clover/docs/en/laser.md

Working with a laser rangefinder

Rangefinder VL53L1X

The rangefinder model recommended for Clever is STM VL53L1X. This rangefinder can measure distances from 0 to 4 m while ensuring high measurement accuracy.

The image for Raspberry Pi contains pre-installed corresponding ROS driver.

Connecting to Raspberry Pi

Note

For correct operation of a laser rangefinder with a flight countroller custom PX4 firmware is needed. See more about firmware in corresponding article.

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Connect the rangefinder to pins 3V, GND, SCL and SDA via the I²C interface:

If the pin marked GND is occupied, you can use another free one using the pinout.

Hint Via the I²C interface, you can connect several peripheral devices simultaneously. For this purpose, use a parallel connection.

Enabling

Connect via SSH and edit file ~/catkin_ws/src/clever/clever/launch/clever.launch so that driver VL53L1X is enabled:

<arg name="rangefinder_vl53l1x" default="true"/>

By default, the rangefinder driver sends the data to Pixhawk (via topic /mavros/distance_sensor/rangefinder_sub). To view data from the topic, use command:

rostopic echo mavros/distance_sensor/rangefinder_sub

PX4 settings

To use the rangefinder data in PX4 must be configured.

When using EKF2 (SYS_MC_EST_GROUP = ekf2):

• EKF2_HGT_MODE = 2 (Range sensor) – when flying over horizontal floor;
• EKF2_RNG_AID = 1 (Range aid enabled) – in other cases.

When using LPE (SYS_MC_EST_GROUP = local_position_estimator, attitude_estimator_q):

• The "pub agl as lpos down" flag is ticked in the LPE_FUSION parameter – when flying over horizontal floor.

Obtaining data from Python

To obtain data from the topic, create a subscriber:

from sensor_msgs.msg import Range

# ...

def range_callback(msg):
    # Processing new data from the rangefinder
    print 'Rangefinder distance:', msg.range

rospy.Subscriber('mavros/distance_sensor/rangefinder_sub', Range, range_callback)

Data visualization

To build a chart using the data from the rangefinder, one can use rqt_multiplot.

rviz may be used for data visualization. To do this, add a topic of the sensor_msgs/Range type to visualization:

See read more about rviz and rqt.