17 replies to this topic

[Avitam]

Hello All 

 

I am curious about modifying the Vixen SD-1 Controller to add autoguiding capabilities. 

 

My equipment: Vixen GPD with an MT-1 motor attached to the RA axis. ZWO guide camera with USB 3.0 and ST4 port. Option of using either NINA/PhD2 or ZWO Asiair.

 

I came across this wonderful document that details the ST4 modification of EQ style dual axis controllers: http://www.store.sho....com/eq_mod.pdf

 

The modification seems simple enough and looks like all I need to buy is an RJ12 cable and do some soldering. 

 

Is there any reason why this cannot be replicated on the SD-1 Controller ?  

 

Many thanks!

 

Avi 

 

 

[BlueMoon]

 

Is there any reason why this cannot be replicated on the SD-1 Controller ?

The SD-1 is a single axis controller and I believe you'd need control signals for both axes for autoguiding. That would be the first hurdle to overcome. Cheers.

[Avitam]

The SD-1 is a single axis controller and I believe you'd need control signals for both axes for autoguiding. That would be the first hurdle to overcome. Cheers.

That is good to know. But where is that limitation coming from ? The hardware inside the SD-1 ? 

 

Mounts like the iOptron Skyguider pro allow for autoguiding only via corrections to RA, so that lead to me believe that the same thing can be done via the SD-1..but that is likely over simplistic. 

 

If I can get a spare SD-1 then I could attempt it and answer this question.

[luxo II]

Is there any reason why this cannot be replicated on the SD-1 Controller ?  

You could add a normally-open contact from a reed relay (one for each button), wired in parallel across each of the switch contacts, which simulates pressing each button manually.  The coil of the reed relay is operated via the ST4 outputs of the guider, which are open-collector NPN transistors. This way the guider and your electronics remain electrically isolated from each other so neither can adversely affect the other.

 

This is easily done to what you have, with little more than 4 reed relays, a soldering iron and a few fine wires, and a suitable socket.

 

However while it may be an interesting exercise, and you will learn from it, at the end of the day I think this will struggle to be useful for imaging. The modern autoguiders assumes they have a GOTO mount connected with programmable backlash compensation, and the motor can slew quickly to take up the backlash; in your case however there is no backlash compensation and the max speed of the motors is very limited.

 

I found that out when I hacked  a Carton Supernova mount in much the same way (it had tiny little steppers and handsets like yours). Ultimately... while it may be an interesting exercise and you'll learn from the experience, if you want to get going with imaging you will end up buying a better mount, one that does GOTO and has autoguider inputs. Up to you as to whether you want to take the slow road, or the fast track.

Edited by luxo II, 11 January 2025 - 07:05 PM.

[BlueMoon]

 

But where is that limitation coming from ? The hardware inside the SD-1 ?

That would be my first guess. I wouldn't assume that what holds true for iOptron also holds true for Vixen.  It would be wise to try on a spare I would agree. Cheers.

[luxo II]

That is good to know. But where is that limitation coming from ? The hardware inside the SD-1 ? 

That mount only has a motor on RA. You cannot guide for long without a motor driving in declination as well - the star will drift N/S out of the autoguider.

 

So let's assume you add a motor and second handset (as I did for the Carton Supernova) - the next challenge is backlash in declination. For autoguiding to work effectively in declination it is essential the mount responds quickly when the guider direction changes from north to south, or vice versa. Where these little mounts fail though is that the motors used were really only chosen to do the sidereal rate in RA and dont go much faster, and they have little spur-gear gearboxes with huge backlash, so when used as a declination drive, they take ages to respond. And by the time they do catch up in dec, the resulting image will have odd-shaped stars.

 

The way to fix that is to fit more powerful/faster (NEMA) stepping motors with a belt drive, and gear ratios to suit, with micro-stepping. And for that you need new electronics (OnStep or a DIY unit built around an Arduino)... this is going to lead you down a very long rabbit-hole.

 

Simpler and quicker to buy a mount that does what you want, if you want to be producing images this side of next Christmas, or the one after that. Time is money, or vice versa.

Edited by luxo II, 11 January 2025 - 07:27 PM.

[Avitam]

That mount only has a motor on RA. You cannot guide for long without a motor driving in declination as well - the star will drift N/S out of the autoguider.

