Wiring & Connections - Robotic Arm System for Beginners

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Port Assignment Overview
VEX IQ Brain Port Map
Wiring Diagram
Motor Connections
Motor Configuration Code
Motor Direction Settings
Motor Torque Settings
Sensor Connections
Sensor Configuration Code
Distance Sensor Mounting
Bumper Sensor Mounting
TouchLED Placement
Serial Communication Setup
Hardware Connection
Cable Specifications
Port Configuration
Message Protocol
Troubleshooting Serial Connection
Camera Connection
USB Camera Setup
Power Considerations
Grounding and EMI
Common Ground
EMI Considerations
Safety Guidelines
Emergency Stop Procedure
Verification Checklist
Wiring Best Practices
Next Steps

This guide provides detailed port assignments, connection diagrams, and safety considerations for wiring the robotic arm system.

Port Assignment Overview

VEX IQ Brain Port Map

Motors (1-4)
Sensors (7-10)
Built-in

Port	Component	Direction	Notes
PORT1	Base Motor	Reversed	360° rotation with inertial feedback
PORT2	Shoulder Motor	Reversed	Max torque: 95%, bumper safety
PORT3	Elbow Motor	Reversed	Max torque: 95%
PORT4	Gripper Motor	Reversed	Current sensing: 0.3-0.5A

Port	Component	Type	Range/Function
PORT7	Gripper Distance	Distance	0-40mm for pick detection
PORT8	TouchLED	LED	RGB status indicator
PORT9	Base Distance	Distance	50-345mm for scanning
PORT10	Bumper Sensor	Digital	Shoulder collision detection

Component	Type	Function
Inertial Sensor	Built-in	0-360° heading tracking
Brain Screen	Built-in	Status display and debugging
Serial Port	`/dev/serial1`	USB communication

Wiring Diagram

Motor Connections

Motor Configuration Code

From vex_brain/src/main.py:169-178:

class ControlModule:
    def __init__(self, sensor_module: SensorModule):
        # Motor initialization (True = reversed direction)
        self.base_motor = Motor(Ports.PORT1, True)
        self.shoulder_motor = Motor(Ports.PORT2, True)
        self.elbow_motor = Motor(Ports.PORT3, True)
        self.gripper_motor = Motor(Ports.PORT4, True)
        
        # Safety torque limits (95% to prevent damage)
        self.elbow_motor.set_max_torque(95, PERCENT)
        self.shoulder_motor.set_max_torque(95, PERCENT)

Motor Direction Settings

All motors are configured with reversed=True. This is specific to the mechanical assembly. If your motors rotate in the wrong direction, toggle the True/False parameter.

Testing Motor Direction:

# Test each motor individually
self.base_motor.spin(FORWARD, 50, RPM)      # Should rotate clockwise (top view)
self.shoulder_motor.spin(FORWARD, 30, RPM)  # Should raise arm
self.elbow_motor.spin(FORWARD, 30, RPM)     # Should extend arm
self.gripper_motor.spin(FORWARD, 20, RPM)   # Should open gripper

Motor Torque Settings

Motor	Max Torque	Reason
Base	100% (default)	Low load, smooth rotation
Shoulder	95%	High load, prevent gear damage
Elbow	95%	High load, prevent gear damage
Gripper	100% (default)	Current sensing used instead

The shoulder and elbow motors are limited to 95% torque to prevent mechanical damage during unexpected collisions or high-load situations.

Sensor Connections

Sensor Configuration Code

From vex_brain/src/main.py:63-71:

class SensorModule:
    def __init__(self):
        self.brain = Brain()
        self.inertial = Inertial()
        self.gripper_distance = Distance(Ports.PORT7)
        self.touchled = Touchled(Ports.PORT8)
        self.base_distance = Distance(Ports.PORT9)
        self.bumper = Bumper(Ports.PORT10)

Distance Sensor Mounting

PORT7: Gripper Distance
PORT9: Base Distance

Location: Mounted on gripper, facing forwardOrientation: Sensor should point toward the center of the gripper openingDetection Zone: 0-40mm directly in front of gripperPurpose: Detects when object is within grasp rangeWiring: Use shortest VEX smart cable to avoid interference

Cable Management for Base Sensor: The base rotates 360°. Ensure the cable has enough slack and is routed through the center of rotation to prevent disconnection.

