A Stitch in Time

Kyle Rankin

https://kylerank.in/talks/misc/a_stitch_in_time.html

Introduction

• I have a lot of hobbies
• Really about learning new things
• Some past hobbies
• My COVID hobby: weaving.

Doubleweave Competition Towel

Silk Shadow Weave Stole

Introduction

• Grew into general interest in fiber arts
• Many interesections with technology
• Got a (free!) flatbed knitting machine
• Ultimately led to building a knitting machine clock from scratch
• Named it "Tempus Nectit" (time knits).

This Talk

• Inspiration
• Design
• Assembly
• Setup And Installation
• The 2023 Scarf
• Future Plans
• Closing Thoughts

Inspiration

• Project inspired by Hackaday post
• Siren Elise Wilhelmsen designed art project clock that knit a stitch every half hour
• After a year, it dropped a completed scarf to the ground
• No build plans, can commission a clock from the artist
• "I want one!" "You should make one!" "OK!"

Design

• Ultimately the clock breaks down into a few components:
• A 48-hook circular knitting machine
• A stepper motor attached to the hand crank
• Electronics to control the stepper motor
• Software to turn the motor one stitch every 30 minutes
• Project split into four corresponding sections:
• Electronics (stepper motor controls)
• Software (rotating stepper a pre-defined amount according to a schedule)
• Knitting Machine (modifying off-the-shelf machine)
• Case (something to put all the components in).

Electronics

• First PoC: Can I control steppers from a RPi?
• Used Adafruit motor hat for RPi
• Combined hat w/ spare RPi and stepper motor
• Followed motor hat docs
• Motor hat needs 5v-12v PS, found 9v and 12v in stash
• Went w/ 9v for size reasons.

Electronics

Hardware Buttons

• Realized useful to control steppers manually
• Instead of SSHing in, decided to add physical buttons
• Dug through con badge stash, found push buttons
• Followed Adafruit's GPIO guide
• Settled on two buttons to move forward/backwards one stitch.

Software

• RPi running Raspbian to match Adafruit examples
• Needed custom software to control knitting machine w/ precise steps
• Examples in Python, so used Python
• Key is figuring out precise steps to move one stitch
• Hooked up stepper to knitting machine w/ 3D-printed part, trial and error
• Wrote some sample scripts to advance machine in different ways
• Sample script to advance one stitch:

Sample Script

#!/usr/bin/python

import time
import board
from adafruit_motorkit import MotorKit
from adafruit_motor import stepper

kit = MotorKit(i2c=board.I2C())

for i in range(54):
#    kit.stepper1.onestep(style=stepper.SINGLE,direction=stepper.BACKWARD)
      kit.stepper1.onestep(style=stepper.DOUBLE)
#    time.sleep(.01)

#for i in range(864):
#    kit.stepper1.onestep(style=stepper.MICROSTEP,direction=stepper.BACKWARD)
#    kit.stepper1.onestep(style=stepper.MICROSTEP,direction=stepper.FORWARD)

kit.stepper1.release()

Software

Steppers, microsteps, and sleep

• Lots of experimentation to find right step type/speed
• Microsteps quieter, precise, but weaker
• SINGLE stronger, louder, DOUBLE even stronger/louder
• Noticed skipping when powering knitting machine, got more powerful stepper
• Settled on DOUBLE w/ short sleep.

Software

Knitting Machine Daemon

• Considered cron job, but needed daemon for button control
• Ultimately wrote knitting machine daemon that runs in infinite loop
• Checks time, at top of hour, moves stepper forward
• Move backwards first to help "unstick"
• Divides steps by hour so clock can "chime"
• Then sleeps 61s
• Otherwise detects button presses and does short sleep
• Added systemd unit file to run automatically at boot.

Knitting Machine

• Started with Sentro 48-hook knitting machine
• Matched hook count in original project
• Makes sense as a clock
• 48 hooks = stitch every 30 mins
• Planned to build wooden case w/ bird house design
• Within 2 weeks from start, had everything completed, mounted to board
• Realized clock was way too large, back to drawing board.

