RobArt – Hardware

This page describes the hardware components of RobArt.

Controller Choice: Arduino vs Raspberry Pi

The Raspberry Pi operating system is not a real-time system. A program can be interrupted by any other process, leading to random delays. Python adds its own timing issues. It is therefore not well suited for generating precise and stable pulse sequences in the microsecond range for stepper motors via software.

Solution: Arduino for stepper motor control (time-critical), Raspberry Pi for everything else (Bluetooth, SVG parsing, coordination).

Mechanics

Chassis

RobArt uses a three-wheeled omnidirectional design:

  • 3 wheels arranged at 120° angles
  • Omnidirectional wheels for movement in all directions
  • Wheel diameter: 58 mm

Pen Lifter

5 pens with servo mechanism for different colors.

Electronics

Components

Component Description Quantity
Arduino Stepper motor control 1
Raspberry Pi 4 Coordination & Bluetooth 1
NEMA 17 Stepper motors (1.8°, 200 steps/rev) 3
Stepper Driver A4988 or DRV8825 3
Bluetooth Module HC-05 or similar 1
Servo Motors Pen mechanism 5
Logic Level Converter 3.3V ↔ 5V bidirectional 1

Power Supply

  • LiPo Battery: SLS 4S1P, 3700mAh, 54.76Wh, 14.8V
  • Alternative: Power supply via boom stand
  • Voltage Converter: LM2596 Step-Down Module
  • Breadboard Power: Joy-it SBC-POW-BB

Wiring Overview

┌─────────────────────────────────────────────┐
│                LiPo 14.8V                   │
└──────────────────┬──────────────────────────┘
                   │
        ┌──────────┴──────────┐
        ▼                     ▼
┌───────────────┐     ┌───────────────┐
│  Step-Down    │     │  Step-Down    │
│  12V          │     │  5V           │
└───────┬───────┘     └───────┬───────┘
        │                     │
        ▼                     ▼
┌───────────────┐     ┌───────────────┐
│  Stepper      │     │  Arduino      │
│  Drivers (3x) │     │  RPi, Servos  │
└───────────────┘     └───────────────┘

Resolution / Accuracy

Calculation

  • Wheel diameter: 58 mm
  • Wheel circumference: π × 58 = 182.21 mm per revolution
  • NEMA 17: 200 steps per revolution
Mode Steps/Revolution Resolution
Full Step 200 0.911 mm/step
16× Microstepping 3200 0.057 mm/step

Calibration

After assembly, RobArt needs to be calibrated:

  1. Chassis Calibration – Test straight line movement
  2. Pen Calibration – Height and pressure
  3. Wheel Speed Calibration – Synchronize all 3 wheels