V Plotter: V-Bot

Technical Objective

Built a V-plotter that draws by hanging a pen carriage from two stepper motors on strings. The motors adjust string lengths to move the pen across a surface based on inverse kinematics calculations.

Development Timeline

I built this over a few days using borrowed time between school and other projects.

• Design: I modeled the frame and carriage during classes.
• Kinematics: I worked out the math for the inverse kinematics by hand.
• Build: I assembled everything and integrated the code in a single 9-hour session after school.

Hardware Integration

The system runs on 12V from a USB-C Power Delivery supply (2A maximum).

• Power Rails: The 12V powers the stepper drivers directly. A 5V buck converter steps it down for the logic board and servo. The ESP32 uses its internal 3.3V regulator.
• Main Controller: ESP32-C3 running a web server for wireless drawing commands and status monitoring.
• Motors: Two NEMA 17 steppers suspended from the frame using high-tensile string.
• Pen Control: A small servo motor raises and lowers the pen (Z-axis).
• Cooling: A small fan blows over the stepper drivers to prevent overheating.

Inverse Kinematics

The math for this robot was the hardest part. I had to write a custom engine that calculates exactly how long each string needs to be to reach a specific point on the whiteboard.

The robot hanging on a whiteboard. It uses two strings to move the pen.

Instead of simple X and Y coordinates, the robot thinks in string lengths. I programmed it to "home" itself by pulling both strings all the way in, giving it a known starting point before it begins to draw.

Bill of Materials

I tried to make this as cheap as possible by using common parts.

• Motion Kit: $20.00
• Brain (ESP32-C3): $1.00
• Power Parts: $2.50
• Servo Motor: $2.00
• 3D Printed Frame: $5.00

Total Cost: ~$30.50

Post-Mortem

One big failure happened during testing: the cheap motor drivers I bought couldn't handle the power needed to lift the pen. They overheated and literally burned out.

One of the motor drivers that failed during testing. Next time, I'll use higher-quality parts.