Frequently Asked Questions (FAQ)

Background for those new to the world of telescope computers

I've looked at the purchasing page but I am still unsure what I need to buy.

What is an optical encoder?

Will the optical encoder move the mount like a motor?

What resolution do the encoders provide?

What is the difference between a Digital Telescope Computer (DTC) and a Digital Setting Circle (DSC)? Is that just a marketing name?

I have an older DSC. Can I replace it with an Argo Navis™ DTC and retain my encoders?

Can I use an inclinometer instead of an encoder on the altitude axis of my Dob?

Using Argo Navis™

How is Argo Navis™ powered?

If I have both internal batteries and an external power source, which one does Argo Navis™ draw power from?

How do I establish the encoder direction senses for my Dob?

Do I need to level the mount?

I've used some digital setting circles where there is no need to perform the FIX ALT REF step. Why do I need to do it with Argo Navis™?

What is AUTO ADJUST?

I spin the DIAL in the BRIGHT STAR catalog, but there appears to be hardly any entries. What gives?

I want to perform the initial alignment on a star that is not in MODE ALIGN STAR. How can I do that?

I have a pair of 20,000 step/32,000 step/40,000 step encoders. Can I use them?

If the lithium coin cell should become depleted, will I lose my setups? Should I replace it now?

What planetarium programs can Argo Navis be interfaced to?

How can I interface Argo Navis™ via WiFi to a planetarium program such as Sky Safari™?

How can I interface Argo Navis™ via Bluetooth to a planetarium program such as Sky Safari™?

How can I interface Argo Navis™ to a planetarium program such as Sky Safari™ using a SkyWire™ adapter?

Answers:

Background for those new to the world of telescope computers

I've looked at the purchasing page but I am still unsure what I need to buy.
In a nutshell, to bring computerized pointing to your mount, you will require an Argo Navis™ Digital Telescope Computer, a pair of optical encoders and an encoder cable. If you are mechanically inclined, you might then devise your own encoder mounting hardware to attach the encoders to the mount. However, if you have a commercial mount, you might wish to take advantage of our large range of encoder mount hardware kits.

The most cost effective way is to consider purchasing one of our Bundled Special Systems. This includes an Argo Navis™, encoders, encoder mount hardware specific to the mount you own and an encoder cable. Use the "Bundled Special System" pulldown on the purchasing page and then enter a Qty of 1.

The options you might then consider are the Argo Navis™ Serial Communications cable, the USB Serial Adapter and the Argo Navis™ External DC Power Cable.

if you are a telescope builder and require a custom encoder mount solution, email us.

What is an optical encoder?
You can find a picture of an optical encoder here. It has a body and a rotating shaft. Inside the body is an otherwise clear optical disk with zebra crossing pattern markings inscribed on it. As the shaft rotates, so does the disk, causing the zebra crossing patterns to alternately block light from an internal LED or allow it to pass to a photodetector. The photodetector converts the light pulses into electrical pulses which are then transmitted to the Argo Navis™ Digital Telescope Computer via a cable.

One encoder is attached to each of the two axes of the mount. Argo Navis™ then keeps track of the pulses in order to determine the physical orientation of each axis.

Will the optical encoder move the mount like a motor?
No. The optical encoder is not a motor. It provides no drive force. Instead, you use your own muscle power to push the telescope in either axes and the encoder rotates under that power. You use what John Dobson might have referred to as "yoghurt power".

Some refer to this type of telescope location system as a 'PUSHTO' system, because you push the mount. It is fast, quiet and reliable.

Having said that, Argo Navis™ can also be interfaced to some third party servo motor controllers, the best known of which is the ServoCAT. When interfaced to a ServoCAT, Argo Navis™ then provides full "slew and track" capability to the telescope. What some refer to as "GOTO".

What resolution do the encoders provide?
Most of our encoder kits provide a resolution of 10,000 steps per axis. That corresponds to around 2.16 arc minutes per step.

Geometric, gravitational flexure and eccentric bearing errors within the mount/OTA along with runout error if the encoder axis is not parallel to the mount axis can degrade the effective pointing performance.

Argo Navis™ has an advanced feature called the Telescope Pointing Analysis System™ (TPAS™) that can help analyze and often compensate for some of the more common forms of systematic errors within a mount/OTA.

What is the difference between a Digital Telescope Computer (DTC) and a Digital Setting Circle (DSC)? Is that just a marketing name?
We refer to Argo Navis™ as a Digital Telescope Computer (DTC) and not as a Digital Setting Circle as there is a technical difference.

