We covered some large robots in the earlier chapters; in this section, you'll build much smaller robots. You can build these small robots from scratch, but I've found that it is much easier and less expensive to take toy robots, which provide the basic capabilities, and add Arduino to them to make them significantly more powerful.

In this first project, you will start with a commercially available robot without a lot of autonomous capability, and then, you'll add Arduino and a sonar sensor and expand the capability of the robot. The robot you'll start with is the Hexbug Spider, which is available at many toy stores and from most online retailers. For specifics, here's the website: www.hexbug.com/mechanical/spider/.

The following is an image of one such unit:

As this robot is very small, you're going to need a very small Arduino so that you don't load the system down too much. One possible choice is an extremely small implementation of Arduino, the TinyDuino. This is...