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  #121  
Old 26-01-2009, 11:58 AM
gary
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Thumbs up Argo Navis on Sky-Watcher Collapsible Flex Dobsonian

Quote:
Originally Posted by Dave47tuc View Post
At late dusk I set the AN on Procyon then Achernar. Then then AN worked a treat for the next 6 hours. No re align through the night. Observed many many objects, way to many to list.
Very happy with the way the AN has come together.
Hi Dave,

Thanks for the post and the two new nice photos showing the rig.

Great to hear the system is delivering objects on demand!

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au
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  #122  
Old 01-02-2009, 02:33 PM
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A little time to spend on things this weekend

I'm still not entirely happy with the encoder mounting bracket I made, a little concerned with how sturdy it will be over time
When my father drilled out the ali I think it might of bent it a little as when i mounted it on top of the bearing trunion it didn't seem square to the outside, put it in the vice and bent it back it seems ok now.

The alt axis as far as i can tell is very close to where It needs to be , the black brass faceing plate there is slotted and the final mounting hole is yet to be drilled, I also have a small amount of adjustment in the tangent arm if needed .
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  #123  
Old 01-02-2009, 02:39 PM
gary
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Quote:
Originally Posted by nightstalker View Post
A little time to spend on things this weekend
Hi Graham,

Looks like you have been busy. Noticed where you have attempted to lighten
up your brass tangent arm a little.

Best regards

Gary
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  #124  
Old 01-02-2009, 02:48 PM
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hi gary

yes its fairly light for 2mm brass now ..behind the encoder is also drilled out extensively, the encoder cable covers the holes nicely .

I'm still not sure what you mean by fixeing the bottom end of the tangent arm ? .. wont a floating type arangement allow play to effect the pointing accuracy of the alt motion ?
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  #125  
Old 01-02-2009, 03:12 PM
gary
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Arrow Floating tangent arm with your Argo Navis

Quote:
Originally Posted by nightstalker View Post

yes its fairly light for 2mm brass now ..behind the encoder is also drilled out extensively, the encoder cable covers the holes nicely .
Excellent.

Quote:
I'm still not sure what you mean by fixeing the bottom end of the tangent arm ? .. wont a floating type arangement allow play to effect the pointing accuracy of the alt motion ?
Imagine for one moment that the far end of the Alt tangent arm was just totally
unattached. It then would have several degrees of freedom.

1. It could move toward or away from the side of the rocker (e.g. encoder shaft not
exactly co-axial with the Alt axis of the mount).
2. It could shift radially outward or inward from the center of the Alt axis (for example,
the bearing was not quite circular or encoder not centered).
3. It could rotate around the Alt axis.

What you want to do is ideally have an arrangement whereby '3' is not allowed
but that '1' & '2' are tolerated.

'3' is not allowed because it is in the same direction of rotation as the encoder
itself and will give rise to a positional uncertainty.

However, any geometric error that results in a pointing error residual
whereby, as a side effect, the tangent arm behaves as in either '1' or '2'
cannot be circumvented by holding the far end of the tangent arm fixed.
Instead, the problem can only be fixed by correcting the mechanical source
of the problem, say by re-centering the encoder.

The risk is that, should 1 or 2 be evident, if the far end of the tangent arm
is fixed tight, then any irregularity, say from encoder not being centered, will
result in a force being translated back up the tangent arm and thence
ultimately be applying a sideways force or moment to the encoder shaft itself.
If the force is great enough, it could damage the encoder.

Thus, use a slot carefully milled in the end of the tangent arm that slides
over a locating pin or shoulder screw. The arm will then be free to float
if '1' or '2' phenomena is evident but will not be free to rotate around the
actual axis.

Hope this textual explanation, for what is often best explained by a few
sketches, is clear. If not, I will attempt to clarify further.


Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au
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  #126  
Old 01-02-2009, 08:09 PM
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erick (Eric)
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I have the scope in this article:-

http://www.iceinspace.com.au/63-401-0-0-1-0.html

Look for the part:-

"Next problem: when I depressed the telescope tube from zenith to horizon, the tube shifts 8 mm to one side. I presume the altitude bearing is not perfectly circular. In any event, the end result is that my encoder assembly – attached as it is to the altitude bearing – also moves 8 mm to the side. The photo above illustrates this shift. My solution was, again, to avoid screwing the encoder arm to the rocker box. This is actually the recommended technique for many telescopes, including the Obsession: don’t completely tighten either encoder arm, to account for such minor wiggling, although the 8mm shift noted here was more than most premium scopes would manifest. On the Obsession Yahoo group, I’d heard about not even screwing the altitude encoder arm down at all, but rather letting gravity hold it motionless. This worked great in my case. As the photo displays, a small hook (same as that used to “fence in” the az arm) catches the notch in the alt encoder arm; gravity holds it in one place. As the tube shifts left-to-right, the “floating” encoder arm moves with it (along the hook’s shaft) but not in such a way as to register rotary motion.
You’ll note the small hair-bungee tied to the encoder. I thought this might be needed, but in fact, I don’t use it anymore. It just sits there without anything – other than gravity –holding it against screw-in hook other. I was just too lazy to take a new picture."

The photo shows the encoder arm tied to the pin, but as Scott says and I have found, gravity holds the Alt encoder arm nicely in place. I just drop it in place on the pin when I screw in the encoder each time I set up, and it can slide in and out as much as it wishes without affecting performance to the level I need. I have done some work to reduce that sideways movement, but still do not restrict the arm moving in the direction of the axis of the encoder. Obviously the pin should be as close as possible to being parallel to the encoder axis. If it sloped up or down, that would be a problem. Drill the hole straight, tighten the pin up and eyeball it for being "true" was all that was done in this case.
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  #127  
Old 02-02-2009, 08:48 AM
ausastronomer (John Bambury)
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Quote:
Originally Posted by erick View Post
I have the scope in this article:-

http://www.iceinspace.com.au/63-401-0-0-1-0.html

Look for the part:-

"Next problem: when I depressed the telescope tube from zenith to horizon, the tube shifts 8 mm to one side. I presume the altitude bearing is not perfectly circular. In any event, the end result is that my encoder assembly attached as it is to the altitude bearing also moves 8 mm to the side. The photo above illustrates this shift. My solution was, again, to avoid screwing the encoder arm to the rocker box. This is actually the recommended technique for many telescopes, including the Obsession: dont completely tighten either encoder arm, to account for such minor wiggling, although the 8mm shift noted here was more than most premium scopes would manifest. On the Obsession Yahoo group, Id heard about not even screwing the altitude encoder arm down at all, but rather letting gravity hold it motionless. This worked great in my case.
Hi Erick,

Allowing the encoder arm to float will certainly ease the mechanical load on the encoder and on the encoder tangent arm. Unfortunately with 8mm of lateral movement large pointing errors will eventuate. Whilst TPAS does a great job of compensating for mount errors, better pointing accuracy will result if the mechanical mount errors are minimised. That lateral movement of the scope on the altitude bearings is easily eliminated by "shimming" the altitude trunions with teflon pads. My 10" scope had about 7mm of sideways movement before I fitted argo to it. I shimmed it with 3mm teflon pads either side and it is now perfect. I will post picks later today when I get home from work. A further improvement can be obtained by "bracing" the side of the rocker box with a 90 degree tapered brace, to reduce flexure of the sides of the rocker box.

Cheers,
John B
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  #128  
Old 02-02-2009, 08:59 AM
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erick (Eric)
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I fitted small plates to either side of the base which are screwed into the sides of the rocker base and go about half way up the trunions. I've got some pics in a thread somewhere - cannot find them now (*). This has substantially reduced the sideways movement but does little for the flexing of the base. I'm working on solving that. Remember the joke - keep the tyres and change the car? I plan to keep the 12" mirror and change just about everything else - working on it!

