Table top tracking mount arms (PDF)<\/a><\/strong><\/em><\/li>\n

Table top tracking mount base arms (PDF)<\/a><\/strong><\/em><\/li>\n

Table top tracking mount base cross bar (PDF)<\/a><\/strong><\/em><\/li>\n

Table top tracking mount main parts half scale (PDF)<\/a><\/strong><\/em><\/li>\n

Tabletop tracking mount wiring diagram (PDF)<\/a><\/strong><\/em><\/li>\n<\/ul>
Tools and materials<\/strong><\/h2>\n
Tools<\/strong>\u00a0\u2013 Coping saw, drill with bits to suit the screws and rod, sandpaper, ruler, pencil, screwdriver, 10mm spanner or pliers.<\/p>\n
Materials<\/strong>\u00a0\u2013 Plywood (12mm thick, fine quality) for the arms and the base, scrap wood for the drive disc gauge.<\/p>\n
Sundries<\/strong>\u00a0\u2013 M6 studding (minimum length of 300mm), hinge, six M5x20 bolts and nuts for hinge, seven M6 nuts, two M6x40 bolts, three rubber tap washers.<\/p>\n
Finish<\/strong>\u00a0\u2013 Exterior-quality gloss paint or spray paints for a nice finish.<\/p>\n
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Building on the basics<\/strong><\/h2>\n<\/div>\n
The principle behind the mount is simple.<\/p>\n
Earth turns one full revolution every 23 hours 56 minutes and four seconds.<\/p>\n
This period is called a sidereal day.<\/p>\n
To an observer on Earth the stars appear to revolve slowly around the polar axis \u2013 which for the northern hemisphere is very close to the star Polaris in Ursa Minor.<\/p>\n
The mount has a hinged upper arm on which the camera is mounted, and the hinge\u2019s axis is arranged to point towards Polaris.<\/p>\n
There is a threaded, curved M6 rod between the arms, and this has the drive disc on it.<\/p>\n
Turning this disc causes the upper arm (and the camera) to rotate at the sidereal rate.<\/p>\n
The clever bit is the maths.<\/p>\n
One full rotation of the disc on the rod causes the arm to move by 1mm.<\/p>\n
For accurate tracking the centre line of the rod must be at the correct distance from the axis of the hinge \u2013 in this case 228.5mm.<\/p>\n
If this all sounds a bit technical or tricky to achieve, don\u2019t worry, we have also provided a template, which you can use to bend your rod to the right shape, and the design is quite forgiving of a few inaccuracies.<\/p>\n
We found that it is easier to bend a whole length of rod by hand, and then choose and cut the best section (you need approximately 200mm) for your mount.<\/p>\n
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The main parts of the mount are made from strips of 75x12mm plywood, which is easy to cut.<\/p>\n
Once you have printed out the A4 templates, lightly stick them to the plywood and cut around each shape.<\/p>\n
The angled tops to the base arms need to correspond to your latitude, which will make polar alignment easier to achieve.<\/p>\n
We made ours for 51\u00b0N; if you are in the UK you will be somewhere in the region of 50\u00b0-60\u00b0N.<\/p>\n
The hinge needs to move smoothly and not have too much \u2018play\u2019.<\/p>\n
We found a good quality and inexpensive stainless steel one on eBay, but a reclaimed one from an old door could be a good candidate.<\/p>\n
While you are shopping you also need a ball joint tripod head, which you will fix to the tracker.<\/p>\n
This allows you to aim your camera in any direction.<\/p>\n
These heads require a \u00bc-20 tpi screw (not M6 \u2013 even though the size might look similar) so you can fix them to the mount from below.<\/p>\n
In the section below we will finish assembly and show you how to add a simple motor drive, but the beauty of a barn door tracker is that it works just as well when hand-driven, and there is something very satisfying about the interaction involved.<\/p>\n
The drive wheel doesn\u2019t need to be turned constantly \u2013 just keep the average rate at one turn per minute.<\/p>\n
Image gallery<\/strong><\/h2>\n