G-11 Goto Gemeni vs Argo Navis

[tempestwizz]

I have finally battered the 'Minister for War and Home Affairs' into submission, and have been given the go-ahead to procure a Losmandy G-11.:)

I note that Losmandy offer the Gemeni goto system at an additional $1500-ish. In the blurb, it is stated that with this upgrade, the standard stepping motors are replaced with a constant drive system, hence a smoother drive due to less stepping action.

Speaking with Gary Kopff at the Border Star Gaze last weekend, he advises that there is a kit made by Losmandy to fit his Argo Navis system and use it as the goto. This path would save approx $500, and the Argo Handbox could be used on other scopes when not required on the G-11.

I wish to use the G-11 for astrophotography - with a TV Genesis refractor.

Does anybody have any experience with the Argo Navis on a G-11?:shrug:

Comments on tracking/guiding with the standard stepper motors vs the constant drive would also be appreciated.

Brian

[JohnG]

The main difference between the Losmandy Gemini system and the Argo Navis is the GOTO function. Gemini has servo motors that have optical disks that read the encoder positions, it is also full GOTO -v- Argo Navis push to using the standard stepper motors, both systems acheive the same result in the end only you push the AN. With the Gemini you can sit at your laptop or PC and using any Star Program, push a key and the Gemini will slew to that position without any help from you.

Having used both systems, one will have to decide yourself whether you want push to, GOTO, or automatic GOTO.

The new AN is a very capable system and, can be used on mutiple telescopes with the correct Digital Setting Circles, whereas, the Gemini is confined to use on the mount it came with unless you buy addition motors and gearboxes.

The new Level 4 + version of Gemini has a host of features and is an excellent GOTO system although you will need to know that using it with a G-11, balance is critical.

I am not sure what Gary has in mind for the future, I am sure he will comment.

Cheers

[[1ponders]]

I have the AN on my G11 and use a Gemini on another. It's a hard call to make on which is better. The AN is a great push to, quiet, quick and accurate. You can link it to a planetarium program to show where you are going but it wont "drive" the G11. AN also comes with TPAS for very accurate modelling of your system that will greatly improve pointing accuracy. Accessing database objects with the AN is much simpler and easier I find than using the Gemini hand controller. I also like the silence when using it. No motor noise when you slew by hand ;)

The Gemini will allow you to "drive" from the computer planetarium program. This is a big plus if you need GOTO rather than PUSHTO. It also has modelling abilities for accuracy, but personally I don't feel it is as accurate as TPAS. You can purchase an aftersales product called TPOINT that does the same thing basically as TPAS, but it is an extra. The biggest let down for me with the Gemini is the hand paddle controller. To be honest once you have learnt to use it, it is ok, but I found it a pita to learn the ins and outs of the menus. It is not instinctive and Losmandy would do well to ditch it and use a more conventional hand controller.

They both have pluses and minuses and I guess it depends on how you are going to use it, permanent semiautomated setup (Gemini) or portability (AN), visual (AN), imaging (Gemini). It doesn't mean you cant use either for each, but this is just my experience.

[gbeal]

The Gemini is good, what little I have seen of it (I have a friends GM8/Gemini here at the moment), and I have used the G11 with AN a while back.
As all will agree, each has pluses and minuses.
As a matter of interest, what is the price of what you are looking at, IE, what is the budget?

[tempestwizz]

Thanks for the replies so far. The main technical difference seems to be pushing vs pulling, which for me is no big deal.

I will be mounted on a permanent pier.

I note no-one has comments on the practical performance difference between the Gemini motors, and the standard steppers.

My anticipated costs are about AUD$4k for the G-11, and $1.5k for the Gemini, or $1K for the AN.

Thanks Brian.

[rogerg]

Just guessing.. .but surely if the Argo Navis is push-to, it wouldn't do PE & backlash correction? Two very important things for astrophotography.

