Made a BarnDoor Star Tracker

[axle01]

I thought i'd have a go at making a BarnDoor Star Tracker to track the stars as the earth turns hoping to be able to get somewhere between 5 to 10 minutes shutter speeds.

First i did a lot of research to work out length, motor speed, gear ratio etc. then i got to work i started with 2 pieces of 350mm x 100mm x 10mm alloy plate and 2 pieces of 120mm x 100mm x 10mm alloy plate.

I then went to Bunnings and got 2 of the best hinges with the least amount of side play i could find.

I drilled and bolted the 2 long plates and the 2 small plates to the hinges.

I then bolted the small plate to the large plate, this is to adjust for our latitude which in my case is 19*16S.

I then mounted the ball head towards the low end of the wedge to allow the least weight resistance to the motor drive.

I had worked out that the distance from the hinge pivot point to the threaded rod mount would be 29cm so i got a length of 1/4' SS threaded rod which i bent in a 29cm radius.

The reason i use a curved rod is if i used a straight rod it would introduce tangent error which means as the angle increases the speed will change.

The gears are 80T x 20T which is 4 to 1 and the motor spins at 4RPM which on the 1/4' x 20 will give me 15* per hour which is what the earth turns at.

I got most of the motor mounting and gear mounting hardware etc from ServoCity in America, was a real pain waiting for the stuff to arrive then having to order more as i needed it.

I had a forward/reverse controller which i mounted on the bottom plate to control the speed.

Now i have it all together i did a test and it rises at 15* an hour which is what i am aiming for.

We have total cloud cover so i won’t be able to test it for a few days,,,,,bummer.

IMG]http://i63.tinypic.com/28i2g61.jpg[/IMG]







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[ameerat42]

It looks a (treat). Can't wait to see test results.

[axle01]

It looks a (treat). Can't wait to see test results.

Thanks mate I can’t either but typically the weather has turned bad.

Al

[ameerat42]

I remembered to ask later - then forgot about it again - is the latitude angle set by the tilt of the tripod?

[axle01]

I remembered to ask later - then forgot about it again - is the latitude angle set by the tilt of the tripod?

I don’t know I can’t remember,,,,,,,,well you started it,,,,,,if you look at the second photo the small Wedge underneath with the curved 8mm bolt, so I level the tripod then adjust the latitude angle with the curved bolt with a inclinometer.

Al

[ameerat42]

I thought the curved bolt was to drive the unit in time with sidereal motion. - Ie, to track the stars...

STOP PRESS

Ah! I see now from the last pic (and wonder how I missed it). You have two hinges: the one with the
curved threaded rod to track the stars, and the other to match your latitude (Or I dunno what I'm talking about)

But that may be a distinct possibility still, because you have the black doo-dad on top which looks suspiciously like...
a sidereal motion drive /

[axle01]

I thought the curved bolt was to drive the unit in time with sidereal motion. - Ie, to track the stars...

STOP PRESS

Ah! You have two hinges (Or I dunno what I'm talking about)
because you have the black doo-dad on top which looks suspiciously like...
a sidereal motion drive

Yes you do, your right about the 2 hinges but the only “black doo-dads” on top are a ball head and a 4 cell battery pack so I don’t think you know what ya talking about.

Al

[ameerat42]

Ah! Too much modern music.

Black is Black, and so I wrongly equated the two blacks with connected function