dr4wbac_k (tem, nikl, jakob)

TODOs

Mechanical

TODO Design

IMPORTANT:

Capstion Line muss auf einer ebene sein
Check, das alles stabil ist

TODO Bauen und testen

Electrical

TODO Design und Herstellung

Motorsteuerung PCB (URUMBU?)
- Design
- Herstellung
PCB für verbindung der Motoren und PC?

TODO Softwareansteuerung

Alternative Names

Drawback
Pencil Punk
HacksyDraw

Requirements

size for painting a3 paper
capstan drive
h bot for movement
easily to assemble / disassemble
- removable thread of the capstan drive

Roadmap

Syntax: 1, 2, 1.1
- task 1 and 2 are independent from each other
- task 1.1 can only be executed after task 1

1 cad & assemble all parts
1.1 print parts (until friday ev)
2 power electronics
- 2.1 user interface (svg to motor control code)
3 toolpath planning: svg in -> toolpath out
100 make video

availability friday

matthias 9 bis 14.30, ab 18.00
niklas 15.00 bis ...
jakob ab 10.00

next steps

friday 12.00: all single parts modeled
friday 15.00: all parts assembled (the other person does driver)

References

https://github.com/SeanP2001/Urumbu_USB_Stepper_Motor
cable carriers 3d printable
urumbu further work
sampo
OSAP web framework for talking with usb-driven hardware modules (e.g. motors), shoving everything you would make on pcbs onto the desktop for rapid prototyping. overkill for our project.
capston drive
alternative draw bot with v guides
flexible-XYstage
Urumbu_IO
UrumbubotXY 2.0
Laid Up Gantries with Capstan Drives
Other Capston mechanism

Other drawing bots

Mechanical Design

TODO insert niclas' sketches
cable carrier
CAD organization
keep folder structure as flat as possible
Have everything as .FCStd. Convert if needed.
one FCStd file per part/assembly
reason: one part can be included multiple times easily (especially if you download separate parts)
motor

BOM

take 3d models from urumbot

model in cad or find 3d models from somewher else, e.g. from here

probabably easy to get

1. v-bearing (5x)
1. capstan (2x) (take from urumbot) ✅
1. idler (2x) (take from urumbot) ✅
7.1. extrusion vertical (1x) ✅
7.2. extrusion horizontal (1x) ✅
1. stepper motor (2x) ✅
1. wire (1x)
1. servo motor ✅

probably model ourselfs

1. mounting plate v bearing (1x)
1. sledge ✅ + assemble it (2x)
1. extrusion cap head (1x)
1. flexture
1. mounting plate servo (1x)
1. mounting plate stepper motor (2x)
1. pcbs

do not model

1. motor enclosure right (1x) (DEPRECATED)
1. motor enclosure left (1x) (DEPRECATED)
1. sledge case (1x) (DEPRECATED)

to ask ferdi

what do you think of our design?
- you somehow have to attach the two carriers. do that in 4 points. maybe print clamps for that
- for the upper carrier, design something on your own. reason is, you need to add somehow the v wheels
which material do we take for attaching motors and v bearings to the end of the extrusions?
- alimunum sheets. thickness 4 to 5mm (we have 5mm, 41mm width). they are in the top right shelf next to the carvera
any ideas for aufnahme of the pencil?
wie geht man bei pcbs vor? erst pcbs entwerfen oder nimmt man irgendein mock?
- einfach nen quader reinklatschen
wie macht man das kabel fest?
- siehe fahrrad baudenzug

design changes

removing 9 to place v bearings on same level as vertical extrusion
to do that we have to put v bearings at the end of the extrusion caps
do not use motor end caps but use metal or 3d printed plastic caps. ask ferdi, maybe also acrylic

Motor Driver

https://www.digikey.com/en/products/detail/texas-instruments/DRV8428PWPR/13563046
not in the lab. ordered
actually, they are in the lab
alternative: hbot firmware together with ramps
we fonud those at the 3d printer in the hackspace: https://www.allegromicro.com/~/media/Files/Datasheets/A4988-Datasheet.ashx
can you use different stepper drivers in one project?

Ferdi's Tipps:

first, try stuff out with cartesian system, then switch to corexy
Den Strom der Treiber stellt ihr so ein (deepseek):

Stepper Motor Driver Voltage (Vref) Adjustment Guide for RAMPS 1.4
⚠️ Safety First
Power Off before adjusting.
Use a multimeter (DC 0-2V range).
Ensure proper heatsinks/fans are installed.
🔧 How to Adjust Vref
Locate the potentiometer on each driver.
Connect multimeter:
Black probe → RAMPS ground (e.g., power supply negative)
Red probe → Potentiometer
Adjust screw:
Clockwise → Increase voltage
Counter-clockwise → Decrease voltage
📊 Recommended Vref Values
Calculation Formulas
Driver	Formula
A4988	Vref = Imax × 0.7
DRV8825	Vref = Imax × 0.5
TMC2xxx	Configure via UART
Common Presets (Volts)
Motor Current	A4988	DRV8825
1.0A	0.7V	0.5V
1.5A	1.05V	0.75V
2.0A	1.4V	1.0V
🛠 Troubleshooting
Symptom	Solution
Skipping steps	Slightly ↑ Vref
Overheating	↓ Vref + check cooling
Grinding noise	Check current + wiring
💡 Pro Tips
Start with lower values and test.
For TMC drivers, use software configuration.
Label adjusted drivers with a sharpie.
📌 Always verify motor specs in their datasheet!

Die Motor-Kabel identifiyiert Ihr, indem ihr erstmal die beiden paare identifiziert. Dazu könnt ihr zwei Kabel zusammendrehen (z.B. rot+grün) und schauen ob sich der Motor dann schwerer drehen lässt. Sobald Ihr ein paar gefunden habt, ist das andere das zweite Paar (schwarz gelb). Dann schraubt ihr zuerst Paar1 und dann Paar2 an die vier Klemmen z.B. rot, grün, schwarz, gelb. Wenn der Motor dann falsch rum dreht, invertiert Ihr ein Paar. grün, rot, schwarz, gelb. Ihr könnt aber auch einfach bis Sonntag warten wenn ich wieder da bin.
jakob checked:
find out pairs: measuring current. current is induced when turning if both are connected to one coil, current can be measured
pairs are:
- blue, red
- green, black

Toolpaths

gcode to motor action
urumbu uses https://github.com/SeanP2001/Urumbu_USB_Stepper_Motor
if urumbu is used, use sampo stuff: https://gitlab.com/fab-lab-oulu/sampo