tracking issue

"David Nakamoto" writes:

Planetary motion is not noticeable at those magnifications or higher. I've
observed Mars at magnifications of 400x to 500x during its opposition when its
motion against the background sky is highest and there isn't any detectable
motion over a few hours.

Oh, yes there _is_ motion. I've done some CCD imaging of a few main
belt asteroids and motion is very apparent even after one hour. At
opposition Mars moves about 1 arc min per hour (retrograde, or
westward), or about 3x its diameter.

On the other hand, from the description of the problem by the OP, it
seems that there is a problem in the mount/drive, rather than
planetary motion (which should require a somewhat _slower_ drift
rate).

pej
--
Per Erik Jorde

I think there is a bit of conflicting answers as to if I can detect a
plant's orbiting motion at 150X. Regardless, I can assume that it's not
impossible. Since it is kinda' pointless to take long-exposure photos
of planets I'll just set the drive up for the deep sky and live with
the difference (if any) during planetary viewing. I have a final
question:

Is there a fine balance proceedure for the OTS on an EQ mount? I run
the typical balance proceedure methodically but I am sure it is not
accurate to the gram. The drive is a pretty small motor. Could that
small an unbalance cause drive irregularities? So far a Google search
has come up with nothing.

The idea behind all this is film exposures up to about 15 minutes. More
than that and I probably run into mechanical shortcomings of the EQ
mount.

"spiral_72" wrote

I think there is a bit of conflicting answers as to if I can detect a
plant's orbiting motion at 150X.

If you can do that, you might win a Nobel in Biology.

Some people purposely offset the balance with a little more weight on the
western side of the mount to "help" the tracking motor.

Jeff
http://www.mindspring.com/~jeffpo

"spiral_72" wrote in message
oups.com...

Is there a fine balance proceedure for the OTS on an EQ mount? I run
the typical balance proceedure methodically but I am sure it is not
accurate to the gram. The drive is a pretty small motor. Could that
small an unbalance cause drive irregularities? So far a Google search
has come up with nothing.

On Thu, 7 Apr 2005 13:42:03 -0400, "Jeff Polston"
wrote:

Some people purposely offset the balance with a little more weight on the
western side of the mount to "help" the tracking motor.

That's a bad idea. You want to have the extra weight on the _east_ side.
If the west side is heavier, stiction and worm gear backlash result in
erratic movement. By having the east side slightly heavier the driven
surfaces between the worm and worm gear are always loaded.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

The best results in loading the worm drive is to use some form of constant
torque
generation. (not always practical in a retro fit)

A weight on one side or the other produces a force on the axis relative to
the cosine of the
gravity vector. mounted on a fork of a previously balanced telescope the
weight will provide the maximum force at the zenith and 0 on the horizon.
Older ( before mead) mounts have a wrap of cable to a hanging weight or in
the more modern scope a constant torque motor pre loading the drive.
In smaller mounts we have use nagator (sp?) spring torque generators thay are
a many turn coiled spring
so the force is with in about 10% over one rotation.

Dan




Jeff Polston wrote:

Some people purposely offset the balance with a little more weight on the
western side of the mount to "help" the tracking motor.

Jeff
http://www.mindspring.com/~jeffpo

"spiral_72" wrote in message
oups.com...

Is there a fine balance proceedure for the OTS on an EQ mount? I run
the typical balance proceedure methodically but I am sure it is not
accurate to the gram. The drive is a pretty small motor. Could that
small an unbalance cause drive irregularities? So far a Google search
has come up with nothing.

What a good idea! Why in the world didn't I think of that already?
That'd reduce backlash ect. Actually I remember reading that some time
back now that I think about it. So I want to balance the OTA, favoring
the west side from now on.

If you can do that, you might win a Nobel in Biology.

Ok. so there is no chance of detecting the difference in motion with my
scope. I guess I need to do a little more hunting for the problem. I
just wish I could verify the drive's consistant speed.

Thanks for the help all....

my astronomy page, info and pics at:
www.geocities.com/spiral_72/Spirals_page.html

On 7 Apr 2005 12:12:25 -0700, "spiral_72" wrote:

What a good idea! Why in the world didn't I think of that already?
That'd reduce backlash ect. Actually I remember reading that some time
back now that I think about it. So I want to balance the OTA, favoring
the west side from now on.

Favoring the east side, you mean (that is, east side heavier).

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"spiral_72" wrote

If you can do that, you might win a Nobel in Biology.

Ok. so there is no chance of detecting the difference in motion with my
scope. I guess I need to do a little more hunting for the problem. I
just wish I could verify the drive's consistant speed.

You have to carefully re-read what you originally wrote to get the joke.

"Per Erik Jorde" wrote in message
...
"David Nakamoto" writes:

Planetary motion is not noticeable at those magnifications or higher. I've
observed Mars at magnifications of 400x to 500x during its opposition when
its
motion against the background sky is highest and there isn't any detectable
motion over a few hours.

Oh, yes there _is_ motion. I've done some CCD imaging of a few main
belt asteroids and motion is very apparent even after one hour. At
opposition Mars moves about 1 arc min per hour (retrograde, or
westward), or about 3x its diameter.

I thought about my answer after I wrote it and you're right, I simply forgot the
small corrections I made during the night, but who remembers these things? ^_^
But the motion isn't something the original poster seemed to be describing. But
more on that later.



On the other hand, from the description of the problem by the OP, it
seems that there is a problem in the mount/drive, rather than
planetary motion (which should require a somewhat _slower_ drift
rate).

Yes, this was what I was homing in on, and oversimplified my answer.

--- Dave
--
----------------------------------------------------------------------
Pinprick holes in a colorless sky
Let inspired figures of light pass by
The Mighty Light of ten thousand suns
Challenges infinity, and is soon gone