Beam bot 9v/Herbie photovore

Im am working on my second bot. I think its called a Herbie bot or something like that.Oobviously I'm new to this. I am currently building the circuit on a breadboard. I had tried many attempts to make it work but i had failed miserably.

Since Im new, how should the motors act? If I cover one of any of the Photodiodes, should one motor stall? If I shine light on one of the photodiodes, should one motor increase speed?

I followed this diagram, built it exaclty as shown but only one photodiode seems effect the motor. The other on the right side doesn't no matter how much or how little light it gets. I tested it out to see if it was broken but it works perfectly fine.


Heres the diagram I am following.This photo was shown to me by a friend, it had been previously posted on this site a while ago.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=6820&d=1233016040

 

When I exchange them, one motor still doesn't change.

 

Nevermind, I got it to work.

 

It is a good bet that the pot was set to nearly 0 Ohms.