Raspberry pi 2

[kenken64]

I have connected the pins to the rpi 2 and also wire up the mbot. Getting distance 0 all the time please help. Running the serial demo. I have added some debug codes myself to the python program .

?U
Tx: [255, 85, 1, 2, 0, 0]
doing ultrasonic
?U1
Tx: [255, 85, 1, 4, 0, 0, 1, 49]
distance 0
doing ultrasonic
?U1
Tx: [255, 85, 1, 4, 0, 0, 1, 49]
distance 0
doing ultrasonic
?U1
Tx: [255, 85, 1, 4, 0, 0, 1, 49]
distance 0
doing ultrasonic
?U1
Tx: [255, 85, 1, 4, 0, 0, 1, 49]
distance 0