Smart Drive (Both Lx100 Models); Smart Drive Features; What Is Smart Drive; Operation - Meade 8" LX100 Series Instruction Manual

-40-
E.
Smart Drive (Both
LX100 Models)
1. Smart Drive Features
o
Permanent Periodic Error Correction (PPEC)
.
Declination Drift
Correction
.
Reversible
Directions
for Dedination Correction
Buttons
o
Two Speed Electric Focus
.
Electric Focus Lock-Out
2. What
is Smart
Drive?
The purpose of a clock drive on any telescope, is to accurately track an astronomical object
-
keeping it
precisely in the center of the field of view.
Sinoe
the motion of a star is perfectly smooth and consistent,
the
telescope clock drive should, ideally, also be perfectly smooth and consistent. ln attempting to achieve
this
ideal,
telescope makers have gone
to great
measures
to procure the most precise gears
and
worms. But
no
matter how accurate the gear and worm, there are always manufacturing tolerances, and these lead
to
minute, repeatable speed variations in the tracking speed
of the
telescope
-
called periodic error.
By far the largest
contributor to
periodic
error is the
worm
itself. Errors as
small as 1/1000'can
lead to errors
as large as 30 arcsec in the tracking of the telescope, and these errors will repeat every time the worm makes
a complete revolution.
For astrophotography
work, this is the major reason that a
long-exposure
photo
must
be 'guided"; this much error will ruin a photograph. While even a telescope with zero periodic error (if
one
existed)
would still require "guiding" during a long astrophoto (due to atmospheric
turbulence), eliminating as
much periodic
error
as possible
greatly
increases the odds for a good photograph.
The Smart Drive
makes a
quantum
leap
forward
in the elimination
of periodic error. lt is laught" the periodic
error due to the worm, so
that
the microprocessor can make the necessary speed
correclions -
usually before
the errors are even seen. Smart Drive is
"taught"
by
'guiding"
on a
star,
as
if
you were taking
an
astrophotograph. This
is
done by tracking on a star and keeping it centered
in the field-of-view by using the
correction buttons
on
the ECC hand controller. By monitoring the
button pushes, the Smart Drive
builds, and
permanently remembers, a
model of the
periodic error. This model is then
used
to vary the frequenry to
the
motor to
eliminate the
worm periodic error.
3. Operation
a. Accessing Smart Drive Functions
All Smart Drive features are accessed by the ECC
hand
controller buttons, with audible feedback for
each
step.
There are two basic categories of Smart Drive
functions.
The Control-Focus functions are used to turn
on
and off the electric focuser, and to train and use the worm model feature of the PPEC. The Control-Dec
functions are used for the
Declination drift feature, and to reverse the Declination motor direction
buttons.
Note: Enler'ng
a
Control mode
is only the
first step of activating
a
Smart
Drive
function. When
a
Control
mode is entered (described below), the ECC buttons are actually being redefined to perform tasks ditferent
than
what they normally do. Think
of
the
Control-Focus
and
Control-Dec
as
the shift key
on
a
typewriter or
function key on a scientific calculator. Once pressed, the next button press will determine the Smart Drive
function being
activated.