thanks
Thanks very much for the responses. Yes, I am already using an Ultasonic sensor for forward obstacle detection.
The micrososwitch sounds like the perfect solution, and I found a microswitch just for this purpose at Maplin electronics website. It has a roller wheel so contact is made when there is pressure on it, perfect! Thanks for the idea.
IR method will deffinately be less reliable compared to a microswitch, as pointed out, due to different coloured grounds absorbing different amounts of IR without reflecting it.
This is my first robot, and it makes me fill with wonder at the human body we are marvell of robotics! Two eyes which are infinately superior than any U.S. or IR sensors with autofocus and full colour 3D vision guiding our way, Legs and arms with muscles allowing us to move and accomplish complex tasks (like the DC/stepper motors but supremely superior), and our extremely complex brain controlling thousands of processes in the body (can be compared to the microcontroller of the robot). Other transducers in the body, touch, taste, smell, sound sensors are all flawlessly designed and connected to the brain (microcontroller).
Deffinately, we are not a product of mere chance, but DESIGNED by a powerful and intelligent Creator. Athiests and evolutionists have got it completely wrong. That's for sure.
Anyway, thanks for the tips, I will be going out to maplins to fetch the micorswitches and some other components.