Motors and solenoids
This section deals with motors and solenoids, basically the things that allow us to manipulate physical things in the animal's environment. These can be solenoid valves that we use to give rewards or olfactory or gustatory stimuli, or motors to move stimuli or to change aspects of the arena (such as closing door to particular regions of a maze).
Solenoids (esp. solenoid valves)
Solenoids are basically just coils of wire that produce electromagnetic force on a central piston which moves when current is applied to the coil. This can be used to move something in the animal's arena, but there are usually better ways of doing this. We most typically use them in the form of solenoid valves that are used to deliver fluid stimuli like liquid rewards, air puffs, smells or tastes.
Stepper motors
Stepper motors are kind of like a discretized version of a normal motor, i.e. they have a number of coils oriented around a central axle, which rotates as it clicks from coil to coil as a series of "step" commands are given by the control circuitry. This step sequence is usually delivered via an H-bridge from the Arduino. We've found these to be the among the fastest and quietest of the basic motor types and thus the OpenMaze shields usually have the basic circuitry to control at least one of these. Their discrete, steplike, motion also makes them quite accurate, however we most often like to have at least occasional checks to prevent them from losing steps.
Servo motors
Servo motors are by far the easiest type of motors to use but they have drawbacks that often make me favor stepper motors. Servo motors have internal circuitry that allows you to specify a particular angle of rotation, however they are loud, slow, and usually don't allow full rotation. We mostly use them for things that don't have to be moved that often or that quickly (like arena doors, or tactile stimulus arrays).
DC motors
DC motors are the most common type of motor, with two wires that allow the motor to be run either forward or backward by reversing the polarity of the voltage across the two wires. They're not very accurate but can be useful along with positional sensors (like Hall effect magnetic sensors).