Re: [ATM] help required

["Bob May" <rmay@nethere.com>]

You don't need a big motor nor a fast motor to do the driving of
the filter.  Slow the motor down by not feeding it so much
voltage and use less of a gear reduction when doing so.  Maxon
and Escap along with others make neat little motors that have a
lightweight armature (they're corless motors which means that
there is no big piece of iron rotating in the motor) and they can
come with gear reductions of whatever you want to a fair degree.
Run the motor at about 1/4 of the voltage and the vibrations will
be a lot less.
In addition, you may want to put a flywheel (don't forget to
balance it well!) on the output to help keep the speed the same.
I'll also note that you do want to feed the motor a more
regulated voltage as unfiltered power can make a motor resonate
to the power variations, especially the lightweight coreless type
motors.
In the surplus market, Pittman is probably the best of the
heavyweight motor types and you want to get a fully enclosed
motor for something like a servo system as these motors tend to
turn slower and usually are well balanced to begin with.  A lot
of Pittman motors are also wound on skewed armatures (the slots
in the armature are not directly down the shaft, but rather
spiral around the shaft a bit) which are a lot smoother in their
operation.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Vladimir Galogaza <vladimir.galogaza1@zg.t-com.hr>
To: <interferometry@yahoogroups.com>
Cc: ATM List <atm@atmlist.net>
Sent: Wednesday, May 21, 2008 2:16 AM
Subject: [ATM] help required


> To speed up interferogram collection in Phase Shift
Interferometry
> Bath interferometer, (PSI Bath), I am using a motor to rotate a
final
> polarizer. Goal is to rotate a polarizer at 5 rpm.
> Therefore motors I used have some gear boxes to reduce the
speed
> of the output shaft.
> But motors rotate at high speed and any imbalance in rotor
caused vibration
> is sensed by interferometer. Motors that have inherently low
speed are not available
> (to me at least). Stepper motors will do in principle but
stepping jerks are
> terrible. I have mounted motors to dumping cushions but
interferometer is
> very sensitive and isolation was always insufficient.
> Does anybody has idea how to solve this problem? I count on ATM
ingenuity.
> ( and traditional sense for low $$$ solutions).
>
> Regards
> Vladimir.
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>

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