DIY Arduino Based EggBot
π Overview
The EggBot is a drawing robot that prints on spheres such as eggs and light bulbs: the egg spins between two axes driven by one stepper, the pen carriage moves along the surface driven by the other, and a servo lifts the pen.
The frame is laser-cut plywood plus 3D-printed parts, driven by an Arduino running GRBL, with desktop software converting images into drawing paths. Drawing an egg for Valentine's Day or a name for a birthday is strangely satisfying.
π§° What you need
- Arduino UNO x1
- Stepper motors x2 + A4988 drivers x2
- Micro servo x1 (pen lift)
- 608 bearings x2 and assorted M3 screws
- Plywood (laser-cut parts) + 3D-printed parts (files provided by the author)
- Breadboard + power (12V for the steppers, 5V for the servo)
π§ Step by step
Gather the parts
Ordinary 42mm steppers are fine: one turns the egg, one moves the pen
The plywood parts can be laser cut or hand-cut with a scroll saw
Understand how it works
One motor rotates the egg about its axis, the other moves the pen left and right
The pen only touches down between rotations, and the servo times the lifts to build the pattern
Cut the plywood parts
Cut the base, brackets, and bearing mounts from the drawings
Hole accuracy directly affects the drawing quality
Print the 3D parts
3D print the egg cups, pen holder, and couplers
The pen holder should accept pens of different diameters
Assemble
Fix the egg first, then fit the pen carriage, and check everything moves freely
The pen tip should just touch the egg; a spring sets the pressure
Wire the electronics
The A4988s drive the two steppers and the servo goes to a PWM pin
Keep driver current low - the egg axis turns easily and too much current causes skipped steps
Flash the GRBL firmware
Flash GRBL to the Arduino and configure the two axes
Convert the rotary axis from steps per revolution so the circumference is accurate
Tune GRBL
Set the axis travel and steps in the $$ settings
Keep the speed down; the sphere has inertia and steps are easy to lose
Install the control software
Use EggBot's own software or a similar tool on your computer
The software converts images into G-code paths
Prepare the image
Convert the picture to single-colour line art for the best result
Very high resolution makes plotting time explode
Start drawing
Calibrate with a simple pattern before running complex artwork
Swap pens mid-draw for multi-colour effects
π‘ Tips
- Choose thick-shelled eggs (or boil them first); thin shells crack easily
- Pen pressure makes or breaks the result: too light and the line breaks, too heavy and it smears - adjust with the spring
- Drawing on a sphere is really an unwrapped map, so scale the artwork to the egg's circumference and height