Historically, mounts were often fitted with mechanical graduated disks known as "setting circles" to assist the user in locating objects. In particular, many equatorial mounts were fitted with disks on the RA axis that were marked in terms of hours and fractions of an hour and on the Dec axis that were marked in terms of degrees.

Toward the end of the 20th Century, microprocessor controlled devices known as Digital Setting Circles began to enter the market. The first were essentially replacements for mechanical setting circles in that they would simply report the telescope's position in a celestial co-ordinate RA/Dec sense. Later ones came with additional features such as built-in databases of objects.

However, there was a major limitation of both mechanical and Digital Setting Circles in that they could not compensate for phenomena such as atmospheric refraction, precession, nutation and they could not analyze or compensate for any geometric, gravitational flexure or eccentric bearing errors within the mount/OTA that would otherwise lead to a difference between where the telescope was really pointing and where the setting circles indicated they are pointing.

The era of Digital Setting Circles drew to a close at the end of the 20th Century.

Argo Navis™ overcame the limitations of setting circles in that it could compensate for atmospheric refraction, precession, nutation and that it could analyze and potentially compensate for many of the common mechanical errors that exist in all mounts to some extent or the other. Such as device is known as a Digital Telescope Computer (DTC).

I have an older DSC. Can I replace it with an Argo Navis™ DTC and retain my encoders?
If you have a legacy system, chances are Argo Navis™ will simply plug and play with your existing encoders and encoder cable. Many users have upgraded to an Argo Navis™ in precisely this manner. Email us for details.

When upgrading to an Argo Navis™ you might also consider taking the opportunity of upgrading to higher resolution 10,000 step encoders as well. We can provide advice specific to your mount and telescope.

Can I use an inclinometer instead of an encoder on the altitude axis of my Dob?
We do not recommend the use of inclinometers in lieu of encoders.

Now and then people stumble across them, have a eureka moment and hope that they can be used in lieu of an encoder on a mobile telescope application.

Geometrically, they don't do what is required.

The problem is that an inclinometer is designed to measure an angle with respect to local gravity. In a Digital Telescope Computer application, rather than measure the orientation of the altitude bearing with respect local gravity, one wants to measure the altitude angle with respect to the azimuth axis. In other words, when the optical tube axis is parallel to the azimuth axis, one wants to use this as the 90 degree reference for the Altitude encoder. If the telescope were perfectly level, then an inclinometer could in theory be used as a substitute. However, few of us have the amenity of a perfectly level surface onto which to seat the telescope. As soon as there is the minutest slope in the ground, the inclinometer is no longer reliably measuring the angle of the altitude bearing.

For example, picture a telescope on, say, a 45 degree slope. As one rotates the telescope purely in azimuth, the altitude inclinometer, which is referencing itself to local gravity, will also change its reading. This is what you don't want. If the telescope is on a smaller, more realistic slope, say a degree, the same holds true and the resultant error in the altitude inclinometer reading will translate into pointing error residual when attempting to locate objects.

If you have a style of altitude bearing that makes it more challenging to install an encoder, for example, the bearing is an open semi-circle and the center of rotation is nothing but free space, then there are several approaches you can take.

One is to have an "outrigger" bracket that affixes, say, the encoder body to the point in space where the center of rotation is. The other end of the outrigger bracket attaches to the movable altitude bearing. A second "tangent" arm bracket has a coupler that mates with the encoder shaft and the other end of the tangent arm is affixed to the rocker box.

One can also use a strip of timing belt on the bearing and this mates with a timing pulley mounted on the encoder shaft.

If you have an unusual mount design, please drop ys an email at sales@wildcard-innovations.com.au and we would be happy to provide some suggestions. There is not much we haven't seen!

Using Argo Navis™

How is Argo Navis™ powered?
By a set of four alkaline AA cells. We even provide a set for you with our compliments to get you started.

Argo Navis™ is optimized to run off ordinary alkaline cells which will typically provide enough power for a couple of weekends of pretty heavy-duty observing use.

You can also use lithium AA cells or rechargeable NiMH cells, but not NiCd cells. If you use rechargeable NiMH cells you will need to recharge them externally.

Alternatively, you can save on batteries and power Argo Navis™ from an external DC power source such as a sealed lead acid battery using the Argo Navis™ External DC Power Cable. Argo Navis™ accepts an external power source of anywhere between 8V and 16V DC.

If I have both internal batteries and an external power source, which one does Argo Navis™ draw power from?
At any instant, Argo Navis™ will always use the power source that has the highest voltage.