 

So let's assume you add a motor and second handset (as I did for the Carton Supernova) - the next challenge is backlash in declination. For autoguiding to work effectively in declination it is essential the mount responds quickly when the guider direction changes from north to south, or vice versa. Where these little mounts fail though is that the motors used were really only chosen to do the sidereal rate in RA and dont go much faster, and they have little spur-gear gearboxes with huge backlash, so when used as a declination drive, they take ages to respond. And by the time they do catch up in dec, the resulting image will have odd-shaped stars.

 

The way to fix that is to fit more powerful/faster (NEMA) stepping motors with a belt drive, and gear ratios to suit, with micro-stepping. And for that you need new electronics (OnStep or a DIY unit built around an Arduino)... this is going to lead you down a very long rabbit-hole.

 

Simpler and quicker to buy a mount that does what you want, if you want to be producing images this side of next Christmas, or the one after that. Time is money, or vice versa.

Super information. I have some homework to do to better understanding the fine details of autoguiding. 

 

But to your original point: I am fairly clear that I want to take the slow road. OnStep on this mount is very much on the roadmap, but I don't want to jump there just yet. I want to take a slow iterative approach where I make the next step once I have hit a technical wall (a pertinent example would be the absence of autoguiding in dec with the above setup). 

[luxo II]

I'll be perfectly frank - don't waste your time - and money - on something that will never really do the job. Perfectly good Atlas EQ-G (aka EQ-6) are going around $500 here in the CN Classifieds. These will blow your pixels off compared to what you could ever hope to end up with that old thing.

 

It's comparable to saying you want to go ocean racing, starting with a 30 year old canoe.

Edited by luxo II, 11 January 2025 - 11:43 PM.

[Cliff Hipsher]

Super information. I have some homework to do to better understanding the fine details of autoguiding. 

 

But to your original point: I am fairly clear that I want to take the slow road. OnStep on this mount is very much on the roadmap, but I don't want to jump there just yet. I want to take a slow iterative approach where I make the next step once I have hit a technical wall (a pertinent example would be the absence of autoguiding in dec with the above setup). 

I think that technical wall has been described in great detail and the warnings have been kind and truthful.

 

I'll give you a clue:  You can't make a silk purse out of a sow's ear..

 

To be completely honest, I went down a similar road with the net result being utter failure and a significantly smaller savings account balance.

 

Having learned my lesson I used an unexpected financial windfall to buy purpose built equipment..

[Skywatchr]

Hello All 

 

I am curious about modifying the Vixen SD-1 Controller to add autoguiding capabilities. 

 

My equipment: Vixen GPD with an MT-1 motor attached to the RA axis. ZWO guide camera with USB 3.0 and ST4 port. Option of using either NINA/PhD2 or ZWO Asiair.

 

I came across this wonderful document that details the ST4 modification of EQ style dual axis controllers: http://www.store.sho....com/eq_mod.pdf

 

The modification seems simple enough and looks like all I need to buy is an RJ12 cable and do some soldering. 

 

Is there any reason why this cannot be replicated on the SD-1 Controller ?  

 

Many thanks!

 

Avi 

I put an ST4 port on my Skywatcher HEQ5 non-goto and it works just fine.  I didn't have wires hanging out like in that article because I had enough room to install an RJ socket in the handbox to plug the guide cable into. 

However without a DEC motor controlled by the same handbox buttons, things can get complicated if you want dual-axis guiding.  And no, you don't need goto for autoguiding. Guiding on one target at a time works fine.  People were using ST4 a lot back before goto mounts were "popular".

If you could get a DD-1 and add a DEC motor, then it would make more sense to add an ST4 port or cable.

[PeterAB]

Hi,

 

I am not as pessimistic about this project as some previous posters.  

 

Phd2 will happily guide in RA only.  There is a check box to enable this feature.   As long as exposures are not too long, the mount is polar aligned, and there is little mechanical cross talk between RA and DEC, results may be acceptable.

 

Once Phd2 is running you have access to the guiding assistant and the log viewer.   This will allow you to accurately characterize how well your mount is performing.    It may be good.    If there are problems you know what to fix.   If it cannot be fixed, you will know to give up and use the mount for visual or very short exposures.  You will also know if an Onstep conversion would be productive.   Onstep will not fix a mount with mechanical issues.

