Scissor type curved bolt camera mount

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Scissor type curved bolt camera mount

Postby theoyork » Thu May 15, 2008 9:20 pm

Hi,

posted this in Cloudynights, but thought it might be of interest here too.

I was thinking of making a curved bolt barn door mount for a while. After seeing the Astrotrac design I decided to try something similar. I thought it might be more compact and have less PE due to the faster nut speed.

Well a month later I managed something like it. It still looks a bit rough - haven't painted it or anything. I tried to only use bits and pieces I already had so the 'gearbox' is particularly diy as you can see. I used a stepper motor (from a printer originally I think) and an outboard adjustable driver kit from www.quasarelectronics.co.uk.

The lower arm is fixed to the tripod head so the upper arm with the camera mount moves as the nut turns and pushes against a bearing. The nut is also lightly clamped to the bearing with a releasable latch so it can be rewound quickly by hand. The RA axis is 1" wooden dowel with a 1/4 " bolt through it. The surface where the arms meet is smooth and well greased and they move smoothly but with no play - I was pleased that worked. The curved bolt radius is 30 cm, which required a nut rotation of ~1rpm, so with the ~30:1 ratio the motor has to turn quite quickly. I fixed an old monocular with a reticule to it to use a polar scope.

To my amazement it worked well first time. The pic below was a stack of 10 x 30sec subs of Corona Borealis using a Sigma 70-300 lens at 70mm. Couldn't see any star trailing in any of the frames. Will try it on longer FL next time.

The hardest part was getting the bolt curvature right (the hole through the bearing is quite a close fit) but I realised afterward that the solution was to attach it to the moving arm with rubber bushings so it can move slightly, the nut-gear has a flange on it that fits snugly in the bearing and that keeps everything straight when its running. I think the total time it can run is about 3 hours.

Don't have any drawings for it - made it up as I went along - but any similar variation should work. Some pics listed below.

Theo

http://homepage.ntlworld.com/t.allnutt/astro/images/RIMG0417.jpg
http://homepage.ntlworld.com/t.allnutt/astro/images/RIMG0418.jpg
http://homepage.ntlworld.com/t.allnutt/astro/images/RIMG0419.jpg
http://homepage.ntlworld.com/t.allnutt/astro/images/RIMG0420.jpg
More detailed pics:
http://homepage.ntlworld.com/t.allnutt/astro/images/IMG_6831.JPG
http://homepage.ntlworld.com/t.allnutt/astro/images/IMG_6834.JPG
http://homepage.ntlworld.com/t.allnutt/astro/images/IMG_6835.JPG
http://homepage.ntlworld.com/t.allnutt/astro/images/IMG_6836.JPG
http://homepage.ntlworld.com/t.allnutt/astro/images/IMG_6837.JPG
http://homepage.ntlworld.com/t.allnutt/astro/images/IMG_6838.JPG
http://homepage.ntlworld.com/t.allnutt/astro/images/IMG_6839.JPG


First light - Corona Borealis, it works!!:
http://homepage.ntlworld.com/t.allnutt/astro/images/cb1.jpg
theoyork
 
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RE: Scissor type curved bolt camera mount

Postby Chanctonbury » Thu May 15, 2008 10:26 pm

An excellent project!
Chanctonbury
 
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RE: Scissor type curved bolt camera mount

Postby psychobilly » Fri May 16, 2008 7:36 am

Nice One Theo [:)]

Billy...
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RE: Scissor type curved bolt camera mount

Postby cyclops » Fri May 16, 2008 10:56 am

Very cool,i love heath robinson engineering like this!
There's coffee in that nebula!
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