RE: Major Mark IV Problem

[mgutzwiller@lanvision.com]

Is it possible that the problem is not vibration but a miscalibrated drive
rate?  It would be easy to tell the difference.  If the star streaks get
longer with longer exposure it's a drive rate problem.  If they are constant
for differing exposure lengths then its most likely a vibration problem.

Mike G.


		-----Original Message-----
		From:	Tom Droege [mailto:droege@wwa.com]
		Sent:	Tuesday, March 16, 1999 11:47 AM
		To:	tass@wwa.com
		Subject:	Major Mark IV Problem

		Well, the Mark IV vibrates in RA due to the pulsed drive of
the stepping
		motor.  I have done what I can with the magic gunk, and
there is still too
		much vibration.  I see two ways to proceed.

		1)  Work on it now until I fix it.

		2)  Get the Mark IVs out into the field taking data.  This
will get a start
		on all the software.  Count on being able to engineer a fix.

		I lean towards 2).  The system is plenty good to take
engineering data.
		Possibly even some real measurements.  For a typical star
see the attached
		IStar.FTS.  In this image, North is to the left and West is
up.  The N-S is
		smeared out because I do not yet have a good north
alignment.  E-W (Up-Down
		in the image) is smeared out from the vibration.  I suspect
in the summer
		it will be better when the rubber is warm.  I am tempted to
put a heater on
		the rubber coupling to see what it does.  

		My present plan is to switch to a synchronous motor for the
RA drive.  This
		would get away from the 8/1 rewind to forward speed problem
as I would
		expect to be able to drive a synchronous motor faster.  This
will take an
		additional electronics card and testing, and ... and would
take a few
		months.  

		So should I continue the production line, get the Mark IVs
into the field,
		and then work on a fix, or should I stop now and work till
it is fixed?

		I would particularly like to hear from all who are due to
get a system.

		Meanwhile, I will spend a few days working on other schemes.
Giant dash
		pots come to mind.  Something to take energy out of the
system.  It will be
		hard as there is a big mass on the RA axis and it is only
moving of order
		0.004" peak to peak.  Sigh!

		Tom Droege