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Dome rotation automation question

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#1 ErikB

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Posted 26 December 2012 - 11:11 PM

My domed observatory is nearing completion. I don't plan initially to automate the rotation, but it is a possibility for the future. I am aware that there are commercial solutions to make the rotation follow the pointing of the scope. Presumably they orient the dome slot center to the azimuth of the target. Of course, with a GEM the scope center will most of the time not be on the symmetry plane at the center of the slot. My question is the following. Does any existing solution use software that is intelligent enough to place the dome slot in the optimal position for where the scope actually is, taking into account the particulars of GEM dimensions?

#2 Christopher Erickson

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Posted 26 December 2012 - 11:46 PM

Yes.

The MaxDome-II controller and LesveDome controllers both do that. Probably others as well.

This is a standard feature of automated dome control.

#3 ErikB

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Posted 27 December 2012 - 12:16 AM

Thanks Chris!

#4 Christopher Erickson

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Posted 27 December 2012 - 05:31 AM

This document might be interesting to you:

http://www.brayebroo...Mill_Resourc...

#5 cn register 5

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Posted 27 December 2012 - 05:56 AM

The ASCOM hubs can handle the dome geometry issues.

Chris

#6 cn register 5

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Posted 27 December 2012 - 12:41 PM

This document might be interesting to you:

http://www.brayebroo...Mill_Resourc...

An alternative way is Paul Bourke's 3D geometry pages, the intersection of a line and a sphere. The line is the direction the scope is looking, starting at the OTA position, and the sphere is the dome.

You end up with a quadratic equation, the solutions are the positions where the line and sphere intersect. It's a lot easier to compute than all that trigonometry, especially if you use the centre of the dome as the origin.

I did this when I automated the dome on my Society's observatory.

Chris

#7 Christopher Erickson

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Posted 27 December 2012 - 01:54 PM

This document might be interesting to you:

http://www.brayebroo...Mill_Resourc...

An alternative way is Paul Bourke's 3D geometry pages, the intersection of a line and a sphere. The line is the direction the scope is looking, starting at the OTA position, and the sphere is the dome.

You end up with a quadratic equation, the solutions are the positions where the line and sphere intersect. It's a lot easier to compute than all that trigonometry, especially if you use the centre of the dome as the origin.

I did this when I automated the dome on my Society's observatory.

Chris


This approach, by itself, would be insufficient for a GEM mount, which has to flip the meridian, which places the axis of the telescope and its pivot point on the other side of the pier.

The ASCOM drivers for the MaxDome-II and LesveDome solutions incorporate meridian flip, as well as offset piers and pier height. No need to write your own software.

I hope this helps.

#8 ErikB

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Posted 27 December 2012 - 10:25 PM

The brayebrookobservatory document looks interesting, thanks.
Regarding meridian flip: Some mounts can function well beyond the meridian without flip. Do Maxdome-II and LseveDome assume that the flip is performed exactly at the meridian? Do any goto mounts provide information about whether the current target is being pointed to on the "correct" side of the meridian or on the "previously correctt" side? If yes, do the dome rotation solutions make use of such info?

#9 Christopher Erickson

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Posted 28 December 2012 - 04:27 AM

The brayebrookobservatory document looks interesting, thanks.
Regarding meridian flip: Some mounts can function well beyond the meridian without flip. Do Maxdome-II and LseveDome assume that the flip is performed exactly at the meridian? Do any goto mounts provide information about whether the current target is being pointed to on the "correct" side of the meridian or on the "previously correctt" side? If yes, do the dome rotation solutions make use of such info?


Actually those decisions are made in ASCOM and not in the dome drivers and yes, this is a common issue and there are well thought-out provisions for imaging past the meridian with configurable limits, based on your particular mount.

Basically, the dome driver only cares about slaving the dome to your scope's pointing. If you slew the mount to a target, the dome driver only cares about what side of the meridian it is told that the OTA is on. The dome driver does not make the decision about which side of the meridian the OTA is on. It also doesn't care about how long you track an object past the meridian. It will faithfully follow where your scope is pointed.

I hope this helps.

#10 cn register 5

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Posted 28 December 2012 - 05:59 AM


An alternative way is Paul Bourke's 3D geometry pages, the intersection of a line and a sphere. The line is the direction the scope is looking, starting at the OTA position, and the sphere is the dome.

