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Equipment Discussions >> Equipment

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rnabholz
scholastic sledgehammer
*****

Reged: 07/25/04

Loc: Iowa
Re: Degree Circles new [Re: SkyArcher]
      #948457 - 05/09/06 03:26 PM

Quote:

Rob, I'm just having a little brain fart here, but I'm thinking that if you're using a tracking platform, wouldn't it be better to use the other set of coordinates (RA-DEC) and set up a different set of degree circles. I confess that I don't know what Ra-Dec coordinates are other than they are used on EQ mounts.




I suppose that you could develop a way to put RA-Dec circles on a platform mounted dob, I have never seen that done, so I can't say that I understand the possible pitfalls.

I guess my way of thinking about this approach is that there may be times when I would use the scope without the platform so the alt/az circles are useful in both settings.

Setting the platform back to level to use the circles can be a quick and simple process on the non-tangent drive platforms, so it seems like a simple solution.

Of course, one could simply get a Equatorial Mount and skin the cat that way if tracking was a requirement.


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THESKY
scholastic sledgehammer
*****

Reged: 02/16/06

Loc: SOCAL
Re: Degree Circles new [Re: rnabholz]
      #948607 - 05/09/06 05:35 PM

I just did some calculation on delta between leveled and full swing platform. It does not work. Because the delta is not a consistant number. The object closer to Polaris for example will have a different delta from an object away from Polaris.

In regard to your inclinometer, I assume when you mount the inclinometer on the tube - it has to be vertical in order to get an accurate reading of the altitude. But . . . when you have a platform swings all the way . . . the inclinometer is not necessarily vertical anymore.
So even using an adjustable mounting, there should be a way to compensate vertical axis.

The RA and Dec method is even more complicated because dobsonian has only two UN-adjustable plane (vertical and horizontal) With RA and Dec, you need to have a 3rd axis in order to make the 2 planes coincide with the true North (Polaris) . . . like the the equatorial mount. . . . Unless I am wrong . . .

Have fun tinkering . . . I am going to sleep on it again . . .

Ridwan


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rnabholz
scholastic sledgehammer
*****

Reged: 07/25/04

Loc: Iowa
Re: Degree Circles new [Re: THESKY]
      #949041 - 05/09/06 10:44 PM

Quote:

I just did some calculation on delta between leveled and full swing platform. It does not work. Because the delta is not a consistant number. The object closer to Polaris for example will have a different delta from an object away from Polaris.




I am curious, as I suggested in the earlier post, I suspect that as you move toward one of the multiples of 90 degrees - 0 - 90 - 180 -270- 360 you reduce the error. Stated another way, at 0 degrees no error - increasing error to 45 degrees - then decreasing error to 90 where it is minimal, or even eliminated. Continuing the same way every 90 degrees all the way around.

Does this make sense to anyone but me?

Quote:

In regard to your inclinometer, I assume when you mount the inclinometer on the tube - it has to be vertical in order to get an accurate reading of the altitude. But . . . when you have a platform swings all the way . . . the inclinometer is not necessarily vertical anymore.
So even using an adjustable mounting, there should be a way to compensate vertical axis.

The RA and Dec method is even more complicated because dobsonian has only two UN-adjustable plane (vertical and horizontal) With RA and Dec, you need to have a 3rd axis in order to make the 2 planes coincide with the true North (Polaris) . . . like the the equatorial mount. . . . Unless I am wrong . . .

Have fun tinkering . . . I am going to sleep on it again . . .

Ridwan




Regarding the inclinometer, the analog unit would be susceptible to mechanical error- the indicator would rub on the housing. I am not sure about my electronic unit, I haven't tried it in anything but a normal attitude.

Have to give that a try.

Interesting to think about. Thanks


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THESKY
scholastic sledgehammer
*****

Reged: 02/16/06

Loc: SOCAL
Re: Degree Circles new [Re: rnabholz]
      #950829 - 05/11/06 03:10 AM

Hey Rod,
Just got back from a few hours of observing. The platform and the inclinometer worked very well. I bought the digital one (smarttool - Craftsman) and mount
using a magnetic strip - the program I use Equinox (for Macs) and the platform I use Tom Osypowski's.

I swing the platform all the way - then look for Jupiter - both the program and inclinometer agrees in the altitude with about 0.25 degrees of error.
Then I turned on the tracking and let it track for about 45 minutes or so and again the inclinometer agrees with the program. It is really cool!

I have not installed the azimuth yet since Kinko messed up the enlargement.
Skyarcher make a 19" degrees circle but my DSH base is 25" (I have a 12" DSH) So I have to calculate the percentage of enlargement. Anyway it is almost done.

Thanks again for sharing the idea . . . now I got a goto system fairly affordable. The smart tool $80 was well worth it. Total was still under $100.

