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Assembly Guide

SPDX-License-Identifier: CERN-OHL-P-2.0

Step-by-step hardware assembly instructions for the 3we robot platform.

Basic SKU Standard SKU
Time 2-3 hours 4-5 hours
Difficulty Intermediate (soldering required) Intermediate-Advanced
Cost ~¥680 / $95 ~¥2,200 / $300
Prerequisites Basic soldering, multimeter use + Linux CLI, micro-SD flashing

Video walkthrough: Assembly Video (coming soon)

Safety Warnings

  1. LiPo batteries can cause fire if short-circuited or punctured. Never leave charging unattended.
  2. Soldering iron temperatures exceed 300°C. Use a silicone mat and keep the tip clean.
  3. E-stop wiring is safety-critical. Double-check before first power-on (Step 7).
  4. Motors under load can draw 2A+ per channel. Do not exceed DRV8833 ratings (1.5A continuous per channel).
  5. Disconnect the battery XT30 connector before any wiring changes.

Tools Required

  • Phillips screwdriver (PH1, PH2)
  • Hex key set (M2, M2.5, M3)
  • Soldering iron (for motor wires)
  • Wire strippers
  • Multimeter
  • 3D printer (for custom brackets, optional)

Parts Checklist

Before starting, verify you have all components from the appropriate BOM file: - hardware/bom/bom_basic.csv (Basic SKU) - hardware/bom/bom_standard.csv (Standard SKU - includes everything in Basic) - hardware/bom/bom_optional_addons.csv (Optional add-ons: Hailo-8 upgrade, 4G, LiDAR, rear camera) - hardware/bom/bom_industrial.csv (Industrial SKU)

Step 1: Chassis Preparation

  1. Inspect the aluminum chassis for burrs or bent edges
  2. Install M2.5 brass standoffs (×4) for PCB mounting
  3. Install M3 threaded inserts (×4) for payload mounting plate
  4. Verify all mounting holes align with the 20mm grid pattern

Step 2: Motor Installation

Motor orientation is critical for correct mecanum movement:

        FRONT
   [FL ╲]     [╱ FR]
   ┌──────────────┐
   │              │
   │   CHASSIS    │
   │              │
   └──────────────┘
   [╱ RL]     [RR ╲]
        REAR
  1. Mount motors in their brackets using M2 screws
  2. Secure brackets to chassis corners with M3×8mm bolts
  3. Route motor wires through internal cable channels
  4. Solder JST-PH connectors to motor leads:
  5. Red → Motor+ (positive terminal)
  6. Black → Motor- (negative terminal)
  7. Green → Encoder A
  8. White → Encoder B
  9. Red (thin) → Encoder VCC (3.3V)
  10. Black (thin) → Encoder GND

Step 3: Wheel Mounting

Critical: Mecanum roller direction matters!

  • Front-Left & Rear-Right: Left-handed rollers (╲ pattern when viewed from front)

  • Front-Right & Rear-Left: Right-handed rollers (╱ pattern when viewed from front)

  • Press wheel onto motor D-shaft

  • Secure with M3 set screw (use threadlocker)
  • Verify wheel spins freely without wobble
  • Check ground clearance ≥ 25mm

Step 4: PCB Installation

  1. Place mainboard on standoffs
  2. Secure with M2.5 nylon screws (to avoid shorts)
  3. Connect motor cables to JST headers (match FL/FR/RL/RR labels)
  4. Connect encoder cables to their respective headers
  5. Verify no cables are pinched or strained

Step 5: Sensor Installation

Ultrasonic Sensors (×4)

  1. Mount HC-SR04 modules at chassis corners, facing outward
  2. Use 3D-printed brackets or hot-glue for secure mounting
  3. Connect to mainboard ultrasonic header (4-pin: VCC, Trig, Echo, GND)
  4. Ensure sensor faces are perpendicular to ground (±5° tolerance)

IMU (BNO055)

  1. Mount at geometric center of chassis, as flat as possible
  2. Secure with M2 screws or double-sided tape (vibration-resistant)
  3. Connect I2C cable (4-pin: VCC, GND, SDA, SCL)
  4. Note mounting orientation (arrow on PCB = forward/X-axis)

Step 6: Battery Installation

  1. Insert 18650 cells into battery holder (observe polarity!)
  2. Verify BMS LED indicates correct voltage
  3. Mount battery pack centrally (lowest possible for CG)
  4. Secure with velcro strap or 3D-printed retention clip
  5. Route XT30 cable to mainboard power input
  6. DO NOT connect yet — wait until final inspection

Step 7: Emergency Stop Wiring

This is a safety-critical step. Double-check all connections.

E-Stop Button (NC contact)
    Pin 1 ──→ Safety Relay Coil (+)
    Pin 2 ──→ Safety Relay Coil (-)
                    │
Safety Relay NO Contact:
    COM ──→ Battery VBAT (7.4V)
    NO  ──→ DRV8833 Motor Power Input
  1. Mount E-stop button on chassis top (accessible, labeled)
  2. Wire NC contact to safety relay coil terminals
  3. Wire relay NO contact in series with motor power line
  4. Verify: When button is UP (normal), relay energized, motors powered
  5. Verify: When button is DOWN (pressed), relay de-energized, motors cut

Step 8: PBC-34 Connector

  1. Mount the 2×17 header on the top payload plate
  2. Wire according to pinout in hardware/pcb/README.md
  3. Install keying mechanism (plastic tab in position 17)
  4. Test continuity on power pins (1-6) before energizing

Step 9: Final Inspection

Before powering on for the first time:

  • [ ] All motor wires connected and secure
  • [ ] Battery polarity correct
  • [ ] E-stop button wired correctly (NC)
  • [ ] No loose wires or exposed conductors
  • [ ] No cables interfering with wheel rotation
  • [ ] All screws tightened
  • [ ] Ultrasonic sensors unobstructed
  • [ ] IMU mounted flat and centered

First Power-On Procedure

  1. Press E-stop button DOWN (motors locked out)
  2. Connect battery XT30 connector
  3. Verify power LED on mainboard illuminates
  4. Check ESP32 serial output for boot messages
  5. Verify all sensor readings are reasonable
  6. Release E-stop button (twist to reset)
  7. Test motor movement with low speed commands

Troubleshooting

Symptom Likely Cause Fix
No power LED Battery disconnected or BMS tripped Check XT30, verify cell voltage
Motors don't spin E-stop active or relay wiring Check relay state, verify NC wiring
Wrong movement direction Motor wires swapped Swap IN1/IN2 wires for affected motor
Robot curves when going straight Wheel type swapped Verify roller direction (Step 3)
Ultrasonic reads max Wiring reversed or sensor blocked Check Echo/Trig pins, clear obstacles
IMU drift Bad mounting or calibration Re-mount flat, run calibration routine

After Assembly

Once powered on and confirmed working:

  1. Flash firmware — See Firmware Guide for ESP-IDF build and flash
  2. Basic SKU: Use Web Control or Web Basic for WiFi teleop
  3. Standard SKU: Install ROS2 on Pi 5, then follow Getting Started (AI)
  4. Full BOM details: See hardware/bom/README.md for pricing and sourcing