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Degree Circles

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#26 csa/montana

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Posted 03 May 2006 - 09:19 PM

Rod: Again, thanks! Didn't realize this. It will save me a lot of work. Can tell I'm an amateur at this, huh? I've got the "0" degree mark on the left side, so a short strip running each way of this would be good?
Carol (p.s. you have a credit of many thousands of $, so I can pick your brain a lot, at 2cents a question, I'm gonna keep you verrrry busy!)

#27 rnabholz

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Posted 03 May 2006 - 10:07 PM

Exactly, just a few inches on both sides of zero will do the trick.

Glad to help.

#28 AtLarge

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Posted 05 May 2006 - 11:51 PM

Exactly, just a few inches on both sides of zero will do the trick.

Glad to help.


This is very informative but let me make sure I have this straight.

The pointer is on the bottom base.
The pointer is aligned with Polaris and the base leveled.
The steel band with magnet on pointer allow for adjustments so you can tweak that alignment by moving the pointer after you test on some known objects. (without having to keep moving the entire bottom base)

If the markings are on the top board and are stationary with the OTA where do you set the gradients to begin with? The zero / zero goes directly below the center of the OTA at the front of the scope? That way you always begin with the scope pointed at the Polar North.

You then match the Azm:159 and Alt:+38 as per your favorite program (my settings at the moment for Jupiter) and your on target or at least in the neighborhood.

Am I keeping up here or did I miss something? :(
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#29 rnabholz

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Posted 06 May 2006 - 06:55 AM

You have it.

In Carol's pictures you can see that she set zero at 90 degrees from the tube, but it really doesn't matter that the scale match the actual azimuth direction, only that the scale and pointer indicate properly. Her approach makes it convenient to see when at the eyepiece when the scope is pointed north.

Using the approach where the scale is attached to the rocker means that you will have to leave the eyepiece position at times to line up the pointer. The approach I used is to put the scale on the groundboard and build some adjustability into the scale rather than the pointer. That allows the pointer, attached to the rocker, to be visible from the eyepiece at all times, a little handier set up, but a little more complicated build.

Let me know if you have other questions.

Clear Skies

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#30 csa/montana

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Posted 06 May 2006 - 09:17 AM

See my new post here "my $12 Go-To" test drive
Carol

#31 SkyArcher

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Posted 06 May 2006 - 06:52 PM

In case any wants it, I've attached the pdf of the file I used to make the degree circle. You can take the pdf to your local "Kinkos" copy center and have them print it out on 24x36 paper. Also while you're there, have them laminate the degree circles.

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#32 Relativist

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Posted 06 May 2006 - 10:08 PM

Just out of curiosity, how good is that home depot inclinometer? Could we maybe make our own that was a bit better?

#33 csa/montana

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Posted 06 May 2006 - 11:10 PM

It's about 4-3/4" high (circular), with magnetic base. As Rod Nabholtz said, using the inclinometer, it's independent of the base, so no leveling is required.The scale is quite small & a little difficult to read at night, but works. During my viewing session, My Altitude degree scale matched the inclinometer with each change. The ideal one is what Rod has now; MD SmartTool digital level. It runs $100 though. I'm quite happy with my setup & accuracy.
Carol

#34 Relativist

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Posted 09 May 2006 - 01:40 AM

Ok, so let me ask this, could you use the inclinometer to "calibrate" the Altitude scale, bypassing the need to level the base? The idea would be to move the arrow as is done with the Azimuth scale.

#35 THESKY

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Posted 09 May 2006 - 02:31 AM

Boy this is such a good thread . . . thank you for all . . . especially Carol who initiate this thread. Also to Rob and SkyArcher who make the Alt/Az degree circle work.

I also plan to do the same since it is doable.
My question will be when you have a tracking platform how do you calibrate the level. When you just start tracking you will have the platform swing to the east side and then it will end as it swing all the way to the west for 60 - 80 minutes.

I guess one solution will be searching for the object while the rocker base is level and after the object is in the FOV - turn on the tracking device.

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#36 rnabholz

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Posted 09 May 2006 - 05:47 AM

Curtis,

Using a scale without a level base is problematic because while you can always set the scale to match an inclinometer determined setting, when you turn the rocker on the base, the scale reading will be off immediately and will not be exactly accurate until you return it to the same azimuth you set it at.

Now, depending in the degree of deviation from level, this error could be small, but it could also be very large and make finding things in a one degree or so field of view very difficult.

The inclinometer takes away the possibility of this error, and so makes it the choice for me. The analog inclinometer mentioned in this thread is about $10, a cheap efficient solution.

Of course leveling the scope is another option, and actually, I do both to make things as accurate as possible.

#37 rnabholz

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Posted 09 May 2006 - 07:08 AM

Ridwan,

I have given the tracking platform issue some thought, as I am conisidering building one for my scope.

I think the only approach that will work is stopping and returning the platform to level during the object acquisition process and then turning the motors on.

You would sacrifice 50% of your tracking period, but depending on the platform you would likely have 20 to 30 minutes of travel left. That would generally be enough for my purposes.

#38 THESKY

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Posted 09 May 2006 - 10:37 AM

Rod,

That is what I thought . . . having the dob level - align to the object (Alt/Az) - then turn on the tracking. Thank you for that confirmation.

Or another idea would be . . . calculating the difference between a leveled platform and a maximum swing platform. Then we can use this different to a Alt/Az value from the pocket star.

What do you think about that one?

#39 rnabholz

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Posted 09 May 2006 - 11:12 AM

Or another idea would be . . . calculating the difference between a leveled platform and a maximum swing platform. Then we can use this different to a Alt/Az value from the pocket star.

What do you think about that one?


Well, here is what I have come up with as I have pondered using a platform.

Remember that if you adopt my strongly preferred approach for altitude - an inclinometer, not a scale, the tube reading is always read independent of the base. So even on a platform the altitude reading will be accurate.

It is the azimuth that is vexing. Visualizing the base and the azimuth scale and the different possible orientations of that scale to the tilt of the platform, it seems to me that you would have an infinitely variable factor to consider.

For example, consider the scope pointing precisely perpendicular to the axis of platform rotation or pointing precisely parallel to the axis of rotation. In these cases, your azimuth is likely to be pretty accurate.

Now consider the scope pointing in between those points. It seems to me that depending on the degree of the platform tilt, you would compromise the accuracy of the scale because you have in effect compressed the spacing of the degree marks by tilting the scale.

If my visualizations are correct (and PLEASE, anybody who sees this differently please let me know your thoughts) you would have a very difficult time quantifying the deviation and therefore could probably not easily adjust for it.

#40 SkyArcher

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Posted 09 May 2006 - 01:33 PM

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.

#41 rnabholz

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Posted 09 May 2006 - 02:26 PM

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.

#42 THESKY

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Posted 09 May 2006 - 04:35 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

#43 rnabholz

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Posted 09 May 2006 - 09:44 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.


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?

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

#44 THESKY

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Posted 11 May 2006 - 02:10 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

#45 rnabholz

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Posted 11 May 2006 - 08:52 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

#46 csa/montana

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Posted 11 May 2006 - 10:16 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

#47 THESKY

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Posted 11 May 2006 - 12:37 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

#48 kestrel0222

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Posted 22 July 2006 - 05:08 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? :question:

Thanks,

#49 SkyArcher

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Posted 22 July 2006 - 07:29 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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#50 kestrel0222

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Posted 22 July 2006 - 08:27 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) :foreheadslap: and I'll be all set!! I will have it laminated.


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