Ridwan


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rnabholz
scholastic sledgehammer
*****

Reged: 07/25/04

Loc: Iowa
Re: Degree Circles new [Re: THESKY]
      #951035 - 05/11/06 09:52 AM

Hi Ridwan,

You got out and tested the SmartTool before I had a chance to. I am pleased to hear that it works properly even if tilted slightly off axis. I had suspected it would, but nothing beats a true field test.

$80 is a great buy on the level. I knew Sears carried them, but at the time I bought mine, their price was higher by $20. My guess is given a year, this tool will be in the $50 range.

The device is quite accurate, my experience matches yours, the error is very small, a quarter of a degree makes this part of the system well within acceptable tolerance. Add that to the resolution possible with a 20" azimuth dial and you have a system that works very well as you and those who have implemented it have discovered.

The whole thing can be done for about $100 to $125. Moving to additional scopes your cost is just that of the azimuth scale and a mount for the level ~$20 or so.

One other advantage this system has over traditional DSC is its ability to work with a scope that is not perfectly orthagonal. Any deviation from perfect orthagonality of the axis on a dob will cause a DSC to not perform up to its capabilities. This system is immune to that issue.

I am very interested to hear of your results with the total system on the platform. Please be sure and post your observations when you have the azimuth dial in place.

Thanks


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csa/montana
Den Mama
*****

Reged: 05/14/05

Loc: montana
Re: Degree Circles new [Re: THESKY]
      #951132 - 05/11/06 11:16 AM

Thanks for letting us know Sears sells the "SmartTool".
My local hardware store & lumber had only the 24"level w/smart tool for $139! Couldn't order just the module; Sears, it is!
Carol


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THESKY
scholastic sledgehammer
*****

Reged: 02/16/06

Loc: SOCAL
Re: Degree Circles new [Re: csa/montana]
      #951316 - 05/11/06 01:37 PM

Oh yeah . . . forgot to include the price of the program (Equinox). It is $50.
I haven't bought it yet though - still using trial version. I like to try the planetarium with Palm pilot before purchasing. I know that the Palm is much smaller and easier to carry/store. But I like the big screen on my laptop -12". I can set to see the whole sky (180 degrees) or part of it (up to 5 degrees). I can also see both coordinates in RA/DEC and Alt/Az. One other advantage of Equinox over Planetarium is that I am able to use the program for tracking What it is invloved - I don't know yet. Oh yeah . . . one more thing MACs hardly crash . . . he he he . . .

So all in all the price for this HYBRID degrees setting is around $150.
Still way cheaper than a DSC which will cost me around $700 (the unit and the mounting kit)

(I use hybrid since the smartTool is digital for the Alt. But for the Az is analog)

Happy Tinkering people.

Ridwan


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kestrel0222
Carpal Tunnel
*****

Reged: 05/21/06

Loc: Milford, Michigan
Re: Degree Circles new [Re: THESKY]
      #1055054 - 07/22/06 06:08 AM

SkyArcher, what program did you use to create the great looking degree circle with? I need one for my scope, but my base is slightly larger than the 19" one you have in your PDF file. My base is 22" outside diameter and the width of the circle needs to be 3/4". Any thoughts on how I can make one of these?

Thanks,


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SkyArcher
Postmaster
*****

Reged: 04/12/06

Loc: 9545' in Colorado
Re: Degree Circles new [Re: kestrel0222]
      #1055130 - 07/22/06 08:29 AM

Hi Tom, I used AutoCad.

An easy way for you to do this is take the file to Kinkos
and have them enlarge the file by 115%. That will give you a 22" circle. Then while you're there, have them laminate it on both sides.



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kestrel0222
Carpal Tunnel
*****

Reged: 05/21/06

Loc: Milford, Michigan
Re: Degree Circles new [Re: SkyArcher]
      #1055183 - 07/22/06 09:27 AM

Thanks, I guess since I work on a high end graphics sytem (CATIA V5) that I will just import that PDF file, plot it out at 115% scale (as you suggested) and I'll be all set!! I will have it laminated.

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Clif
member


Reged: 07/19/06

Loc: Perrineville New Jersey
Re: Degree Circles new [Re: SkyArcher]
      #1055323 - 07/22/06 11:32 AM Attachment (589 downloads)

Similar approach: I discovered that the plotting accuracy of today's ink jet printers is quite impressive (on a Mac at least, don't know how well it works on a windows system) and the drafting ability of many drawing programs (MacDraw, ClarisDraw, Canvas, probably the CAD packages too) is just as good. Combining these, I have found that one can make setting circles which are very servicable by just drawing them on the computer, printing them out on the ink jet printer and laminating them to plywood circles using liquid epoxy. They are at least as accurate as 0.1 degrees which is about as good as you can read a circle anyway. I have even made verniers for the circles this way. If anyone wants details, I can expand on the technique. Attached is a picture of a 24" RA circle I made this way. The small divisions are one minute of RA in size. The circle is for a big reverse fork mount I am working on.

