argo navis initial setup issues

[programmer]

Hi AN/dob owners. I'm happy to report my unit arrived today and is in my hot little hands. I might be getting ahead of myself here (I'm still at work) but I was warned about fixing any side-to-side play in my GSO dob base, which is around 18 months old. I had this problem when trying to get my previous DSC's going (I never did) and I can see I'm going to have to do something about it. Any elegant solutions from other GSO dob (or similar) owners? Photos a bonus!

Thanks in advance.

[erick (Eric)]

OK, here is a place to start for some info:-

http://www.iceinspace.com.au/index.p...63,401,0,0,1,0

Scott "fenced in" the encoders, allowing them to move along their axis relative to the base.

I now have Scott's dob and I have taken off the encoders and fittings until I can invest in an ArgoNavis.

However, in preparation, I have tried a modification. I got the idea from here:-

http://www.iceinspace.com.au/forum/s...ad.php?t=28865

On each side, on the outside, I have fitted a thin plate that goes about half way up the alt bearing. I have to place the OTA fairly carefully onto the base now so it fits between the two plates, but they don't seem to be adding any additional friction and they seem to be completely stopping the side to side movement of the OTA in the base - or greatly reducing it.

The other thing I am thinking of doing is fitting a brace over the tube unit which rigidly holds the base sides at a set distance. It would have to be removable to allow the OTA to be inserted and removed, but there is an additional benefit - I can add an eyepiece rack at a much more convenient height.

My thoughts
Eric

[gary]

Originally Posted by programmer

I might be getting ahead of myself here (I'm still at work) but I was warned about fixing any side-to-side play in my GSO dob base,

Is the side-to-side play in the rocker box with respect to the ground board
or with the OTA with respect the rocker box?

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

[programmer]

Originally Posted by gary

Is the side-to-side play in the rocker box with respect to the ground board
or with the OTA with respect the rocker box?

Gary, it's movement of the OTA with respect to the rocker box, as in the diagram in Eric's first link.

Eric, thanks, am reading now.

[programmer]

Well everything went well with the mounting of the encoders. Trouble is, during initial setup, I'm getting 'alt encoder error'. I start from vertical, and slowly move the scope down in Alt. At about 36deg from vertical, the deg/min/sec readout starts to falter, then I get the above error. It seems to start up again as I get close to horizontal. If I just take the alt encoder off the scope and twiddle the thing by hand, it's happy. Obviously it has issues with the mount, but I'm not sure what it's unhappy about. Anyone have similar problems initially? Edit: ok seems to be the problem solved by the 'fencing in' of the encoder, in your first link Eric. Re-reading that now...

I do still have some side-to-side play, but I can't really see how that would cause the above.

PS: Changed the name of the thread to be more generic

[gary]

Originally Posted by programmer

Well everything went well with the mounting of the encoders. Trouble is, during initial setup, I'm getting 'alt encoder error'. I start from vertical, and slowly move the scope down in Alt. At about 36deg from vertical, the deg/min/sec readout starts to falter, then I get the above error. It seems to start up again as I get close to horizontal. If I just take the alt encoder off the scope and twiddle the thing by hand, it's happy. Obviously it has issues with the mount, but I'm not sure what it's unhappy about. Anyone have similar problems initially?

I do still have some side-to-side play, but I can't really see how that would cause the above.

PS: Changed the name of the thread to be more generic

As cited in the reference by Eric to the write-up by Scott Tannehill, it could
be that your Alt bearings have some eccentricity. If this is so, when the scope rotates
in Alt, the Alt tangent arm might be putting a sideways force onto the encoder,
mechanically stressing it. As an experiment, unfasten the screw and and wingnut
that holds the tangent arm in place and let it just hang free. Then rotate the scope in Alt
and note if the bottom of the tangent arm is shifting with respect the side of the
rocker box. Also note when doing this whether the ALT ENCODER ERROR message
now disappears.

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

[programmer]

Originally Posted by gary

As cited in the reference by Eric to the write-up by Scott Tannehill, it could
be that your Alt bearings have some eccentricity. If this is so, when the scope rotates
in Alt, the Alt tangent arm might be putting a sideways force onto the encoder,
mechanically stressing it. As an experiment, unfasten the screw and and wingnut
that holds the tangent arm in place and let it just hang free. Then rotate the scope in Alt
and note if the bottom of the tangent arm is shifting with respect the side of the
rocker box. Also note when doing this whether the ALT ENCODER ERROR message
now disappears.

