# Rubik's Cube Solver

160,049

558

178

Published

## Introduction: Rubik's Cube Solver

So here's a project I've been working on for a while...

This robot that can solve a Rubik's cube using Arduino.

I learned how to solve a Rubiks cube last year, and I was also into Arduino, so eventually I ended up with an idea to make my own Rubik's cube solver.

Like many people searching for "Rubik's Cube Solver" on Google, one of the first robots I found was the Tilted Twister design by Hans Andersson:

I looked around at some other Rubik's cube solvers, but I liked that design because of it's (relative) simplicity, so I built a similar version of it with popsicle sticks, an Arduino and 2 servos.

In the end, my robot takes about 20 minutes to enter the cube state and solve.

## Step 1: Materials

Electronics:

- Arduino UNO R3

- 2 servos (I used Hitec HS-311's)

- wires

- USB cable

You can get all of these parts from any robotics store. I got them from canadarobotix.com

Hardware:

- popsicle sticks

- wooden skewers

- thin plywood

- wooden wheel (skewer must fit inside the hole)

- hot glue

- paper towel roll

Software:

- Arduino IDE - (Algorithms in C++)

- Python 2.7+ and Tkinter - (GUI)

- Pyserial

## Step 2: Electronics

Wiring up the servos to the Arduino is pretty straightforward

1. Connect the yellow (signal) wires from the push and rotation servos to pin 6 and 9, respectively.

2. Connect the positive and negative wires to the 5v power source and ground. Sometimes the servos had jitters, so I think a few capacitors could have smoothed out the current.

## Step 3: Mechanical Design

I looked at a few designs but settled on the Tilted Twister because it only required 2 servos to operate, which wasn't as complex mechanically as other robots such as the Cubestormer.

So here's how the mechanism basically works:

1. A platform holds and rotates the cube.

2. The arm pushes and holds the cube.

When I first tried to build the solver, I tried to follow building instructions here:

But I was pretty lazy and didn't follow the instructions, so I made a wooden replica with a few tweaks.

I haven't documented every step of the build process, but I think you can reproduce the tilted twister design with a few tweaks:

1. Slanted sticks to prevent the cube from snagging.

2. To build the arm joints,

- I drilled a hole into ends of the popsicle sticks.

- I cut out 2 cm of a wooden skewer.

- I inserted the skewer into the sticks

- Glued wooden wheels that act as washers on each end.

Honestly building the physical solver was a lot harder and complex than I expected, so if you have any questions on how I built the solver, just ask.

## Step 4: Arduino Sketch - Cube Solving Algorithm

So basically the code I wrote uses combinations of pushes, holds and platform rotations to apply algorithms to the cube.

There are 3 main parts of my code: the algortihm, GUI (enter cube state) and the serial communications

Let's start with the Arduino sketch. It basically uses algorithms to manipulate the cube colours:

1. There are 6 char arrays represent each face of the cube.

2. Using a basic layer by layer method of solving the Rubik's cube, I made a function, cube_decide(), that goes through each stage or the cube solving process.

3. Within each stage, such as cube_decide_cross() (solving the cross), the program would check for specific locations of colours in the cube, and if an algorithm was matched with the condition, cube notation like 'U' (Up) or entire algorithms, like fix_cross_instance_1() would be run.

4. The cube notation and algorithms control the servo functions, such as push_cube() or rotate_one().

Here's a basic overview of the code structure (layers of abstraction):

Cube Decide functions < Cube Algorithms < Cube Move functions < Servo functions < Move Function

One major breakthrough I had was that I actually simulated the cube's movements in the program. The program reassigns the values in the arrays to simulate and cube rotation. This way, the program can simulate the cube move before it physically executes it.

## Step 5: Python GUI

I needed a better way of entering the cube state than directly typing them into the Arduino sketch, so I got the idea of creating a GUI from this robot:

Because I'm new to making Tkinter GUI's (Graphical user interface) and didn't want to make one from scratch, I found a tic tac toe GUI here: http://www.dzone.com/snippets/gui-tic-tac-toe-less...

Then I turned the 3x3 array of buttons into something resembling a cube and added a few buttons. I also added buttons that would change colour each time they were clicked. Finally I made 5 more windows that would pop up one after the other, and transfer the colours entered into a local array in the script.

However, I really slapped the code together in a mess, since I simply copy and pasted 6 separate windows, with almost identical functions. Any suggestions on how I could clean up the code are welcome!

## Step 6: Connecting It All - Serial Communications

Once the algorithm in the Arduino sketch and the python GUI were ready, I needed something something that would use the cube state collected from the GUI and transfer it to the Arduino sketch. After the sketch receives the data, it can put the cube state through the algorithms and physically solve the cube.

To do that, I used a library called Pyserial, which helps my python script communicate with the Arduino over a serial interface.

Basically, this is how I coded the the serial communication:

1. After the cube colours were entered in the GUI in Send_Cube_State.py, I converted the data into a string

2. Used a 'handshake', which in this case the Arduino tells the computer it's ready, then the computer transfers the data to the robot.

