Make a wall avoiding Robot!

Objective: To create from scratch a working robot that is able to avoid walls and obstacles.
Ever wanted to make a robot that could actually do something, but never had the time or knowledge to do it? Fear no more, this instructable is just for you! I will show you step by step how to make all the necessary parts, and programs to get your very own robot up and running. I was first inspired to build a robot when I was ten, and saw Lost in Space, with that famous B-9 robot, I wanted one! Well six years later I finally built a working robot, its name- Walbot of course!

To find out more...Go to step one.

Now is a good time to order and collect some of the things you will need for this project. The "brain" of Walbot is a Microcontroller by Atmel called the Atmega168, it is very fast, easy to use and cheap, so that is what I will be using in this project. If you prefer to use PIC, or other Microcontrollers thats fine, however I can't help you out with the code then! Since I did not feel like wasting my time building a prototyping board for the Atmega168, I bought the USB Arduino; it is very easy to use, supports USB, has the boot-loader already burned in, quite cheap, and has free programming software that is similar to C++. Well enough of that talk, let's get on with what you will need!
note: these are only the prices I found from a quick search, if you look harder you probably will find better prices somewhere else, also the DIgiKey links might be broken or timed out, just search for the part description and whatever price matches the one listed here.

Parts:
Arduino USB board - $34.95
LV-EZ1 Ultrasonic Rangefinder- $25.95
2X 54:1 16mm Spur Gearmotor, FF-050- $13.80
2XPack of 4 Energizer NiMH AA Batteries- $4.85
9Volt Energizer NiMH Battery- $8.99
2X3mm Aluminum Bearing Block- $3.50
2X 3xAA battery holder (DigiKey part # SBH-331AS-ND - $0.98
2.1 x 5.5 x 9mm Right angle DC Power Plug - $0.95
2X Noise Suppression Capacitors - $0.50
L298 double full H-Bridge - FREE SAMPLE!
12"X12" sheet of 1/4" Lexan polycarbonate - $16.36
3X Aluminum 1" 8-32 standoffs - $0.45
4X 2-56 X 1/4 BUTTON CAP SCREW - $0.37
BOX of 100 4-40 X 3/8 BUTTON CAP SCREWS - $5.40
3X 8-32 X 3/8 BUTTON CAP SCREWS - $0.29
Neoprene Foam Tire - 3"D x 0.75"W (pair) - $5.36
Mounting Hub - 3mm (pair)- $8.00
9Volt battery clip (DigiKey part # 234K-ND)
Break Away Headers - $2.95
2 red 2 green and 1 yellow 3mm LED - $2.20 total
4X 1N5818 SCHOTTKY Diode (DigiKey part # 1N5818-E3/1GI-ND) - $0.15
2X 47k and 2X 2.2k and 1X 10k resistirs (digikey part #'s P47KBACT-ND and P2.2KBACT-ND and P10KBACT-ND) - $0.34
Ping Pong ball or other small low friction sphere for a caster- Free????

Custom order Arduino circuit shield see step 4

Optional / If your a complete beginner:
22AWG High Strand Count Silicone Wire Combo Pack - $16.80
Polarized Connectors to make things look neat, you will need crimp pins, 4X 2 pin header and housing, 4 pin header and housing - $6.45
Velcro for sticking things to base

Tools
these are the suggested tools to have for this project, you could either buy borrow or use something else you have for the same purpose.
Bandsaw for cutting the Lexan base and various parts.
Drill Press for drilling straight holes in Lexan base.
Tap and Die set for tapping holes in the Lexan base.
Good soldering iron for soldering various parts on the robot.
Digital Multimeter for debugging electrical components.
Wire strippers
Needle-nose pliers for gripping and crimping the connectors