🚀 go-pugleaf

In article <biber.675348684@faramir>, Frank2.Simon@arbi.informatik.uni-oldenburg.de (Frank 'Biber' Simon) writes:
> markh@csd4.csd.uwm.edu (Mark William Hopkins) writes:
> 
>>    I'm not very familiar with robotics in general, but keep seeing stepper
>> motors mentioned in this context.  How fundamental are stepper motors,
>> especially in relation to the issue of precision in speed and positioning?
> 
> There's a big difference between "normal" motors and stepper motors:
> 
> The function of a "normal" motor is to turn around while getting current.
> For example to turn around one time it must get 1 second. To get a half
> round it must 1/2 second and so on. To get an exact round-partition you
> need a very exactly time-generator. But there's a next problem: The turn-
> around-time depend of the weight of the moved thing by motor. If the
> motor move empty a round takes for example 1 sec. If there is a big work
> to do it take a lot more for example 2 sec. Because of this a exact
> move isn't possible with different weights.

Well....

Not exactly.  While it is true that a motor running at constant
speed will turn a given fraction of a revolution in some specific
period of time, that isn't the way they are generally used.  When
motors of this type are used for position control where exact
position is critical, they are generally used in some sort of servo
system together with position sensing.  A position sensor such as a
synchro or a shaft-position encoder or such is used to sense actual
position.  This information is fed back to the servo where it is
compared with the desired position and the motor is driven
accordingly.  Drive is a function of the difference between the
actual and the desired positions and, ideally, as this difference
approaches zero, the motor comes to a stop.  The problem with such
systems is that they are relatively complex and, hence, costly.

Most stepping-motor systems use no feedback but rather count pulses
applied to the stepper and, therefore, count the number of
rotational steps that *should* have been taken.  Within their
limits, such systems may permit precise positioning at lower cost
than a full-fledged feedback control system or servo system.

Best,

Charlie Sorsby						"I'm the NRA!"
	crs@lanl.gov