Short note on Stepper motors
A stepper motor's shaft has permanet magnets attached to it. Around the body of the motor is a series of coils that
create a magnetic field that interacts with the permanet magnets. When these coils are turned on and off the
magnetic field causes the rotor to move. As the coils are turned on and off in sequence the motor will rotate forward
or reverse. This sequence is called the phase pattern and there are several types of patterns that will cause the motor
to turn. Common types are full-double phase, full-single phase, and half step.
To make a stepper motor rotate, you must constantly turn on and off the coils. If you simply energize one coil the motor
will just jump to that position and stay there resisting change. This energized coil pulls full current even though the
motor is not turning. The stepper motor will generate a lot of heat at standstill. The ability to stay put at one position
rigidly is often an advantage of stepper motors. The torque at standstill is called the holding torque.
Because steppers can be controlled by turning coils on and off, they are easy to control using digital circuitry and
microcontroller chips. The controller simply energizes the coils in a certain pattern and the motor will move
accordingly. At any given time the computer will know the position of the motor since the number of steps given can
be tracked. This is true only if some outside force of greater strength than the motor has not interfered with the motion.
An optical encoder could be attached to the motor to verify its position but steppers are usually used open-loop
(without feedback). Most stepper motor control systems will have a home switch associated with each motor that will
allow the software to determine the starting or reference "home" position.
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