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

Gary you're too quick! Indeed, I edited my previous post after a re-think. And I did as you suggest and let the tangent arm hang free. This has improved the situation (can now go through maybe 70deg before errors). Will have to continue tomorrow after some sleep.

[gary]

Originally Posted by programmer

I do still have some side-to-side play, but I can't really see how that would cause the above.

If the OTA has side to side play within the rocker, then if the tube should shift from
side to side, unwanted forces are then being translated onto the encoder via the
tangent arm if it is fixed to the side of the rocker.

Drop me an email at sales@wildcard-innovations.com.au and we are looking
at a solution whereby we supply you with smooth shanked locating pins
to allow the tangent arm to float.

Best regards

Gary Kopff
Wildcard Innovations Pty Ltd

[programmer]

Originally Posted by gary

If the OTA has side to side play within the rocker, then if the tube should shift from
side to side, unwanted forces are then being translated onto the encoder via the
tangent arm if it is fixed to the side of the rocker.

Drop me an email at sales@wildcard-innovations.com.au and we are looking
at a solution whereby we supply you with smooth shanked locating pins
to allow the tangent arm to float.

Best regards

Gary Kopff
Wildcard Innovations Pty Ltd

Yes it seems logical now, with a clearer head

Email sent.

[programmer]

Originally Posted by erick

The other thing I am thinking of doing is fitting a brace over the tube unit which rigidly holds the base sides at a set distance. It would have to be removable to allow the OTA to be inserted and removed, but there is an additional benefit - I can add an eyepiece rack at a much more convenient height.

My thoughts
Eric

Hi Eric. I'm interested in your design thoughts for this aspect, as I've been wondering how to do a similar thing without obstructing the OTA movement. By the way, I have done a similar thing to your plates (for my original DSC's), but still get significant lateral movement of the OTA, enough to upset the alt encoder. Holding the rocker sides firmly at a set distance should do away with the need for the plates, shouldn't it? That would be nice.

[erick (Eric)]

I have a few pictures in my head, but nothing down on paper as yet. Sometime in the next few months, I'll try something, I hope.


Gary's locating pins look like a very good idea.

[programmer]

Ok.. while I'm waiting for a more permanent solution I decided to try my best at getting some results with the AN. I have reduced the lateral movement of the OTA, I think, completely. But then I thought about another aspect that can throw out pointing accuracy, which is the 90deg altitude reference point, i.e. pointing the OTA straight up. With the whole shebang set up inside the house on a level floor, I discovered the OTA is definitely *not* vertical when at it's vertical stop. Or more accurately, not perpendicular to the base. In fact it's possibly several degrees out. I have now glued a piece of timber of appropriate size where the OTA hits the vertical stop position, and now the scope is perpendicular (or much closer than before). Now I can't see any reason why my pointing shouldn't be accurate enough. I'll set my location as well, and turn on refraction modelling, just to cover all bases, although I can't point close to the horizon from my back yard anyway.

Unfortunately the clouds are rolling in, but it's still early!

PS: Last night (to cut a long story short) I couldn't get a 'warp', or error, value less than about 1.3, which is several times what it should be (close to zero). I'm still interested to compare notes with anyone else who has their Argo Navis hooked up to a GSO type dob, and how they fared getting theirs working.

[erick (Eric)]

I had my scope out last night and took the opportunity to carefully watch for lateral movement of the bearings in the base now that I have put these two plates in place. On my observation, if there is any movement, it is small, a mm or less. I did notice, however, that the upper part of the base is moving sideways a bit against the ground board! I'll have to look at the pivot bolt and see what is happening.

I can only tell you that the previous owner of this dob quite happily used his Argo Navis on it, so you will be able to get yours working.

Now I look at it, I see I have the same problem, if it is necessary to point the scope accurately to the zenith - there is no accurate stop on the OTA to achieve that.

Perhaps if you bring the AN unit to me and leave it with me for some testing, I'll let you know how it goes. Probably a few years of testing would be enough. Seriously, if you do get stuck, I'm happy to let you see how it works on my scope. You'd only need the unit. The scope has the encoders and cabling already.

