![]() ![]() IOW it is probably possible to get the parts for about £30-35 if you really find the bargains. A pound or two could have been shaved off the cost of switches / power jack too, by sourcing from eBay instead of maplin. This would have cut approx £12.00 off the cost, but I was not confident it would have sufficient torque for direct drive of the threaded rod, so I went for the sure bet. I could have reduced it by going for one of the lower spec stepper motors which are bundled with a driver circuit board. Thus the total cost for the electronics was £46.21, a little bit higher than I was originally hoping for. Even better, they provided a sketch of their circuit diagram for wiring it up.Ĭost being king, I headed over to eBay to source the big ticket parts, and a maplin store for a few odds & ends I wanted to see in person before purchase. A little bit of searching on google revealed someone who had built a barn door controlled by an Arduino Uno and a stepper motor. When you need a cheap, low power microcontroller, the first option that comes to mind is an Arduino. The easy solution to this problem is to use a programmable microcontroller to drive the mount, allowing arbitrary errors to be corrected in software. Sadly the more complicated designs also increase the mechanical errors due to construction inaccuracies. There are various more complicated barn door designs which use 3 pieces of wood to eliminate the tangent errors. The latter is commonly referred to as the tangent error. Some of the error is caused by construction inaccuracies but the bigger part is due to the inherent design decision to produce angular motion (opening hinge) from linear motion (rotating threaded rod). This isn’t as hard as it sounds for short exposures (10-15 minutes) but as the desired exposure time goes up the errors quickly spiral out of control. They are very simple to build, but the pain point should be clear from the end of the previous sentence – you need to control the dimensions such that one rotation of the threaded rod, causes the hinge to open at precisely the right rate. At their simplest, they consist of two parallel planks of wood hinged at one side, with a threaded rod which is manually turned once a minute to gradually open the hinge at a rate which matches the speed of rotation of the Earth. As a result many amateur astro-photographers choose the DIY option, building what’s commonly known as a “ barn door mount“. Commercially available mount options have a starting price of several hundred pounds and range up to thousands. Serious astronomical imaging requires an equatorial mount for the camera / telescope, which tracks the rotation of the earth for anywhere between 5 minutes and several hours. ![]()
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