TheSkySearchers

Hi all. I was fortunate to have found a used 8’ Exploradome at a good price. It certainly will make my winter imaging more enjoyable. However I do have to automate the rotation at least and would appreciate any ideas how to do this without a huge expense.
I was looking at the Nexdome 2.2m Rotation kit at $869. I believe that is just the motor and tracks.
Would that be a good choice? Also I have no idea what other software or hardware would be required. I use SGP and would like whatever software needed to play nice with it. Could really use some help here as this is outside of my comfort zone. Thx!

I did the automation myself. Total cost was under $200. I used an Arduino as the controller and a geared stepper motor to drive the rotation. The drive pinion and ring gear were from the automation kit that came with the Exploradome that I never liked.

Does your dome have the aluminum dome rings or the older plastic ones? It is not hard to drive the dome on aluminum rings with a stepper, but I wouldn't vouch for it being able to drive one on the plastic rings.

A stepper is much simpler and more accurate than a DC motor for this task. With a DC motor, you need some feedback mechanism to find out where the dome actually ended up after you shut off the motor. With the stepper, as long as it has enough torque for the job, the dome will be exactly where you told it to go, to an accuracy, in my case, of 9 arc-seconds.

If you go that route, I can help you with the Arduino code and an ASCOM driver for it.

Wow Kathy, $200 I’d be thrilled if I could install a rotation kit for double that.
I am picking up the dome tomorrow morning so once it’s taken apart I will be able to tell if it has the plastic or aluminum rings. It does not have the Exploradome gear and track but I can get one.
https://optcorp.com/products/explora-do ... tion-kit-1
For the stepper motor are you talking about a high torque one like this?
https://canada.desertcart.com/products/ ... camera-diy
And I would definitely appreciate any help you could provide. Obviously you’ve succeeded very nicely automating your dome.

That's not the same stepper that I used, but it looks pretty similar. The one I used produces 416 oz-in of torque. It works fine, but the larger 650-ish oz-in motor would have had more reserve capacity.

I used a spring scale to measure the pull required to rotate the dome by hand, both a steady motion and a reasonable acceleration. I used those numbers and the gear ratio of the pinion and ring gear to calculate the required torque at the motor.

I drive the motor at 2000 kHz when at full speed, but I programmed in a 1-second acceleration to that speed to ensure that I didn't demand more torque than the motor could deliver. It wouldn't harm the motor, but you'd lose steps and therefore precision in the motion. By staying within the motor's capability, you know exactly where the dome is.

Well I picked up my Exploradome and gave it a good cleaning, it’s looking like new and I’m very happy with it so far. Unfortunately it does have the plastic dome ring so this week I’ll be fabricating an aluminum one. I’ve also ordered the rotation kit sprocket and track. Things will be on hold until the new ring and track are installed.
In the meantime Kathy I would appreciate some advice as to where I should start and what to buy as far as the stepper motor and controller are concerned. Thx so much.

Alex, I am hesitant to recommend a motor until you have measurements of the force necessary to rotate the dome. If you had the same rings and wheels as I do, I could recommend one based on my measurements. But I would recommend getting it all assembled and measuring your actual force required.

Earlier in this thread, you linked to a motor that produced something in the ballpark of 800 oz-in of torque. I am working with a 416 oz-in motor, so the 800 ought to be plenty if you have to get one ahead of time.

You will need an Arduino to control things, and a stepper controller. I used this controller: https://www.robotshop.com/ca/en/tb6600- ... river.html.

For the shutters, you will want a relay shield to plug into the Arduino. This is the one I used: https://www.robotshop.com/ca/en/relay-s ... duino.html. I have a couple of external components to operate the shutters. The important one is the door sequencer. It is a home-brew contraption of relays and diodes. If you choose to bypass this, you could operate each door independently from the Arduino, with some reprogramming. The hard part of doing that, though, is not the reprogramming, but getting the signals to the door motors in the rotating dome. Two contacts are not hard to arrange, but more than two is difficult.