[programmer]

Originally Posted by erick

I had my scope out last night and took the opportunity to carefully watch for lateral movement of the bearings in the base now that I have put these two plates in place. On my observation, if there is any movement, it is small, a mm or less. I did notice, however, that the upper part of the base is moving sideways a bit against the ground board! I'll have to look at the pivot bolt and see what is happening.

I can only tell you that the previous owner of this dob quite happily used his Argo Navis on it, so you will be able to get yours working.

Now I look at it, I see I have the same problem, if it is necessary to point the scope accurately to the zenith - there is no accurate stop on the OTA to achieve that.

Perhaps if you bring the AN unit to me and leave it with me for some testing, I'll let you know how it goes. Probably a few years of testing would be enough. Seriously, if you do get stuck, I'm happy to let you see how it works on my scope. You'd only need the unit. The scope has the encoders and cabling already.

Gee thanks for the generous offer Eric Seriously though it would be interesting to see.. I'll have a think about that.

I can report significant improvement! After the tweaks I described above, my 'warp'/error factor is now consistently < 0.2 (it's recommended +-0.5 is adequate, but less warp is better). Objects are certainly within my finder scope but not within, say, my 12.5mm EP. I'm going to have to improve this, because unless you're going to a bright target it can still be difficult to locate the object. Mind you, tonight is not the night to be looking for anything faint.. thanks to Luna.

Interesting about your base movement with respect to the ground board.. I'll have to check mine. I think tweaking out any play in the mount will certainly get my pointing closer to the mark. I might be able to get the vertical stop more accurate.. I think I'll rather still have Gary's solution though

Edit: Eric, the one thing that keeps nagging me with the "plate" solution to stop lateral movement, is that the OTA can still move side to side within the limits of the plates. At least, mine does (I don't have plates, but similar braces). I guess this is due to outward stretching of the verticals over time.

[erick (Eric)]

Originally Posted by programmer

Edit: Eric, the one thing that keeps nagging me with the "plate" solution to stop lateral movement, is that the OTA can still move side to side within the limits of the plates. At least, mine does (I don't have plates, but similar braces). I guess this is due to outward stretching of the verticals over time.

Mine is a snug fit - the sides of the bearings touch each plate. I'll take some photos at some stage and post them. I still want to put the brace in place - mainly to put an eyepiece rack up at reasonable height. On the 8", it wasn't a problem. On the 12" I find myself having to reach down too far from my gaslift chair.

[Tannehill]

Hi to everyone from Wisconsin.

Peruse thru your manual, or talk to Gary K. Use Auto Adjust ON to obviate the need to have your tube at pure 90 vertical during the Fix Alt Ref stage. Manual will describe, also, how to run through this to establish the auto adjust setting for your particular scope. Most GSO dobs run just past 90 degrees.

FYI, the Yahoo group argo_navis is a great resource, altho Gary K is the main guru there, too! The dude does not sleep....

When it was mine, that side-to-side translation of the trunnions atop the sideboard did not affect pointing accuracy of the Argo, once I removed all the stress from the encoder.

I confess I haven't read thru all the posts on this thread. But, if you have applied a plate to keep the trunnions captive (relative to the sideboard edge) on BOTH sides, and there is some eccentricity in the trunnions, that eccentricity WILL need to 'go somewhere' when you depress your scope. If you prevent the trunnions from overlapping the edge of the sideboard, and there IS some trunnion eccentricity, then either both your sideboards will 'flex' outward to accomodate the eccentricity, or the trunnions will lift up off the sideboards (esp if you have metal right angle brackets keeping your sideboards captive - prevented from flexing out- to the baseboard). Bottom line, those issues could give you some encoder stresses that may not be as easy to identify visually, unless you step back and watch for that effect, or line up a stationary laser pointer at the assembly center and see if it migrates during that motion. (fix a laser pointer at a point on the edge of the sideboard, so that if it flexes 'out' you'll see the laser point move relative to the edge of the sideboards). Unless I misunderstand these plates, in which case ignore this entire paragraph!

In truth, I wasn't consistently able to get objects in the center FOV of high power EPs all the time. Always it was within a medium power EP FOV. These are chipboard scopes with plastic bearings; you won't be able to dial in the same level of precision as a metal EQ mount or premium dob. I did use a 9mm reticle EP for the two star aligns, to make the alignment process as accurate as possible....

