I'm doing this project with evilknight... using a computer is outta the question as i) its too bulky if placed along wit the bot and ii) we are not suppose to control the bot in anyway after it has entered the arena... we are thinking of using a microswitch with spoons... do u think this would be feasible? or do u have any other suggestions? please advice..
I still think the computer would be the best choice:
i)There are really small computers (15cmX15cm)
ii)If you use a computer you dont need to control the robot. The computer IS the brain of the robot.
I mentioned a computer because is easier to program a camera-computer-robot than a camera-controller-robot.
Of course, controller-robot is much lighter, and that would be an advantage.
For controllers my suggestions are Freescale 8bit controllers(for $70 you get a powerfull controller, a development environment for C called Codewarrior and the compiler and it is available in anywhere in the world) or H8 from Renesas/Hitachi if you manage to import from Japan. Another good enough option is PIC, but I have never used. Freescale controllers are not very popular between hobbyst, so you will not find a lot of stuff on the net. I only use them because they are one of my sponsors. H8 is very popular where I live, when you buy it it comes as a complete set like freescale but most of its comunity only speaks Japanese which I think is out of question for you guys. PIC on the other hand is not so user friendly for beginners but it has a huge comunity in US and EU. It is very easy to find sample programs for it. Even this site has some.
For sensing then I would go for 3 sharp PSD sensors gp2d12 (the "range finder" as KambeiX said, but it is not the correct way to call it, I cant understand why everybody in this board call PSD range finders, the function might be the same but they are pretty different devices, range finders are very expensive). I would put one in the front and two on one side of the robot and all of them would face towards the ground. They would keep a certain range of values until one of them get over a pit. In this moment the reading in the front sensor will change widely. That will tell your robot that there is a pit. Then the robot will turn left or right, it depends where are your side sensors, and with the side sensors it will follow the pit like if it was following a line.
| o <----sensor
| | <----robot
Try to put your sensor like in the above ASCII diagram, in such a way one sensor will be facing the pit and the other the ground. Program your robot so that it will always keep one sensor over the pit ond the other over the ground. If you succeed in doing this you will not only manage to not to fall in the pit but also will find the bridge and pass it.
The next problem will be stooping the pit following routine after passing through the bridge. For that you could use the stepper mottor. That is very simple: you have to make your robot turn about 90 degrees in order to enter the bridge. If you succeed writing the above program your robot WILL pass the bridge. So the only thing you have to do is write another subroutine that will detect that your robot rotated about 90 degrees by counting the number of PWM pulses the controller sent to the motors/motor controller(you need one: google for h-bridge). If the function returns true it will stop the pit follower function and the robot will just go forward to the exit.
Those are the basics of my solution. Of course there a other solutions. There is nothing more I can say. Everything I mentioned here you can easy find on the net how to build or control. I think now it is up to you. I don't think this contest is THAT difficult at all so a simple robot may be easily able to succeed (even simpler that I suggested) if you are good enough with C or maybe just luck will be enough(believe me luck is a huge factor when building your very first robot).