This instructable will introduce some of the simplest and most elegant robotics conepts I have ever seen. The concept came from a book called Vehicles : experiments in synthetic psycology by a guy named Valentino Braitenberg, and appropriately, robots based off of this concept have come to be known as braitenberg vehicles.
These braitenberg vehicles can be built using nothing but a pair of motos, a pair of sensors, a battery, and a power opp amp, but they are able to move in ways that seem so biological that braitenberg chose to attribute them to emotions.
"Robots that emote? this is not possilbe" you say, and you're probably right, but I've made a short video to demonstrate the robots and show you what I mean.
Step 1: Step 1 - the electronics
as you can see it's just a voltage divider feeding into a non inverting op amp. for the resistor R1, you can either use a trimmer like I did, or you can use a resistor that matches the resistance of your light sensitive resistor (LSR) when it is fully saturated with light. as the light levels surrounding the LSR increase, it's resistance will go down. In the current configuration, the voltage measured across the light sensitive resistor will be 9v*R1/(Rlsr+R1). As such, when no light is sent to the LSR it's resistance will be very high relative to R1 so the voltage sent to the motor will be almost zero. In contrast, if the light sensor is fully saturated the voltage sent to the motor will be half of the supply voltage (4.5v). This explains why the figure above is labeled excitation - the more light it sees, the faster the motor will turn.
To switch the motor out of excitation mode and into inhibition mode, all you have to do is swap R1 and the LSR as shown in the second figure. This will cause the motors to spin fast in the dark, but slow down as the light increases.
It would be nice if we could connect our motors directly to our voltage dividers, but motors need too much current for that to work. To make sure that our motors have plenty of current to nom on, we'll put some beefy op-amps in between them and the voltage dividers. The lm272 is a great choice for this sort of application. It can put up up to 1 amp of current, and it doesn't need a negative voltage supply. In addition to the connections shown in the figure above, you will also need to connct the op-amp to power and ground. the resistor values shown in the figure above will set the gain relating our input voltage to our output voltage to about 1.1 (1+1k/10k).
Once you've completed your circuit, your robot should look a little somthing the breadboard in the third figure.
Step 2: Put it on a platform
Step 3: Choose your destiny! (setting the modes)
The modes in the top half of the picture (fear and agression) both operate with the voltage dividers configured for excitation (symbloized by the little plus signs beside the wheels). In contrast, the bottom two operate with the voltage dividers configured for inhibition (symbolized by the negative sign by the wheels).
The modes on the left side of the picture (fear and love) require that the left sensor is controlling the left motor and the right sensor is controlling the right motor. In contrast, the modes on the right side of the picture (agression and exploration) have crisscorssed leads. In these modes, the left sensor feeds the right motor and the right sensor feeds the left motor.
And bam, just like that you have four robots in one. W are done here. be free. The time has come for you to impress your firends and annoy perfect strangers with your newfound robotics knowledge.