20
CONTROLLING YOUR GTOCP5 MOUNT
Your Astro-Physics GTO mount has a remarkable servo control system that combines with the precise mechanics of the
physical components to give the mount its superb performance. Contrary to popular assumption, the brains of the mount
are not found in the keypad, nor are they in an external computer that is used to send the mount pointing here or there.
The real brains of the Astro-Physics GTO Micro-step Servo System are in the CP5 control box. Simply think of your
Keypad or computer as being an input device for the CP5. If you understand this from the start, you will always have a
better concept of how things work, and you will be less likely to make operator errors.
We divide the types of control functions that the CP5 control box performs into three principal categories. The parameters
and values for these control functions along with the commands to execute certain functions are given to the CP5 control
box by the input device(s) that are in use.
1.
Primary Control Functions.
Primary control functions include all the functions that define HOW the servo will make
decisions. In particular, these are the initialization functions – time, date and location – along with Park, Meridian De-
lay, ReCal and Sync. These are the most important functions to get right. Primary control functions allow the servo to
know where the meridian is and to determine whether a slew requires a meridian flip.
It is of vital importance that your input device handles primary control functions correctly, and that input for primary
control is limited to just one device. The concept of initialization is introduced on page 21 and discussed more fully in
"Initialization and Shut-down" on page 36.
2.
GoTo / Move Functions.
GoTo / Move functions include coordinates, move commands, and rate commands. All of
the listed input devices provide some way to command the CP5 to move the mount. Most provide pretty complete
movement inputs. The exception is the guider signals from a guide camera, which, of course, cannot command a GoTo
slew. Most of what you do during a typical night under the stars uses the GoTo / Move functions.
3.
Absolute Encoder Functions.
PEC curves are no longer needed. One of the most advanced features of the Mach-
2GTO mount is the integration of the absolute encoders with the micro-step motor servo system. The CP5, via the
absolute encoders, constantly monitors the servo positioning and provides near-instantaneous feedback correction with