Since a set of fresh AA batteries provide just over 6V and the external DC source should be between 8V and 16V, then when the external source is provided, it will power the system.

The external DC power source is also "hot pluggable". You can insert or remove the external power cable and either the internal batteries or the external power source will seamlessly take over. There is no need to power off the unit.

You can determine which power source is in use by dialing up MODE STATUS, STATUS POWER.

How do I establish the encoder direction senses for my Dob?

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.

To check the SETUP AZ STEPS sign, rotate the scope in Azimuth clockwise whilst observing the left-hand displayed value in MODE ENCODER. The Az angle should increase. If it does not, reverse the SETUP AZ STEPS sign.

Do I need to level the mount?
The mount does not need to be level.

The ALT REF point is with respect the mount's own axes.

For example, an ALT REF point of +90 degrees when the OTA is parallel to the Az axis and pointing at the sky.

I've used some digital setting circles where there is no need to perform the FIX ALT REF step. Why do I need to do it with Argo Navis™?
One only need perform a FIX ALT REF step when using an Alt/Az mount, such as a Dob, or a non-polar aligned mount.

The designers of Argo Navis™ could have completely automated the FIX ALT REF step and hid it from the user but they purposely designed the system to make the user conscious of it so that the user would be in the best position to diagnose any problem they may encounter in the field.

What's more, they included a feature called AUTO ADJUST and provided the ability for the user to turn it ON or OFF at will.

When AUTO ADJUST is ON, one only needs to provide a rough hint as to where the ALT REF point is and AUTO ADJUST will refine it based on your two star alignment.

What is AUTO ADJUST?
The encoders installed on the telescope are incremental encoders.

When an incremental encoder is powered on, it has no inherent zero reference point.

As it turns out, one only need establish a reference point for the Altitude encoder.

The WARP factor is measured in degrees and it is the difference between the angular separation of the two stars according to their catalog positions and as a function of time compared to what angular separation the encoders moved through with a co-ordinate system established by your ALT REF point.

AUTO ADJUST is a feature that the user can switch ON when performing the FIX ALT REF step.

What AUTO ADJUST ON does is assumes the only predominant error is the initial ALT REF point and it takes the initial ALT REF point as a rough 'hint' and adjusts it so that the angular separation the encoders moved through then equals the angular separation of the corresponding alignment stars.

Thus, by definition, it tries to make the WARP factor 0.00 after a two star alignment.

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.

Our advice is that once you have correctly established the encoder direction senses for your mount, we also recommend you start using 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.

In that instance, you can use MODE ENCODER to check that both encoders are responding on their corresponding axis and if need be, switch AUTO ADJUST to OFF and examine the WARP value after a new two star alignment. If the WARP value is large, it will give you reason to pause, as you may have simply misidentified a star. Now and then, it happens to the best of us.

However, armed with the above knowledge, one can further appreciate why Argo Navis™ reports WARP values and the diagnostic power that being able to switch AUTO ADJUST to OFF can provide. When combined with other diagnostics such as MODE ENCODER, you will be in the best possible position to be able to solve problems for yourself, particularly if it is late at night and you are a long way from home.

I spin the DIAL in the BRIGHT STAR catalog, but there appears to be hardly any entries. What gives?
You will simply be having a little 'finger problem'.

3081 stars are listed in the BRIGHT STAR catalog alone.

Rather than just spin the DIAL, you need to spin the DIAL to select the first desired symbol in the name and then press the ENTER button to advance the cursor to the right to the next editable symbol, so you can 'spell' out the name.

When spinning the DIAL clockwise, numbers appear before upper case letters, upper case letters appear before lower case letters and in some catalogs Greek symbols like Sigma appear at the end.

You might like to try and access the bright star BETELGEUSE as an exercise. You will notice when you access the BRIGHT STAR catalog, the first character of the name of the star will be blinking. This is the cursor position. Spin the DIAL to change the letter to a 'B' and ignore the rest of the characters. Argo Navis™ performs word completion as you go. Then press the ENTER button to move the cursor to the right and spin the DIAL until the letter 'E' occurs. Repeat this process and after just a few edits, the unit will complete the full name for you.

The names of constellations are accessed in a similar way in MODE IDENTIFY and MODE TOUR as are many other fields.

We refer to this method of entry where Argo Navis™ performs word completion for you as the Intelligent Editing System™

Some have asked, "why not have a numerical keypad?". The answer to that is try entering the name BETELGEUSE or URSA MINOR DWARF using a numerical keypad. The Intelligent Editing System™ allows you to access named objects such as this extremely rapidly. For example, the galaxy known as URSA MINOR DWARF is uniquely accessed in only two button presses.

