Maze Solving Robot
13 Steps

In this instructable I will be showing you how to build a maze solving robot. This is actually my 3rd attempt at making one. The first was a complete failure. The second was alright at finding the end of the maze, but it could not go back and drive the quickest path. This is my current and 3rd one. It is able to find the end of the maze and then, when put back at the start, drive the shortest path to the end of the maze without going down any dead ends. What surprises me is that it really does not mess up.

This was just a short introduction, everything else from theory, building, and programming will be explained in later steps.

Parts list:

General Parts:
• 3 1in Spacers (Home Depot)
• Bolts and nuts that fit the spacers (Home Depot)
• Hook up wire (I use 22 gauge)
• Solder
• .100" Female and Male headers
• Velcro

Tools:
• Soldering Iron
• Philips Screw driver
• Wire Strippers
• Something to cut the wire with
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## Step 1: The Theory Part 1

What are the steps In maze solving?
There are basically 2 steps. The first is to drive through the maze and find the end of it. The second is to optimize that path so your robot can travel back through the maze, but do it perfectly with out going down any dead ends.

How does the robot find the end of the maze?
I use a technique called the left hand on the wall. Imagine you are in a maze and you keep your left hand on a the edge of the wall at all times. Doing this would eventually get you out of a non-looping maze. This instructable will only deal with mazes that do not loop back on themselves.

This left hand on wall algorithm can be simplified into these simple conditions:
- If you can turn left then go ahead and turn left,
- else if you can continue driving straight then drive straight,
- else if you can turn right then turn right.
- If you are at a dead end then turn around.

The robot has to make these decisions when at an intersection. An intersection is any point on the maze where you have the opportunity to turn. If the robot comes across an opportunity to turn and does not turn then this is consider going straight. Each move taken at an intersection or when turning around has to be stored.

L = left turn
R= right turn
S= going straight past a turn
B= turning around

So let us apply this method to a simple maze and see if you can follow it. View the photos to see this method in action.
The red circle will be the robot.

As you can see in the photos for this example, the final path is LBLLBSR.
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frafi1 says: Oct 25, 2011. 1:28 AM
can i use a arduino uno to do this project..
and could you plz tell more specifically how to make the motor controller?
patrickmccb (author) says: Oct 30, 2011. 12:02 PM
Any Arduino should work. The motor controller is outlined on step 8. I provided the schematic in the photos. A schematic is about as clear as I can make it. You can also google for L293D or SN754410, both have the same pinout and are pretty common so there are probably other articles on them.
arunpandian says: Jan 24, 2013. 8:42 AM
how to get motor controller from dorkbot..?
plz help me.!
kumaran201 says: Aug 12, 2012. 12:23 AM
Great work!!!! i had a query... Do i have to make changes in your coding When i use Arduino UNO?
evilcomputer says: Jul 15, 2012. 10:38 PM
can i use cny 70 sensors for this project ?
muno1 says: May 13, 2012. 3:29 PM
So I wrote some code to test the sensors and I realized that the sensors are not sending any signal back to the microcontroller. So I removed the sensor from the design and I put on 5V from the board and the ground from the board and put the entire senor on a piece of black tape (for it to set all of the outputs to around 5V) then I put an led on each hole and realized that it isnt lighting up at all. Is it an adequate conclusion to come to that the sensor is defective? Thanks again for all the help.
muno1 says: May 12, 2012. 6:52 PM
I have finished building the design with the same motors and chips you have used except I used an arduino uno. but I am running into issues when I first put in the power both motors go forward about an inch and then stop. I am not sure what to do to solve this issue I have it on a straight black tape maze right now just to see if it is working but I am not sure what could be the issue, is there any way to test if the sensors are working or any way to isolate the problem, and as always thank you for your help.
patrickmccb (author) says: May 12, 2012. 7:02 PM
You can write some code to see if the sensor readings are correct. A common issue I have seen is that people do not put their sensors close enough to the ground. How high off the ground is your line sensor? The optimal distance is 0.125" (3 mm)
muno1 says: Apr 17, 2012. 3:34 AM
thank you for this posting first and foremost, I was wondering do I have to have the same gear ratio or will any two motors work (i want to maintain your code to be consistent), also will the same code work on a arduino uno...Thank you very much for your time :)
patrickmccb (author) says: Apr 18, 2012. 8:29 PM
No matter what motors you use, parts of the code will have to be changed unless you copy my design perfectly. Everything is based off of timing.

The same code will work on an Arduino Uno.
muno1 says: Apr 22, 2012. 6:38 PM
mr.kitux says: Apr 7, 2012. 1:44 PM
Next step could be to change L for R and R for L so it would come back to the start by itself and then go back to the goal through the shortest path :)
pingpongkid5 says: Feb 24, 2012. 1:53 PM
We purchased the motor controller that you suggested (http://www.sparkfun.com/products/9457), and we are now having trouble deciding which holes are corresponding on the two boards (yours that you made personally and the one on Sparkfun). Could you please tell me which hole on your board corresponds to which hole on my board? Such as In-1A = AIN1 or something like that. Thank you.
(an image of my board is attached)
pingpongkid5 says: Feb 22, 2012. 7:40 PM
A couple questions.
1. What happens when you plug it in? Should some kind of software or something pop up? Does it need to be a mac or windows or can in be both?
2. does the arduino need power when it is connected for the program to be put on it?
3. Is there alternate software I need to read this code or put it on the arduino?
patrickmccb (author) says: Feb 22, 2012. 10:43 PM
1. Nothing happens when you plug it in. Operating system does not matter.
2. The programming cable supplies power for you.
3. You need to install the Arduino IDE (http://arduino.cc/en/Main/Software) to view the code, edit it, and upload it.
pingpongkid5 says: Feb 16, 2012. 6:55 PM
Is there an alternative site to get this board? Or would you happen to have an extra? I need this for a school project and the guy at Dorkbot will not respond to my order. Thanks.
patrickmccb (author) says: Feb 18, 2012. 5:54 PM
The board is a very simple circuit which you could make yourself. Really most motor drivers will do. Something like this would work fine http://www.sparkfun.com/products/9457

