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Hey probe folks;

Here I am again with something that's been bothering me.  Our workhorse
733 decided not to completely flip one of the spectrometer crystals
during a run recently, it kinda turned the motor half way and gave up.
Nobody observed it at the time so not really sure what happened.  We
turned it back by hand and it's been fine since.

That's not what's been bugging me though.  I've never had to do anything
to those little motor-flip assemblies before, and in looking at them I
came to the conclusion that I have no clue on how it actually knows what
it's doing.

I thought at first "yeah, little stepper motor"... no, only two wires.
So it's probably just a DC motor?  It has mechanical stops at either end
of the rotation travel (this is a two-crystal assembly, so 180 degree
flip).

How does this silly thing function normally?  Does the software just
drive it for n-seconds, until it's sure it bumped up against the stop,
or does it have some feedback that I'm not seeing?  What bugs me is if
it just drives up against the stops what keeps it from shredding up it's
little gears?  Some kind of clutch?  Does it ever know if it's
misaligned, or what state it's in when it powers up?

I'm more and more convinced as the years go on that the mechanics on
these machines is purely for show, and it all runs on magic.  Beautiful
wonderful magic.

I took a picture of the fellow here, in case you don't know what one I mean:

http://www.flickr.com/photos/stevencogswell/3491352250/

Wish: I want a probe with lots and lots of spectrometers.  Have a great
day, everyone.


Best regards,

Steve