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Old 31-10-2018, 11:25 AM
Saturnine (Jeff)
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Saturnine is offline
 
Join Date: Jul 2008
Location: Wollongong
Posts: 2,134
Barn Door trackers are a relatively cheap , simple solution to being able to do longer exposure images, 30 to 60 sec is enough when also stacking several ( or many ) together. Made myself one last year , though it is a bit more high tech, as it is powered by an 12VDC Geared Motor.
Guess I'm a bit fortunate in that I was a Fitter & Machinist by trade, now retired and still have access to a lathe and milling machine. Did some basic math for the curvature of the 6mm x 1mm pitch, threaded rod, motor speed and gear ratio vs the distance from the hinge to the threaded rod ( radius of curvature ) to achieve the desired tracking rate.
Speed is not perfect, is out by about 1 deg. an hour which equates to 1 arc/ min for an 60 sec exposure. for wide angle lens is hardly noticeable.
Intend to add an PWM unit to fine tune the speed for greater tracking accuracy soon but I'm happy with the results so far.
All up the bits and pieces cost about $30, motor , ball head , hinge, paint etc. and machined the pulleys to suit with an "o" ring as the drive belt. Had some aluminium plate already but wood can be used quite successfully .
Polar alignment is achieved by mounting an old finder scope butted against the hinge, held by an elastic band and pointing at Sigma Octans and offsetting the required distance to the SCP.
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