Robotic Rubik's Cube

2013/04

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# Introduction

This is a Rubik's Cube that contains electric motors and sensors so that it can automatically solve itself. This project was created for the course MECH 423: Mechatronics. However, it never really worked as well as we intended.

I created this with my project partners Vicky Wang and John Yuen. [A Youtube Video](https://www.youtube.com/watch?v=B3_guhHiack) shows the cube rotating one of its faces while John is narrating.

# Mechanical design

I did most of the mechanical design for this project, while my project partners worked on the electrical aspect. The cube consists of 26 cubies surrounding a spherical core. The core consists of two halves, each with three motors. The bottom cubie has a hole in it allowing a stem to support the cube and let wires pass through. The motors used are the [Solarbotics Gear Motor 7](https://solarbotics.com/product/gm7/), chosen for its high torque and small size. 

All parts were printed using a [PP3DP](http://pp3dp.com/).

pic assembled.jpg The assembled cube sans the stalk : The assembled cube sans the stalk, placed upside-down on the table.

## Core

pic core_inside.jpg Disassembled core : Disassembled core, showing the six geared motors (Solarbotics GM7).
pic core_outside.jpg Assembled core : Assembled core, showing the central cubies mounted on the black spherical core.
pic isometric.png Isometric view of core : Isometric CAD drawing of core. In red and green are the motors. Notice the bevel gears inside for driving the bottom cubie.
pic front.png Front view of core : Front CAD drawing of core.
pic right.png Right view of core : Right CAD drawing of core.
pic top.png Top view of core : Top CAD drawing of core.

## Cubies

The cubies are of varying colours since we ran out of some materials while printing. The intention was to paint them in the end, but we did not have enough time to do so.

pic disassembled.jpg Disassembled cubies : Cubies and the core scattered on the table.
pic cubies_side.png Side view of cubies : CAD drawing of the side of cubies. From left to right: Corner cubie (×8), edge cubie (×12), bottom face cubie (×1), normal face cubie (×5), motor bevel gear, and cubie bevel gear.
pic cubies_top.png Top view of cubies : CAD drawing of the top of cubies. Left to right, top to bottom: Corner cubie (×8), bottom face cubie (×1), cubie bevel gear; edge cubie (×12), normal face cubie (×5), motor bevel gear.

# Electrical design

The idea was to use [QRD1114](https://www.fairchildsemi.com/datasheets/QR/QRD1114.pdf) brightness sensors in the core to read black-and-white encoders on the interior surface of the cubies.

pic motordriver.jpg Motor driver : Motor driver circuit.
pic qrd.jpg QRD comparator : Comparator circuit for QRD1114 sensors.

# Results

Due to thermal stresses arising from the 3D printing process, the cubies vary in some dimensions by up to 5 mm and may be curved. Therefore, the twisting action is prone to jamming. However, under ideal conditions, we have found the motor is indeed capable of turning an entire face.

pic pp3dp.jpg 3D printing process : Photo of two face cubies being printed. Notice the severe warping on the left one as it detached from the printing surface.