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Using the Lord Microstrain IMU

This tutorial demonstrates how to use the Lord Microstrain IMU with the Open Source Leg platform.

Hardware Setup

  1. Connect the Lord Microstrain IMU to your computer via USB
  2. Note the device port (typically /dev/ttyUSB0)
  3. Mount the IMU securely with proper orientation
  4. Verify the LED indicators are active

This example shows how to:

  • Initialize and configure a Lord Microstrain IMU
  • Read orientation, angular velocity, and acceleration data
  • Log IMU measurements

Code Structure

The tutorial script is organized into several main sections:

1. Initialization

from opensourceleg.logging.logger import Logger
from opensourceleg.sensors.imu import LordMicrostrainIMU
from opensourceleg.utilities import SoftRealtimeLoop

FREQUENCY = 200
DT = 1 / FREQUENCY

if __name__ == "__main__":
    imu_logger = Logger(
        log_path="./logs",
        file_name="reading_imu_data",
    )
    clock = SoftRealtimeLoop(dt=DT)
    imu = LordMicrostrainIMU(
        tag="LordMicrostrainIMU",
        port=r"/dev/ttyS0",
        baud_rate=921600,
        frequency=FREQUENCY,
        update_timeout=500,
        max_packets=1,

This section:

  • Creates a data logger for recording measurements
  • Sets up a real-time loop for consistent timing
  • Initializes the LordMicrostrainIMU with specified parameters
  • Configures variable tracking for roll, pitch, and yaw angles

2. Main Loop

        offline=False,
    )
    imu_logger.track_variable(lambda: imu.roll, "Roll")
    imu_logger.track_variable(lambda: imu.pitch, "Pitch")
    imu_logger.track_variable(lambda: imu.yaw, "Yaw")

    with imu:
        for t in clock:
            imu.update()
            imu_logger.info(f"Time: {t}; Roll: {imu.roll}; Pitch: {imu.pitch}; Yaw: {imu.yaw};")

The main loop:

  1. Updates the IMU to get the latest reading
  2. Logs the time and current orientation data
  3. Updates the logger

IMU Parameters

When initializing the LordMicrostrainIMU, several important parameters can be configured:

    imu = LordMicrostrainIMU(
        tag="LordMicrostrainIMU",
        port=r"/dev/ttyS0",
        baud_rate=921600,
        frequency=FREQUENCY,
        update_timeout=500,
        max_packets=1,
        return_packets=False,
        offline=False,
    )

Parameter Details

  1. tag (str):

    • Unique identifier for the IMU instance
    • Useful when using multiple sensors
    • Defaults to "LordMicrostrainIMU"

  2. port (str):

    • Specifies the serial port where the IMU is connected
    • Default is /dev/ttyUSB0
    • Use ls /dev/ttyUSB* to see available devices

  3. baud_rate (int):

    • Communication speed for serial connection
    • Default is 921600 baud
    • Must match IMU's configured baud rate

  4. frequency (int):

    • Data streaming frequency in Hz
    • Default is 200 Hz
    • Higher rates provide more data but increase processing load

  5. update_timeout (int):

    • Timeout for data packet retrieval in milliseconds
    • Default is 500ms
    • Increase if data retrieval is unreliable

  6. max_packets (int):

    • Maximum number of data packets to retrieve per update
    • Default is 1
    • Higher values can buffer more data

  7. return_packets (bool):

    • If True, returns the raw data packets in the update() method
    • Default is False
    • Useful for advanced processing

Available Properties

The LordMicrostrainIMU provides several useful properties:

  1. Orientation (roll, pitch, yaw):

    • Current angular orientation in radians
    • Returned as Euler angles 
      imu.roll    # Rotation around X-axis
imu.pitch   # Rotation around Y-axis
imu.yaw     # Rotation around Z-axis

  2. Angular Velocity (vel_x, vel_y, vel_z):

    • Angular rates in radians per second 
      imu.vel_x   # Angular velocity around X-axis
imu.vel_y   # Angular velocity around Y-axis
imu.vel_z   # Angular velocity around Z-axis

  3. Linear Acceleration (acc_x, acc_y, acc_z):

    • Linear accelerations in m/s² 
      imu.acc_x   # Acceleration along X-axis
imu.acc_y   # Acceleration along Y-axis
imu.acc_z   # Acceleration along Z-axis

  4. Raw Data:

    • Access to complete data packet 
      imu.data    # Dictionary with all available channels

Running the Example

  1. Navigate to the tutorial directory: 

    cd tutorials/sensors

  2. Run the script: 

    python imu.py

  3. Expected behavior:

    • IMU begins reading orientation data continuously at 200Hz
    • Data is logged to ./logs/reading_imu_data.csv
    • Roll, pitch, and yaw values update as you rotate the IMU

Common Issues

  • Device Not Found: Verify connections and run ls /dev/ttyUSB*
  • Permission Denied: Add user to dialout group: sudo usermod -a -G dialout $USER
  • Incorrect Readings: Check IMU orientation and mounting
  • Missing Data: Verify baud rate and connection quality
  • MSCL Import Error: Install the MSCL library from Lord Microstrain

Additional Resources

If you have any questions or need further assistance, please post on the Open Source Leg community forum.