Knitting Machine

Take Two

• Sentro also makes 22 hook machine
• Much smaller, half the price
• 22 hooks messed up 30-min stitch plan
• Went with hourly chime, marked "hour hand" with foil tape
• Two full rotations per day
• Sentro 22 different case design, had to disassemble to mount to wood
• Would need to add structural elements to keep machine together in wooden case.

Case

• Realized disassembled machine fit on my 3D printer bed
• 3D printed case an option
• Problem: no 3D modeling experience
• Solution: 3-4-week crash course in 3D modeling with Tinkercad
• Iterative process using calipers, prototyping sections at a time
• Machine mount most critical part for fit
• Design mimics bird house, mounts everything to large bottom case
• Top splits into three sections that slide into bottom case
• Allowed access to electronics w/o disturbing knitting in progress.

Case

3D Printing

• Bottom case took 2 days to print
• Completely filled print bed
• Took three prototypes to perfect
• Also designed additional parts:
• Plastic button covers
• Clips to hold ring gear to case
• Standoffs to mount RPi
• Spool to hold yarn
• All designs on project's Printables page.

Assembly

• Full installation steps on my project page
• Bill of Materials:
• Sentro 22-hook knitting machine
• Raspberry Pi
• Adafruit Motor Hat
• (2) Tactile Button switches
• Solid core 22AWG wire (multiple colors)
• NEMA17 stepper motor
• 9V/1A DC power supply
• 5V/1A USB adapter
• 3-4 meter AC extension cord
• 3D printed parts from my Printables page
• (3) size 4 1/2" wood screws
• (4) M2x16mm screws and matching nuts
• (2) M3x8mm screws

Assembly

Bottom Case

• Everything attaches to bottom case, then lid slides on
• Start with RPi, then knitting machine, motor, motor hat
• Next push buttons, AC outlet
• Used zip ties to fasten AC outlet, tidy cables.

Assembly

Top Case

• Top case split into three parts
• Necessary to fit on 3D printer bed
• Gives easier access to electronics
• Bottom cover needs different print orientation than "roof"
• Also reduces support material in print.

Assembly

Top Case A

• "A" part attaches first at angle
• Must pop in place to avoid extended hooks
• Holds pink plastic hook covers in place.

Assembly

Top Case B and C

• "B" part has name, slides in place
• Used two colors so text more visible
• Also covers up joint between pieces
• "C" part covers stepper, acts as "roof".

Assembled Clock

Setup And Installation

• Start by casting on waste yarn, following knitting machine instructions
• After ~10 rows, ran script to perform one day's knitting, to catch up to current day:

#!/usr/bin/python

import time
import board
from adafruit_motorkit import MotorKit
from adafruit_motor import stepper

kit = MotorKit(i2c=board.I2C())

steps = (2220)
for i in range(steps):
    kit.stepper1.onestep(style=stepper.DOUBLE,direction=stepper.FORWARD)
    kit.stepper1.release()

The 2023 Scarf

• Decided to mark notable events with colored stripes in scarf
• 2023 an eventful year. Scarf documented:
• Major holidays
• Awards/residencies
• My layoff
• 3+ week, ~9k mile road trip across the country
• A stroke
• Moving family across the country
• Death in the family.

The 2023 Scarf

Future Plans

• Tweaked step sleep to make chime quieter
• Ring gear wore down in places, need to replace
• Will probably design 3D-printed ring gear
• In the mean time manually advancing from 8-9:00
• Never use the buttons
• 2024 scarf is in progress
• Ultimately might stitch together into blanket.

Closing Thoughts

• My Hackaday-inspired project was featured on Hackaday!
• Clock was made "from scratch" but not really
• Open source tools made everything possible
• From RPi to Adafruit hat + open source scripts
• Went from idea to working prototype in 2-3 weeks
• I had to learn new skills, but all possible because of shared knowledge
• OSS makes hard, almost impossible tasks accessible to non-experts.

Thank You

Additional Resources

• This talk: https://kylerank.in/talks/misc/a_stitch_in_time.html
• The Tempus Nectit Project Page: https://kylerank.in/tempus_nectit/