David,
Let me respond in line.
Rick
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-----Original Message-----
From: gingery_machines@yahoogroups.com
[mailto:gingery_machines@yahoogroups.com] On Behalf Of David Frantz
Sent: Tuesday, September 06, 2011 2:00 PM
To: gingery_machines@yahoogroups.com
Subject: Re: [gingery_machines] new article: A Low Cost "Digital" Angle Gage
Hi Rick;
Another useful article in less than a week, working over time I see.
I just got to this article so I've read most of the thread up until now.
First in car you are wondering the spread sheet opened fine in Numbers, the
Mac spread sheet. It did complain about missing fonts but that is normal.
This should mean that the formal would be usable on my iPhone!!
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>>> I am running the spreadsheet on my iPod touch using Documents To Go.
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It is a great piece but it would be helpful to see how you derived the
formula. There are a couple of reasons one is verification, it is always
nice to check that the numbers we are getting are good and the ranges for
which they are good. You noted the limit at the lower range of angles but
I have to wonder what happens past 90 degrees. This probably isn't an
issue with a sin plate but your arrangement of parts would allow
mechanically for angles beyond 90 degrees. Sometimes + 90 degree angles
can make for far easier setups.
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>>> I'm almost ready to publish the updated article.
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I noticed you are having issues with embedding the spread sheet within the
PDF.
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>>> I solved this by just including the spreadsheet in .xls format below the
article.
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Unfortunately PDF is kinda of limited here and the use of Word doesn't
help any. Thus I'm wondering if you have considered coding in
HTML/Javascript. Yeah I know in some respects more work but it does allow
you to integrate interactive code with the content. Of course HTML files
are less than ideal in their own right as they have to be distributed as a
collection of loose files. Modern web browser address this to some extent
also. Unfortunately there is no perfect solution here for distribution of
complex documents that are open and freely available for use.
You pointed out the need to keep your caliper square to the stud and showed
using a washer to do that. I might suggest that you get rid of the washer
and simply cut a shoulder on the stud to support the blade. It will of
course impact the ability to close up the angle but as you note accuracy
suffers anyway.
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>>> One of my assumptions is that the two posts are the same diameter. The
best way to do this is to not reduce their diameter. However, I could cut a
better washer that would be 1/8" thick and have an ID of a little over 3/8".
I just added that idea to the article.
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The thread then teeters off course a bit with discussion about how to better
measure the angle. First it isn't likely that a DIY approach will be
anywhere nears as compact nor robust as a factory engineered job. In any
event in industry we use a lot of linear transducers, everything from
encoders, to resistive to Temposonic with each and everyone having its own
issues. A resistive solution might be fairly easy to implement but you
would need a fairly large radius to wrap the element on to get suitable
resolution. Or you could drive a linear sensor with a rack and pinion of
some sort. This would give you a linear voltage representing the angle.
The big problem with instrumentation resistors is that they aren't cheap and
are surprisingly bulky for what they are.
In the end I would think the best effort would be had with a rotary encoder
of some sort. For example a 4000 count rotary encoder would give you a
resolution of 0.09 degrees out of 360 degrees. Of course 4000 count
encoders aren't cheap but you can find stuff under a $100. example:
http://usdigital.com/products/encoders/incremental/rotary/kit/e5, another
example: http://www.avagotech.com/pages/home/
As a side note I found this
http://usdigital.com/products/interfaces/pc/usb/qsb#description looking for
encoder info. This is an incredibly cheap encoder and stepper motor
interface and should make for an low cost interface to a stepper driven
indexer.
Honestly I think it is a waste of time to spend excessively on building a
digital protractor. Such time could be put to better use building a
digitally controlled rotary table or other shop apparatus. Maybe that is
use me.
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>>> I agree. It is one thing to make the simple instrument in the article.
Anything more elaborate than that quickly looses my interest. However, with
care, I think this simple instrument can be rather accurate. I wish I had
the data to prove it.
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In any event thanks for the great article.
Dave
http://groups.yahoo.com/group/gingery_machines/app/peoplemap/view/map
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