Servo Motor Wiring

Connect servo motors to PCA9685 channels for panel actuation

Learn how to connect and organize servo motors to the PCA9685 controller.

About MG996R Servo Motors

Specifications

• Torque: 10 kg·cm @ 4.8V, 11 kg·cm @ 6V
• Speed: 0.17 sec/60° @ 4.8V
• Voltage: 4.8V - 6V (5V optimal)
• Current: ~500mA stall, ~200mA idle
• Rotation: 180° (0° to 180°)
• Connector: 3-pin standard servo connector

Wire Color Code

Orange/Yellow

Signal (PWM control)

Red

Power (+5V)

Brown/Black

Ground (−)

Servo Channel Assignments

The PCA9685 has 16 channels (0-15). Each channel controls one servo motor. Channel assignment determines which motor moves when the code executes. Map your servos to channels based on your physical panel layout.

Standard 4×3 Grid Layout (7 Active Motors)

Default configuration for cloth folding robot. Motor numbering starts from top-left, going row by row.

Channel #	Panel Name	Panel Type	Physical Location
0	Motor 1	Motorized Module	Top-Left
1	Motor 2	Motorized Module	Top-Center-Left
2	Motor 3	Motorized Module	Top-Center-Right
3	Motor 4	Motorized Module	Top-Right
4	Motor 5	Motorized Module	Middle-Left
5	Motor 6	Motorized Module	Middle-Right
6	Motor 7	Motorized Module	Bottom-Center
7-15	Unused	Available for expansion	—

💡 Tip: You can customize this mapping for different layouts. The motion plans inconfig.py reference channel numbers, not physical locations.

Wiring Procedure

Step 1: Prepare Servo Connectors
- • Servos come with 3-pin female connectors (fits PCA9685 pin headers)
- • Check wire colors match standard: Orange/Yellow (signal), Red (power), Brown/Black (ground)
- • If colors differ, consult servo datasheet before connecting
Step 2: Identify PCA9685 Channel Headers
- • 16 servo output headers labeled 0-15 on the board
- • Each header has 3 pins arranged vertically
- • Pin arrangement (top to bottom): Signal (yellow), V+ (red), GND (black)
Step 3: Connect Servos to Channels
- • Ensure power supply is disconnected
- • Align servo connector with channel header (noting wire color positions)
- • Firmly press connector onto header pins (should click into place)
- • Repeat for all servos according to your channel mapping
Step 4: Verify Connections
- • Check each servo connector is fully seated (no exposed pins)
- • Verify wire colors align with PCA9685 pin labels
- • Ensure no connectors are inserted backwards
- • Tug gently on each connector to confirm secure fit

Servo Connection Diagram


    PCA9685 Servo Driver Board
    ┌─────────────────────────────────┐
    │                                 │
    │  Channel Headers (3-pin each)   │
    │  ┌───┬───┬───┬───┬───┬───┐     │
    │  │ 0 │ 1 │ 2 │ 3 │ 4 │ 5 │...  │
    │  ├───┼───┼───┼───┼───┼───┤     │
    │  │ S │ S │ S │ S │ S │ S │ S   │  ← Signal (Orange/Yellow)
    │  │ + │ + │ + │ + │ + │ + │ +   │  ← V+ (Red)
    │  │ − │ − │ − │ − │ − │ − │ −   │  ← GND (Brown/Black)
    │  └─┬─┴─┬─┴─┬─┴─┬─┴─┬─┴─┬─┘     │
    │    │   │   │   │   │   │       │
    └────┼───┼───┼───┼───┼───┼───────┘
         │   │   │   │   │   │
         │   │   │   │   │   │
    ┌────▼┐ ┌▼──┐ ┌▼──┐ ┌▼──┐ ┌▼──┐ ┌▼──┐
    │Srv 0│ │Sr1│ │Sr2│ │Sr3│ │Sr4│ │Sr5│
    │(M1) │ │M2 │ │M3 │ │M4 │ │M5 │ │M6 │
    └─────┘ └───┘ └───┘ └───┘ └───┘ └───┘

    Each servo receives:
    • PWM signal on orange/yellow wire (0-180° position control)
    • 5V power on red wire (from external power supply via V+ terminal)
    • Ground on brown/black wire (common with Pico and power supply)

📷 Servo Wiring Photo Placeholder

Photo showing multiple servos connected to PCA9685 will be added here

Cable Management Tips

Organization

• Route servo cables along panel frame edges
• Use zip ties or cable clips every 10-15cm
• Group cables by row or section
• Leave slack (5-10cm) at servo end for panel movement
• Label each cable with channel number

Extension Cables

• Use servo extension cables if servos are far from PCA9685
• Maximum recommended length: 1 meter per cable
• Longer cables may cause signal degradation
• Match extension cable polarity (colors align)
• Avoid running extensions near power wires

Testing Individual Servos

Single Servo Test

1. Connect only ONE servo to Channel 0
2. Power on the system (USB + 5V power supply)
3. Upload the Fabrica code to Pico
4. Servo should initialize to 0° position on startup
5. Press Button 1 to trigger motion plan for Channel 0
6. Servo should rotate 0° → 180° → 0° smoothly

Troubleshooting Servo Issues

❌

Servo doesn't move:

Check power connections, verify servo connector polarity

❌

Servo jitters/buzzes:

Insufficient power supply current, add capacitor, reduce servo count

❌

Wrong rotation range:

Calibrate SERVO_MIN_PULSE and SERVO_MAX_PULSE in config.py

Best Practices

✅ Do

• Test each servo individually before full assembly
• Use high-quality servos (metal gears recommended)
• Secure servo cables to prevent pulling on connectors
• Keep spare servos for quick replacement
• Document your channel mapping

❌ Avoid

• Forcing servo rotation beyond 180° (damages gears)
• Hot-swapping servos while powered on
• Using damaged or stripped servo connectors
• Running all servos at max load simultaneously without adequate power
• Mixing different servo models (different speeds/torques)

Code Configuration

Servo settings are defined in config.py:

# Servo Channel Configuration
NUM_SERVOS = 7  # Total servos connected (0-15 max)

# Servo Calibration (MG996R defaults)
SERVO_MIN_PULSE = 500   # Minimum pulse width (0°)
SERVO_MAX_PULSE = 2400  # Maximum pulse width (180°)
SERVO_FREQ = 50         # PWM frequency in Hz

# Motion Control
SERVO_SPEED = 100       # Degrees per second
SERVO_ACCELERATION = 50 # Smoothing for starts/stops

# Channel Mapping (customize for your layout)
CHANNEL_MAP = {
    0: "Motor 1 (Top-Left)",
    1: "Motor 2 (Top-Center-Left)",
    2: "Motor 3 (Top-Center-Right)",
    3: "Motor 4 (Top-Right)",
    4: "Motor 5 (Middle-Left)",
    5: "Motor 6 (Middle-Right)",
    6: "Motor 7 (Bottom-Center)"
}

Adjust MIN_PULSE and MAX_PULSE if your servos have different rotation range.