V Plotter: V-Bot

System Architecture

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.

Mechanical Design & Fabrication

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.

Electrical & Firmware Implementation

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.

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

Total Cost: ~$30.50 CAD

Validation & Failure Analysis (Post-Mortem)

One A4988 driver failed during testing while moving the pen carriage. This happened before I added the cooling fan described above. I did not record the VREF/current-limit setting, driver temperature, or whether the motor was ever disconnected while energized, so I cannot establish the electrical root cause after the fact. An incorrect current limit, inadequate thermal management, or a transient can each damage a stepper driver; the failure alone does not tell me which occurred. The useful lesson is to verify the driver's current limit against the motor, provide suitable cooling, and avoid connecting or disconnecting a motor while the driver is powered, then validate those conditions during testing.

An A4988 driver that failed during testing, before the cooling fan was added.