My eldest son and I occasionally play a game called Android Netrunner together. It's a 1v1 competitive card game where each player assembles a deck of about 50 cards from a pool of a few hundred. It went out of print a few years ago but then a community group took over designing and making new cards. It's similar to Magic: The Gathering in some ways, but without the scummy expensive blind card pack collectathon. You buy a Netrunner set and you get all the cards.

The game has two main factions, Runner and Corporate. When building a deck you choose cards from your faction. There are rules that define what cards a valid deck can contain, and different deck compositions have different strengths and weaknesses. My eldest plays the Runner faction, and I play Corporate.

A problem arises when you're always playing against the same person: Each player is trapped in a constant cycle of adaptation to their opponent's deck. Exploiting their weaknesses and mitigating your own. This tends towards a see-saw pattern of wins and losses, and involves a lot of deckbuilding which neither of us particularly enjoy.

I think it would be fun to build a robot that can do deckbuilding for you. The entire card pool is well-documented with online tools like Jinteki.net, and the rules for deck validity are easy to codify. I think it might be fun to have a computer formulate a random-but-valid deck, and to build a robot to physically pluck those cards out of the pool so you can be ready to play.

I've used stepper motors in a few projects, recently my sand drawing robot. A stepper motor is able to turn its shaft like a regular motor, but can also move it in tightly-controlled “steps”. Usually 200 steps per revolution, but “microstepping” can divide a step up into sub-steps. 16 or 32 microsteps-per-step are common, giving angular accuracy in the range of 0.1° to 0.01°. You can make a normal motor turn by applying the appropriate voltage. In contrast stepper motors require carefully sequenced pulses to turn.

I've been looking for an excuse to play with closed-loop stepper motors. These have the stepper control circuitry built-in, and a sensor to measure the angle of the shaft. You provide the motor a DC voltage and step/direction signals to make them turn. They also have a serial UART interface, which means you can send them commands from a microcontroller rather than counting out hundreds of step pulses.

Matthias Wandel has an excellent video on them:

I settled on a MKS Servo42C because they are cheap, readily-available and have a UART interface.

I was shocked to learn there was no batteries-included python library for controlling these steppers, so I wrote one and published it on pypi. Now you can control your stepper with code like

from time import sleep
from servo42cUart import Servo42CUart

s = Servo42CUart("/dev/ttyUSB0", 9600)

# Start turning clockwise at full speed
s.set_constant_speed(Servo42CUart.Direction.CLOCKWISE, 127)

# Wait a second
sleep(1)

# Stop turning
s.stop();

# Turn 360 degrees, assuming 16x microstepping, as fast as possible.
s.set_angle(Servo42CUart.Direction.CLOCKWISE, 127, 200 * 16)

The robot will need to be able to identify a card for it to be sorted. I plan to do this with a webcam and tesseract-ocr. This is a very powerful text recognition engine that Google publishes open-source. Some early testing has yielded promising results. I set up a HD webcam with a goose-neck worklight, with a white background. The webcam is connected to an old Raspberry Pi Model 3, running Debian 10.

A cobbled-together test rig.

The view through the webcam.

tesseract-ocr read:

NOISE

IDENTITY: G-mod

Whenever you install a virus program,
the Corp trashes the top card of
R&D.

“Watch this. It'll be funny,”

Which is pretty impressive for such a bodge-fest.

The view through the webcam.

Result:

INFILTRATION
Gain 29 or expose | card
Bring back any memories, Monica?’
John “Animal” McEvoy
0 2012 oats le Coast LLG, @2012FFG