You end up with a quadratic equation, the solutions are the positions where the line and sphere intersect. It's a lot easier to compute than all that trigonometry, especially if you use the centre of the dome as the origin.

I did this when I automated the dome on my Society's observatory.

Chris


This approach, by itself, would be insufficient for a GEM mount, which has to flip the meridian, which places the axis of the telescope and its pivot point on the other side of the pier.

It works.
I know this because I wrote the software to do it. I read the side of pier from the ASCOM telescope driver and use this, with the offsets from the mount centre to the OTA, to determine the position of the OTA in dome coordinates. I take the offset, allow for the pier side, and rotate it by the site latitude, hour angle and declination, the trick is to get the order of the rotations correct.

Users of established systems don't need to do this for themselves because someone else (such as me) has already done it.

Chris

#11 Christopher Erickson

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Posted 28 December 2012 - 12:14 PM


An alternative way is Paul Bourke's 3D geometry pages, the intersection of a line and a sphere. The line is the direction the scope is looking, starting at the OTA position, and the sphere is the dome.

You end up with a quadratic equation, the solutions are the positions where the line and sphere intersect. It's a lot easier to compute than all that trigonometry, especially if you use the centre of the dome as the origin.

I did this when I automated the dome on my Society's observatory.

Chris


This approach, by itself, would be insufficient for a GEM mount, which has to flip the meridian, which places the axis of the telescope and its pivot point on the other side of the pier.

It works.
I know this because I wrote the software to do it. I read the side of pier from the ASCOM telescope driver and use this, with the offsets from the mount centre to the OTA, to determine the position of the OTA in dome coordinates. I take the offset, allow for the pier side, and rotate it by the site latitude, hour angle and declination, the trick is to get the order of the rotations correct.

Users of established systems don't need to do this for themselves because someone else (such as me) has already done it.

Chris


As I suspected, by itself, that approach was incomplete. Thank you for filling in the details.

Have you decided to share your program and/or source code for others to use?

What other details are you willing to share about your program?

What program language did you use?

#12 cn register 5

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Posted 28 December 2012 - 02:49 PM

I thought that "starting at the OTA position" would have been enough of a clue that I had considered the OTA position.

I don't plan to provide the code free, I provide enough other code and free support to be considerably in credit.

Basically the system uses an electronic compass with a PICAXE and wireless transmitter that's bolted to the dome to send the dome compass heading wirelessly to an Arduino based dome controller that handles the dome motor control and communication with the PC.
The PC has an ASCOM driver and an observatory control program, I've attached something to show what it looks like.

It's coded in PICAXE basic, C, C# and WPF.

Chris

Attached Files



#13 Christopher Erickson

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Posted 28 December 2012 - 10:25 PM

I thought that "starting at the OTA position" would have been enough of a clue that I had considered the OTA position.

I don't plan to provide the code free, I provide enough other code and free support to be considerably in credit.

Basically the system uses an electronic compass with a PICAXE and wireless transmitter that's bolted to the dome to send the dome compass heading wirelessly to an Arduino based dome controller that handles the dome motor control and communication with the PC.
The PC has an ASCOM driver and an observatory control program, I've attached something to show what it looks like.

It's coded in PICAXE basic, C, C# and WPF.

Chris


Interesting. You must have a complicated, articulating mounting bracket for the PICAXE/compass/transmitter assembly to deal with the axial rotation of the OTA and the required planar orientation of the compass module.

It seems it would have been much simpler to just invest $100 or so in in the LesveDome solution.

One solution I came up with a number of years ago was an ultrasonic pinger on the front of the OTA with three ultrasonic transducer/microphones, one on either side of the dome aperture and one opposite of the aperture, wired to a single Atmel ATmega microcontroller, coded in C. Measuring the time deltas between the three ping detections on the transducers allowed me to always keep the dome correctly synched with the OTA. It was simple and reliable but didn't incorporate shutter control, failsafes or any ability to rotate flat frames or other things into the OTA'a view.

#14 Tandum

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Posted 29 December 2012 - 11:04 AM

I built my own foam dome and use the lesve driver to drive it. I use ascom POTH to mix the scope and dome drivers and POTH does the geometry to keep them in sync.

