Re: Group Design

From	Don Y <blockedofcourse@foo.invalid>
Newsgroups	comp.arch.embedded
Subject	Re: Group Design
Date	2020-07-09 23:53 -0700
Organization	A noiseless patient Spider
Message-ID	<re93a0$544$1@dont-email.me> (permalink)
References	<a4d4857d-e915-49ef-a7d7-6015277edbeco@googlegroups.com> <cd08f78f-3d9a-491d-a259-2a3c44f71a28o@googlegroups.com>

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On 7/9/2020 10:48 PM, Rick C wrote:
> There is presently a decision being made about various methods of detecting
> end of travel for the back stroke of the motor.  One of the selection
> criteria is "simplicity", 1 to 3.  I don't see that as an objective value,
> rather a subjective rating of what they think of each approach.  Cost is
> rated from 1 to 3 without any real consideration of a dollar (or pound)
> figure.  The three methods that use a detector each are rated 1 on cost
> (because there is some) and two methods are rated 3 on cost because they use
> timing (guessing) or motor current on reaching a mechanical stop.

A "binding" mechanism will fail to achieve its goal in a fixed period
of time AND will likely indicate a higher current draw, prematurely.
How *important* is that indication to the proper operation of the device?

How regularly do you expect the device to be maintained/serviced?
What sort of skill level do you expect from the parties doing that servicing?
(this goes to my previous comments re: third-world applications; first-world
likely have staff on-hand to maintain ALL of the kit that they utilize -- as
well as equipment suitable for those tasks)

> So do Hall effect sensors have any real issues such as magnetic
> interference?  They work off of a magnetic field, but not a rapidly varying
> field (the motor output is single digit RPM in use) so will local magnetic
> effects impact it, like the motor current?  The sensor will probably be 9
> inches away.  Is a magnet built into Hall effect sensors or is that required
> to be added?

Typically added if you're trying to monitor the presence of an
object (motor shaft) in a particular location.

> Another choice is an optical sensor.  They list as a disadvantage optical
> interference!  That seems rather unlikely in a closed box especially.  There
> are openings, but not large.  For some reason this one is listed as poorest
> in simplicity.  Seems simple to me.

What about dust/crud/*critters* interfering with the emitter (or detector)?

> They list circuit boards as being needed for those two and a micro switch.

You can put a HE sensor on the end of a cable.  Ditto for an optical sensor.
But, mounting to a PCB -- and affixing a cable to *that* -- may be easier
to manufacture/service (imagine having to reattach a pigtail to a bare
sensor)

> I know these can be mounted on cables, but is there a reason why that would
> be a bad idea for reliability?  I recall in my very early days in
> engineering seeing front panels with switches and LEDs being wired up by
> hand via ribbon cable and heat shrink tubing.  That was equipment for a NASA
> ground station, forty years ago.  Likely they would not accept that now?

Adding strain relief to a bare sensor becomes problematic.  A sensor mounted
on a PCB is reasonably robust.  And, even a cable fabricated from a set of
individual wires can have an improvised strain relief (loop it through a
set of holes before leaving the PCB).

(Again, how will this be serviced?  How likely are folks to be
tinkering around INSIDE the enclosure?  How skilled are those folks
likely to be?)

> There is also the option of the motor shaft encoder, but that is
> significantly more expensive and I recall there was a strong dislike of the
> $15 price.  I suggested they include a couple of the options in the circuit
> board and after development is done leave out the one you don't use.  They
> seem to think they can make all the decisions without knowing for sure how
> this will need to be designed.

What are you hoping to monitor with the shaft encoder?  Are you hoping to
resolve a fraction of a rotation?  Or, count *numbers* of rotations?
In the latter case, you can use a very crude encoder with one or two
pulses per revolution -- a "home" sensor and "index" pulses.

We manufactured a maritime radar unit, many years ago.  You need to
know the actual position of the antenna to synchronize it with the
display.  The "obvious" solution was a fine-pitch shaft encoder
where each discernible antenna "position" was directly indicated by
the encoder.

Another company *copied* our basic design.  But, made several improvements
to increase manufacturability.  One such change was replacing the fine
(photographically produced!) encoder with a very coarse encoder -- mounted
on the antenna motor shaft BEFORE the gear reduction assembly!  So, their
encoder rotated at a much faster rate -- but, would output pulses at the
exact same rate as ours!  "D'oh!"

Thread

Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-07 18:46 -0700
  Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-07 19:02 -0700
    Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-07 20:36 -0700
      Re: Group Design David Brown <david.brown@hesbynett.no> - 2020-07-08 09:31 +0200
        Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 07:08 -0700
  Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-08 14:13 +0200
    Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 07:19 -0700
      Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-08 18:57 +0200
        Re: Group Design Theo <theom+news@chiark.greenend.org.uk> - 2020-07-08 18:28 +0100
        Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 11:12 -0700
          Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-08 23:34 +0200
            Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 15:20 -0700
              Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-08 23:00 -0700
              Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-10 10:09 +0200
              Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-07 00:01 +0100
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-06 17:37 -0700
                Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-08-07 03:06 -0700
                Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-06 21:50 -0400
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-06 19:12 -0700
                Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-06 22:27 -0400
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-06 19:36 -0700
                Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-06 23:39 -0400
                Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-07 12:30 +0100
                Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-07 09:57 -0400
                Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-08 00:37 +0100
                Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-07 20:29 -0400
                Re: Group Design upsidedown@downunder.com - 2020-08-08 08:59 +0300
                Re: Group Design David Brown <david.brown@hesbynett.no> - 2020-08-10 15:43 +0200
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-10 09:18 -0700
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 07:12 -0700
                Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-08 00:00 +0100
                Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-07 20:30 -0400
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 17:57 -0700
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 17:56 -0700
                Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-08-07 18:10 -0700
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 19:43 -0700
                Re: Group Design Dimiter_Popoff <dp@tgi-sci.com> - 2020-08-07 20:42 +0300
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 13:48 -0700
      Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-08 14:11 -0700
      Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-07-09 04:25 -0400
        Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 11:37 -0700
          Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-09 11:54 -0700
          Re: Group Design Tom Gardner <spamjunk@blueyonder.co.uk> - 2020-07-09 20:02 +0100
          Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-07-09 15:31 -0400
            Re: Group Design lasselangwadtchristensen@gmail.com - 2020-07-09 15:36 -0700
              Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 18:36 -0700
                Re: Group Design Clifford Heath <no.spam@please.net> - 2020-07-10 16:17 +1000
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 23:36 -0700
                Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-10 10:22 +0200
      Re: Group Design David Brown <david.brown@hesbynett.no> - 2020-07-09 14:40 +0200
  Re: Group Design John Speth <johnspeth@yahoo.com> - 2020-07-09 07:59 -0700
  Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-09 18:33 -0700
    Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 19:01 -0700
      Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-09 22:32 -0700
      Re: Group Design George Neuner <gneuner2@comcast.net> - 2020-07-10 17:36 -0400
        Re: Group Design Ed Prochak <edprochak@gmail.com> - 2020-07-14 11:09 -0700
          Re: Group Design George Neuner <gneuner2@comcast.net> - 2020-07-16 00:26 -0400
  Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 22:48 -0700
    Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-09 23:53 -0700
      Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-10 01:15 -0700
        Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-10 02:22 -0700

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