I recently built my first robot and figured I'd share the steps and results. It is a simple line-follower built on the PlastoBot platform in Gordon McComb's Robot Builder's Bonanza and driven by an ATmega328 chip connected to an SN754410 dual H-bridge motor driver. I'm also a big fan of David Cook's Intermediate Robot Building and website, so I highly recommend anyone interested in amateur robotics check them out.
After building the wood, plastic, and metal bases in the first section of Gordon McComb's book, my next goal was to make one actually move. I considered adding a remote control receiver and turning one into a DIY RC car, but I wanted my first robot to move autonomously, so I decided to try building a classic line follower.
I had seen several amazing videos of Pololu's 3pi Robot and I wanted to see if I could build a simplified version. I've never seen a 3pi in person, but Pololu has documented everything so well, and their tech support is so helpful that I figured I could find out whatever I needed to know online. This version does not have an LCD display, LEDs, buttons, a timing crystal, or any of the other bells and whistles that the 3pi does, but the heart of it is rather similar - the microcontroller, motors, sensors, power module and software algorithms are taken right from the 3pi, hence, the 2pi.