WT901C485 ROS 2 Driver (RS-485 Modbus IMU)

This repository provides a ROS 2 driver for the WT901C485 RS-485 IMU operating in Modbus RTU mode.

The package offers plug-and-play ROS 2 nodes that communicate with the WT901C485 over RS-485 (Modbus RTU) and publish standard ROS sensor messages, making it suitable for:

• robot_localization
• Nav2
• Mobile robots
• Mapping, localization, and sensor fusion pipelines

This driver follows the industrial-correct Modbus polling model required by the WT901C485.

⚠️ Important
The WT901C485 does NOT support UART streaming.
All data must be acquired using Modbus RTU polling.

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🔌 Hardware Setup

Required Hardware

• WT901C485 IMU (RS-485 variant)
• USB → RS-485 converter
  (CH340 / FTDI based, auto-direction control recommended)
• External 5V power supply for the IMU

Wiring

WT901C485	RS-485 Adapter
A / A+	A / A+
B / B−	B / B−
GND	GND
VCC	External 5V

⚠️ Do NOT power the IMU from TTL VCC pins on the converter
⚠️ Do NOT use UART / TTL mode — this IMU works only in RS-485 Modbus mode

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🖥️ Software Requirements

• Ubuntu 22.04 or Ubuntu 24.04
• ROS 2 Humble or ROS 2 Jazzy
• Python ≥ 3.10
• pyserial

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📦 Installation & Setup

Clone and Install

cd ~/ros2_ws/src
git clone https://github.com/Smokey8979/wt901c_ros2.git
cd wt901c_ros2
chmod +x install.sh
./install.sh
sudo reboot

What the Install Script Does

• Installs required system dependencies
• Enables USB–RS485 kernel modules (CH340 support)
• Removes conflicting services (brltty)
• Adds udev rules for stable device naming
• Adds the user to the dialout group
• Installs the IMU plugin for rviz2

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🔨 Build the Package

cd ~/ros2_ws
colcon build --packages-select wt901c_imu
source install/setup.bash

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🚀 Running the Nodes

⚠️ Important Notes

• Temperature data is available
• Altitude data is currently inaccurate (derived from pressure)
• Altitude improvements are planned in future releases

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1️⃣ Basic IMU

Accelerometer + Gyroscope + Orientation

ros2 run wt901c_imu wit_basic_imu_node \
  --ros-args \
  -p port:=/dev/ttyUSB0 \
  -p frame_id:=imu_link

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2️⃣ IMU + Magnetometer

ros2 run wt901c_imu wit_imu_node_mag \
  --ros-args \
  -p port:=/dev/ttyUSB0 \
  -p frame_id:=imu_link \
  -p rate:=20.0

Temperature is currently a placeholder in this node.

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3️⃣ Test / Diagnostic Node

IMU + Magnetometer + Barometer

ros2 run wt901c_imu test_imu_node \
  --ros-args \
  -p port:=/dev/ttyUSB0 \
  -p rate:=20.0 \
  -p mag_reg:=61 \
  -p baro_reg:=63

Alternative:

ros2 run wt901c_imu wit_imu_node

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4️⃣ Full IMU (Robot Deployment & Calibration)

This node is intended for real-robot integration and supports on-device IMU calibration.

⚠️ Important Notes

• Altitude is derived from pressure and is currently inaccurate
• Allow the IMU to complete calibration after startup
• Gravity compensation can be optionally disabled
• Recommended for EKF / real-world navigation setups

ros2 run wt901c_imu wit_imu_with_cal_node

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🔍 Verification & Visualization

Check Topics

ros2 topic list

Visualize in RViz2

rviz2

Set the fixed frame to imu_link and add IMU-related topics.

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🧪 Debug & Diagnostics

Scan IMU Registers (Low-Level Debug)

Use this only if IMU data is not publishing correctly.

cd ~/ros2_ws/src/wt901c_ros2/
chmod +x check_reg.py
python3 check_reg.py

Official Register Documentation

WT901C485 register map and functions:
https://images-na.ssl-images-amazon.com/images/I/A1YLf4otHWL.pdf

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📡 Published Topics

Topic	Message Type	Description
/imu/data	sensor_msgs/Imu	Acceleration, angular velocity, orientation
/imu/mag	sensor_msgs/MagneticField	Magnetometer
/imu/temperature	sensor_msgs/Temperature	Temperature
/imu/pressure	sensor_msgs/FluidPressure	Barometric pressure
/imu/altitude	std_msgs/Float64	Altitude (derived, inaccurate)

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✨ Features

• Industrial-grade RS-485 Modbus RTU polling
• Accelerometer, gyroscope, magnetometer support
• Orientation (Euler → Quaternion)
• Barometer / pressure data
• ROS-standard message interfaces
• Parameter-driven configuration
• Compatible with robot_localization and Nav2
• Works on ROS 2 Humble and Jazzy
• Designed for real-robot deployment
• Supports EKF fusion with wheel odometry and other sensors

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📌 Important Notes

• WT901C485 does not support UART streaming
• Modbus polling is mandatory
• Register addresses may vary by firmware version
• USB–RS485 adapters must support automatic TX/RX direction switching

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🆘 Support

For questions, issues, or contributions:

📧 sdhudu@gmail.com

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📄 License

MIT License