A barn door tracker, also known as a Haig or Scotch mount, is a device used to cancel out the diurnal motion of the Earth for the observation or photography of astronomical objects. It is a simple alternative to attaching a camera to a motorized equatorial mount. Astronaut Don Pettit operates a barn door tracker located in the Destiny lab of the International Space Station. He made the mount from spare parts he had accumulated from aboard the station. The barn door tracker was created by George Haig. His plans were first published in Sky & Telescope magazine in April 1975. Modified versions of the tracker were published in the magazine's February 1988 and June 2007 editions. In late 2002 and early 2003, NASA astronaut Don Pettit, part of International Space Station Expedition 6, constructed a barn door tracker using spare parts he had accumulated from around the space station,[2] permitting sharper high resolution images of city lights at night from the ISS. A simple single-arm barn door tracker can be made by attaching two pieces of wood together with a hinge.
A camera is mounted on the top board, usually with some sort of ball joint to allow the camera to be pointed in any direction. The hinge is aligned with a celestial pole and the boards are then driven apart (or together) at a constant rate, usually by turning a threaded rod or bolt. This is called a tangent drive. This type of mount is good for approximately 5–10 minutes before tracking errors become evident when using a 50 mm lens. This is due to the tangent error. That length of time can be increased to about 20 minutes when using an isosceles mount. A curved drive bolt in lieu of either a straight tangent or isosceles mount will greatly extend the useful tracking time. These designs were further improved upon by Dave Trott, whose designs were published in the February 1988 issue of Sky & Telescope. By using a second arm to drive the camera platform - thus adding complexity to the fabrication - tracking accuracy was greatly increased, and can lead to exposure times of up to one hour.
The most accurate of these designs is the Type-4. A modified double arm design minimizes tangent error by raising the point of rotation of the arm on which the camera is mounted. This has the effect of tilting the arc traced by the camera arm backwards causing it to follow a better path. A basic geometrical analysis of the tangent error shows that it can be fully compensated for by inserting a specially shaped piece between the threaded rod and the top board. Such solution was already known for a long time before the original G. Haig publication. The most basic of these designs are manually operated, although some have added electric motors to automate and improve the accuracy of the tracking process. ...shoot stars, planets and other nebulae, with a camera that is.No Arduino, no stepper motors, no gears, just a simple motor turning a threaded rod, this barn door tracker rotates your camera at the exact same rate as the rotation of our planet, a requirement for taking long exposure photos.
The concept isnt new, its been around since the 70's, back in the days of 35mm film, my version updates it to motor drive and adds a corrective cam to remove the inherent error in the original version. Briefly, the common ways of doing this are the single hinge 2 boards with a straight threaded rod, the single hinge 2 boards with a curved threaded rod and the doubled hinged 3 boards version. All versions can be motorised, but the 2nd version with the curved rod has the motor driving a nut through gearing and the curved rod is held stationary. //?q=node/52 Finally Dave Trott who invented the double-arm tracker. /inventions/double-arm-barn-door-drive/Step 1: Parts and Tools Mostly hand tools were used with the exception of a mitre saw to get the ends for the hinge mount nice and square. I also used a drill press for drilling the holes for the sliding motor rails so that they are parallel to each other, as well as the hole for the drive rod to ensure it was nicely perpendicular.Parts A decent hinge with very little play, I went with a solid brass 63mm one seeing as the plank width was 69mm.
The main part of the tracker, 500mm pine 22m X 69mm. The camera mount, approx 300mm of 22mm X 44mm meranti (a hard wood, well harder than pine anyway) A brass 1/4" 20 modified machine screw for mounting the camera. M8 nut and bolt for mounting the cam mount to the main body. M6 rod ~ 90mm with wingnuts and washers for the tilt axis in the camera mount. M6 nut and bolt 50mm long for attaching the tracker to the tripod. 16 wood screws, 6 for the hinge and 10 for reinforcements in the camera mount. A 70mm X 50mm section of plastic cutting board for the corrective cam. A 230V AC synchronous 1 rpm motor. 2 x steel rods to fit the motor mounts, 4mm in this case. M6x1mm threaded rod 135mm long out of which I get a usable length of 90mm, @ 1mm pitch that translates to 90min M6 coupling nut to connect the motor shaft to the drive rod with split pins to fit. M6 Tee nut for the bottom board's drive rod. An existing sturdy mount like a camera tripod or a diy contraption to suit, bear in mind some tripods have a plastic pan tilt head assembly and wobble a fair amount.
Something to note with the drive rod, M6 is a nice middle size, M5 would have a smaller board length of 185mm hinge to drive rod distance and possibly very flimsy, M8 would be more robust but would need a hinge to drive rod distance of 285mm which might become very bulky. Lastly, a camera is also a requirement, preferably a DSLR with remote in order to use the "bulb" setting for long exposures. On my Nikon D70S I use an infrared remote because the camera wont allow bulb setting with the timer, it just overrides with 1/5 sec exposure. That said, it might be theoretically possible to use a Canon PowerShot (point n shoot range) and load it with the CHDK software to utilise the intervalometer scripts. « PreviousNext »View All Steps DownloadTo photograph the stars, you need a gadget that can track the revolving night sky in a perfectly timed arc. Otherwise all you’ll see is streaks and blurs. You can buy fancy motorized “equatorial mounts” for telescopes and cameras, but it’s way cheaper and more satisfying to build your own simple “barn door” tracking mount using a long bolt or threaded rod as a drive screw.
You mount your camera on the “door,” then aim the hinge straight at the North Star, Polaris. The motor opens the door very slowly to match the sky’s rotation, for blur-free exposures of minutes or even hours. You can set the speed using a microcontroller or a simple circuit. But there’s a catch: A straight drive screw turned at a constant rate won’t produce a constant angular motion. It’s called the “tangent error” — and here’s how some of our favorite DIY barn door trackers solved it. Sky & Telescope contributing editor Gary Seronik of Victoria, British Columbia, built a lightweight, portable tracker that drives a simple 4RPM DC motor with an adjustable voltage regulator to dial the rotation rate, and a curved bolt to reduce tangent error. He’s shared his design and schematics in this great tutorial. “It’s hard to beat a DC motor and simple regulator circuit for simplicity and performance,” he says. Seronik went on to create an even more compact Hinge Sky Tracker using an 8″ strap hinge in place of the plywood doors.
A straight bolt introduces tangent error, but he solves that by taking shorter exposures and “stacking” them in freeware called DeepSky Stacker. » For the best of both worlds, build Seronik’s new motorized Hinge Sky Tracker, with a curved bolt, DC motor, and regulator circuit. Find the project here. Chris Peterson in Guffey, Colorado, used a straight bolt in pivoting mounts and cleverly programmed a Freescale/Motorola 68HC705C8 microcontroller to drive a 1.8° stepper motor at a variable rate to produce constant angular motion. He’s taking 20-minute exposures with a 300mm lens, and has shared his schematics and code. University student David Hash (now an aerospace engineer) updated Peterson’s build with an Arduino Pro microcontroller, 1.8° stepper, and Pololu microstepping driver board to give 3,200 microsteps per rotation (Figure B). He’s shared his build and code on Reddit. He gets great photos by stacking multiple 90-second exposures; check out his Andromeda Galaxy pictured above, and more on Imgur.