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Old 29-07-2015, 11:24 AM
Ilmenite (Nick)
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DIY electric (auto?)focuser...

Having had a look around at the assorted commercial and homemade electric and autofocusers, it seems that there should be a very simple way to make an electric autofocuser. In the crudest version, the electric focuser consists of a single on-off-on switch which controls the polarity of the voltage to a geared DC motor mounted on the telescope focuser in some way. To this can be added a speed controller which varies either voltage or duty cycle (PWM) to slow the motor.
Autofocus is simply the computerisation of the switch (and possibly the speed controller) to move the focus one way of the other according to some quality algorithm.
Thus, coupling the two aspects together should be very simple, the computer controlling the switching aspect. The projects I have seen to do this invariably seem to use the ASCOM standard so that they can be driven using assorted software packages.
My thought is to pick a very simple (and cheap) USB relay controller with two relays and write an ASCOM compatible driver for it. This will then do pretty much everything an autofocuser is required to do (move in, out). A third relay could give a high-low speed control.
Does anyone else have any thoughts on whether this is possible, or has already been put into operation?
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Old 30-07-2015, 08:59 AM
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ZeroID (Brent)
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It's obviously possible, depends on your fabrication skills. The important ctriteria as I understand is accuracy and reproducability, ie focus home, focus set positions can be reproduced by the same settings. Hence most electronic focussers use a stepper motor rather than voltage controlled systems.
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Old 30-07-2015, 07:27 PM
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AlexN
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Google the SGL ascom focuser or SGL motorfocus. I built a couple of arduino based focusers and they work every bit as well as robofocus
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Old 31-07-2015, 07:56 AM
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wasyoungonce (Brendan)
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Nick contact Dave Trewan build one of his units, cheap, ASCOM compliant easy to build and use.

http://www.dt-space.co.uk/SharpSky/
http://www.dt-space.co.uk/SharpSky_Kit/
http://dt-space.co.uk/SharpSkyClient/
http://www.dt-space.co.uk/SharpSky_TC/
http://www.sharpsky.net/
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Old 07-08-2015, 02:38 PM
brown_rb (Robert)
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or build you own based on this

http://sourceforge.net/projects/mydc...ativedcfocuser
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Old 07-08-2015, 05:10 PM
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Bassnut (Fred)
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There are 2 kinds of focuser positioning, absolute and relative. Absolute involves encoders or steppers from a home position, relative is simple DC drive. Both work, but have different performance.
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