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Computer chess engines have become very advanced and are great for learning how to play or for improving your skills. However, playing on a computer is just not the same as seeing the physical pieces move across the board!
This project aims to design and build a mechanised chess device, allowing users to play against the StockFish chess engine on a physical board. An X-Y positioning table will use an electromagnet to execute the computer-generated moves, moving the physical pieces across the board, mimicking a real chess expert.
Playing games on a computer screen can be great - but it takes away from the game. Ghost Chess allows users to detach from their everyday computer use to really invest in the game itself, providing a more engaging gaming experience. Variable difficulty levels allow users to improve their chess skills. Not to mention that it is really cool!
All project-related software can be found in folder "src", and all required schematics/CAD files/PCB designs/footprints are located in folder "Docs".
- The full Bill of Materials: X-Y positioning:
- 3x Stepper Motors (Nema 17)
- 3x Stepper motor drivers (Pololu A4988)
- 1x Electromagnet (3/4' Diameter, 4.5kg pull force) and 40x Button Magnets (3mm diameter, 2mm height)
- P36NF06L FET
- 2x 700/900 mm plywood sheets
- 2x 700mm and 1x 500mm T-slot bar
- 3x 125mm oak shuttles
- 6x T-bolts
- 1x 500mm oak bar
- 6x 40T GT2 6mm Timing Pulley
- 5M 6mm GT2 fiber-glass re-enforced rubber timing belt
- 1x 500mm metal shaft and 1x 30mm metal shaft
- 6x Flanged Corner Bracket BZP
Sensor Matrix:
- 64x Latching Hall-effect Sensors (SS361RT) and 64 10kohm resistors
- 2x 8-1 FET Mux/Demux (SN74CBT3251)
Other:
- Laser-cut Acrylic chess board and 3D printed pieces
- Raspberry Pi 3 Model B
All measurements in mm.
A Plywood base is used to ensure that there is no unwanted lateral motion under tension. T-slot bars act as runners for oak shuttles, held in place by T-bolts. The Y plane movement is supported by two T-slot bars, each 700mm in length. Mounted to both the Oak shuttles on the Y plane is an oak bar which holds the 3rd, X plane, T-slot bar in place (500mm in length). Each shuttle is moved using a timing belt which is mounted through 2 pulleys to a stepper motor.
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- Cut and bevel the two 915mm/70mm Plywood sheets which form the base and top plate of the design
- Bolt down the 2 700mm length T-slot bars through the base plywood sheet (4 bolts spaced evenly)
- Cut the 3 125mm/35mm oak shuttles and the 500mm/35mm oak cross bar
- Mount the oak cross bar to two of the oak shuttles using miter-fast bond and screws
- Bolt the 500mm T-slot bar to the oak cross bar (4 bolts spaced evenly)
- Cut oak blocks to stand the pulleys and motors (x6, 3 for motors and 3 for pulleys), plane to match heights (the bottom of the pulleys should be at the same height as the top of the oak shuttles to ensure that the timing belt can be fixed securely)
- Fix the oak blocks to the plywood base using miter fast bond and screws
- fix the flaged corner brackets to the oak blocks, ensuring they are parallel to the T-slot bar and in line
- attach the motors to the flanged corner brackets by drilling holes in the corner bracket and bolting the motors through them
- attach pulleys to motor shafts, 500mm metal shaft, and 30mm metal shaft
- attach timing belt to oak shuttles through pulleys with tension using miter fast bond
The electromagnet is controlled using a GPIO on the RASPI, connected to the gate of a N-Channel FET (P36NF06L) with a R10k to GND. 12V DC from the power supply connected Electromagnet with the other connection to the Drain of the FET and the Source to GND.
