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Yet another Barn Door Tracker question..


caerus_sam
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I've finally salvaged the floppy disk drive from my old PC (Hitachi Deskstar HDS722580VLAT20 if anyone was wondering). I've seen '555 Timer IC' mentioned on the forum and I'd just like to know a little more. In my head, I can't figure out how a small chip can reduce the 7200rpm on the floppy disk drive to 1rpm. Any explanation would be greatfully received.!

I do have a couple more questions that may be easier to answer:

How do I connect the drive to the bolt.?

Would it have enough torque behind it to raise my Canon 400D and battery pack.?

Would anyone have any circuit diagrams that could be of assistance.?

Thanks in advance. :)

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Thanks for the diagram, Steve.

It may be expensive and hard to find Billy, but as is widely known, Astrophotography/Astronomy is an expensive hobby. It will be a while until I can get a scope so I don't mind putting the money into a Barn Door to make the most of it.

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Hi Sam, I think you must be referring to the motor which rotates the floppy disk rather than the stepper motor which steps the read/write heads in and out across the surface of the disk. Don't know if it was my post you saw - I replied to Barn door tracker motor by Tadakun on page 5 of this section which explains how I did mine. Also, your floppy disk drive is probably only 3.5" so the stepper motor might not be up to the job. I think it's a lot of work to make from scratch. You could start by trying it hand driven like the one shown in Steve's link. Here's a table I found somewhere.

Scotch mount: Turn Frequency Compared to Focal Length of Lens

Lens Focal Length

Turn Frequency

Maximum Exposure

Wide Angle (i.e., 35mm or less)

180 degrees every 30 seconds

35 min

Normal (i.e., 40mm to 65mm)

90 degrees every 15 seconds

20 min

Telephoto (i.e. 70mm to 200mm)

30 degrees every 5 seconds

10 min

Notes:

1. Maximum practical exposure assuming perfect polar alignment.

2. In general, 200mm is the longest practical focal length that can be used successfully with the original Scotch mount.

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Further to my previous post, just spotted this: First barn door tracker by Tadakun on page three of this section. This shows how you have a marked hand wheel to show how much to turn the wheel after 15 or 30 seconds or whatever. As you can see, he's got a good image of Orion with it.

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Astrophotography/Astronomy is an expensive hobby. /QUOTE]

Gosh :D you suprise me... :icon_eek::evil6::rolleyes:

Used to use them by the bucketful back in the late 80's ... should have kept a few....

You might find this thread (elsewhere) helpful for alternatives... althought that driver borad is even more expensive but will dribe "meaty" motors...

http://www.astrochat.co.uk/forum/viewtopic.php?t=5464&sid=d6a4d8eab380c464a76deffb751266ef

I have been playing with the driver board from Virtual Village... took a couple of weeks to arrive from china... it can either be used in "dumb" mode step and direction or from the onboard micro controller...

http://www.virtualvillage.co.uk/search?VIEW_SIZE=10&PAGING=Y&SEARCH_OPERATOR=AND&SEARCH_ANYPRESUF=N&SEARCH_CATALOG_ID=VVCatalogUK&SEARCH_STRING=stepper

http://www.virtualvillage.co.uk/stepper-motor-controller-driver-006408-001.html

Billy...

Edited by Psychobilly
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You could start by trying it hand driven like the one shown in Steve's link.

More details (parts list adn construction details) at Hand-driven Scotch Mount

This shows how you have a marked hand wheel to show how much to turn the wheel after 15 or 30 seconds or whatever.

Another clever alternative I have seen is to put the hinge on the other side (so you drive it by closing it) and have a cheap analogue watch with a second-hand as the "knob" on the drive bolt -- you merely turn the watch so as to keep the second-hand pointing the same direction.

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Thanks for the link, Steve. Most of the pages about building one of these seem to assume a basic knowledge and therefore leave 'gaps'. This one seems to assume you (or in this case I) are (am) a complete ignoramus - exactly what I need to seriously consider construction of one.

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I have here, a RS 4 phase 12v 7.5 deg step angle Stepper motor, attached to a RS 1 rpm gear box. The G/Box has a 12 toothed pinion loctited on to the shaft, it would need care to remove it to use as a final drive shaft.

Also in the pic, is 2 x555 and 1x 556 Timers.

Ron.

post-13213-133877558347_thumb.jpg

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Thanks for the information guys.

If I went for a 'manual' option on the tracker, could I get away with rotating the arm 45* every 15 seconds and still retain sharp detail in the images as opposed to constantly rotating the arm for a whole 60 seconds.? I'd be working with the short end of my 18-55mm lens, so from what I've learnt so far, I can't see any initial problems with that method.

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Thanks for the information guys.

If I went for a 'manual' option on the tracker, could I get away with rotating the arm 45* every 15 seconds and still retain sharp detail in the images as opposed to constantly rotating the arm for a whole 60 seconds.

No. You'd only be rotating at half a turn a minute instead of the required whole turn a minute. You should be OK with 90* every 15 secs. The reason I never did this was that you are in most danger of knocking the mount when you return your hand to it and, being the ham-fisted oaf that I am, I found it less likely if I just concentrated on one thing, i.e. turning the handle.

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I got my degree's mixed up then.! Only just realised my mistake. :):o

I'm usually quite gentle with such sensitive movements. I can get a pin sharp image, hand held down to about 1/4th of a second, so just so long as I attack with a bit less haste, I shouldn't fare too badly. I'll try the options and see what works.

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