Step 1: Materials
Step 2: The Circuit
The value of the resistor can be determined by looking at the technical specifications of your transistors, phototransistors and motors. I bought the first two components from RadioShack and the motors were just spare parts, so I had no specifications. I experimented with different resistors until I achieved a motor speed that I liked, settling upon a 5k.
You will probably want to add a switch or two in this circuit for convenience. Place it so that it cuts off the flow from each of the power supplies.
Step 3: The IR Beacon
Step 4: Assembly and Testing
I am not going to lie. I had to make many modifications to the circuit in order to get this thing to sloppily follow me. I am trying to make a video of it in action, but it is still very problematic and I want to resolve some of the bugs first. However, this is the crude first version of what I hope will develop into a highly functional, sleek device. Such a working product could also carry your umbrella or your drink. I can't wait to see suitcases that follow their owners around the airport. I would really appreciate feedback and hope that more instructables will be posted about human-following robots in general. Almost all I could find about such robots online was very high tech research with computers and facial recognition software. There is a lot of information about photovores as well, although the two are only vaguely related. I believe that the ability of a device to follow its owner gives it a new dimension of interactivity, and I hope to see some cool robots that do just that.