Bumper Sensor Mounting

PORT10: Bumper

Location: Mounted at maximum shoulder extension point
Trigger: Should activate only when shoulder reaches mechanical limit
Safety: Prevents shoulder from exceeding safe range of motion
Wiring: Route cable along shoulder joint, secure to prevent snagging

TouchLED Placement

PORT8: TouchLED

Location: Visible location on robot body (front or top)
Purpose: Visual status feedback for debugging and operation
View: Should be visible from normal viewing angle
Wiring: Short cable, can be mounted near brain

Serial Communication Setup

Hardware Connection

Cable Specifications

Type: Standard USB A to Micro-USB cable
Length: 1-2 meters recommended for flexibility
Quality: Use shielded cable to minimize EMI

Port Configuration

VEX Brain Side
Raspberry Pi Side

Device Path: /dev/serial1Initialization (vex_brain/src/main.py:32-36):

def initialize(self):
    try:
        self.serial_port = open('/dev/serial1', 'rb+')
    except:
        raise Exception('serial port error')

Settings:

Baud rate: Not specified (USB CDC virtual serial)
Data format: 8N1 (default)
Flow control: None

Device Path: /dev/ttyACM1 (or /dev/ttyACM0 if only one device)Initialization (communication/serial_manager.py:18-24):

def __init__(self, port: str='/dev/ttyACM1', baudrate: int = 115200):
    self.port = port
    self.baudrate = baudrate
    self.message_end = b'\n'

Connection (communication/serial_manager.py:52-74):

def connect(self) -> bool:
    try:
        self.serial_port = serial.Serial(
            port=self.port, 
            baudrate=115200,
            timeout=10,
            write_timeout=10
        )
        self.is_connected = True
        
        # Start read loop thread
        self._read_thread = Thread(target=self._read_loop, daemon=True)
        self._read_thread.start()
        return True
    except Exception as e:
        log.error(f'Error connecting to serial port: {str(e)}')
        return False

Settings:

Baud rate: 115200
Timeout: 10 seconds
Threading: Daemon thread for continuous read

Message Protocol

Format: JSON messages terminated with newline (\n) Structure:

{
  "type": "service_name",
  "data": { /* service-specific data */ }
}

Example - Scan Service Request:

{"type": "scan_service", "data": {"speed": 20}}

Example - Scan Service Response:

{
  "type": "scan_service",
  "data": {
    "state": "detected",
    "angle": 127.5,
    "distance": 180,
    "size": 342
  }
}

Troubleshooting Serial Connection

Raspberry Pi cannot find /dev/ttyACM1

Check connected devices:

ls /dev/ttyACM*

Possible outputs:

/dev/ttyACM0 - Use this instead
No output - VEX Brain not detected

Solutions:

Try different USB port
Check USB cable (must support data, not just power)
Verify VEX Brain is powered on
Check dmesg for connection errors:
```
dmesg | tail -20
```

Connection established but no messages received

Check:

VEX Brain program is running
Serial port opened correctly on both sides
Message format is valid JSON

Debug VEX side:

# Add to VEX main.py
self.sensor.print_screen("Serial OK", 1, 1)

Debug Raspberry Pi side:

# Enable debug logging
import logging
logging.basicConfig(level=logging.DEBUG)

Messages corrupted or incomplete

Possible causes:

Baud rate mismatch (should be 115200)
Buffer overflow from too many messages
Cable quality/EMI issues

Solution:

# Both sides validate JSON before processing
try:
    data = json.loads(message)
except json.JSONDecodeError:
    log.error(f'Invalid JSON: {message}')
    continue

Camera Connection

USB Camera Setup

Connection: USB camera → Raspberry Pi USB port Configuration (perception/vision/camera/main.py:6-9):

class CameraManager:
    def __init__(self, camera_index: int = 0, width: int = 1280, height: int = 720):
        self.cap = cv2.VideoCapture(camera_index)
        self.cap.set(cv2.CAP_PROP_FRAME_WIDTH, width)
        self.cap.set(cv2.CAP_PROP_FRAME_HEIGHT, height)

Camera Index:

0: First camera (built-in or first USB)
1: Second camera
/dev/video0: Specific device path

Test Camera:

# List available cameras
ls /dev/video*

# Test camera with v4l2
v4l2-ctl --list-devices

# Capture test image
fswebcam -r 1280x720 test.jpg

Power Considerations

Raspberry Pi Power

Supply: 5V 3A USB-C (Pi 4/5) or micro-USB (Pi 3)Consumption:

Idle: ~2.5W
With camera: ~3.5W
With AI inference: ~5-7W

Recommendation: Official Raspberry Pi power supply or equivalent quality

VEX Brain Power

Supply: VEX IQ Battery (rechargeable)Capacity: Typically 2000mAhRuntime: 1-2 hours depending on motor usageRecommendation: Keep spare battery charged

Do NOT attempt to power the Raspberry Pi from the VEX Brain or vice versa. Each requires its own independent power supply.

