First. I agree with John_S responce. Need schematics, code, possible block diagram and a step-by-step of what you want the robot to do.
Let see if I understand correctly...
Input : A bumber switch
Opto coupler sensor of a encode disk
Output : 2 motor
Process : Arduino
So far... Correct ?
And you want us to code for you ? Hmm... Good luck on that one. If I have a robot being build, I will share my code, but the hardware maybe differents.
Let see for a pseudo-code...
Move motors
Check Switch
- hit --> Back up
Read opto
Store opto data
repeat...
That it. Unless you forgot to mention others things like com link and others stuffs.