If you are south of the equator like me then you need to reverse the east and west result you get before entering it into POTH. ie: if you come up with a positive number, make it negative and it all works fine. They always seems to forget about us down here :)

When I first got it all running, I was surprised to see the slot pointing south when I was imaging east but it turned out to be quite correct. The dome actually points west while still imaging east near meridian. You get used to it eventually.

Or is all that reversed up there :lol:

#15 Tandum

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Posted 29 December 2012 - 11:36 AM

Saw your post about flips. POTH makes the dome track the mount. lesve does no math at all, it only turns the dome and for me remotely turns the lights on ...

#16 ErikB

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Posted 29 December 2012 - 11:15 PM

My ED II will initially be rotated by hand, but Maxdome-II is offered for it. My Titan with Gemini 1 have been in storage for 5 years. The software I acquired back then included Maxim DL and TheSky 6 Pro. Back then ASCOM seemed irrelevant to me but now it seems to be needed if I want to automate the dome. Prompted by the replies above I just had a look at the ASCOM website. There is a description of how to make ASCOM work with TheSky6, and another section about using POTH for dome control and Cartes du Ciel for pointing. I don't see an example that includes both TheSky6 and POTH. Can I assume that I would be using the POTH example and just substitute TheSky6 for Cartes du Ciel, perhaps with TeleAPI inserted between TheSky6 and POTH?

#17 cn register 5

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Posted 30 December 2012 - 03:58 AM

TheSkyX (TSX) can control the dome separately in which case you connect the dome and telescope to TSX. TSX will handle synchronising the dome to the scope. The dome add on for TSX is extra.

Or TSX could connect to POTH through the telescope interface and POTH would connect to the telescope and dome. In this case POTH handles the synchronising and TSX knows nothing about the dome. This is the replace CdC with TSX scenario. BTW the current connection from TSX to ASCOM goes through an X2 interface. I'm not sure about TS6, that may need the TeleAPI interface but I've never looked at this.

Hope this helps,

Chris

#18 ErikB

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Posted 31 December 2012 - 05:34 PM

Chris, thanks for your views on this. Further comments are welcome. BTW, has anyone used a dome controller from Foster Systems?

#19 gillmj24

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Posted 01 January 2013 - 09:18 PM

I haven't been able to get my foster systems controllers figured out yet. I had 2 PC's fail last year, that has slowed me down. Others have had more success recently.

#20 Christopher Erickson

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Posted 02 January 2013 - 01:55 PM

I have not yet heard of any successful installs using Foster Systems controls so I have not yet formed an opinion about them.

#21 Lorence

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Posted 02 January 2013 - 04:40 PM

Chris, thanks for your views on this. Further comments are welcome. BTW, has anyone used a dome controller from Foster Systems?


http://fostersys.websitetoolbox.com/

#22 Tandum

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Posted 03 January 2013 - 10:44 AM

The software I acquired back then included Maxim DL and TheSky 6 Pro.

I use SKy6 with the ascom TeleAPI plugin to get it talking to POTH which then talks to an ascom mount and the dome for on screen FOV stuff etc. I also have Maxim 5 connected to POTH so I can use the maxim cattledog to slew to target and pinpoint/sync the object. That way the target name is used as the major part of the filename for each image. That also lets me pulse guide via maxim.

Can't comment on SkyX, don't have it and don't need it ...

#23 ErikB

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Posted 03 January 2013 - 11:42 PM

Lorence, thanks, I see quite a few interesting posts on the foster site you pointed to.

Tandum, that is just the kind of information I was asking for, thank you so much.

Also, I looked at the Exploradome website, and in the price list I see that their rotation packages use Foster controllers. Somehow I had the understanding that they used Maxdome-II, but maybe that was at an earlier time.

#24 frank17601A

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Posted 04 January 2013 - 03:49 PM

I have a foster systems automation system. It has matured into a dependable option from my exploradome. It also has many built in functions that have proven to be handy, such as switched outlets and relays.

Frank

#25 ErikB

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Posted 05 January 2013 - 03:59 PM

It sounds like the foster systems units are good, but they are certainly not cheap bought separately, and the complete rotation systems from Exploradome with 2 motors seem to be about 3x the price of the controller alone. Did you find a way to cut cost, such as alternative motors, or using a single motor?






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