On Sun, 23 Dec 2018 12:15:41 +0100
Gerhard Reithofer  wrote:

>On Sun, 23 Dec 2018, The Natural Philosopher wrote:
>> On 22/12/2018 17:24, Gerhard Reithofer wrote:
>> > Hi Theo,
>> > On Sat, 22 Dec 2018, Theo wrote:
>> > > Gerhard Reithofer  wrote:
>> > > > Sounds interesting, but how do I controll these shields with a
>> > > > raspberry?
>
>...
>
>> > What I'm dreaming of is a controller which allows defining a step input
>> > (including speed and maybe acceleration paramaters) and the motor moves
>> > to the position without any additional input. The final positition is
>> > sent back or confirmed on request via the used interface.
>> > Think of an axis contorl of a robot arm. The combination of several such
>> > modules can be controlled by a raspberry because the hardware part and
>> > the real time components are not important on that level. As example it
>> > I would be very simple add a GUI for programming, etc.
>> >
>> > Is there a cheap solution known?
>> >
>> With that spec I'd certainly be thinking 'arduino or picaxe and stepper
>> motors'
>
>Yes, that would also definitely be my approach (I only know the Atmega
>world and have never used PICs).
>What astonisches me is the fact that there are many "simple analog
>servo controllers" but a relatively limited number of solutions for
>steppers.
>And the mature developmemts I've found are fully integrated into a
>specfic solutions and cannot be easy taken over into other requirements
>(examples are the NC and 3d-printer area).
>
>THX to *
>
Something that seems to be coming more common in industry is a stepper
combined with a precision absolute encoder. This combination is very good at
staying *exactly* where you put it, with zero drift even when aged. Also, all
the precision (hence cost) is only needed by the encoder.

For a dumb waiter type control the people I work for used this with a
multi-turn
absolute encoder at 4096 pulses per rev, and 4096 revs. In over 10 years, the
only time it needed to be adjusted was when someone managed to jam it up but
kept trying to make it run until the chains broke :(

--
W J G

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