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.
This is the base from Chapter 10 of Robot Builder's Bonanza - "Build A Motorized Plastic Platform".
I started with a 12.6" x 7.6" x 0.156" piece of white PVC foam, which was about $5 at a local art supply store. (I was looking for 1/8" thickness but 1/6" was the closest I could find.) PVC foam is incredibly light for its strength, although unlike ABS, it can't be tapped and you have to be careful the screws don't compress it too much.
I copied the 4" x 4" 2D layout from the book into Indeeo's iDraw, a terrific vector drawing program that is far less expensive than Illustrator but worked better on my Mac than the free Inkscape. I printed out the design, temporally glued it to the PVC foam with spray-on adhesive, and then cut it out on MicroMark's mini bandsaw and disc sander then drilled the holes with a Dremel mini drill press. All three of these tools are variable speed so they are great for working with plastics, woods, and soft metals, although this shape is simple enough that it could also be cut by hand.