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Digital Compass (Just an Idea)

Macavity

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Macavity

Macavity

Posted
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I'm sure Alt-Azimuth devotees are aware of the uses of the (splendid) "Wixey" Digital Inclinometer (Dobsonian pointing and MORE!). Just wondered if anyone had ever tried out a "Digital Compass" in ANY application? They seem to be "good" to about 2 Deg(?) or so, and thus sufficient, in conjunction with accurate Altitude measurement. Moreover, telescopes (aside from steel screws) are mostly non magnetic. :)

I see some companies even make "magnetic transducers" for digital readout on circuit boards etc. :rolleyes:

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beamish

beamish

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Curiously I was thinking the same thing re digital compasses, but having found quite a few, none seemed to be accurate enough for astro use. I may be wrong. Most except for the really specialised and expensive versions (100's pounds !!) are accurate only to 1 degree resolution .

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philsail1

philsail1

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Hello All,

just a thought - does any have any ideas if using an ordinary (good quality) "map bearing" compass (used in conjunction with the "Wixey") be accurate enough to get you to an object so that you could find it within the field of view of a low powered eyepiece?

(There must be a way to "construct" a "push to" system, which is easier to use, and more accurate than setting circles - and much cheaper than the commercial "Go-To" installations?).

The "Wixey" seems to take us half way there by sorting out the "declination" angle.

Regards,

philsail1

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Macavity

Macavity

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Hi Philsail,

Yes, it would be NICE to sort out the "other coordinate", but...

This is my "work in progress". The (rather poor) photograph shows my Giro III mount with ST102 adapted to "PushTo". As you say, one can rely on the Wixey to ~0.1/0.2 Deg. Then I use a simple MDF circular "table" (the White Thing atop the Tripod!) carrying a computer-drawn Azimuth Scale. I limited this to (only) 2 Deg. (PC virtual memory? etc.) Note also strategic use of Jubilee clips [LOL] and (really naff!) Aluminium pointer - But these to be improved and doubtless some red LED lights added too! :)

The general principal HERE relies on doing a (the occasional?) "One Star Alignment". This Wixey now has little "screw adjusters" and the Azimuth Table is split to allow it to rotate. So basically I point the scope to an object of KNOWN Alt-Az and set these up. Even without exhaustive testing, I am pretty sure this setup will bring objects AT LEAST within typical finder width over some (largish?) part of the sky. I'm happy enough with this idea, at the moment. Oh for a proper workshop (and skills) though! :rolleyes:

All a bit mount specific, but I'm sure the idea can be (And has been!) replicated for other systems...

Pushto2.jpg

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philsail1

philsail1

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Looks like an excellent set up you have there Macavity!

I have not seen the "Giro" 111 Mount before. It obviously looks like it is designed to take two scopes. I like the way you have added the circular scale atop the tripod head, and I can see how it will work for you.

So, the "Wixey" has facilities for fine adjustment? Is this so that you can check if it is level against a bubble level?

I suppose one could adapt the large circular scale to fit an "EQ" mount?

All in all you seem to have "cracked" the "Push-to" technicalities. Yes, "Jubillee Clips" and aluminium for the moment, but the basic principal is good - and it works!

That's certainly set me thinking now!

Thanks for that Macavity.

Regards,

philsail1

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The Warthog

The Warthog

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If you can lay down an accurate north-south line in your back garden, then all you need is to have a 360 degree scale marked on your Dob base. That would allow you to point, probably to within 1 degree accuracy, and use an inclinometer to get the altitude. There are various ways to get an accurate n-s, using the sun, or using a magnetic compass and knowing the proper offset for your location.

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Macavity

Macavity

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So, the "Wixey" has facilities for fine adjustment? Is this so that you can check if it is level against a bubble level?

The "Wixey" has a zeroing button that sets the scale to ZERO, whatever the inclination (Doh!). I have another digital level that has a much more sophisticated system (zero it, rotate 180 deg, zero it again etc.). BUT that one cost about 3x as much and weighs 10x as much, so wasn't very practical. :rolleyes:

I think it's easier (more convincing!) to zero things in the field, indeed, a bubble level, or what better source of information than the Stars? Thus the Wixey on my mount has a simple (external) MECHANICAL adjustment to trim it's inclination, when the scope is pointing at an object of known altitude. The hardest part (for ME anyway!) is the "mental arithmetic" that may come into these proceedings... :mrgreen:

As WH points out, with a Dobsonian, you have a nice BIG Azimuth circle to do with what thou wilt. But I am genuinely impressed at the precision of even quite small mounts (I did the same thing with an Alt-Az modified EQ3-2). Standard dovetails seem to be "resettable" to around 0.2 deg, so the whole thing can retain settings quite well from session to session. And, what if you have to do the odd "star [re]alignment"? You'd have to do those with GoTo's, Equatorials etc. :)

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philsail1

philsail1

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Ah! I see (said the blind man!) Macavity.

I'm just waiting for my "Wixey" to be delivered. Thenks for "speeding" up the understanding process.

The North, South line idea sounds good too - and if one haas a "Dobsonian" the base is ideal for adding a degree Scale.

Many thanks to all for those tips and explanations - I'm sure they'll come in handy to many people.

Regards,

philsail1

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Starflyer

Starflyer

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If anyone needs a scale for a dob base I have one drawn in Autocad that has an external diameter of 500mm with marks every degree and labels every 5 degrees. This is in pdf format, the idea is to print them out, laminate the individual sections, cut them out and stick them onto the base.

2 pdf files should be attached.

Cheers,

Ian

Scale_1.pdf

Scale_2.pdf

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