If you don't have shutter motors already, you will need to get them. I didn't include them in my $200 figure, since I already had them.

If that sounds like biting off more than you can chew, you might want to investigate an off-the-shelf dome controller.

Ditto what Kathy said.

Ekos claims "Support for dome slaving" on their web site, see https://indilib.org/domes.html . It requires an INDI driver, there may be some examples and you can ask around on the INDI forum. This is an alternative to Ascom, in case you have not made a choice yet. Otherwise, Kathy has an Ascom driver not to be ignored.

If you are looking for Arduino shields to power stepper motors, my OnStep uses a CNCv3 shield to power the stepper motors with. OnStep does not have dome support though.

Thx for your excellent advice. Yes I am the impatient type so I will go ahead and order that stepper motor and controller you suggested. I don’t think I will tackle the shutter control quite yet as I have a lot to learn. I would be extremely happy with getting the dome rotation synced to the scope for now. This whole thing with the Arduino is very daunting. Im very good at the technical aspects of this hobby but no nothing about Arduino
I’m of course willing to learn and am a quick
Study. Should I purchase a complete Arduino starter kit or just an UNO R3 board. This is outside my wheelhouse and definitly will need a lot of guidance.

You don't need a starter kit. That is for robotics hobbyists who want to play and learn what an Arduino can do. In your case, you have a specific application in mind, so all you need is the Arduino Uno.

Here is the code you need:

Dome control firmware for Arduino:
WalkerDome Arduino

ASCOM driver to communicate with dome control Arduino
WalkerDome ASCOM driver

Optional dome control software, synchronizes dome slot to mount:
DomeSync

Hi Alex,

Can’t help with your dome, but great to hear about your new equipment! Man, that is very exciting!

Juno16 wrote: ↑Mon Nov 09, 2020 2:18 am Hi Alex,

Can’t help with your dome, but great to hear about your new equipment! Man, that is very exciting!

Thx Jim! It was something I have wanted to do for a long time and was not looking forward to another winter hauling my equipment in and out in the cold. Although I’m not sure I’ll get everything up and running in time but with all the expert members help available on this forum i think I have a good chance of getting it done before the snow flies.
I must say having been a member of most of the astronomy forums over the years the Skysearchers has to be by far the most cordial helpful non judgemental forum out there. A super amalgamation of so so much expert knowledge in this field. Although I don’t contribute as much as I should I thoroughly enjoy reading ever post! Congrats to all the administrators who put this together and keep it going!!

Alex, it’s great to hear that you enjoy it here at TSS. Your contributions are much appreciated!

Keep us updated on your dome!

It’s been a typical fall here in that I didn’t have even one decent imaging night since October but it did give me a chance to work on my observatory.
The Exploradome had the old ABS track in the dome and I was contemplating on replacing it with an Aluminum one. Unfortunately my skills at welding aluminum were not up to the task so I made a new track using 1/8” stainless. It did add an extra 18lbs to the dome which is not excessive as the stepper motor I will be using is rated to 4000 oz-in. It took me a while to find the raw material but have finally finished it and today mounted the dome with the new track.
Thank you Kathy for your generous offer to share your expertise in the rotation kit you assembled and the programming of the Arduino and stepper motor. I soon realized though that while I’m skilled in the construction phase required to assemble the rotation kit that I’m totally ignorant as far as the programming goes.
So I have decided to use the Nexdome rotation kit instead as it’s a complete ready to go solution. I just received the kit this week and hopefully will have it installed by next weekend. For now I’ll be operating the shutter manually but maybe next year will automate it as well. I also upgraded my mount from the CEM60 which has been a fantastic mount to the CEM70G and am looking forward to trying it out soon as we can get a clear night.

Well I finally have everything connected and running. The Nexdome stepper motor easily turns the Exploradome and SGP and the dome Ascom Device Hub all communicate nicely. I just have one major issue in that the dome slit does not line up with the scope, it’s off by roughly 15 degrees. I’ve taken and entered the geometry measurements for the scope position E/W, N/S, UP/DOWN, and the dome radius and GEM offset as close as I could measure them. My question is how do I go about troubleshooting this? Is there one parameter that I should be looking at?

