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Equipment Discussions >> ATM, Optics and DIY Forum

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Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: Big mirror boxes - KB style new [Re: gatorengineer]
      #6193751 - 11/13/13 11:32 PM

Quote:

Jeff - what do you mean by force multiplier?




Meaning it vastly increases your observing efficiency per unit of time.

Firstly, there is the tracking aspect. On recent threads some folks have enthusiastically stated it is like adding aperture. I understand the sentiment, but a more accurate thing to say would be that it lets you fully utilize your existing aperture, vs. manual guiding that effectively knocks you down a step. It's a pretty big deal for detail viewing, although probably not as big for 3F viewing (Faint, Fuzzy, Featureless). And the ability to take a break from the action, come back and have the object centered in the field is golden. Outreach potential is great too.

Secondly, the GOTO portion. For the last five years one of the friends I observe with has been using ServoCAT. So I was aware of it, but not wholly impressed with the Argo user interface. While rugged and simple, (being limited to two buttons and a dial) it involves a lot of steps through menus. I could operate nearly as fast via star hopping, provided it was over a small area of sky. But the advantage of the GOTO system grows over the night as human fatigue sets in. So while I had to admit my friend was seeing more targets every night than I was, spending the $$$ was not yet justified.

What really changed it all for me was SkySafari to handle the interface duties. Fast, flexible, and graceful. I can use planning software (AstroPlanner in my case) to develop lists during my "off" times and export those lists to SkySafari. (SkySafari's internal list generation, search, and sort capabilities are nonexistent, but it is very effective at using a list like a script.) And of course it eliminates paper charts and references (20 pounds less stuff to schlep).

Once the scope is set up I launch SkySafari, connect wirelessly to the scope and pull up a list of say, 50 objects. Tired of challenge objects and want to take an eye candy break? Or your buddy wants to confirm an observation? No problem, I can slew across the sky in 5 seconds and have some fun. When it is time to get back to "work" (that is, my observing plan for the night), I'm back to that obscure 4 arc second 14th magnitude planetary nebula next on the list, all in about 5 seconds.

Or for the free spirits, you can just tap on interesting map targets. ServoCAT does the rest.

So overall, the gain in productivity made replacing the structure a worthwhile venture.


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Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: Big mirror boxes - KB style new [Re: careysub]
      #6193785 - 11/13/13 11:59 PM

Quote:

Jeff, is this your second double truss scope?

http://www.cloudynights.com/item.php?item_id=2571

I would be interested in hearing more about this build, could you post a write up on this forum about it so that we can learn from your experience? It incorporates a number of unusual or innovative features (the double truss itself, construction materials).

I would have thought that the lengthy set-up time would be due to the double truss instead of the ServoCAT.




Yes, my second double-truss. Maybe I'll put together a write-up over the winter. There was some good things there, and some mistakes. It was very much a test bed.

The original plan was to use it on an equatorial platform, which would have been fine. ServoCAT was a late change in specification. Since ServoCAT proved very much worth keeping and the system was really conceived for Obsession-style scopes the path of least resistance was to re-build that way. It could have taken me a couple of more rebuilds to adapt the system to double-truss. When you have a nice Zambuto mirror sitting around, you feel the time pressure.

In terms of set-up time, the extra truss set really only adds about 3 minutes (just like a normal set x 2). But the total set-up time was the sum of many steps since the scope totally dis-assembles. I was even installing the primary mirror every time! It all adds up.

One error I will point out right away to all builders - note the orientation of the Moonlight truss block clamps - outwards. The clamps are stainless steel 1/4-20 rods threaded through a thin Delrin section. (In the article you linked to, notice the hand knobs all face inwards!) The Delrin blocks are very susceptible to handling and transport damage should those thumb knobs bang into anything. I ruined several blocks in this fashion. I like the Moonlight system, but that is a weakness to be aware of.


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Jeff Morgan
Postmaster
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Reged: 09/28/03

Loc: Prescott, AZ
Re: Big mirror boxes - KB style new [Re: VĂ­ctor MartĂ­nez]
      #6193786 - 11/14/13 12:00 AM

An elegant beauty indeed!

Edited by Jeff Morgan (11/14/13 12:01 AM)


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B9Robot
member


Reged: 10/08/13

Re: Big mirror boxes - KB style new [Re: VĂ­ctor MartĂ­nez]
      #6194604 - 11/14/13 01:34 PM

Quote:

For me, a compact mirror box design for a telescope from 16 ", it has more advantages over the K-B classic mirror box, especially less primary box weight and acclimatization. My mirror box.






Victor - very nice build. A question about your Alt encoder. It looks like it is supported only by a single flat bar attached to the alt bearing. If so does the bar movement cause issues with accuracy?

thanks


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VĂ­ctor MartĂ­nez
sage


Reged: 02/05/07

Loc: Cadiz - Spain
Re: Big mirror boxes - KB style [Re: B9Robot]
      #6194779 - 11/14/13 03:12 PM

There isn´t movement. If the center is well calculated, no problem with accuracy. If you look closely the bar, this is fixed to the Alt bearing with two screws, preventing tilt up.

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B9Robot
member


Reged: 10/08/13

Re: Big mirror boxes - KB style new [Re: VĂ­ctor MartĂ­nez]
      #6194824 - 11/14/13 03:41 PM Attachment (5 downloads)

Hi Victor, I was wondering about the movement, if any, orthogonal to the plane of the alt bearing. Like in the pic below. Does this causing any error in the encoder?

Edited by B9Robot (11/14/13 04:05 PM)


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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Big mirror boxes - KB style new [Re: B9Robot]
      #6194913 - 11/14/13 04:21 PM

he has stays [where the teflon is on the rocker box] that keep it from moving like that.

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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Big mirror boxes - KB style new [Re: Jeff Morgan]
      #6194920 - 11/14/13 04:24 PM

and they only cost $4 to make.



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B9Robot
member


Reged: 10/08/13

Re: Big mirror boxes - KB style new [Re: Pinbout]
      #6195154 - 11/14/13 06:21 PM

You missed the question. I am talking about the bracket for the encoder - not the trusses.

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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Big mirror boxes - KB style new [Re: B9Robot]
      #6195162 - 11/14/13 06:24 PM

Duh!

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VĂ­ctor MartĂ­nez
sage


Reged: 02/05/07

Loc: Cadiz - Spain
Re: Big mirror boxes - KB style new [Re: B9Robot]
      #6195932 - 11/15/13 04:23 AM

Quote:

Hi Victor, I was wondering about the movement, if any, orthogonal to the plane of the alt bearing. Like in the pic below. Does this causing any error in the encoder?




The orthogonal movement is minimal and it does not affect the operation of the encoder (AutoCAL ServoCAT test pass with value for encoder 0, and it is a very sensitive test for encoder slipping or with another problem). Most compact telescope systems use this formula to determine the altitude encoder, for example, Obsession UC or SDM telscopes with compact design.


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B9Robot
member


Reged: 10/08/13

Re: Big mirror boxes - KB style new [Re: VĂ­ctor MartĂ­nez]
      #6196097 - 11/15/13 08:41 AM

Cool - thx

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