What's more, the system is optimized for using wearing gloves in cold environments.

I want to perform the initial alignment on a star that is not in MODE ALIGN STAR. How can I do that?
Argo Navis™ allows you to align on any object at any time including during the initial alignment.

MODE ALIGN STAR simply contains a list of convenient bright stars.

To align on, say, JUPITER, dial up MODE CATALOG, PLANETS, JUPITER, EXIT out and go to MODE ALIGN, ALIGN JUPITER, press ENTER and you are aligned.

Or you can select any one of the thousands of stars in MODE CATALOG, BRIGHT STARS and use MODE ALIGN to align on it.

I performed a FIX ALT REF step and a two star alignment, but when I went to guide to an object, the unit reported NOT ALIGNED. What gives?
When the unit powers on, the default menu that appears is MODE FIX ALT REF. You should position the OTA to the appropriate reference point, hit ENTER once to enter the MODE FIX ALT REF menu and then hit ENTER again to tell the system "this OTA altitude position corresponds to this reference point".

So if you subsequently see the NOT ALIGNED message you would have simply had a little 'finger problem' and not hit ENTER that second time to tell the system "this OTA altitude position corresponds to this reference point."

When the NOT ALIGNED message appears, if you hit ENTER, the unit will provide a description of what step in the alignment process was missing.

You may then be surprised that when the unit enters GUIDE mode, it correctly locates the object despite the NOT ALIGNED warning.

The reason is that when the unit first powers on, it sets the ALT REF to where the OTA happened to be at that instance. In other words, if the OTA had already been pre-positioned to the point that you would normally perform the FIX ALT REF step, then when the unit powered on, in the absence of you performing the FIX ALT REF step, it used that reference position.

One can perform the FIX ALT REF and star alignment in any order and repeat any of the steps at any time if need be.

I have a pair of 20,000 step/32,000 step/40,000 step encoders. Can I use them?
Argo Navis will operate with these encoders.

Be sure to enter the number of encoders steps in the SETUP ALT STEPS & SETUP AZ STEPS menus.

As these encoders have a different internal architecture to the 10,000 step encoders, you will need to tell Argo Navis to apply power continually to them. In the SETUP ENC TIMING menu, set TON=any positive value and TOFF=0.

Since the power consumption of these encoders is much higher than 10,000 step encoders, battery life will be shorter. We recommend you consider powering the unit from an external DC source.

If the lithium coin cell should become depleted, will I lose my setups? Should I replace it now?
The setups are stored in a non-volatile memory that has the remarkable attribute that it can retain its contents for a century or more in the absence of any power source.

The lithium coin cells plays no part in supplying power to the non-volatile memory. Instead, its job is to power the time-of-day clock when the power switch is OFF.

The lithium coin cell will typically last 5 to 7 years before needing replacement. When it is depleted, you will see an RTC BATTERY FLAT message when the unit is powered on and the time and date will be reset to JAN 1 2000 12:00. Even if this should happen whilst you are in the field, simply manually enter the date/time in the SETUP DATE/TIME menu and replace the battery at your convenience when you return home.

If the lithium coin cell depletes and the unit will not start normally, power OFF the unit and then immediately power it ON again without hesitation. This procedure may need to be repeated five or six times in rapid succession before the display shows the initializing message. When returning home afer your observing session, replace the lithium coin cell (See Argo Navis™ User Manual Appendix F) and the unit should start normally. Enter the date/time and the lithium coin cell will then continue to power the time of day clock for several more years.

What planetarium programs can Argo Navis™ be interfaced to?
Argo Navis™ can be interfaced to all known planetarium programs. The way it can do this is because it supports several third party telescope interface protocols. For example, it supports the ubiquitous Meade™ protocol and all planetarium programs support that protocol. Most planetarium programs provide a tracking cursor display of where the scope is pointing against a chart of the sky.

How can I interface Argo Navis™ via WiFi to a planetarium program such as Sky Safari™?
Use a device such as the Simulation Curriculums SkyFi™ device interfaced to the Argo Navis™ Serial Cable.

How can I interface Argo Navis™ via Bluetooth to a planetarium program such as Sky Safari™?
Use a device such as the Simulation Curriculum SkyBT™ Bluetooth Telescope Controller interfaced to the Argo Navis™ Serial Cable.

How can I interface Argo Navis™ to a planetarium program such as Sky Safari™ using a SkyWire™ adapter?
Simply use the Argo Navis™ Serial Cable. One end plugs into the Argo Navis and the other into the SkyWire™ adapter.