As for Dorkbot, you have to send him the files and he normally responses in a day or two.
pingpongkid5 says: Feb 18, 2012. 7:01 PM
Thank you very much. Is the schematic any different?
patrickmccb (author) says: Feb 19, 2012. 8:14 PM
It works the same as a basic motor controller. You have to input power for the chip, the motors, and you have inputs and outputs. You also have pwm speed control.
janoo4u says: Feb 6, 2012. 1:51 AM
Can we use Arduino UNO instread of freeduino.
If yes then can u explain PIN Diagram.
patrickmccb (author) says: Feb 6, 2012. 5:27 PM
Yes you can. The connections are the same.
pingpongkid5 says: Jan 25, 2012. 5:41 PM
How do you add the code to the arduino? Like how is it connected to the computer?
patrickmccb (author) says: Jan 25, 2012. 5:44 PM
Did I leave that out? Sorry, it takes an FTDI Programming cable
Here is one: http://www.sparkfun.com/products/9718
frafi1 says: Nov 9, 2011. 5:08 PM
i need help, i think i'd prefer buying the motor driver, so how about this?? http://www.pololu.com/catalog/product/713 and can i use regular DC motors with these??

and could you tell me how to connect this motor driver to the arduino (the same way you told in step 8)and about the DC motor..

plz reply soon, i want to do this robot very soon..
thank you
patrickmccb (author) says: Nov 14, 2011. 5:10 PM
That motor driver is fine. It is very similar to connect as the one I used. The AIN1, AIN2, BIN1, and BIN2 are the direction inputs. AO1, AO2, BO1, and BO2 are the outputs that go to the motors. There are also PWM pins which I make use of in my latest code, but I have yet to update the tutorial. You can tie these to +5v to use the controller as I did in this tutorial. Then connect power to the controller and your motor supply voltage to VMOT.

Do not use a regular DC motor. Use a 5-6V gear motor.
frafi1 says: Oct 25, 2011. 6:25 AM
hi. I dont get the exact parts which you used. firstly, can i use a arduino uno instead of the one which you used?

can i use regular DC motors? (http://www.rhydolabz.com/index.php?main_page=product_info&cPath=121&products_id=815)

and can i use a motor driver (http://www.rhydolabz.com/index.php?main_page=product_info&cPath=108&products_id=858)

if yes, could you please guide me through the process, it would be of great help.
thanks
patrickmccb (author) says: Oct 30, 2011. 12:05 PM
That motor driver will work, but you do not want that motor. That motor operates at 12 volts. You would have to get a 12v battery pack and regulate it down to 5v for the other parts. I would find a 5v motor.
rmartin27 says: Oct 10, 2011. 5:01 PM
How long does it take to build this robot?
patrickmccb (author) says: Oct 10, 2011. 7:45 PM
If you have all the parts then it is up to how quickly you can solder for the most part. Maybe an hour with all the parts in front of you.
BeFit says: Jul 26, 2011. 12:11 AM
Great work!
jobard says: Jul 22, 2011. 10:58 AM
What happens if after the first recognizing run, you place it in a different start location?
patrickmccb (author) says: Jul 22, 2011. 11:20 AM
It would not work properly. It is meant to solve it from the same starting position. It has to be reset if you want it to solve it from another.
Nice. How do you reset it if you want it to go the long way agaibn AFTER it has calculated the shortest path.? Nice, though.
patrickmccb (author) says: Jul 21, 2011. 7:15 PM
Hit the reset button on the Arduino or turn it off and on again.
kimvellore says: Jul 14, 2011. 3:29 PM
Nice concept. Thank you for explaining in detail. I enjoyed reading it.
hyruler_ says: Jul 6, 2011. 2:23 PM
that is awesome
maximeke2 says: Jul 6, 2011. 11:36 AM
Can you please give me some information about your sensor? Does it use LEDs or infrared, and also the type/datasheet of emitter/transmitter?
patrickmccb (author) says: Jul 6, 2011. 11:38 AM
On the first page of the instructable I provided the links to all of the different parts, including this one. Here is the link where you can find more information about it http://www.pololu.com/catalog/product/960
maximeke2 says: Jul 6, 2011. 12:15 PM
oops... I was just looking for the sensor and didn't read it. Sorry about that
error32 says: Jul 4, 2011. 11:00 AM
I have used some parts from the pololu store before. Very good quality!
Though i personally liked it better to make my own PIC based board instead of the too easy arduino solution.
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