Re: Balance Procedure


Joe Zeglinski
 

Hi Roland,

Not knowing the centre of gravity of your (160/F7.5) OTA, but assuming it
is at mid point (23.6 inches), that would be approximately a moment of 189
inch-lbs.
O.K. that is a useful working example to know, to judge our own OTA
conditions.

I am a bit surprised that AP uses "weight" instead of "moment (torque)"
when talking about imbalance. I found the same terminology used on page 23 of
the AP900 user manual: Troubleshooting - (additional explanation) - "It
typically takes about 4 lb. of unbalance to trip the overload circuit ...
etc."
This is a "weight", not a "moment arm" reference, which really depends on
which OTA you are using on the mount. A long OTA with 4 lbs is different from
a short SCT with the same 4 lbs. of unbalance.

As for not being concerned about "damaging the worm gear teeth", once
again, the user manual page 15 - RA & DEC Clutch Knobs: "3: How tight can they
be...etc." warns:
"You should not attempt to push your scope by hand against this locked up
resistance, or undue stress will be placed on the worm wheel/worm an
bearings".

My concern arose from reading that section in the mount set-up manual. In
using the mount for astrophotography, it is "recommended" to tighten the
clutches a bit more (1/8 turn by wrench). An overly "unbalanced OTA" may
introduce the same stress situation as "pushing the mount by hand", as
described in the manual. No "guideline" is given about how many "inch-lbs of
torque", potentially from OTA imbalance, are considered crossing the line on
too much stress on the worm gear.

Of course, the safest bet is to minimize any imbalance, as best as one
can.

Joe

----- Original Message -----
From: <chris1011@aol.com>
To: <ap-gto@yahoogroups.com>
Sent: Wednesday, April 25, 2007 10:47 AM
Subject: Re: [ap-gto] Balance Procedure


In a message dated 4/25/2007 9:21:36 AM Central Daylight Time,
J.Zeglinski@rogers.com writes:


You use the phrase "8 lbs out of balance", do you mean 8 inch-lbs?
Being "out of balance" with an 8 lb camera overhand at 6 inches is
different

from the same weight overhanging 2 feet away.
I have had an imbalance of 8 lb at the end of a 160F7.5 refractor. You will
know when the imbalance is too large because the motors will have a problem
slewing in one direction, but it will take more than 8 lb except maybe when
it is
bitterly cold outside. Also, if the clutches won't hold, it is probably too
much imbalance. I doubt very much that you could ever damage the worm gear
teeth. These are quite large and rugged.

Rolando


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