*Edit:- OK, for those interested, there is information in this thread and other threads referenced there:-
http://www.iceinspace.com.au/forum/s...59&postcount=2
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  #129  
Old 02-02-2009, 07:49 PM
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Thanks guys I'm understanding things a little better now
I've milled some slots in the ends of my tangent arms now and will fit a
small shoulder screw with a spacer that will do two things ..keep the arm reasonably close to being perpendicular to the encoder mounting bracket at the top of the bearing with a small amount of play .. and if needed allow some sideways movementshould the encoder become a little off centre ?
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  #130  
Old 03-02-2009, 12:22 AM
gary
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Quote:
Originally Posted by nightstalker View Post
Thanks guys I'm understanding things a little better now
I've milled some slots in the ends of my tangent arms now and will fit a
small shoulder screw with a spacer that will do two things ..keep the arm reasonably close to being perpendicular to the encoder mounting bracket at the top of the bearing with a small amount of play .. and if needed allow some sideways movementshould the encoder become a little off centre ?
Hi Graham,

Great, you are on-track.

Best Regards

Gary Kopff
Wildcard Innovations Pty Ltd
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  #131  
Old 16-02-2009, 12:13 PM
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Messier Marathon ?

Haven't thought this all the way through as yet but what's the easy (non-thinking!) way to undertake a Messier Marathon with the Argo Navis?
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  #132  
Old 16-02-2009, 04:49 PM
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Dave47tuc (David)
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Erick,
Once set up go to mode catalog. Messier objects and start at M1 then go to M2, M3 etc etc. Some will not be in the sky at the time but just move onto the next one. Record what you have observed then go back to ones you have missed if they have come up above the horizon.

Gary will answer this one as I'm not sure but you maybe able to go to tour mode and them select Messier objects??

Be something you can do at Snake valley camp this March.


Quote:
Originally Posted by erick View Post
Haven't thought this all the way through as yet but what's the easy (non-thinking!) way to undertake a Messier Marathon with the Argo Navis?
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  #133  
Old 16-02-2009, 08:10 PM
ausastronomer (John Bambury)
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I would set all the Messier objects in an Excel spreadsheet. Sort them by declination and then delete those that have too northerly a declination for you to see from your latitude.

Take the remaining targets and sort them by right ascension. Work out which is the most westerly target that is visible at sunset and put this target first on the list. Then re sort the list by cutting and pasting so that everything follows in right ascension order from your first visible target on the list. Save the file as a comma delimited ascii file, upload it to Argo Navis as a User Defined Catalogue.

Start your scope, wait for dark, align argo; and then just go through the targets in right ascension order by turning the detent wheel one click at a time. Everything in your list will be visible at the appropriate stages of the night this way and you just turn the wheel one click at a time.

I am pretty sure if you hunt around you will find a user defined catalogue of Messier Targets ready for uploading to AN, just for such a purpose.

Cheers,
John B
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  #134  
Old 16-02-2009, 10:30 PM
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Quote:
Originally Posted by Dave47tuc View Post

Be something you can do at Snake valley camp this March.
You read my mind, Dave! Yes, this weekend (Mar 28) is the only weekend listed in 2009 to conduct a successful MM!

Thanks John, that sounds like the approach. I have located lists in "viewing order" with plenty of hints to deal with the difficult ones. Particularly M74 and M77 that have to be nabbed in dusk and M30 in dawn. I suspect our southerly latitude will make these early and late ones a great challenge.

I can probably get a head start with the excel spreadsheet on this page:-

http://www.astro-tom.com/messier/mar...thon_order.htm

I've already decided to cheat and use the Argo Navis-directed scope for those I cannot find quickly in binoculars - shame on me!
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  #135  
Old 18-02-2009, 11:12 AM
gary
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Messier Marathon with your Argo Navis

Quote:
Originally Posted by erick View Post
Haven't thought this all the way through as yet but what's the easy (non-thinking!) way to undertake a Messier Marathon with the Argo Navis?
Hi Erick,

Great to hear you want to perform a Messier Marathon.

