ST4 and Stellarium ?

[Astro-Geek]

I've got a very basic question about ST4 interfaces, (and despite a lot of searching I haven't been able to resolve it !) ?

It's a follow up from my Celestron CG5 motor control thread, but I thought it might be better to give it this new thread as it's a more general concept.

My understanding so far is that ST4 ports are mostly used to connect a camera to the slewing controls to enable long exposure photography.

.. but am I also right in thinking that an ST4 port can also enable a computer to connect to slew via programs like Stellarium ?

The proprietary handset goto systems like Celestron and Skywatch have bespoke non-standard sockets and cables to give PC connectivity, so would the generic non-branded Chinese "dual drive enhanced motor set" with ST4 port give the same functionality ?  (I've attached a pic of the fairly common set that I'm thinking of).

I have an element of doubt because I believe these motors don't have optical feedback sensors like the ones in Syscan and Nexstar mounts.

Another thing that's confusing me is that the Onstep program can interface with Stellarium and provide goto facility with these simple non-sensor motors, but maybe that's because the Arduino board is interpretting the commands and "remembering" how many  revs gave X degrees of slew ?

 

[Cornelius Varley]

The ST4 port on the handset is used for autoguiding not goto so can't be used for controlling the mount through Stellarium.

[lenscap]

You cannot achieve goto using the enhanced dual drive motor controller.

This is a dumb controller. It cannot communicate with Stellarium etc.

It cannot know where the scope is pointing. It cannot calculate how to move to a target.

It can slew  in RA or DEC at various speeds in response to button presses

or be remotely moved through the ST4 port (usually for autoguiding), and it can  track in RA- thats it.

 

For goto you need a smart controller such as Onstep or AstroEQ or one of the commercial systems which has software which can be used to align the scope, keep track of its position, calculate how to move and, if you wish be used in conjunction with planetarium software.

 

Most telescope controllers are "open-loop" They count stepper-motor steps to determine scope movement.

Some have encoders or the option of using encoders (closed-loop control) so that they can keep track of the mount even if it is moved by hand. (Eg SW Freedom Find)

 

[Astro-Geek]

Thanks for the replies.

I thought Onstep could give goto functionality with "almost any motors", including simple non feedback motors like those by being programmed with the gear ratios and using the Arduiono's processimg power to keep track of where the scope is pointing.

I'd then assumed that programs like Stellarium used Ascom with the PC's processing power to do the same thing.

When Stellarium (and similar progs) connect via proprietary "smart" controllers like Nexstar and Synscan, I also assumed that they used the PC's processing power to directly slew the motors, rather than using any of the handset's processing power, which I thought was miniscule by comparison.

(That's another plan down the drain then !!  ? )

[lenscap]

Stellarium etc does not control the motors directly.

It can communicate ( a two-way process ) with a smart controller to direct the mount to a target using either a LX200 protocol or the mounts Ascom driver.

(Since you cannot communicate with a dumb controller like the "enhanced dual axis" you cannot write an Ascom driver for it.)

The smart controller "knows" its gear ratios and step angles and calculates how to drive  the mount to the target. 

The "enhanced dual axis" controller has neither the hardware or software to communicate with Stellarium etc.

14 hours ago, Astro-Geek said:

I thought Onstep could give goto functionality with "almost any motors", including simple non feedback motors like those by being programmed with the gear ratios and using the Arduiono's processimg power to keep track of where the scope is pointing

Yes, provided they are stepper motors. The enhanced dual axis motors are described as "DC Motors"

Are they steppers? I dont know. I doubt it. Anyway I assume  you would not  want to use them since you already have steppers on your CG-5.

[Astro-Geek]

Thanks for that, it's saved me possibly going down a blind alley.

So my best option to get round my CG5 DEC runaway keeps coming back to Onstep software and an Arduino, or the elusive wildly overpriced Celestron replacement motor control board.

(......and with the replacemant Celestron board it may well fail again, judging by the number of runaway dec drives on CG5's...  ? )

 

[lenscap]

It is a long shot but you could put out  want ads for an AstroEQ controller.

AstroEQ is similar but less versatile than Onstep but it has been around longer so they come up occasionally.

A complete AstroEQ kit with a ready made controller was sold cheap on here in July.  AFAIK you cant buy ready-made controllers new any more.

I would have bought it myself but I had already ordered the Onstep bits.

This is the AstroEQ site;

https://www.astroeq.co.uk/tutorials.php

 

 

[Astro-Geek]

Thanks Lenscap,

I'll have a look at AstroEq.....

[Astro-Geek]

I've spent the past few days reading up on Onstep and AstroEQ and I think I understand them a lot better now, (but I'm ready to be corrected on any of my deductions !).

Neither appears to be available ready-made, (and certainly not at an advertised price).

Onstep is assembled from a handful of ready-made Arduino comptible modules, as listed by Lenscap on this thread.  (Thanks for that ?  ).

AstroEQ has to be constructed from approx 40 individual components soldered onto a bespoke printed circuit board created and sold by Thomas Carpenter, together with two pre-programmed ICs, also sold by him.

I find the AstroEQ project more attractive because the completed controller looks  to be a neater solution, even with a made to measure Hammond plastic case, (albeit needing holes cut out for the sockets and LEDs etc..)

I've researched most of the components and they all seem readilly available for just under £50, but the crucial PCB and two pre-programmed ICs have to be obtained via membership of Tom's forum, and so far I haven't been granted access to it.

I believe I'm right in saying that both Onstep and AstroEQ will work with the standard mass-produced (6 volt) dual axis motor kit for the EQ5 ?

I can now understand that the simple 4 button controller (and the "enhanced" version) cannot interface with Stellarium type goto progs because it lacks the functionality of keeping track of where it is from what pulses it has ent to the stepping motors, (as pointed out to me on here).

However, am I right in assuming that the two 6v motors in the very common EQ5 dual axis kit can interface ok with Onstep and AstroEQ once their characteristics are set in the prog ?

I've read that their maximum stepping speed for goto is very slow, but I could live with that.

The reason I keep coming back to those is because I'm thinking that with the scope permanently fitted with those simple RA and DEC motors, I'm then free to sometimes plug their RJ11 plugs into the existing simple 4 button hand controller (and therefore not need the computer as well), or I could plug them into an Onstep/AstroEQ box and get full synchronisation with stellarium type progs.

Needless to say, I've given up on my CG5's "advanced goto" Celestron controller setup because a replacment motor board is ludicrously overpriced and virtually unobtainable here in the UK, and the runaway gotos seems to be very common, so it might easily go faulty again..... ?

[Astro-Geek]

Update on my previous post - AstroEQ PCB and pre-programmed ICs now ordered.

Just the rest of the components to order from Farnell and then I'll be all set for the build.

Fortunately I already have temp controlled mini soldering irons and thin multicore solder from my other electronic hobbys. ?

I'll keep the forum updated with my progress in case anyone else is interested in AstroEQ.

Maybe via a new thread though, as my original title "ST4 and Stellarium ?" is way off beam now........