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The difference between stepper and brushed dc motor

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They are not even close. A stepper motor drive will typically use a set of direction, and move pulses or a set of CCW, CW pulses. They need a driver to operate. They come in bipolar and Unipolar configurations. Some drivers are capable of micro-stepping. The Driver moves the stepper motor given angular displacement per pulse. Microstepping, holds the position somewhere between the stepped pulse. They can be used in open loop positioning systems where only the Origin is known.

A brushed DC motor can act as a generator when not loaded. It's current is proportional to torque. Unloaded voltage is proportional to speed. This type of motor will start rotating at some DC voltage.
 
DC motor requires a continous DC voltage between it only two terminals, while Stepper Motor, with more than 3 terminals, do its designed job if it gets plused dc voltage in a proper sequence to make rotate CW or CCW. In fact ,you can use a stepper motor ( witch certain connection ) in place of brushed DC motor, but you can not use brushed DC motor in place of stepper motor.
 
A brushed DC motor can act as a generator when not loaded. It's current is proportional to torque. Unloaded voltage is proportional to speed.

Oddly enough, I've not played with steppers the way they were meant to be used. They also can be used as generators, generating a quadrature waveform (sine rather than square) that allows it to be used as a speed/direction input. Unloaded, a stepper can put out quite a bit of voltage, so if interfacing to electronics, especially CMOS, you have to clip the output so you don't destroy IC inputs. Unlike most rotary quadrature input devices, steppers, especially larger ones, have a nice tactile feel to them as they rotate. The down-side is that they can be large and a heck of a lot heavier compared to made-for-the-purpose quadrature input devices and their output gets small and almost useless at very slow rotational speeds.

If you have two identical larger steppers, connect the like wires together, put a crank on one of their shafts and then turn it. The other (slave) stepper will follow the first (master) stepper much like a syncro/servo system. Now, using the stepper as a stepper motor, well .... how do you do that anyway? :)
 
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