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Which 'Barn door' tracker?


Leebert

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Hi all,

Whilst I save for a scope and eq mount, I thought I'd get a little practise in with stacking some astro photos.

There seems to be a few different designs around but I was thinking of making a simple one with a curved threaded rod with a motor drive.

Is that design fairly accurate? I'm looking to practise on M31 / M42 and brighter objects to start so not looking for a super accurate set-up for very long exposures.

I was thinking that I would take 10 to 20 exposures of up to 30 seconds long and the same dark frames so it only has to be good for about 1/2 hour approx.

Would I get reasonable results or should I wait until I get an EQ5?

Many thanks.

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Our club worked on a group project involving a barn-door tracker with the curved rod as discribed in the original post. So far, only one person has responded to my queries to give me feedback regarding the success or failure of the tracker. That was our club's President ( bless his heart ! )

Unfortunately, this version of the tracker uses an electric motor to drive the threaded rod and open the leaves of the barn door. The speed of the electric motor was governed with a reostat in series with the battery power. This has resulted in poor regulation of the speed, and thus, the stars trail when anything more than minimal exposure time, or camera/lens weight is attached to the cameral mount.

It would seem to me, based on the explaination of the curved rod drive mechanism, that the accuracy would be quite good, IF the friction and weight of the drive being loaded down with a camera and lens could be overcome.

I suggested that an electronic stepper circuit be used to drive the motor, the idea being that the pulses of higher energy electricity would overcome the friction, and the time between those pulses could regulate the tracking speed.

Think of a clock with an escapment regulating the time, rather than just a weak spring trying to drive the hands slowly ! Is that a good analogy ?

Cheers! Jim S.

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Our club worked on a group project involving a barn-door tracker with the curved rod as discribed in the original post. So far, only one person has responded to my queries to give me feedback regarding the success or failure of the tracker. That was our club's President ( bless his heart ! )

Unfortunately, this version of the tracker uses an electric motor to drive the threaded rod and open the leaves of the barn door. The speed of the electric motor was governed with a reostat in series with the battery power. This has resulted in poor regulation of the speed, and thus, the stars trail when anything more than minimal exposure time, or camera/lens weight is attached to the cameral mount.

It would seem to me, based on the explaination of the curved rod drive mechanism, that the accuracy would be quite good, IF the friction and weight of the drive being loaded down with a camera and lens could be overcome.

I suggested that an electronic stepper circuit be used to drive the motor, the idea being that the pulses of higher energy electricity would overcome the friction, and the time between those pulses could regulate the tracking speed.

Think of a clock with an escapment regulating the time, rather than just a weak spring trying to drive the hands slowly ! Is that a good analogy ?

Cheers! Jim S.

Hi,

Thank you for this. I quite liked the simple but accurate design of the curved threaded rod tracker.

I hope to construct the tracker with the balance of the unit and minimum friction in mind. For the drive, I have raided my spares box for RC models and have a 3 phase brushless electric motor and controller along with a few pinions and gears of various sizes. The drive was originally from an electric model helicopter and is quite smooth and has plenty of torque.

I hope that if I take a little care in the building, I'll end up with a fairly accurate tracker (well, as accurate as a couple of pieces of ply and some other bits found in the shed can get!) - watch this space :)

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Had some spare time today so sloped off to the shed...

The Scotch Mount is coming along. Gearing calculated. Just the drive to mount.

I changed my mind on that. It's now a Futaba 3152 servo modified for continous rotation and geared down with some RC helicopter gears from my spares box. All connected to a battery via an adjustable regulator to control the speed.

Hopefully have some test photos in the next couple of weeks weather permitting :)

post-28721-133877660344_thumb.jpg

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  • 3 years later...

Hi I'm searching plans to make a manual double barn door with curved rod, is this the best design for tracking up to 5 to 10 mins,

I've seen designs tho no measurements, also curved rod measurements and arc radious for the bend in rod,

Any help much appreciated,

Tyson Queensland Australia

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You have to calculate the curve radius etc.

Not sure with manually turning that 5-10 minutes is over estimating what you will achieve, perhaps if using a wide lens you stand a better chance.

I don't have the page that had a barn door calculator to hand.

http://www.garyseronik.com/?q=node/52

I will be motorising my mount using a different approach to that one.

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