Grounding and EMI

Common Ground

The USB connection between Raspberry Pi and VEX Brain provides a common ground reference. No additional grounding is required.

EMI Considerations

Potential interference sources:

Motor PWM signals
Switching power supplies
Long unshielded cables

Mitigation:

Use shielded USB cable for serial connection
Route power cables away from sensor cables
Secure all connections to prevent intermittent contact
Use cable ties for strain relief

Safety Guidelines

Electrical Safety

Never hot-swap motor or sensor connections
Power off VEX Brain before changing wiring
Inspect cables for damage before operation
Ensure all connections are fully seated

Mechanical Safety

Verify bumper sensor triggers before full operation
Test emergency stop procedures
Keep fingers clear of moving parts
Secure loose cables away from rotating base

Emergency Stop Procedure

Software Emergency Stop (vex_brain/src/main.py:200-202):

def general_stop(self):
    for m in [self.base_motor, self.shoulder_motor, 
              self.elbow_motor, self.gripper_motor]:
        m.stop()

Hardware Emergency Stop: Power off VEX Brain

Verification Checklist

Visual Inspection

All motors connected to correct ports (1-4)
All sensors connected to correct ports (7-10)
USB cable connected between Pi and VEX Brain
Camera connected to Raspberry Pi USB
Both devices have independent power supplies
No cables obstructing moving parts

Power-On Test

VEX Brain powers on (screen lights up)
Raspberry Pi powers on (LED activity)
TouchLED lights up (white on init)
Camera detected (ls /dev/video*)

Hardware Check Service

Run the check service:

robot.serial_manager.send_message('check_service', {})

Expected response:

{"type": "check_service", "data": {"state": "approved"}}

Check service passes
All motors respond
All sensors read values

Communication Test

Serial connection established (/dev/ttyACM1)
Messages sent successfully
Responses received
No JSON decode errors

Safety Test

Run the safety service:

robot.serial_manager.send_message('safety_service', {})

Shoulder raises until bumper pressed
LED turns red on collision
Shoulder retracts automatically
Gripper opens fully
LED turns green when complete

Wiring Best Practices

Cable Management

Use cable ties to secure bundles
Leave slack for moving joints
Route through center of rotating base
Label cables for easy identification

Strain Relief

Secure cables near connectors
Avoid sharp bends
Use clips or guides for routing
Test full range of motion

Connector Care

Push connectors fully until click
Don’t pull on cables, hold connector
Check for bent pins
Clean contacts if intermittent

Documentation

Take photos of final wiring
Mark port assignments on robot
Keep wiring diagram accessible
Note any custom modifications

Next Steps

Software Architecture

Learn how the hardware components are controlled by software

Communication Protocol

Deep dive into the serial communication protocol

Quick Start Tutorial

Get your system running with a step-by-step tutorial

Sensors

Architecture Overview

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Getting Started

Hardware Setup

Software Architecture

Computer Vision

Tutorials

​Port Assignment Overview

​VEX IQ Brain Port Map

​Wiring Diagram

​Motor Connections

​Motor Configuration Code

​Motor Direction Settings

​Motor Torque Settings

​Sensor Connections

​Sensor Configuration Code

​Distance Sensor Mounting

​Bumper Sensor Mounting

​TouchLED Placement

​Serial Communication Setup

​Hardware Connection

​Cable Specifications

​Port Configuration

​Message Protocol

​Troubleshooting Serial Connection

​Camera Connection

​USB Camera Setup

​Power Considerations

Raspberry Pi Power

VEX Brain Power

​Grounding and EMI

​Common Ground

​EMI Considerations

​Safety Guidelines

​Emergency Stop Procedure

​Verification Checklist

​Wiring Best Practices

Cable Management

Strain Relief

Connector Care

Documentation

​Next Steps

Software Architecture

Communication Protocol

Quick Start Tutorial

Build docs developers (and LLMs) love

Port Assignment Overview

VEX IQ Brain Port Map

Wiring Diagram

Motor Connections

Motor Configuration Code

Motor Direction Settings

Motor Torque Settings

Sensor Connections

Sensor Configuration Code

Distance Sensor Mounting

Bumper Sensor Mounting

TouchLED Placement

Serial Communication Setup

Hardware Connection

Cable Specifications

Port Configuration

Message Protocol

Troubleshooting Serial Connection

Camera Connection

USB Camera Setup

Power Considerations

Grounding and EMI

Common Ground

EMI Considerations

Safety Guidelines

Emergency Stop Procedure

Verification Checklist

Wiring Best Practices

Next Steps