RTS2-ROTAD(7)
============

NAME
----

rts2-rotad - generic manual page for rotators (or derotators)

SYNOPSIS
--------

*rts2-rotad-'rotator driver'* [-s 'hostname[:port]'] [--modefile 'filename'] [-d 'device name']

DESCRIPTION
-----------

Rotads represent various hardware used to position instruments, so they are
correctly oriented. Rotators are natural part of Alt-Az telescope, where they
have to offset for parallactic angle. Rotators can also be part of various
instrument setups attached to the telescope.

For description of options common to all devices, please consult
linkman:rts2-device[7].

SETTING UP ALT-AZ DEROTATORS
-----------------------------

Alt-Az derotators must have configured zero angle offsets, so when they are 
tracking, parallactic angle is correctly applied. Also hard coded min and max
values are required. Follow those steps to setup a derotator (once you have working instrument
driver):

* see maximal and minimal allowed rotation in **CUR_POS**, move rotator (disengage
  motor if possible, e.g. if rotator has encoders independent to motor operation)

* put those values to **MIN** and **MAX** fields of the derotator, and write
  those to derotator default file (see linkman:rts2-device[1] for details).

* make sure **parangle_track** is set to **off**, so the derotator will not move
  when you move attached telescope

* verify that the derotator will not move outside limits, particularly with new
  hardware - by setting **TAR_POS** to angles both inside and outside the limits

ADJUSTING ZENITH BASED LIMITS
-----------------------------

Usually rotators are used for rotating field in Alt-Az telescopes, so north
keeps same orientation on the image plane, regardless of the telescope
orientation. In order to facilitate this job, the derotator is usually attached
to altitude axis - so it (if held at position) move as the telescope altitude
axis moves.

You might be happy with specifying only **MIN** and **MAX** limits put above.
Put please keep in mind, that those are limits in derotator plane. So if you
move telescope in altitude, those limits will not move (but derotator will
move) - in a sense, those are the limits attached to altitude axis.

Your telescope will have some instruments attached to derotators, which would
need cables to being powered and commanded. Those of course form a problem, as
those are fixed in altitude, humming peacefully on azimuth support platform. In
order to calibrate zenith angle based limits, independent of telescope axis
orientation, please follow this procedure (after completing basic setup,
described above):

* if possible, make sure that motor is powered down (if you have encoders independent of motor)

* make sure that **parangle_track** is set to off

* point telescope somewhere

* check that telescope altitude and azimuth are visible in **TELALTAZ** field
  (hit **F5** in monitor or execute **info** command to make sure you are
  getting actual value)

* make sure that **TELALTAZ** altitude and azimuth corresponds to telescope
  position

* move derotator, and see how **zenith** value moves to reflect zenith angle

* adjust **ZEN_MIN** and **ZEN_MAX** values so the derotator stays within limit

* turn derotator motor on

* turn **parangle_track** on

* move telescope to various position (derotator's zenith angle depends just on
  altitude, so moving telescope close to zenith, doing tests and then close to
  horizon and doing tests would be enough) and check that derotator stays
  within **ZEN_MIN** and **ZEN_MAX** limits (change **OFFSET** value).

OPTIONS
-------

Please see linkman:rts2-device[1] for options description.

Rotator drivers
---------------

* linkman:rts2-rotad-sitech[1] SiTech custom made (de)rotator

SEE ALSO
--------

* linkman:rts2[7]

* linkman:rts2-device[7]