 

Regarding the question if you can connect your camera or a shoestringastronomy adapter to the hand controller.   The answer is yes.   It could be easy or more difficult depending on how the switches are wired in the hand controller.   If the hand controller switches are wired in the most common way with a bias resistor to positive grounded with a spst momentary switches, you are all set.   Just follow the shoestring astronomy instructions.     Any other hand controller configurations will require more electronics and/or modifications of the hand controller circuit board.

 

My thoughts are if you are willing to spend the time tinkering as a hobby, this may be a fun project.  You won't know how good the results will be until you try it.

 

Peter

Edited by PeterAB, 12 January 2025 - 10:32 AM.

[BlueMoon]

 

I am not as pessimistic about this project as some previous posters. It could be easy or more difficult depending on how the switches are wired in the hand controller.   If the hand controller switches are wired in the most common way with a bias resistor to positive grounded with a spst momentary switches, you are all set.  Any other hand controller configurations will require more electronics and/or modifications of the hand controller circuit board.

Pessimism has nothing to do with it. Realistic is more like it. Some of us have done these kinds of mods and understand the potential difficulties and pitfalls.

[PeterAB]

Pessimism has nothing to do with it. Realistic is more like it. Some of us have done these kinds of mods and understand the potential difficulties and pitfalls.

I have also done this type of modification.    Results have been variable between satisfactory and hopeless.   I'm thinking, in the simplest case here,  the cost of the experiment is a st4 cable and three tack solder connections.  Plus some time spent learning Phd2 and the log viewer.

 

If the goal is to get on with astrophotography, I agree the best approach is to purchase the best mount that can be afforded.  On the other hand, tinkering with mounts and learning along the way may also be worthwhile to some.

 

Peter

Edited by PeterAB, 12 January 2025 - 11:51 AM.

[Avitam]

Hi all, 

 

I really appreciate arguments on both sides here. I am very very new to AP so it's great to see both sides of the story. 

 

I am aligned with Peter on my approach though. I am very very careful with my budgets and spend and I am honestly not afraid of being wrong or making a mistake. Astrophotography for me is not just about the final image but also about the process to get there and I do aspire to at least learn the basics of every step in the process between setting up the equipment and getting the final image even if it comes at the cost of time and some mistakes. Like I said the worst that can happen here is I come to the conclusion that my endeavor was futile, which like Peter said very well, costs me nothing but time and an RJ12 cable. But in that process I will get a strong grasp of why the exercise ended up being futile and will really help me appreciate all the technical points you all have mentioned here, which frankly,.I am unable to fully grasp with my current knowledge in hand. 

 

Sincerely 

 

Avi 

[BlueMoon]

If your intention is to do astrophotography with this mount, you only need movement on the RA axis. Actually adding DEC movement will contribute to a potential decrease in the accuracy of tracking. In essence, having RA movement already puts you in a better position for AP. Either way you go, good luck with your endeavors. 

Edited by BlueMoon, 12 January 2025 - 12:47 PM.

[TxStars]

There is nothing wrong with using the equipment you already have..

Just because your mount does not currently have a Dec motor does not keep you from adding one to it..

You could add a Dec motor and wire up a control for it to allow for autoguiding in both RA & Dec..

 

I have seen some good images done with just a basic RA driven star tracker..

With digital imaging requiring only short exposures to obtain data you will be able to get images with the Vixen GP mount..

It may take longer than with a new GoTo mount, but you can do it..

[Avitam]

There is nothing wrong with using the equipment you already have..

Just because your mount does not currently have a Dec motor does not keep you from adding one to it..

You could add a Dec motor and wire up a control for it to allow for autoguiding in both RA & Dec..

 

I have seen some good images done with just a basic RA driven star tracker..

With digital imaging requiring only short exposures to obtain data you will be able to get images with the Vixen GP mount..

It may take longer than with a new GoTo mount, but you can do it..

Totally agreed. I don't intend on adding RA autoguiding from the get go. 

 

But just doing the research for if and when I am ready. 

 

Thank you.

 

Avi

[triplemon]

If you ever want to add dec guiding you also first have to bring down backlash to manageable amounts first.