[JohnG]

The standard G-11/GM-8 uses Stepper Motors, they are, just that, stepper motors, they move a tiny step at a time, with my mounts (G-11 and GM-8) I did not notice any apparant high magnification vibration caused by the steppers, PE, yes, but that was addressed by the use of the new High Precision worm. The Gemini uses high torque servo motors which deliver a smooth, non stepping, constant rate to the drive shaft, you can now order the G-11 (with Gemini) with the new Maxxon motor's which are a step above the standard servo's and, therefor, give a smoother drive rate.

Your case, using the TeleVue for imaging, I doubt very much it would make all that much difference, start using a larger instrument with a longer focal length, I would be using the servo's.

Cheers

[gary]

Hi Brian,

Thanks for the post and firstly thanks to John for the follow-up.

John, it was great to meet you at Border Stargze!

As John points out, Argo Navis on its own does not directly drive stepper motors or
servo motors. It is a PUSHTO system rather than a GOTO. (However, see
further below).

Therefore, in the configuration you discuss above, you would retain your existing
tracking motors which would continue to perform tracking. In order to locate
objects during a manual slew, you would then install Losmandy part numbers
DSCH (Digital Setting Circle Hardware) and DGC (Delrin Gear Covers)
which we stock as our part number pn-g11-l-spec. These parts include a pair
of optical encoders, the hardware for mounting the encoders, a pair of
gear covers and an encoder cable. The optical encoders are positional devices
that then interface to the Argo Navis to allow it to keep track of the position of
the scope.

You can find a scanned copy of the installation instructions for the kit here -
http://www.wildcard-innovations.com.au/images/enc_losmandy.gif

Many people prefer PUSHTO over GOTO because of its fast, quiet and reliable
operation.

Argo Navis also provides a modern and sophisticated user interface and
detailed databases and object descriptions including the type of coverage
the southern hemisphere warrants. Dialing up an object by name takes
seconds and there are sophisticated modes of operation such as identify
and tour modes as well as user loabable object catalogs which can help
bring rigour to an observing program.

As far as pointing performance goes, Argo Navis doesn't hide the facts and
tells you how it is. For example, it can assist you in measuring the raw,
whole-sky pointing performance of the mount and can analyse and
potentially compensate for many common systematic fabrication and
gravitational flexure errors within the mount/OTA. It can then also tell
you the "modeled" pointing performance of the scope and will provide
you with statistical metrics of the various mount errors as well as the
amount of polar misalignment so you can then judge whether they are
"real".

What's all this mean?

It can mean the difference between landing the object within the FOV of
your eyepiece of choice or blind pointing onto a CCD array.

This case study on a G-11 may be of interest to you -
http://www.wildcard-innovations.com.au/group_post_5573/
You will need a free Adobe SVG plugin to view the graphics.

Getting back to GOTO for just one moment. I mentioned Argo Navis does
not directly drive servo or stepper motors. However, it can be used in
conjunction with some third party motor controllers to provide full
GOTO operation. For example, use of the Argo Navis with a ServoCAT
servo controller is a popular choice on some Alt/Az and equatorial scopes.
I believe some users may have also retro-fitted third party servo systems
to the G-11 and are using it in conjunction with the Argo Navis.

Finally, Argo Navis is designed and manufactured in Australia and exported the
world over. It bears the C-Tick logo which makes it legally approved for
use in Australia. Always ask whether imported electronic goods carry the
C-Tick marking.

Thanks again for the post and for considering Argo Navis.
It was great to meet you at Border Stargaze.

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

[JohnG]

Hey Gary, was great to finally meet you, felt like I had known you for ages :lol:.

Something else I would take into consideration is if you intend taking your mount into the field, ie, star parties etc. The G-11/Gemini draws a considerable amount of power during slews, about 3 amps from memory, so any battery power has to be able to supply that sort of power, another thing is that the Gemini does not like straight 12 volts, it likes a regulated power of around 13.8 volts to operate without motor stalls.

It is my intention to equip my GM-8, which is my field mount, with an AN in the near future because of the power requirements.

Cheers

[gary]

Hi John,



Since April 2002! We talked on the phone often enough so a face to face
was a long time coming! :)



That sounds like good anecdotal advice.