As mentioned by other respondents, an optimal way to observe them is
in ascending RA order.

As you will be aware, with the rotation of the Earth, just as the sun and the stars
rise in the East and set in the West, so do lines of Right Ascension. For this
reason, RA is measured in units of time and at any given fixed Azimuth and elevation,
RA sweeps by at a sidereal rate.

With this in mind, you might want to grab an Argo Navis User Catalog with
the Messier objects sorted in RA order. You can find a user contributed
copy of such a catalog on the Argo Navis User's Group under the name
jk_messier marathon_cap.txt which can be found in this folder here -
http://tech.groups.yahoo.com/group/a...20Catalogs%20/

Load the User Catalog as per the instructions starting on page 163 of the
Argo Navis User's Manual.

To use the catalog, you need to determine the starting point. On the night
in question, perform a star alignment. Then point the scope due west and
dial up MODE IDENTIFY, FIND USER OBJECT, FAINTEST MAG ANY,
IN ANY CONSTEL. Argo Navis should then identify the Messier object that
is closest to where the telescope is pointing.

Now, if you then press EXIT and DIAL up MODE CATALOG, USER OBJECTS
and press ENTER, the object that you last identified will be the default object
displayed. Press ENTER in the usual way a few times until the GUIDE
mode display appears and GUIDE to it.

To go to the next object in the User Catalog, you then use a special feature of
MODE CATALOG which is that whilst in GUIDE mode, if you spin the DIAL
clockwise one detent click, you go to the next object in the catalog, which
by definition, will be slightly further East than the one you just observed.
Continue this way for the rest of the night.

For casual touring of Messier objects at any other time of the year, you can
simply push the scope toward the zenith and DIAL up MODE TOUR,
FIND MESSIER, FAINTEST MAG ANY, IN ANY CONSTEL, WITH 180 ARC
and Argo Navis will take you on a tour of all Messier objects currently
above your local horizon. Use the DIAL to advance through the tour by
spinning it clockwise or backtrack through the tour by spinning the DIAL
counter-clockwise.

You can depart the tour, say to look at other objects of opportunity and then
rejoin it at any time. To do this, simply press EXIT whilst in MODE TOUR.
You then might use MODE CATALOG to view some other object. When
you want to continue the tour, DIAL up MODE TOUR, REJOIN LAST TOUR.

Good luck on your Marathon and I hope you get clear weather on the night!

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au
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  #136  
Old 18-02-2009, 12:02 PM
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Many thanks Gary. I knew there would be a ready solution.
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  #137  
Old 21-02-2009, 03:15 PM
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Wow isnt this great now its sticky and never to be lost......cheers Kev.
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  #138  
Old 22-02-2009, 12:53 PM
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Sure is kev.. my encoder mounting seems ok .. I get a very small deflection on one point on one of my alt axis .. I'm thinking its one or both of my alt bearings arn't exactly the same at this point .. anyway the amount of movement at the end of my tangent arm is 1/2 mm and would then likely be much smaller again if measured closer to the encoder and if my thinking is right??.

Gary I reset the encoder resolution to 10 000 steps on both axis
thats right isn't it ?

I finished making my stalk for mounting the unit .. built a small box to fit it in and welded a bit of flat to the 32 mm tube ...cables up the middle .. those cradles on the newer
models would be a real time saver in regard imo .

spose I'm not to far from giving it a try .. not sure how a two cloud alignment will work out but we'll see

cheers graham
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  #139  
Old 23-02-2009, 12:53 PM
gary
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Arrow Encoder direction sense establishment

Quote:
Originally Posted by nightstalker View Post
Sure is kev.. my encoder mounting seems ok .. I get a very small deflection on one point on one of my alt axis .. I'm thinking its one or both of my alt bearings arn't exactly the same at this point .. anyway the amount of movement at the end of my tangent arm is 1/2 mm and would then likely be much smaller again if measured closer to the encoder and if my thinking is right??.
If the movement of which you write is toward and away from the side of the
rocker, then of course the arm will deflect less in distance if measured toward
the encoder end, but the angle by which it deflects will be the same, irrespective
from which end it is measured.

if the movement is radial, toward or away the Alt axis, the radial distance the
arm moves by will be the same irrespective of where it is measured along the arm.

