For the disabled, and for those who have their hands full, a hands-free light source can be desirable. The goal of this project was to create a simple robotic flashlight that would follow its user around, rather than be carried.
Step 1: Materials
This robot follows an infrared beacon clipped to one of the user's shoes. The infrared light is generated by four infrared LEDs harvested from old TV remotes. The robot sits on two wheels from a K'nex set and moves using two small hobby motors controlled by the input from two infrared phototransistors to the bases of two NPN transistors. I wanted to use photoresistors rather than phototransistors, but I found that these have a very wide angle of sensitivity and are not exclusively sensitive to infrared light. They also contain the toxic metal cadmium, and proved difficult to find in shops. Phototransistors are similar in shape and size to standard LEDs, and infrared phototransistors are widely available. Resistors were needed to bias the transistor. The robot is activated by two switches, and powered by 3 AAs and 1 9V battery. Everything is housed in some PVC tubing, and rubber bands hold everything together. The k'nex wheels are attached to the motors with hot glue. A disposable plastic fork was stuck on to provide support. This truly is version 1, and I am working to improve this system.
Step 2: The Circuit
The circuit is designed to speed up the motor on one side if light is detected on the opposite side. In this way, it turns towards the light. This doesn't work perfectly, but for such a simple solution it performs quite well. I made a quick video demonstrating this circuit, but it was too large to upload. It can be seen here.
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
The IR beacon consisted of a short length of PVC pipe with one AA battery inside. A rubber band held the contacts to the battery, and a switch controlled power to four IR LEDs, which were wired in parallel.
Step 4: Assembly and Testing
Solder the circuit together after much testing on the prototype board. Put everything inside the case, and be sure that the phototransistors stick out and can "see" the beacon. Go somewhere dark, and set your robot on the ground. Turn on your IR beacon and clip it to your shoe. Tun on your robot, and try walking around. What does it do?
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.