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Barn Door Tracker Help Please

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#1 schwimmair

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Posted 13 October 2013 - 09:10 PM

A nice member in my club just gifted me a manual single arm barn door tracker. Does anyone sell a complete motor/circuit board kit preferably battery operated? I searched and only found ones you had to build and was completely overwhelmed by the wiring schematics.

I am going to donate it to my son's school so even if it's unfeasible to retrofit to electrically track I am sure manually turning by hand would be just as effective as a teaching tool.

Do you thinking posting this in the ATM section would be helpful as well.

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Thanks,
Schwimm

#2 Phil Sherman

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Posted 13 October 2013 - 11:39 PM

That's a really nice implementation of the barn door mount. The curved threaded rod will allow long tracking sessions without introducing rate errors as the door "opens".

It should be easy to motorize because all that's needed is to set a small motor against the edge of the CD that will rotate it at 1rpm. Anything using a DC motor will require a regulated power supply to give a constant rotation rate for the CD. A stepper motor kit, once adjusted for the correct step rate, might be easier to use.

Check around and see if there's an amateur radio club or a "ham" in your area where you can get some assistance with the electronics.

Phil

#3 schwimmair

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Posted 14 October 2013 - 08:11 AM

Thanks Phil good ideas!

#4 wormstar

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Posted 14 October 2013 - 12:17 PM

How does the curved threaded rod work? Is the cd turning a nut?

#5 schwimmair

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Posted 14 October 2013 - 06:29 PM

Hi Wormstar, yes the cd is attached to a nut and is the manual turning wheel. You turn the cd at a constant rate for 360*. The cd has 4 lines on it to guide you where the wheel needs to be in 15 sec intervals. Please don't hold me to this as I just got it and am still figuring it out but I believe the rod is curved to help the mount track better. It would still work with a straight rod but the motor would need to be programmed to speed up and slow down during the one revolution where the curved rod is constant. I hope I explained this right, please anyone add to this if you can help explain.

Schwimm

#6 wormstar

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Posted 15 October 2013 - 08:10 AM

That's close enough, when I first looked I thought the bent rod rotated, which would be pretty awful mechanically.
Thanks

#7 Phil Sherman

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Posted 15 October 2013 - 10:28 AM

The barn door "drive" relies on the rate at which the threaded rod separates the two hinged pieces of wood. As the pieces separate, a straight rod will contact the bottom plate in different places, changing the rate at which the upper plate moves because the length of one side of the triangle formed by the hinge, boards, and rod changes as the hinge opens.

The curved rod keeps this distance constant, allowing for a long period of tracking without changing the dimensions that make this device work. An alternative to the curved rod is to use a straight rod and add a curved wedge to the bottom board that keeps the hinge to rod contact point distance constant as the hinge opens. The wedge approach will severely limit the tracking time when compared to the curved rod design but it allows the rod to be turned instead of rotating a captured nut to open the hinge, a simpler design.

Phil






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