Set the scanning frequency of the X2 lidar

[ggjj11]

Thank you again for your nice product and software! I am trying to get the X2 do what I want :)

I noticed that the X2 rotates extremely fast (probably around 20 Hz, but surely above 10 Hz, although I only measured it "by eye") when plugging in the USB-C cable (and not running a program in the beginning). It rotates so fast that I wonder whether this is healthy for the X2. However, when starting a python script or (one of the provided programs in the SDK) which reads lidar data, the rotation speed is reduced to roughly 6Hz +/-1 Hz (standard deviation). I tried increasing/decreasing the speed of rotation via increasing the ROTATION_FREQ, e.g. to 10 [Hz]

laser.setlidaropt(ydlidar.LidarPropScanFrequency, ROTATION_FREQ); ... scan = ydlidar.LaserScan()

but having a look at two successive 'scan.stamp' times (in nanoseconds) only showed that I cannot really adapt the scanning frequencies like this: The scanning frequencies remained 6Hz +/-1 Hz (standard deviation).

Below you find the example script which I adapted from the example in this repository:

''''

import os import ydlidar import time import sys import matplotlib.pyplot as plt import matplotlib.animation as animation import numpy as np

ROTATION_FREQ=10 # in Hertz

fig = plt.figure() fig.canvas.set_window_title('YDLidar LIDAR Monitor') ax = plt.subplot() ax.autoscale_view(False,False,False) ax.grid(True) ports = ydlidar.lidarPortList(); port = "com3" for key, value in ports.items(): port = value;

laser = ydlidar.CYdLidar(); laser.setlidaropt(ydlidar.LidarPropSerialPort, port); laser.setlidaropt(ydlidar.LidarPropSerialBaudrate, 115200) #115200 laser.setlidaropt(ydlidar.LidarPropLidarType, ydlidar.TYPE_TRIANGLE); laser.setlidaropt(ydlidar.LidarPropDeviceType, ydlidar.YDLIDAR_TYPE_SERIAL); laser.setlidaropt(ydlidar.LidarPropScanFrequency, ROTATION_FREQ); laser.setlidaropt(ydlidar.LidarPropSampleRate, 3); laser.setlidaropt(ydlidar.LidarPropSingleChannel, True); scan = ydlidar.LaserScan()

scan_times=[]

def animate(num):

r = laser.doProcessSimple(scan);
if r:
    angle = []
    ran = []
    intensity = []
    scan_times.append(scan.stamp) #begin of scan, returned in nanoseconds 
    for point in scan.points:
        angle.append(point.angle);
        ran.append(point.range);
        intensity.append(point.intensity)
    print(len(intensity))
    angle = -np.array(angle) #minus because the ydlidar increases the angle clock-wise
    xs=np.array(ran)*np.cos(angle)
    ys=np.array(ran)*np.sin(angle)
    #timestamps=np.linspace(scan_times[-1]-scan_times[-2],num=xs.shape[0])
    ax.clear()
    ax.axis("equal")
    ax.set(xlim=(-3, 3), ylim=(-3, 3))
    ax.scatter(xs, ys, c=intensity, cmap='hsv', alpha=0.95, marker ='x')
    print('freq. in Hertz', 1/(np.diff(scan_times)*1e-9))
    plt.plot([0],[0], "go")

ret = laser.initialize(); if ret: ret = laser.turnOn(); if ret: ani = animation.FuncAnimation(fig, animate, interval=10) plt.show() laser.turnOff(); laser.disconnecting(); plt.close();

''''

This is maybe related to: https://github.com/YDLIDAR/ydlidar_ros/issues/1

Why can't I perform scans at this initial rotation frequency? This would be awesome! For the SLAM application I have in mind, it would be beneficial to have high frequency updates of measurements.

[yangfuyuan]

X2 cannot adjust the scanning frequency through sdk, it needs external pwm. The serial port DRT of the lidar adapter board is connected to the M_SCTR of the lidar. The DTR has two states, high and low, and the frequency of the fixed lidar is only two states.

[scholzol]

How can I stop the lidar (X2L) over the USB- adapter ? I couldn't find any command in the API. when I switsch off, the lidar rotates with that high frequency, which is really not healthy.

[halcyon1945]

i saw datasheet. x2 interface is only send to PC. no input(receive).