3. The Arduino converts the string received into chars, which are assigned to arrays in the sketch.

4. Now that the cube colours have been successfully transferred from the computer to the Arduino, the cube colours can be put through the algorithms and solve the Rubiks cube.

## Step 7: How to Use

If you're trying to build the robot yourself, or just trying out the code, here's a checklist to help you out:

- Arduino IDE (http://arduino.cc/en/Main/Software)

- Pyserial (https://pypi.python.org/pypi/pyserial)

3. Copy and paste Cube_Solver.cpp on to the Arduino IDE.

4. Plug the Arduino in and upload the sketch.

5. Right after uploading, take note of the serial port number at the bottom right corner. (See picture above)

6. In Send_Cube_State.py, change the address in line 18 to match the number on the IDE. (See picture above)

7. Open the command prompt (Windows) or terminal (Mac/Linux)

8. Go to the directory where you put the source files in:

- using the command 'cd', for example:

- cd 'path/to/Cube-Solver'

9. Run the .py script with: python send_cube_state.py

10. If you see a series of 'y's being print on the screen:

- Exit using ctrl-c or command-c

- Repeat step 9 again.

- There should be a GUI that shows up.

11. Enter the Cube colours in the correct orientation:

Colour in Front | Colour on Top

1. Yellow | Blue

2. White | Green

3. Blue | White

4. Red | White

5. Green | White

6. Orange | White

12. Put the cube inside the solver in the orientation seen here: http://goo.gl/tSqSpp

13. Click 'Solve!'

14. If that didn't work:

- Copy and paste Cube_Solver_No_GUI.cpp on to the Arduino IDE

- In line 32-54, enter the cube colors in the same convention as in step 11.

- Do step 12

- Upload the sketch on to the Arduino.

## 6 People Made This Project!

• See 2 more that made it

## Recommendations

• ### Arduino Class

69,892 Enrolled

• ### Casting Contest

We have a be nice policy.

## 7 Questions

0

I have many problems with this step, the link you have already been deleted.
koala.mitzy@hotmail.com

0

1.tengo una duda en uno de los giros el servo que sostiene el cubo queda un poco inclinado y al hacer el empuje el el otro servo no concuerda me gustaria si me puedes ayudar

0

Can i use sg90 servo to built this.... or any other cheaper than hs311

0

Hi i’m Ciro an italian boy and i want to Made the same robot. Do you have any drawings of the robot? For answering this is my email : ciro199920@gmail.com

0

Friends some of you have all the codes it is impossible to download, I am a university student and I am ECUADOR, you can help me with that, please if thanks. This is my email: elperfil1993@gmail.com

0

Can you please give us the measurements of the arm and the positions form the arm to the cube?
We are really desperate....

0

Can i use Sg90 servos? instead of HC-311 servos that you are using?

Any Cheap servo I can replaced with your guided servo?

SG90's have less torque than the HC-311, so depending on the Rubik's cube there's a chance that it won't be able to turn it. You could still try and see if it works.

Can you please send me instructions on how to actually build the device. My email is: Tanzinator1@gmail.com

can you send me photos and instructions on how to create the pad where the Rubik's cube goes?

can someone give me scatch(drawing) to build?

I have a question. I have not tested with the servos yet, but it's been over an hour since python is running the code. it's normal?

I need help as fast as possible!! TKS!

You are using python 3+. The code is written in 2.7. The syntax is slightly different

How did you go about solving the Rubik's cube within the program? What method did you use to decide how to solve the program?

Dear Matt2uy,

I have installed Python 2.7.13, Pyserial-3.4 on the window 7 and change the code in line 18 to open COM port successfully but I can't open the GUI by both CMD-DOS command or Python GUI. When I run the code of GUI, there do not occur on the screen but if i see in task manager window, I see that It still run. Can you give me any idea to fix this issue?

Hello, it would be possible for you to send me the step by step of this construction and programming. I am a mathematics teacher and would like to build with my students. email:

Very nice project. Can you plz make an instructable on how to make that popsicle stick hardware model

Can micro servo be used instead

voilaaa!! i just tweeked the mechanism a little to get the best accuracy for a the 5 to 8 min solves...thanks man for this project.

5 replies

Hello, it would be possible for you to send me the step by step of this construction and programming. I am a mathematics teacher and would like to build with my students. email:

Cassianomarbo@gmail.com

plz give a your ardino programme

Nice robot!
How did you get it to solve in 8 minutes?

Hi Matt, I cannot wait to see the video of this 5/8 min in action, man that's fast. Bet you cannot wait to see the code tweaking as well, he must be using a negative wait time between actions ?.

Hi, 5/8 min that is mega fast, you will have to do a video of it in action and upload the code, I tried to speed up the one i made and got it down to 15ish min from17ish min but it was shaking it's self to bits and would start to walk round the table when in action.

I see you have powered your servos from a separate power supply as the Arduino will not pass enough mAh's. I have modded my one so it can do two different cubes that I have 55mm and 57mm (one at a time that is)

for some reason when I send the info from GUI, CDM does everything and prints on the screen everything perfectly but the servos do not move a bit. Also many a times arduino IDE says 'uploading' for half an hour but does not upload. Also one of the servo jitters a lot. HELP PLZ