Unstable flight with LD-06 lidar for obstacle avoidance

Nightfury · September 16, 2024, 10:26am

Hello all,
I am trying to implement obstacle avoidance using LD-06 lidar on a quadcopter and I am facing problems with Lidar. The lidar seems to be measuring faulty distance when viewed on the proximity screen. When the copter takes off and when switched into obstacle avoidance mode in loiter the copter freaks out and starts to move abruptly. I tried to take it to a height where there were no obstacles and it seemed to let me control the directions. but once the copter comes close to an obstacle even though the obstacle is out the the minimum detection range the copter freaks out.
I did try to check whether the sensor is faulty using Rviz but the sensor works fine.
Please help me to sort out this issue
obstacle_param_list.param (19.5 KB)
link to drive for videos and log data:obstacle avoidance - Google Drive

Thanks in advance!

geofrancis · September 16, 2024, 10:51am

The sensor doesn’t work outdoors in direct sunlight.

Nightfury · September 16, 2024, 1:31pm

Dear Geofrancis,
Thank you for your inputs, but the Ld-06 lidar works well outdoors as mentioned by the manufacturer and I did test the sensors indoors. I have attached a Google Drive link testing sensors. It does fluctuate indoors. I believe that the driver present for the sensor is somehow bugged or out of date.

geofrancis · September 16, 2024, 1:36pm

good to know, I will look at my setup again, I couldn’t find any documentation on outdoor use I assumed it was the sensor, as I had seen similar noise in the results of the lidar it replaced when in direct sunshine.

I Have added a filter to my code to only use high-intensity returns to filter out the false returns but i have not tested it yet.

looking through the Ardupilot driver I don’t see it using the signal intensity for anything. so its probably the same issue as I am having with no filter set. where Rvis will have its filter set correctly so it’s not getting noise from sunlight around you.

does all the lidar noise go away on ardupilot if you take it into a dark room?

there is mention of the function but i cant find it implemented.

github.com

ArduPilot/ardupilot/blob/091ba2782cbee8f5eea59a5ffa87c8cdebc97ba0/libraries/AP_Proximity/AP_Proximity_LD06.cpp#L55


      
          
          /* ------------------------------------------
             Data Packet Structure:
             Start Character : 1 Byte
             Data Length : 1 Byte
             Radar Speed : 2 Bytes
             Start Angle : 2 Bytes
             Data Measurements : 36 Bytes
                 Contains 12 measurements of 3 Bytes each
                 Each measurement has 2 Bytes for distance to closest object
                 Each measurement has the 3rd Byte as measurement Confidence
             End Angle : 2 Bytes
             Timestamp : 2 Bytes
             Checksum : 1 Byte
             ------------------------------------------ */
          // ----> 47 data bytes in total for one packet
          
          // Update the sensor readings
          void AP_Proximity_LD06::update(void)
          {
             // Escape if no connection detected/supported while running

RVIS driver has the confidence set very high to filter out noise.

github.com

linorobot/ldlidar/blob/a85055214da78cd89e7a7b43d3aec62829f68d4d/include/tofbf.h#L12


      
          #define __TOFBF_H_

          

          #include <stdint.h>

          #include <vector>

          #include "lipkg.h"

          

          class Tofbf

          {

          private:

          	const int CONFIDENCE_LOW = 15;         /* Low confidence threshold */

              const int CONFIDENCE_SINGLE = 220;     /* Discrete points require higher confidence */

              const int SCAN_FRE = 4500;             /* Default scan frequency, to change, read according to radar protocol */

              double offset_x, offset_y;

              double curr_speed;

              Tofbf() = delete;

              Tofbf(const Tofbf &) = delete;

              Tofbf &operator=(const Tofbf &) = delete;

          public:

              Tofbf(int speed);

          	std::vector<PointData> NearFilter(const std::vector<PointData> &tmp) const;

              ~Tofbf();

@peterbarker could you have a look at this? I dont see signal confidence implemented on ardupilot for the ld06.

Nightfury · September 17, 2024, 9:10am

Hello Geofrancis,
I am eliminating the possibility of sunlight because I tested the lidar in a dark room and it still flickered. It still shows vague distance measurements. As we suspect, it should be done with the driver for LD-06.
let’s see if anyone has any other theories regarding this issue.
Thank you for responding

geofrancis · September 17, 2024, 12:23pm

It might be this buffer overflow issue. Try using the custom firmware builder to make the latest firmware to see if it’s fixed.

github.com/ArduPilot/ardupilot

AP_Proximity: prevent buffer overflow in LD06 driver

ArduPilot:master ← peterbarker:pr/ld06-fix

opened 01:51AM - 14 May 24 UTC

peterbarker

+21 -11

We're using a value off the wire before it has been validated. That value is us…ed to limit indexing into a buffer, and that buffer isn't big enough to handle all possible "bad" values that index could take on. Note that "read" here returns int16_t.... I've tried to simply make minimal changes in this driver to avoid the buffer overrun.

Nightfury · September 29, 2024, 9:12am

Hello again,
I’ll go through this and see whether it solves the issue.
Thanks for the advice:)