The Feathertouch 3" focuser is the industry standard for a high-quality, large focuser and is included as standard equipment or an optional upgrade on many different telescopes. However, due to the nature of its fine-focus mechanism, which uses bearing balls for the planetary reduction, the focuser can slip when moving heavy payloads such as a large-format CCD camera with filter wheel, off-axis guider, etc.
The Starizona MicroTouch Direct Drive motor is an upgrade to the standard motor normally included with our MicroTouch autofocuser. The standard motor simply runs a gear mounted to the fine-focus shaft of the Feathertouch, hence it is possible for slippage to occur. With the MicroTouch Direct Drive, the motor assembly bypasses the fine-focus mechanism and runs the focuser pinion directly, eliminating the possibility for slippage.
In order to maintain the precision of the Feathertouch, the MicroTouch Direct Drive uses a high-ratio gear reduction system. This produces an impressive 44:1 focus reduction. The resulting precision is 13,200 steps of the motor per turn of the focuser pinion, or just 1.6 microns (0.000063") per step. The motor has been tested to lift at least 70 pounds!
How It Works
When you remove the manual focus knobs on the standard Feathertouch focuser to install an autofocus motor, you can see the internal reduction mechanism. The fine-focus shaft (to which the motor gear normally mounts) is pinched by three stainless steel bearing balls held in a brass housing. When the coarse-focus knob is turned, the brass housing and balls are turned directly. This drives the pinion shaft which moves the focuser drawtube. When the fine-focus knob (or focus motor) turns the fine-focus shaft, the balls are turned more slowly because of the difference in radius between the shaft and the bearing balls. This gives the 10:1 fine-focus reduction. (With the 2:1 gearing of the standard MicroTouch motor, the resulting ratio is 20:1.) Unfortunately, with a heavy load, the drawtube resists the upward pull of the payload against gravity. The fine-focus shaft can then slip against the bearing balls and precision focus ability is lost.
The Starizona MicroTouch Direct Drive avoids this problem by using a high-ratio gear reduction assembly. The motor drives the pinion directly, bypassing the fine-focus mechanism. In this way there is no possibility of the drawtube slipping and focus is much more precise and repeatable.
Features
The MicroTouch Direct Drive Motor is available separately for current owners of the MicroTouch Autofocuser, or as a package with the MicroTouch wired or MicroTouch wireless autofocuser system.
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