Double check the couplers. The encoder bearing fits into that well drilled into the alt and az coupler bolts, the ones that Wildcard sells with the retrofit kit. The encoder bearing is secured with a grub screw. One of my couplers was not quite perfectly drilled, causing the bearing to precess a bit in the coupler. Gary happily swapped it out and problem solved. To check this, remove the coupler completely from the scope. Secure the encoder bearing into the coupler with the grub screw. Place the encoder body flat on a table; the coupler end will now be sticking straight up. hold the encoder body with one hand, gently to prevent it from moving, and with the other hand 'spin' the coupler. It should spin without any precession (wobble) if the well is drilled perfectly parallel to the axis of the coupler. If it wobbles, there may be a contribution to your inaccuracies.

If your azimuth bearing has any play in it, it could affect accuracy a bit. There is no bushing to protect the chipboard around the az bolt (either the stock bolt or the Wildcard coupler bolt). Over time, esp if you torque it, that bolt will wear away at the edges of the chipboard and give you some play. If you can nudge your rocker side to side at all relative to groundboard and/or hear a 'knack' sound at the same time, this may be your issue. Gary could probably explain what part of the sky would be most affected, too, but damnifino.
If you have this I'm sure you can fix this, but might involve bolting a metal plate with hole over the area, to tighen away this slop. I noted a grizzled Synta dob (very similar to GSO) at a star party that had this az bolt wear issue in a big way....thing moved about a cm there was so much wear.

Lastly, you might want to play with the fabulous TPAS system; if there are systematic issues with the mount (reproducible issues that can be modeled - the above situations aren't so) then you might improve your accuracy this way. I meant to play with it, but since I had no issues of merit, I never got around to it....

Regards

Scott

Originally Posted by programmer

Ok.. while I'm waiting for a more permanent solution I decided to try my best at getting some results with the AN. I have reduced the lateral movement of the OTA, I think, completely. But then I thought about another aspect that can throw out pointing accuracy, which is the 90deg altitude reference point, i.e. pointing the OTA straight up. With the whole shebang set up inside the house on a level floor, I discovered the OTA is definitely *not* vertical when at it's vertical stop. Or more accurately, not perpendicular to the base. In fact it's possibly several degrees out. I have now glued a piece of timber of appropriate size where the OTA hits the vertical stop position, and now the scope is perpendicular (or much closer than before). Now I can't see any reason why my pointing shouldn't be accurate enough. I'll set my location as well, and turn on refraction modelling, just to cover all bases, although I can't point close to the horizon from my back yard anyway.

Unfortunately the clouds are rolling in, but it's still early!

PS: Last night (to cut a long story short) I couldn't get a 'warp', or error, value less than about 1.3, which is several times what it should be (close to zero). I'm still interested to compare notes with anyone else who has their Argo Navis hooked up to a GSO type dob, and how they fared getting theirs working.

[erick (Eric)]

Thanks Scott. I was looking forward to your comments and suggestions!

Eric

[programmer]

Thanks Scott, all tips noted. I have also corresponded with Gary K and will try Auto adjust tonight, weather permitting. I will also try and resolve remaining mount issues, i.e. tighten things up all round. TPAS will wait a bit longer. I also need to do a daytime encoder test. I'm sure with more tweaking things will come together. All this, in advance of receiving Gary's solution.

I'm now a member of the Yahoo AN group, which has lots of great info.

Thanks again

[goober (Doug)]

Originally Posted by programmer

I also need to do a daytime encoder test. I'm sure with more tweaking things will come together. All this, in advance of receiving Gary's solution.

I'm now a member of the Yahoo AN group, which has lots of great info.

Definitely do the encoder test - they are sort of important! There is tons of good TPAS info on the AN yahoo group.

[programmer]

Originally Posted by goober

Definitely do the encoder test - they are sort of important! There is tons of good TPAS info on the AN yahoo group.

Hi, yes I've just downloaded one of the files on the Yahoo group.

Trouble is, from my back yard there are no distant terrestrial object visible I'll just have to wait until I can get the scope out somewhere in the open. I'll still hack away with the assumption that the encoders are ok. I still have several things to try, which I'm sure will improve my pointing.