In ROS2 Basics Python Real Robot Project, the robot's rear side reading doesn't change

[navjotsinghsodhi52]

Hello, I was testing the real turtlebot robot in the lab environment. I found an issue with the robot’s rear side reading. I found that regardless of the position of the robot, the rear side’s distance reading stays almost equivalent to 0.073m. Seems like there is some element blocking the rear side reading. I created the debug script and also checked the laser data. I got the readings for all the sides using the script. I was testing the part-2, where the robot has to find the nearest wall, however, it always shows the nearest wall to be at the rear side because that reading remains the minimum of all. Due to this, I am not able to align the robot to the nearest wall. My program worked perfectly in the simulation. I have attached the images for reference as well. The rear side is at 180 degrees. Please check it and update accordingly. I checked this at different positions of the robot. Even when right wall was the nearest, it still showed rear to be the nearest. So, I am pretty sure that the rear reading isn’t correct.

Here, is the debugging output:
user:~/ros2_ws$ ros2 run lidar_utils laser_debugger_executable

[INFO] [1769263672.636345905] [laser_debugger]: Laser Debugger Node Started

[INFO] [1769263673.009498286] [laser_debugger]: [SCAN META] angle_min=0.000, angle_max=6.283, increment

t=0.01399, ranges=451

[INFO] [1769263673.010179777] [laser_debugger]: [FRONT (0°)] angle=0.00 rad | idx=0 | dist=1.075 m

[INFO] [1769263673.010776564] [laser_debugger]: [LEFT (90°)] angle=1.57 rad | idx=112 | dist=0.393 m

[INFO] [1769263673.011420238] [laser_debugger]: [REAR (180°)] angle=3.14 rad | idx=225 | dist=0.073 m

[INFO] [1769263673.012072193] [laser_debugger]: [RIGHT (270°)] angle=4.71 rad | idx=337 | dist=0.472 m

[INFO] [1769263673.012646551] [laser_debugger]: --------------------------------------------------

[INFO] [1769263674.109149948] [laser_debugger]: [SCAN META] angle_min=0.000, angle_max=6.283, increment

t=0.01406, ranges=449

[INFO] [1769263674.109822351] [laser_debugger]: [FRONT (0°)] angle=0.00 rad | idx=0 | dist=1.075 m

[INFO] [1769263674.110407840] [laser_debugger]: [LEFT (90°)] angle=1.57 rad | idx=112 | dist=0.393 m

[INFO] [1769263674.111021106] [laser_debugger]: [REAR (180°)] angle=3.14 rad | idx=224 | dist=0.797 m

[INFO] [1769263674.111684462] [laser_debugger]: [RIGHT (270°)] angle=4.71 rad | idx=335 | dist=0.471 m

[INFO] [1769263674.112043227] [laser_debugger]: --------------------------------------------------

[INFO] [1769263675.206980012] [laser_debugger]: [SCAN META] angle_min=0.000, angle_max=6.283, increment=0.01406, ranges=449

[INFO] [1769263675.207937122] [laser_debugger]: [FRONT (0°)] angle=0.00 rad | idx=0 | dist=inf m

[INFO] [1769263675.208577974] [laser_debugger]: [LEFT (90°)] angle=1.57 rad | idx=112 | dist=0.393 m

[INFO] [1769263675.209235142] [laser_debugger]: [REAR (180°)] angle=3.14 rad | idx=224 | dist=0.072 m

[INFO] [1769263675.209812944] [laser_debugger]: [RIGHT (270°)] angle=4.71 rad | idx=335 | dist=0.471 m

[INFO] [1769263675.210424864] [laser_debugger]: --------------------------------------------------

[rtellez]

Hi,
there are two points there:

1. There is an object behind the real robot at the point you specify: it is the stick that holds the power cable, so the robot can be powered 24/7. You should filter that ray and discard it as it did not exist, since the distance it is measuring belongs to its own body not to a real obscale.
2. The simulation differs from the real robot. This is an error that we are going to correct in the short term, so both simulation and real robot have the same type of lidar configuration (same number of rays and so on.

So you need to adapt your robot program to those variations from simulation in the real robot in order to work.

Let me state that those things usually happen in real life. The simulation and the real robot do not always match, so you need to take this into account.

Let me tell you that I was impressed by your analysis of the situation and how well you explained the problem. Keep pushing, you are doing an excellent job!