The sensor matrix is comprised of 64 latching (0/1 state will be preserved until reset) hall-effect (detecting magnetic field, turned on by a North magnetic pole and off by South magnetic pole) sensors, with one sensor below each square. The sensor (SS361RT) has three terminals - Supply voltage (V_cc), Output and Ground. The most basic circuit is created by connecting a resistor (10k recommended) between V_cc and Output - the transistor in the sensor would act like a short circuit when turned on (pulling the output to Ground), and as an open circuit when exposed to North magnetic pole (the resistor pulling the output to V_cc or 5V, when supplied from the RaspberryPi). More can be seen in the datasheet: https://sensing.honeywell.com/honeywell-sensing-latching-digital-hall-effect-sensor-ic-datasheet-ss361rt-ss461r-005901-3-en.pdf
To assemble the sensor matrix, follow the steps outlined below. Apart from the components mentioned in the beginning, you will need:
- Solder iron (possibly with a fine tip) and a large amount of solder;
- Long multi and single-core wires;
- Wire strippers;
- Hot glue gun and sticks;
- Cardboard and drawing instruments;
- Duct tape.
- Copy the exact dimensions of the laser-cut acrylic board and draw lines through all square diagonals, so you find the exact center. Prepare your multi-core wire for the SMD hall-effect sensors:
- Solder the sensor terminals to wires and start supergluing them to the cardboard, making sure they are positioned exactly in the center:
- After you have glued all sensors, trim the wires so you have working space:
- Strip single-core wires, which will serve as "rails". Place them along each column line, starting from the side of the ground terminal. Solder the ground terminal sensor wires to the "ground net".
- Cover "ground net" with at least 2 layers of duct tape, then place 8 column wires (V_cc) in parallel with the ground wires. Cover the intersections with the rows with duct tape, and place 8 row wires (Output) along the row lines.
- Solder the resistors and corresponding sensor wires between the supply and output wire nets:
- Solder multi-core wires to the two multiplexer/demultiplexers and superglue the sensor, so the SMD legs would not break from bending.
Prior to connecting everything together, test the output of each hall-effect sensor using a magnet, by iteratively supplying voltage to each column and reading each row. The circuit for the matrix can be seen in Docs/PCB/sensor_array.pdf. Bear in mind that the sensing part of this project is still in alpha.
The Bill of Materials for this project can be seen here: https://docs.google.com/spreadsheets/d/1Xdm7poSaMNww_U4s14YsQG5IgNS09zYjubY1kuaMT44/edit?usp=sharing
To build this project's software: first clone the repository then run
cd GhostChess
cmake .
make
./GhostChess
NB Requires QT5, to install:
sudo apt-get install qt-5 default
Moves can be entered through the GUI or through the CLI (both entered in Algerbraic Chess Notation eg e2e4...).
The software forms an interface between the user and the StockFish API, updating the API with new moves and reading out the computers moves to pass to the motor control software. A full software flow diagram can be found in Docs/Software_flow_diagram.
Motor control is performed using digital GPIO outputs which control the Pololu A4988 stepper motor driver. The stepper motors are rotated in 4 stages which relates to 4 configurations of the H-bridge inductor which is used to turn the motor shaft. A single rotation therefore relates to:
To move pieces accross the board the control software performs the following steps:
- Move to coordinate y1 x1 (the coordinate of the piece to be moved)
- Turn on electro magnet
- Move to edge of square (to ensure that the peice being moved will not collide with any pieces in surrounding squares)
- Move to coordinate y2 x2 (the space to be moved to)
- Return piece to the centre of the square
- Return to origin of the board (located at square A1)
Responsiveness of the system. How long the system will take to move a piece. Latency permitted for the piece -> dependant on where the piece has to move ( Sampling rate of 2Hz for board state of 64 elements. Thread will poll the board every 2Hz and check for changes/validate and make sure user has moved a piece correctly then the engine will respond. Bus Protocol, communicating to motor drivers. Channels? 1 Kernel space usage was not deemed necessary since the latencies were in the order of seconds/ms. For simpicity and faster development time then staying in user space was preferred. Data flow is shown in the software diagram (formats, latencies, processing and conversions) Buffers for the move history of the game as well as the engines returned moves are stored.
Threads operate for fetching the user input for the CLI as well. The board array will also be updated using a thread executed at 2Hz.
- Alex Angelov - 3D Pieces Modelling, Board Production, Position Sensing and Related Software
- Tim Ness - Design Assembly, Accurate Motor Control and Related Software
- Alex Smith - Chess Engine Integration and QT GUI Interface
Issue tracking and Project Tracking through github's associated tools.
How does the project acheive the goals that are set out above?
Q: QLabel: No such file or directory
A: QT5 must be installed to build the software, run sudo apt-get install qt-5 default