {
if (randNumberDir > 150){
rightMotor.writeMicroseconds(1000);
leftMotor.writeMicroseconds(1500);
digitalWrite(2, LOW);
digitalWrite(3, HIGH);
{
playTone(750, 300);
delay(750);
}
}
else if (randNumberDir < 150){
rightMotor.writeMicroseconds(1500);
leftMotor.writeMicroseconds(2000);
digitalWrite(2, LOW);
digitalWrite(3, HIGH);
{
playTone(750, 400);
delay(750);
}
}
}
}

if (averageDistance > 25) {
// go forward
digitalWrite(2, LOW);
digitalWrite(3, LOW);
delay(1000);
leftMotor.writeMicroseconds(2000);
rightMotor.writeMicroseconds(1100);
}
}


// duration in mSecs, frequency in hertz
void playTone(long duration, int freq) {
duration *= 1000;
int period = (1.0 / freq) * 1000000;
long elapsed_time = 0;
while (elapsed_time < duration) {
digitalWrite(pinSpeaker,HIGH);
delayMicroseconds(period / 2);
digitalWrite(pinSpeaker, LOW);
delayMicroseconds(period / 2);
elapsed_time += (period);
}
}

[greentree89]

Heheh got 3 problems all at once, i tried this but it still does the same thing.
It simply continues to move in rotation, it seems to be the left motor that is going the wrong way no matter where ever i set it to 0, 180 or 90

And of course it does not stop but rather instead moves backwards when there is an obstacle.

I also tried that code for the sensor servo, it moves it all the way to the right but then nothing else happens, same for the robot code, nothing moves it to the left again.

Its ok if you cant figure this one out, you've been an amazing help with all my questions, i will continue to try and work on it.
Thanks again.

[fjohn]

hey nice post....by the way could u make the code for two geared motors instead of the continues servos/? please!!!

[generalgeek314]

Are you using a motor controller for those geared motors? You're going to need one to get good control. I need to know what you're using in order to help you. If you look at the documentation for your motor, you should be able to do it yourself. Whenever you see something such as rightMotor.write(RForward) for example, just change it to whatever code makes the right motor move forwards using your controller.

[fjohn]

a im using a motor driver like the l239d the motor just acts like a normal one it just have gears and dont need special programming so could ya make one ??? u know so if it finds an obstacle it turns????than ks

[generalgeek314]

Take a look at this http://luckylarry.co.uk/arduino-projects/control-a-dc-motor-with-arduino-and-l293d-chip/. It has some info on programming the L293D. First get your motors spinning with it and figure out how to use it in a circuit, then if you can't modify my code suitably I can try to help you more.

[greentree89]

I found this: http://www.meanpc.com/2012/01/hc-sr04-ultrasonic-sensor-added-to.html
though i much prefer your code where the ping servo rotates to choose the best path.
I shall now try and combine both codes to suit my robot :)

[generalgeek314]

Sorry, I made a slight mistake. As well as replacing int distanceFwd = ping();, you have to replace all uses of "ping()" with "ultrasonic.Ranging(CM)".

[greentree89]

Hey this is great! thankyou very much.

I spent a while trying to combine the codes but i kept getting so many errors but after i tried what you sent me, it works perfectly.
Just wondering do i change the Ranging(CM) to an actual number like Ranging(15) ? just to be sure.

I have just ordered the right batteries and i must also get a new servo motor as for some reason it gets really hot but it no longer moves.

I will be sure to upload photo's and a vid to show you :)
Thanks again.

[generalgeek314]

No problem, I'm happy to help. No, you don't change Ranging(CM) to an actual number, it means you want to get the value of the distance away something is in centimeters. You could do Ranging(IN) instead, which would give you the distance in inches. You could use that in my code if you wanted, as long as you changed what the variable dangerThresh is in the beginning to how far away you want something to be in inches when the robot stops and turns. I hope you get your parts soon!

[generalgeek314]

Good luck! I have done so more research, and I think I can help you specifically.
In the beginning, with all the variables, you want to create your ultrasonic sensor. Declare it like this: Ultrasonic ultrasonic( trigPin, echoPin);
Of course, make trigPin and echoPin whatever pins you plugged them into on the Arduino. Now, this library is actually quite handy, so you can delete the whole ping() function I wrote. Find the code that looks like:
void ping()
{
some stuff in here
}
and delete all that. Then, where it says int distanceFwd = ping();, change it to say int distanceFwd = ultrasonic.Ranging(CM);

Good luck, and feel free to ask if you need any more help. I'd like to see your robot when you finish, so if you could post pics/a video of it online that would be nice :)

[greentree89]

Hey my ultrasonic sensor has 4 pins, the 5v, gnd, echo and trig.
How should i connect them and what should i add to the code to make it work?
Thanks :)

[generalgeek314]

Hi,
I haven't used a sensor like that myself, so I can't give any personal help. However, this link has some useful information on how to use it with Arduino: http://letsmakerobots.com/node/30209. I'm not sure what your level of experience is, because unfortunately the link I provided doesn't go into much detail about what to do. If you need more help, just ask and I'll do what I can.

[greentree89]

Hey thanks for your reply and link, i have tried combining the code with your one but i am very new with programming and it does not take long for me to get lost.
I am not sure what i should take out of your code and replace.