Chapter 1
Functional Overview
The SteelDrive digital motor focuser is used for automated telescope focusing. It may be used stan-
dalone as a hand-held device, as well as remotely in conjunction with a computer. It comprises a
motor unit which is attached play-free to the mechanical focuser of the telescope by means of a timing
belt as well as a controller unit which houses the electronics and does also serve as a hand-held key-
pad. Controller and motor unit are connected via a standard RJ45 (Cat7) patch cable. Temperature
sensors may be connected to each of the units. The sensors are used for the automatic compensation
of focus drifts due to changes of the external temperature. The temperature sensors may also serve
as the input signal for a PID controlled fast-PWM power output. It can be used to precisely control
the temperature of dew-heaters, optical filters, mirrors etc.
1.1
High precision focusing of heavy loads
The high-torque stepper motor is directly engaged with the focuser via a timing belt. This eliminates
the backlash (and potential cause of defects) induced by gearboxes which would have to be used with
lower power motors. The SteelDrive can quickly move loads up to 8 kg. The default focusing resolution
is
≈
2
.
3
µm
(in conjunction with a
Baader Diamond SteelTrack
R
focuser).
1.2
Contactless Homing Sensor
The SteelDrive motor unit features a contactless (wearfree) homing sensor (hall-effect sensor). It is
activated by a magnet attached to the moving part of the focuser. It enables precise homing and
repeatable approach of saved absolute positions as well as reference of the mechanical endstop. How-
ever the SteelDrive is also usable without the homing sensor as the absolute position is kept in a
persistant circular eeprom buffer. Even if a power failure occures, the last absolute position is loaded
upon restart of the SteelDrive.
1.3
Standalone Temperature Compensation
SteelDrive II provides two sockets for the attachment of digital temperature sensors (one sensor is
included, sockets on motor unit and controller unit). It is possible to used multiple (up to 8, use
3-pin audio Y-adapter) sensors in parrallel at one sensor socket, their temperature will be averaged
(This enables the measurement the temperature eg. above and below the telescope tube, or inside
and outside etc.).
For the automatic temperature compensation, the sensor socket to be used may be selected, or the
average temperature all sensors attached to both sensor sockets may be used.
The temperature
compensation factor can be calculated with the
SteelGoII
software and is saved internally in the
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