GEM at our latitude

[Robin Lee]

Since the GEM working at our latitude will act more or less like an altazimuth mount, does this affect its tracking performance?

Do any of you have experience of modding the GEM of which latitude scale doesn't up to here like a CGE, G-11 and so on?

[MooEy]

it doesn't work as altazimuth unfortunately. to become altaz it has to be at 90 degrees, not 0 degrees.

~MooEy~

[Robin Lee]

What I meant is the gears are placed either horizontally or vertically which may not allow smooth movement for the gears.

[Meng Lee]

True, Thats why ball bearings in the RA axis is our favourite word. People who have EQ-6, G11, GM-8, GPD2 did not meet with any tracking problems.

By the way, Remus modified G11 in order to reach our latitude.

[Robin Lee]

Meng Lee, so ball bearings are very fine for us? Do ball bearing and worm gear serve the same job or they play different role in GEM?

I'm going to reach Remus.

[Meng Lee]

Essentially high end mounts have ball bearings inside both RA and DEC axes, this is to ensure smooth motion on both axes despite heavy loading. In fact, mount loading capacity is dependent on how much the ball bearings inside can handle.

Worm gear essentially does the job of tracking. If the worm gear is precisely machined, then tracking will be more accurate and less jerky. Also, autoguiding will work much better with better worm gears.

[Robin Lee]

Thanks a lot for explaining.

[Robin Lee]

By the way, how do you guys align your GEM? Just doing the star alignment built in the controller?

[Meng Lee]

What kind of alignment do you mean? If you mean GOTO alignment, yes, then just do star alignment in the controller. If you mean polar alignment, then just roughly alignment the RA axis with the magnetic compass and roughly set the atitude of the GEM to the latitude of the location. Then do a brief drift-alignment by observing the N-S drift of star in the telescope and appropriately adjust the altitude and azimuth adjusters on the GEM depending whether the star being observed is at the eastern (or western horizon) or at the meridian.

[Robin Lee]

Oh, I get it. Polar alignment + GOTO alignment make the GEM working. I was told that some GEM can compensate for the error of the polar alignment by checking the star alignment.

Thanks Meng Lee for being so helpful.