As you know, the Argo Navis can either operate off just a set of AA
dry cells or an external DC source that can be anywhere between 8V to 16V.
It typically draws only 0.15A.



Thanks!

Best Regards

Gary Kopff
Wildcard Innovations Pty. Ltd.

[leon]

Although it has all been covered here, my two cents worth.

I too have a G11 with Gemini Go-To, use a regulated 13.8 volts, plus the Maxxon motors, and it's like driving a V8 compared to a 4 cylinder, the combination is fantastic.

Leon :thumbsup:

[netwolf]

Brian,

You could get the G-11 mount then add the Argo Navis for push too.

Later you could order the Sitech or Servocat system and add this to the mount both will work with Argo Navis to provide complete goto without the need for a computer. They can also operate independently with computer control to provide goto. The trick is needing to bolt on the Pittman servo motors (usually sold with these kits) to the losmandy mount, this will require some custom brackets etc. Alternativley you could buy the Servo motors from Losmandy that bolt straight on and use them with these systems, this does require some rewiring of the cables. The Losmandy motors however by themselves seem quiet expensive, about 210USD each.

For the Sitech using Losmandy motors
Its Sitech 350 for controller + 95 for handpad + 420 for two losmandy motors + 30 for the cable. Thats about 900USD add the Argo Navis and your geting to 1300 to 1400USD not as much as the Gemini but not that much less. Unless you reduce the overhead spent on the Losmandy motors by using surplus Pitmann motors and making your own brackets. This has been done by one person i have talked with on the Losmandy_users yahoo group. One other user has used the Losmandy motors. Neither however have got the Argo Navis yet. The are using a computer to provide the goto database.

I like the Argo Navis as it has a much more user friendly menu. Though the Gemini has many features I think the Argo is equally as good from what i have read.

You can also initially go for the Argo based push too and add the other goto modules later. Or go the Goto without Argo and add the Argo later. Spread out the spending to get by the minister of finance.

Regards
Fahim

[allan gould]

Just my 2 cents worth. I have a G11 with Gemini Level 4. Just love the gotos and when used with PAS and PAC puts my object on the chip every time without fail. For astrophotographt its brilliant. Cannot comment too much on AN however from what I have seen its an excellent push-to. It is an excellent Australian system.

[rogerg]

Agreed with respect to the pointing accuracy. If just doing casual astro photography or viewing I will only use a compas to align my scope. Then after 4 or 5 alignment objects the pointing is amazing - near centre of eyepiece or chip all the time. That is a life saver for astrophotography with an astronomy CCD camera where you don't have a view finder to look through.

[Gerald Sargent]

I had a Gemini on a G8, got through 4 motors and one mother board. I Know the author Rene Goerlich and the software as such is first class, but the implimentation is a different story. On the G11 with 360 tooth pinion the servos are not subjected to the same stress as on the 180 thhth G8 pinion. Balance is critical as also the removal of all tight spots on thetwp worms, a tedious task which I have done a few times. As accurate but far
more reliable is the FS2 which does all the "goto" that the gemini does.
Argo Nevis is probably the simplest solution as one can stay with the
original stepper motors, pay significantly less and have the reliability of the steppers. If I were ever to try a Losmandy again it would be a toss-
up between FS2 and Argo Nevis- my pennth' (a fraction of what the G8
cost to maintain with Genimi)

[tempestwizz]

I'd like to thank everyone for their input into this topic. I certainly have some things to consider.

I think I will almost definitely purchase an AN, if for nothing else, for my Dob(s).

I also think I may try the astrophotography mount in a stand-alone configuration initially. In retrospect, the goto/pushto functions allow you to find the target initially, but after that do not improve tracking/guiding accuracy. The guiding control feedback loop is probably more important.

After my (limited) experience with the dobs, I can find many of the larger targets quite manually. And, with a TV Genesis at 500mm FL as my imaging optic, I am in relatively widefield mode.
If I later decide to put on a longer focal length imaging optic, I will perhaps revisit the initial pointing issue.

Many thanks again to all those who have contributed.

Brian