Chess Bot Client Webapp to interface intepreted camera and Stockfish results with EV3.
Message-passing done via flashing the screen and using an NXT light sensor to recognise the data.
Available at: https://wernjie.github.io/ev3-chess-bot/engine/
Run the webapp on a phone in landscape mode. Initiate full screen mode if possible. Mount it with the camera pointing to the chessboard, perfectly parallel, and taking up most of the viewfinder with edges in view. Automatic cropping and normalisation of the camera footage will take over, and you should see a perfect low resolution checkerboard image from the camera shown in the second preview from top left.
You may calibrate an empty chessboard by tapping Calibrate Full Board and mounting the phone in the same position and lighting conditions as you would be planning to permanently mount it for chess piece movement detection. This ensures highest possible accuracy.
If you want to recalibrate small portions of the chessboard midgame, you may also find the partial Calibrate Selected... useful. Follow the instructions for details.
If possible, utilise uniform lighting for best performance, or if not available, use your phone's flashlight option (can only be enabled using Chrome on Android or browsers with similar engines).
Please ensure screen is at full brightness for best detection performance by the chess_reader EV3.
Important caveats as of writing:
- Chrome on Android required for toggling flash.
- On iPhone, Safari might be necessary for fullscreen-like functionality using the Hide Toolbar option.
Use the legacy EV3 Lab software to open the EV3-G code and install it on three separate EV3 bots.
All movements are on repeated LEGO Technic 1x4 geared racks (3743) with 36 tooth double bevel gears (32498).
The default names for the three 'robots' are listed below and should be self-explanatory.
- Movement using Large Motor B.
- Runs in reverse direction (negative power drives movement from column A to column H), offset -80° rotation away from chessboard column A (outside of the board).
- Pickup mechanism on Large Motor A.
- range of motion approx slightly under 90°. Positive rotation to move mechanism down.
- Claw mechanism on Medium Motor D.
- Jammable to close and open positions at 100% power in under 0.2 seconds. Positive rotation for closing.
Run program x-axis and wait for calibration confirmation beep. Should rest slightly before column A.
Range of motion available from 80° motor rotation before column A (jammed completely at full power) to column H.
- Movement Medium Motor C for left side (next to chessboard column A; clockwise goes from rows 8-1)
- Movement Medium Motor B for right side (next to chessboard column H; anticlockwise goes from rows 8-1).
Run program y-axis and wait for calibration confirmation beep. Should rest slightly past "row 9", ready to play as black.
Range of motion available from row 1 to 95° motor rotation past "row 9" (i.e. one imaginary row out of chess board, jammed completely).
- NXT Light Sensor at port 3. Mount in less than one piece distance above the screen. Ensure screen is at full brightness.
Run program phone-reader and ensure successful connection to the two other EV3s. Asynchronously reads screen flashes from phone and interprets as movement.
- Press Center button to calibrate black levels at any time.
- Press Left button to forcibly terminate all pending requests and request movement to top left (1,0) position, then terminate
phone-reader. Useful in event of corrupted transmission. - Press Right button to send an arbitrary request to perform move b7g3 or g7b3 to test movement accuracy. Warning: Only initiate when idle or may cause transmission corruption.
Transmission is performed by flashing the information to the EV3 from the phone screen to an NXT light sensor as basic coordinates in three light levels.
- Black: separation gap (
_) - Gray : coordinate counter (
X) - White: coordinate separator (
|) (twice as long in transmission time as well)
A flash of |_X_X_X_X_|_X_X_|_X_X_X_X_|_X_X_X_X_|_ is interpreted as "move piece on (4,2) to (4,4)", starting from bottom right from robots perspective (playing as black), with left+up as positive axes.
The range of values for x-axis is 1-8, and y-axis is 0-8. Note that 1-8 are within the chess board, so values outside of 1-8 are out of the chessboard.
Thus, "move piece on (4,2) to (4,4)" is equivalent to move d7d5.
The above format and translation to d7d5 is considered a single move. A move consists of 5 coordinate separators, terminates with a separation gap, and has the desired amount of coordinate counters in between.
Transmission information is processed asynchronously, so the robot starts moving as soon as the starting coordinate pair of the first move is received to save time.
Currently, a maximum of two moves in total can be queued asynchronously to allow for captures and castling. Any extra moves result in undefined behaviour.
Uses average ∆E of pixels as a metric for detecting the presence of a piece. (with the assumption that chess pieces have a different hue from the chessboard, which is not uncommon).
∆E measures the distance between two colours, commonly used for measuring monitor colour accuracy [Details].
For our case, the higher the ∆E value for a particular square tile, the more likely there is for a colour difference and thus presence of a piece. This is especially effective for detecting black pieces on dark tiles with slight hue differences.
Piece colour detection is then done with luminosity thresholds at the center of the square tile.
I suffered from these issues for way too long, so hope these will help alleviate some pain points. As of writing,
- EV3 cannot simultaneously establish a connection to a computer and one or more EV3 at the same time.
- Ensure EV3 is not actively connected to a computer to allow connections to other EV3(s).
- Ensure EV3 is not actively connected to other EV3(s) to allow connections to a computer.
- Closing an EV3 running program does not terminate connections to other EV3(s). Ensure to disconnect from settings if you want to connect to a computer.
- Pressing the disconnect EV3 button on your computer does NOT guarantee that the EV3 is disconnected from your computer. Ensure to check EV3 as well.
- Pressing the back button on your EV3 while it is attempting a bluetooth connection, performing a bluetooth search etc., in a program or settings has a high chance of crashing the internal EV3 bluetooth driver. Try to wait till it completes instead.
- The program has automatic workarounds to determine whether a connection failure occured. However, it may not detect a bluetooth driver failure or a mid-transmission disconnection, in which the symptom would be an unresponsive bot when a command was sent. Since all transmissions are programmed with corresponding acknowledgements, all bots would freeze mid-action in the event of a connection failure.
- In the event of an immediate program termination with a system error, either the internal EV3 bluetooth driver likely crashed or has never paired with the target bots.
- Ensure the bots were paired manually through EV3 settings and are of the correct name.
- If they are already paired but the issue still occurs, restart the EV3 to resolve.