| This JMI battery-operated micro-slew drive is designed for use with the Vixen Porta altazimuth mount to give you precise and responsive hands-free/vibration-free pushbutton tracking of celestial objects in altitude and azimuth (but not both simultaneously). It also works for terrestrial observing, but its slewing speed may not be rapid enough to track fast-moving terrestrial subjects. Terrestrially, it is more suited for scanning scenery, following sail boats and harbor traffic, etc.
There are five parts to the dual axis drive. They include two DC motors (the type used in JMI electric focusers and declination drives), two mounting brackets, and a battery-powered hand control (plus the necessary cables and hardware to install and operate the system). The motors move the Porta mount across the sky by electrically turning the mount’s manual slow motion altitude and azimuth controls to track objects so you don’t have to grope for the manual controls in the dark.
The mount’s existing slow motion control knobs are removed and replaced by the JMI motors, which are held in place by the supplied mounting brackets. A small hand control box plugs into the motors using the supplied coiled cords. The hand control has a switch which selects either altitude or azimuth operation. Pushbuttons control the direction of mount travel, while a three-position slide switch sets the drive speed. Moving the three-position switch to the left provides slow speed centering for low and medium power observing. The center position provides fast slewing. Moving the switch to the right provides very slow centering for use at very high magnifications. The slow and very slow centering speeds automatically switch to high speed slewing if the pushbutton is held down for more than three seconds. The motor has electromagnetic braking for very precise control. The control box holds a 9-volt battery (supplied) that should power the drives for several months of normal use, depending on the temperature (cold batteries do not last as long) and how much power-hungry high speed slewing you do.
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