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Astraforce Paul
Carpal Tunnel
*****

Reged: 04/05/05

Re: Degree Circles new [Re: Clif]
      #1064589 - 07/28/06 11:20 AM

Clif, yes, please describe more about what you did. Do any of those programs automatically put the circle number in? I presume so. Is there a freebie program or demo program for the Mac that one could test this with? Anyone besides Cliff who knows please chime in, too!

I'm interested in rolling my own template (I like your BIG numbers--easier to read) with my own degree markings (e.g., longer 5 degree line, no outer checkerboard, etc.).

How did you handle the overlapping? I've found that my inkjet does NOT print to the border so that there is a white, unprinted border. It's a bit tricky overlapping the sheets.


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Clif
member


Reged: 07/19/06

Loc: Perrineville New Jersey
Re: Degree Circles new [Re: Astraforce Paul]
      #1129368 - 09/03/06 10:22 AM

No, everything is put in by hand, but it was not very difficult. The tic marks are really lines going all the way across that were put into final position by copying, rotating, grouping, copying, rotating, etc. The numbers had to be rotated also and individually placed. Masking white opaque circles with black borders were plotted on top of the maze of crossed lines to leave the tic marks sprouting from the edge of the circle. I used MacDraw Pro which is just the grown up version of MacDraw that used to be given away free with all Macs. ClarisDraw, Kalaidadraw and Canvas would probably have enough tools to let you do it, PC or Mac.

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chmee
super member


Reged: 05/11/05

Loc: Takoma Park, MD
Digital all the way? new [Re: csa/montana]
      #1131690 - 09/04/06 02:33 PM

How about using the smarttool w/ well-designed mount (a la Rod's) for altitude ($80 at sears), and a digital compass for azimuth (see also at sears, for example, $20), total price $100 plus tax.

I don't know how accurate the compass is. It only reads out to the nearest degree. However, Rod points out that by calibrating the smarttool mount onsite, one can get the altitude spot-on every time. This reduces the searching to just azimuth, and a search on only one axis is trivial.

The other problem w/ the compass is the magnetic declination, as pointed out above. However, one can look this up ahead of time (it appears to be 10 degrees 45' west for my location near DC), and compensate onsite.

Does this sound reasonable to anyone? Anyone have experience w/ digital compasses and have an idea how precise they are?

Cheers,
pete


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Curt B
sage
*****

Reged: 08/02/05

Loc: Regina, Canada
Re: Digital all the way? new [Re: chmee]
      #1133696 - 09/05/06 07:23 PM

I use Planetarium on my Palm to look for my objects. There is an option for magnetic azimuth on it, so it should solve the problem of knowing what true north is. My only concern is will the metal OTA interfere with the compass?

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chmee
super member


Reged: 05/11/05

Loc: Takoma Park, MD
Re: Digital all the way? new [Re: Curt B]
      #1134694 - 09/06/06 09:52 AM

Quote:

I use Planetarium on my Palm to look for my objects. There is an option for magnetic azimuth on it, so it should solve the problem of knowing what true north is. My only concern is will the metal OTA interfere with the compass?




Good question. I ordered the cheap wayfinder from amazon ($17) and will try it this weekend. I don't have a big tube, but do have four long aluminum poles (2" diameter), so it would probably be similar. However, it's supposed to work inside a car or truck, w/ an indicator when bothered by interference from metal, so we'll see.

pete


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Curt B
sage
*****

Reged: 08/02/05

Loc: Regina, Canada
Re: Digital all the way? new [Re: chmee]
      #1135648 - 09/06/06 07:33 PM

Looking forward to hearing about your results chmee....please keep us posted!

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chmee
super member


Reged: 05/11/05

Loc: Takoma Park, MD
Re: Digital all the way? new [Re: chmee]
      #1137639 - 09/07/06 08:23 PM

Quote:


Good question. I ordered the cheap wayfinder from amazon ($17) and will try it this weekend. I don't have a big tube, but do have four long aluminum poles (2" diameter), so it would probably be similar. However, it's supposed to work inside a car or truck, w/ an indicator when bothered by interference from metal, so we'll see.

pete




No go, it only registers in increments of 5 degrees, and even that might be overstating its accuracy. My sense is that this is representative of other cheap digital compasses as well.

Oh well, at least it works quite well for its intended purpose, i.e. in the car.


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Curt B
sage
*****

Reged: 08/02/05

Loc: Regina, Canada
Re: Digital all the way? [Re: chmee]
      #1139412 - 09/08/06 07:53 PM

Sorry to hear that....was looking forward to hearing about your results...

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YankeeJeff
professor emeritus
*****

Reged: 08/11/06

Loc: Brooklyn, NY
Re: Digital all the way? [Re: Curt B]
      #1139541 - 09/08/06 09:17 PM

I picked up the wayfinder v7000 for 50 bucks from overstock.com it's supposed to be accurate to 1 degree and I can set to true or magnetic north. I'll let you folks know how it works out. I don't really need it but I think it may be a cool looking gizmo to add on that also gives me the weather and some other neat tricks.

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