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Gemini Users Manual 10

2.2.3 Encoders

Gemini can take advantage of optional encoders on your mount. Plug the encoder cable

into the 8-pin socket below the HC input. The layout is compatible with the Y-cable of

the usual DSCs, like the Losmandy DSC or the NGC Max. The encoder ratios and

directions can be set using the “Setup→Encoder” menu item. The default setting is

(minus) -4096 for both axes, as used for the G-11 mount. The sign indicates whether the

encoder is moved in the same or the opposite direction as the axis to which it is

connected. Refer to the table below for other Losmandy mount encoder settings.

Mount Encoder Tics

GM-8 -4096

G11 -4096

HGM200 +8192

Although Gemini does not require encoders to function, there are some advantages to

using them. Encoders allow the system to keep track of the telescope's position even

when you are moving the telescope manually with the clutches loosened. Unless you

have encoders, you should never loosen the clutches because to do so will cause the

system to lose information both about where it is pointing, and about how close the

mount is to the safety limits. The system must know where the eastern and western limits

are, and when it has to make a meridian flip. Using encoders, the system is informed

about manual movements and can take them into account, thereby avoiding exceeding the

limits.

The Gemini software is designed to give you the best of both worlds. As long as the

position signaled by the encoders is consistent with the motor position within two

encoder ticks, the far more accurate motor position is used. But if the encoders signal a

change, the system trusts them and corrects its internal address values.

When this happens, you see the characters R (for RA address correction) or D (for Dec.

address correction) displayed at the rightmost place of the system's display. This can be

an indication of manual movement, mechanical slippage, or a wrong encoder resolution

setup.

Even if the encoders are set "Online" (by selecting “Setup→Encoder→Use Encoder”)

you can use the system without the encoders being connected. Encoder values are

ignored until the first time a position change is signaled (the encoders are auto-detected).

On the other hand, you must not connect encoders while the system is running. If you

intend to use them only at certain times, you can enable or disable them using the

“Setup→Encoders” menu items.

Although Gemini supports encoders, the vast majority of Gemini users do not them.

Once you are familiar with slewing using the hand controller, the database, Identify and

GoTo functions there is little need to move the telescope manually. Even if you do move

it manually it can easily be synchronized again.

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Equinox Systems GEMINI Manuel d'utilisateur Page 15