6
L-350 MECHANICAL INSTALLATION GUIDE
INTRODUCTION
Direct-drive motion systems oer a number of
advantages over the more traditional systems
used in astronomy:
1) Direct-drive systems do not use gears:
Traditional, gear-based motion systems can
only move as precisely as their gears are cut.
Surface imperfections in gears inevitably result
in periodic tracking-errors.
Gears require lubrication, and consequently re-
quire routine cleaning and relubrication. This
is exacerbated in dusty environments, where
lubrication rapidly contaminates.
2) Without gears, there is no PE:
Direct-drive systems are eectively free of pe-
riodic error.
To be completely accurate, there is a small
amount of periodic error in the motion of
each of the individual bearings in the system.
However, due the number of bearings in each
assembly, there is negligible eect to motion
of the total system. Additionally, each axis is
equipped with high-resolution encoders read-
ing at 8Mhz, that are more than capable of de-
tecting miniscule deviations from the proper
tracking-rate.
3) Lower hysteresis:
Mechanical hysteresis (the dierence between
where something was, when measured, and
where it is now) is greatly reduced in a system
that does not use gears. Remember all of that
advice about how to properly balance by being
out of balance, to keep gears engaged? None
of that applies to direct-drive, and tracking is
equally good on both sides of the meridian.
Total hysteresis of the L-Series mount is further
reduced by the use of high-resolution encoders
(18.8M counts/axis, 0.069 arc-second/count).
These on-axis encoders allow the control-elec-
tronics to know precisely where the mount is
pointed, more than 100 times per second. No
auto-guider provides that volume of feedback.
4) Faster response:
Not only are the L-Series drives capable of far
greater rates of speed, their response-times
are also much faster. Consider all of the sourc-
es of backlash in a traditional system (plane-
tary-gears, elasticity in belts, and the worm/
worm-gear interface itself), and know they are
not present with direct-drive. As soon as an
L-series motor moves, your telescope moves.