Is your pier centered in the observatory? If so look at this comment here: https://www.nexdome.com/forum/installat ... centerline
This was a question I asked regarding the proper location of things. Go to near the bottom and you will see several illustrations on the "necessary" dimensions. If the pier is centered then the number of needed dimension is reduced.

Hi Lenny, thx for the link but since my last post with the help of KathyNS I figured out my problem. Yes the pier is centred perfectly in the dome centre and all the entered parameters were correct. My problem was that the Nexdome controller was programmed with the step size for the Nexdome so once I calculated the step size for the Exploradome it solved the problem and the dome sync works perfectly.

Hi KathyNS,

I've recently setup a Pulsar 2.2m obs. I would like to attempt the automation diy you've successfully implemented. Initially, I'd like to get the shutter moving at siderial. I've asked Exploradome re their drive pinion and ring gear from the automation kit that came with the Exploradome , but there's a wait time till January maybe longer plus I'm not US based. I can sort the Arduino and the geared stepper locally. However, you mention aluminum dome rings . Do you have a link for an example of the aluminum dome rings you mean that could be assembled with the drive pinion and ring gear you also refer to to?

Colm

KathyNS wrote: ↑Mon Nov 02, 2020 4:18 pm I did the automation myself. Total cost was under $200. I used an Arduino as the controller and a geared stepper motor to drive the rotation. The drive pinion and ring gear were from the automation kit that came with the Exploradome that I never liked.

Does your dome have the aluminum dome rings or the older plastic ones? It is not hard to drive the dome on aluminum rings with a stepper, but I wouldn't vouch for it being able to drive one on the plastic rings.

A stepper is much simpler and more accurate than a DC motor for this task. With a DC motor, you need some feedback mechanism to find out where the dome actually ended up after you shut off the motor. With the stepper, as long as it has enough torque for the job, the dome will be exactly where you told it to go, to an accuracy, in my case, of 9 arc-seconds.

If you go that route, I can help you with the Arduino code and an ASCOM driver for it.

cbweb wrote: ↑Fri Nov 12, 2021 4:47 pm Hi KathyNS,

I've recently setup a Pulsar 2.2m obs. I would like to attempt the automation diy you've successfully implemented. Initially, I'd like to get the shutter moving at siderial. I've asked Exploradome re their drive pinion and ring gear from the automation kit that came with the Exploradome , but there's a wait time till January maybe longer plus I'm not US based. I can sort the Arduino and the geared stepper locally. However, you mention aluminum dome rings . Do you have a link for an example of the aluminum dome rings you mean that could be assembled with the drive pinion and ring gear you also refer to to?

Colm

If Exploradome is backed up for the drive gears, they will probably be backed up for the rings, too. And there is a really good chance that the rings would not fit your dome, since they are designed for the 8' Exploradome.

Here is an old photo of the original rotation motor, the drive pinion and ring gear, and the aluminum dome rings. The lower ring is fixed, and the upper ring rotates and supports the dome.

Hi Kathyns,

Thanks for pic and heads up re possible mismatch between Exploradome kit.

Re..
Here is an old photo of the original rotation motor, the drive pinion and ring gear, and the aluminum dome rings. The lower ring is fixed, and the upper ring rotates and supports the dome.

... acquiring the aluminum dome rings aspect I'll focus on for Pulsar use Or alternative approach. That aspect needs sorting before I proceed further.

Thanks,

Colm

Hello ,
I am trying to make Arduino Walker dome.
I made a breadboard circuit, trying to open and close dome.
I had manage the fact I have only one motor.
I understand, the home switch is open when home.
When I try to open and close the dome, in serial terminal with OOLF or O1LF, I need to trigger the home switch to iniate the movement of the dome. Is it normal because I have'nt made the calibration of the rotation ? Or I have an other problem ?

Any help will be appreciate.
Thanks
Martin