Quote:
Gary I reset the encoder resolution to 10 000 steps on both axis
thats right isn't it ?
That is correct.

To determine the encoder direction senses, you may find the following
alternative procedure beneficial -

To check the SETUP ALT STEPS sign, point the Optical Tube Assembly (OTA)
to the vertical and DIAL up MODE FIX ALT REF, ALT REF=+90, AUTO ADJUST
OFF and then press ENTER. Now DIAL up MODE ENCODER. The right-hand
displayed value should be close to +90 degrees. Now push the OTA
downward in Altitude toward the horizon. The right-hand displayed value
should decrease, +89, +88, ... +3, +2, +1, 0 as you go from the zenith
toward the horizon. If not, reverse the SETUP ALT STEPS sign and repeat
the test.

Once the ALT STEPS sign is correctly established, perform a FIX ALT
REF and two-star alignment. Now DIAL up MODE RA DEC (not MODE
ENCODER). Point the OTA at the approximate intersection of the
meridian* and celestial equator* (see below). Now sweep the OTA from that point
toward the East, roughly following the celestial equator. RA (left-hand value) should
be increasing on the display (it will wrap at 23:59.0 back to 00:00.0).
If it is decreasing, reverse the SETUP AZ STEPS sign and repeat the
test.


One you have established the signs, try the following test as well.
Firstly, go to MODE SETUP, SETUP GUIDE and set the number of GUIDE
DECIMAL to 2 DECIMAL PLACES. Perform a FIX ALT REF and two-star
alignment. GUIDE back to one of the original two alignment stars. Note
that the display shows close to 0.00 0.00. Wait 15 minutes and GUIDE
back to the same star. Does the display still show close to 0.00 0.00?
Now GUIDE to a third star, well away from the original two in some other
part of the sky, and check that the angular error residual of this third
star is small.

As mentioned in the User Manual, irrespective of which way the
arrows point in GUIDE mode, always push the scope in a direction
that makes the GUIDE angles closer to zero. One can later change the
convention of which way the arrows point using SETUP GUIDE as a
matter of personal preference for your particular installation.

Once you have correctly established the encoder direction senses,
we also recommend you use AUTO ADJUST ON when you perform the FIX
ALT REF step. To set it up, DIAL up MODE SETUP, SETUP ALT REF and
enter a value of +090.000. Then when you perform the FIX ALT REF
STEP, DIAL up ALT REF=+090.000 AUTO ADJUST ON. Perform your two star
alignment as normal. The WARP factor should then be 0.00 (A) where
the (A) indicates the ALT REF point was automatically adjusted. If
you see a non-zero WARP factor when AUTO ADJUST is ON or an (X)
instead of an (A), it means something is amiss, such as a
misidentified star or cable not plugged in. Keep in mind that though
a WARP factor of 0.00 is a prerequisite for good pointing
performance, it does not necessarily guarantee good performance. The
reason is that the AUTO ADJUST mechanism bends over backwards to
correct the ALT REF point so as to produce a WARP factor of zero
wherever possible, even if you have misidentified the alignment
stars.

Quote:
spose I'm not to far from giving it a try .. not sure how a two cloud alignment will work out but we'll see
Hope you have some clear nights ahead!

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Phone +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au
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  #140  
Old 23-02-2009, 10:30 PM
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well I did get out but didn't have much luck getting things to work.. so will have to visit the manual some more to see what I'm missing.. though I didn't spend a lot of time with the guide angles they were completely off ( differant part of the sky off )track to any objects I knew of ... but strangely in another mode the unit was identifing all constellations all over the sky.. again I'm not very well read on all the set up it seems and am likely missing something important ... pity it was a very clear evening for a change.
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