bottom IR sensors looks inconsistent

[nohzen]

I have tested IR sensors and noticed that bottom left and right IR sensor values are not consistent.

I used the following script to check sensor values.

from zumi.zumi import Zumi

zumi = Zumi()

ir_datas = zumi.get_all_IR_data()
front_right = ir_datas[0]
bottom_right = ir_datas[1]
back_right = ir_datas[2]
bottom_left = ir_datas[3]
back_left = ir_datas[4]
front_left = ir_datas[5]

print("IR datas:\nFront   left {}, right {}\nBack    left {}, right {}\nBottom  left {}, right {}\n"
      .format(front_left, front_right, back_left, back_right, bottom_left, bottom_right))

Upside down

IR datas:
Front   left 171, right 172
Back    left 163, right 133
Bottom  left 239, right 240

All sensor values are large because there are no obstacle to reflect IR radiation.
It looks fine.

Obstacle in front of zumi

IR datas:
Front   left 29, right 14
Back    left 157, right 132
Bottom  left 13, right 68

Front IR sensor values become smaller due to obstacle.
Bottom IR sensor values also become smaller, but there are more than 50 discrepancy between left and right values.

Obstacle behind zumi

IR datas:
Front   left 168, right 180
Back    left 18, right 13
Bottom  left 13, right 76

Back IR sensor values become smaller due to obstacle.

Box bellow zumi

IR datas:
Front   left 169, right 173
Back    left 158, right 132
Bottom  left 39, right 113

Floor of zumi are changed from white paper to cardboard box.
There are still large difference between left and right IR sensor values.
Do you have any idea why bottom left and right sensor values are so different?

[nohzen]

@robolink_leila Thank you very much for your quick reply.
I see, I will use different threshold for each IR sensors!

[robolink_leila]

@nohzen Not all IR sensors will be exactly the same so that behavior is very normal. Just set different thresholds for each IR sensor for detecting objects