Motion Planning LiDAR A1M8

RPLidar A1M8 Setup and Use

RPLidar

These instructions are for an SLAMTEC RPLIDAR A1M8. This unit is used on the TurtleBot4 and can be added to the Unitree Go2.

Architecture

The collision avoidance and path checking code pre-computes 9 different paths, 4 to the left, one straight ahead, 4 to the right, and one to the back. For each of the 9 possible paths, the code checks whether the path approaches any detected object to within half_width_robot. If not, the path is considered to be a valid choice and the motion system can execute that path.

Assumptions

The code assumes that any unpredictable barriers (e.g. humans crossing the path of the robot) will be avoided using separate code within the action driver, such as by issuing a "STOP" command when an object is detected in front of the robot.

Setup

Run rptest.py (located in system_hw_test) to determine the sensor_mounting_angle and the angles_blanked. These values depend on how you mounted the sensor and the radial position of any fixed obstructions, such as mounting brackets.

"""
Robot and sensor configuration
"""
half_width_robot = 0.20  # the width of the robot is 40 cm
relevant_distance_max = 1.1  # meters
relevant_distance_min = 0.16 # meters
sensor_mounting_angle = 180.0  # corrects for how sensor is mounted
angles_blanked = [[-180.0, -160.0], [32.0, 46.6]]

How to determine the sensor_mounting_angle and the angles_blanked

• sensor_mounting_angle: The sensor_mounting_angle refers to the angle between the LIDAR sensor's scanning plane and the horizontal plane of your robot or platform. The sensor_mounting_angle can be read physically from the LIDAR. Refer to the following image for guidance:

sensor_mounting_angle

• angles_blanked: The angles_blanked array can be used to prevent fixed obstructions in the field of view of the LIDAR from producing erroneous object avoidance messages.

Unitree RPLidar

Determine the serial port the sensor is using:

ls /dev/tty.*
ls /dev/cu.*

Then, run

uv run rptest.py --serial /dev/cu.usbserial-0001

TurtleBot4

By default, the TurtleBot4 is configured to use the RPLidar A1M8. You can verify this by running:

ls -l /dev/RPLIDAR

To see the raw LIDAR data, provide the robot's URID (such as OM742d35Cc6634) and run:

uv run rptest.py --URID OM123435Cc1234

Typically, this command would be executed on your laptop, connected to the TurtleBot4 via Zenoh.

Using the RPLidar A1M8 in OM1

Configure the .json5 as needed:

"""
Robot and sensor configuration
"""
{
  "type": "RPLidar",
  "config": {
    "use_zenoh": true, # or false, if you are using serial to connect directly to the LIDAR
    "serial_port": "/dev/cu.usbserial-0001",
    "half_width_robot": 0.21, # the width of the robot is 40 cm
    "relevant_distance_max": 1.1, # meters
    "sensor_mounting_angle": 180.0, # corrects for how sensor is mounted relative to robot
    "angles_blanked": [[-180.0, -160.0], [32.0, 46.6]]
  }
}