Build guide
Parts and cost
18.72 USD in parts (Rezeck et al., Autonomous Robots, 2023). Retail, one-off buys at the time of the paper.
Specifications (paper)
| Specification | Value |
|---|---|
| Size (L × W × H) | 0.068 × 0.073 × 0.076 m |
| Weight | 0.156 kg |
| Wheel distance | 0.0631 m |
| Wheel diameter | 0.0492 m |
| Linear speed | 0.25 m/s |
| Inertia | Ixx = Iyy = 1.27×10⁻⁴ kg·m², Izz = 1.04×10⁻⁴ kg·m² |
| Battery | 3.7 V, 1800 mAh Li-Po |
| Autonomy | up to 3 hours with all components in continuous use |
| MCU | ESP8266, 32-bit 160 MHz, 4 MB, Wi-Fi 802.11 |
| IR ring | 8 × TCRT5000, 45°, pulsed over-current, range up to 20 cm |
| Encoder | Kailh / mouse rotary, 48 PPR; 1:6 wheel–encoder gear → 1.25° / 0.54 mm per step |
| Motors | 2 × SG90 continuous servos, 1.8 kgf·cm |
Cost per robot (paper)
| Parts | Qty | Cost (USD) |
|---|---|---|
| Servo motors SG-90 | 2 | 2.06 |
| Mouse encoder 48 PPR | 2 | 0.10 |
| ESP8266 NodeMCU | 1 | 2.50 |
| Rubber O-ring 38 mm | 2 | 0.10 |
| IR TCRT5000 | 8 | 0.68 |
| LED RGB WS2812b | 2 | 0.51 |
| IMU MPU6050 | 1 | 0.85 |
| Li-Po 3.7 V 1800 mAh | 1 | 5.85 |
| PCB board and components | 1 | 4.30 |
| 3D-printed PLA parts and fasteners | 1 | 1.50 |
| Total | 18.72 |
What to buy (assembly checklist)
From the build tutorial (September 2025). Use this on the bench; the paper table above is the cost reference.
Drive and locomotion
- SG90 continuous-rotation servos ×2 (green-label variant recommended), with horns and screws
- O-ring tires ×2
- 623ZZ bearings ×2
- Steel balls 4 mm ×2 (casters)
- M2.5 self-tapping screws plus assorted M3 screws, nuts, and washers
Electronics
- Blank HeRo v2 PCB (see Order the PCB)
- ESP8266 / NodeMCU
- Li-Po 103450 (1S, 3.7 V 1800 mAh)
- MPU6050 IMU (optional e-hat)
- Two mouse-style quadrature encoders
- Passives and ICs listed on the solder page
Print set — chassis A/B, wheels, casters, cover, USB slider, e-hat, gloves, motor gears, motor shafts, encoder shafts. See Print the body.
A printable spreadsheet is still in the repo: assembly_materials.pdf.
Tools
Phillips and flat-head screwdrivers, needle-nose pliers, diagonal cutters, wire strippers, precision knife, fine-tip soldering iron, flux, desoldering braid, multimeter, ESD tweezers, safety glasses, isopropyl alcohol. Optional: current-limited bench PSU, hot-air station, PCB vise.