
Gemini Users Manual 68
DEC Spur:
DEC Worm:
RA M. Enc:
DEC M. Enc:
In addition to using the Setup command, you are able to change the Mount Type
immediately after a Cold Start. Refer to section 2.4.2.1 Cold Start Setup Options for an
explanation of how this is done.
Use the "Mount Type" menu item to select one of the telescope mounts listed above.
IMPORTANT: You must restart the Gemini after changing the mount type (power off,
then power on and select “Cold Start”).
All of the selectable mount types except “Custom Mount” are recognized immediately
upon their selection. Selecting “Custom Mount” brings up a submenu consisting of six
mount parameters; each numerical parameter must be entered within the following
ranges:
RA & DEC Spur (Spur Gear Ratio): 20 to 150
RA & DEC Worm (Worm Gear Ratio): -720 to +720, excluding -99 to +99
RA & DEC M. Enc (Motor Encoder Resolution) range: 100 to 2048
Note: For any given Custom Mount, the RA or DEC angular movement θ for each tick of
the mount’s synchronous motor is computed by the following formula:
θ = 1.296 x 10
6
/ (Worm Gear Ratio*Spur Gear Ratio*Nominal Motor Encoder Resolution)
where 0.1 ≤ |θ| ≤ 2.5 arcseconds / tick
The sign of θ indicates the direction of the mount’s tracking movement.
For custom mount designs, besides this given step range you also have to consider how
much torque the planned gearing is able to deliver. Additionally, the product of the
nominal motor encoder resolution and the spur gearing must not exceed 26,800.
5.3.10.2.6 Set Safety Limit
• Confirm to Set
• Reset to Defaults
• Set East:
• Set West:
• Set GoTo:
The nature of a German Equatorial Mount is that while it will never make a complete turn
in RA, at the extreme ends of its RA movement, the optical tube assembly (OTA) can
collide with the tripod legs or other equipment, causing damage. Gemini has factory-set
default limits as to how far the mount can turn to the east and to the west. These limits
were established with the selected mount in mind, but without knowing which OTA will
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