1. 1x 2222A transistor (similar to 3904, black thing w/ 3 wire)
2 . 1x LM 386 low power amplifier (chip w/ 8 wires)
3. 1x dpdt relay (black w/ 10 wires)
4. 2x motors
5. 1x 1k resistor (brown - black- red bands)
6. 1x 10k resistor (brown - black -orange bands)
7. 1x 100uF capacitor (blue thing)
8. 1x red LED
9. 1x toggle switch
10. I used two plastic battery boxes, each of which holds 2 AA batteries
11. double-sided sticky foam
12. 2x photodiodes - Jameco
and others stock themHere
is a nice and simple one page description of the circuit. It also goes through some errors in the Make magazine Herbie and the Instructable version.
I soldered my circuit together on a piece of perfboard that I measured to fit between the chassis and servos.
The servos were bolted to the chassis with 3/8" #6 bolts and nuts. Then the two servos were attached with a piece of double-sided foam tape, which is remarkably strong.
I removed the "brain" in each servo and just soldered two wires directly to the motor. This way you don't need PWM signals to run the servos, they just go!