From: "Tom Krajci" 
To: , 
Cc: , 
Reply-To: "Tom Krajci" 


From: "J&S" 

>In my mind, (and construction techniques aside) there is nothing
>simpler than an equatorial when we're talking about siderial tracking,
>simply because we are only having to deal with ONE axis - we are only
>trying
>to counter the earth's rotation - a single movement that runs at a
constant
>rate (barring atmospheric refraction).

I agree with what you say, when it comes to:
- parts count
- number of axes that need to be driven all the time

I do not agree that EQ mounts are 'simpler' when you consider:
- cantilevered loads that subject bearings to moments

Don Clement has made the same comment...and considers it easier to make a
field derotater than to design a stiff/well performing eq. mount.  And
considering his work, RTMC awards, etc...I think his statement should be
listened to with some weight and emphasis.

>...True, to even begin to consider [a 3-axis] mount we must
automatically
>assume computer control, which may or may not be easy for some of us
(not
>easy for me)...

Mel has written the software.  Bless him!  Without his effort I'd be in a
world of hurt.  Mel's software is complex...so that mechanical and
electrical implementations can be less complex.  Because of Mel's
generosity...this is almost a free lunch.  ;-)

>...[As an aside, after examining the drawing of the massive alt-az
design
>at the top of your website....

I was hoping it would be stiff - that is my primary concern.  I'm trying to
do it with monocoque fork arms.  If you know of a lighter-weight
construction approach, please tell me.

>...Visuallize slicing off the lower azimuth cone just under the fork
arms
>and stretching/tilting the cone's lower bearing over into one
corner....
>...You now can track with a single
>simple motion (though it will, of course, not be able to track for a
full >24 hours, being limited to how far you want to allow the forks to
tilt over)....

My goal is time-series photometry on one target, for as long as it's
visible in the sky.  In winter that can be 12 hours for a circumpolar
object.

>But realistically, when it all boils down to it (bearing in mind that
>this is a permanent installation) wouldn't a regular old horseshoe,
split
>ring, or English yoke be much better and simpler? With these mounts all
the
>mass is still within the span of the bearings and you only need the two
>degrees of movement. Less machining, and only one motor needed.

For small scopes I agree with you.

What is the largest, amateur-built, equatorially mounted scope you've seen
or heard of?

What is the largest, amateur-built, alt-az scope you've seen or heard of?

What is the largest, amateur-built, alt-alt scope that you think can be made?

What is the largest, amateur-built, 3-axis scope that you think can be made?

As you mention further:

>Poorly constructed split rings and horseshoes can result in a wandering
>polar axis as well. Just because the mount is supported by three points
>does not mean that the true axis of rotation stays put.

You need to make the eq. mount well...and you need to make the 3-axis mount
to close tolerances also.

Which mount is more forgiving of fabrication errors:  eq. or 3-axis...or
are they equally difficult (easy) to make to close tolerance?

Tom Krajci
Tashkent, Uzbekistan


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