Dual RASA 8 rig - nearly there

[wimvb]

43 minutes ago, tomato said:

Like most good Astro kit they are currently out of stock.😉

Like most Astro kit they are also expensive.

[gorann]

4 hours ago, Sp@ce_d said:

Wow that's a pretty impressive "sky hoover" Goran! Looking forward to seeing the results of this in action.. when will you have time to process all that data!! 🤣

I've just got a CEM70 myself to set up another rig with my 2 Esprit 80's on a side by side & have the same JTD saddle. I got it a few years ago when the Robin Casady ones were like gold dust.. knowing it would come in handy one day  

I see ADM now do the same design here.. https://www.admaccessories.com/product/tgad-tandem-guiding-aiming-device-altaz-aiming-device-for-side-by-side-systems/ 

I'm still putting the bits together for mine but I saw that the recommended imaging weight of the CEM70 is 2/3rds of the 31.8kg payload so ~21kg?  So it'll be interesting to see how you get on!

How did you go about moving the saddle around to 90 degree? I see there's no option in the handset to re home and when I unbolted and had a look under the saddle I can see there's a cut out for the PCB of the onboard USB/power ports that protrudes down. So it won't rotate and reseat at 90 degrees as the deeper cutout is on the lower side of the DEC housing only. I also read that the hard stops are there to stop damage to the wiring loom and not to remove them?

I'm expecting one of these to arrive today to try https://www.firstlightoptics.com/dovetails-saddles-clamps/cgx-sbs-celestron-cgx-side-by-side-adapter.html but all the bars/saddles and this really knocks the weight up! Plus I'm now wondering if that payload is reduced by any extra counterweights added.. it probably does!

It is obviously a worry if I cannot tell the mount in some way that I have turned the saddle 90°. I have to look into that. Maybe my Mesu is the only option. Maybe someone with a CEM mount have a suggestion.

[wimvb]

To all RASA owners out there; in for the category "fun to have, but easily self built" you can find this

https://www.firstlightoptics.com/adapters/buckeyestargazer-cable-router-for-scopes-with-front-mounted-cameras.html

[gorann]

On 24/08/2021 at 22:01, wimvb said:

To all RASA owners out there; in for the category "fun to have, but easily self built" you can find this

https://www.firstlightoptics.com/adapters/buckeyestargazer-cable-router-for-scopes-with-front-mounted-cameras.html

Interesting but the attachment to the rim may make it difficult to fit the dew shield that is absolutely neccessary for a RASA. It is easy enough to curve the cables by tapeing them to a curved metal wire and let the cables out of the slit of the dew shield as I do. And with the FLO thing you would have to lead the cables down along the side of the camera which could make them casue spikes since the diameter of an ASI2600 is the same as the central obsruction (90mm) so you do not want anything to stick out.

Edited August 30, 2021 by gorann

[masjstovel]

How is the CEM70 performing? pros and cons? Have been looking into it for quite a while, but theres not TOO much info around.

[ollypenrice]

On 24/08/2021 at 07:08, wimvb said:

Nice. If differential flexure turns out to be a pro lem  you may have to add a bar at the top also, connecting the two scopes there.

 

18 hours ago, tomato said:

I definitely needed a bracing plate across the top of my scopes, but RASA8s are much lighter and shorter than Esprit 150s. 

@FLO   What we need for dual rigs is a bracing arm with some kind of angle-adjustable joint at each end. It would pass from one scope tube ring to the other, find its own angle, and then be bolted up firmly. I think it would need only two simple components at manufacture, the L bracket and the arm. The customer would buy two L brackets, of course.  (The tubes are naturally parallel but are offset relative to the saddle plate because one is on the tilt-pan adjuster. The arm would need slotted holes to allow for a range of tube separations. Slight variance in the fore-and-aft position of the L clamps would be taken care of by tightening them onto their tube rings last.

Two potential sources of flexure remain intractable in dual rigs, though. Mirror movement and drawtube sag. The RASA might suffer mirror movement (or might not) but it has no drawtubes.

Olly

[tomato]

I like the idea of the flexible joints which can be tightened when the scopes are aligned, the only concern I have is if the two tie bars would be rigid enough to prevent flexing on heavy set ups.
 

The plate is inherently more rigid, at least in one axis, I have threaded collars and oversized holes to allow for scope alignment, the fun starts when these are tightened down. You could say it’s an iterative process, adjust, tighten, inspect, loosen slightly, adjust, tighten, inspect… It usually consumes half a clear night’s session.

[ollypenrice]

55 minutes ago, tomato said:

I like the idea of the flexible joints which can be tightened when the scopes are aligned, the only concern I have is if the two tie bars would be rigid enough to prevent flexing on heavy set ups.
 

The plate is inherently more rigid, at least in one axis, I have threaded collars and oversized holes to allow for scope alignment, the fun starts when these are tightened down. You could say it’s an iterative process, adjust, tighten, inspect, loosen slightly, adjust, tighten, inspect… It usually consumes half a clear night’s session.

I did wonder about ball joints at the attachment points. That's what you need to avoid so many iterations, I think., if you could find the right kind.  We don't need the range of angles provided by a camera ball head but a joint using just a section from a sphere would provide the range of angles required. I found some high end industrial self aligning joints on the net but nothing suited to a small application like this. They probably exist, though, since the engineering problem is highly predictable. We need someon in light mechanical engineering to enlighten us.

Olly

Edit: 

 

Edited August 25, 2021 by ollypenrice
Link

[ollypenrice]

13 hours ago, gorann said:

Interesting but the attachment to the rim may make it difficult to fit the dew shield that is absolutely neccessary for a RASA. It is easy enough to curve the cables by tapeing them to a curved metal wire and let the cables out of the slit of the dew shield as I do. And you would have to lead the cables down along the side of the camera which could make them casue spikes since the diameter of an ASI2600 is the same as the central obsruction (90mm) so you do not want anything to stick out.

I've followed your principle using the rim of a 7.5cm jam jar lid. (Cheapskate!)    The dewshield is curved round out of thin alloy sheet from the hardware shop. You're right about it not dewing: we had a heavy dew this morning on all the kit but nothing at all on the corrector. An unexpected bonus.

Olly

 

 

[ollypenrice]

4 hours ago, tomato said:

I like the idea of the flexible joints which can be tightened when the scopes are aligned, the only concern I have is if the two tie bars would be rigid enough to prevent flexing on heavy set ups.
 

The plate is inherently more rigid, at least in one axis, I have threaded collars and oversized holes to allow for scope alignment, the fun starts when these are tightened down. You could say it’s an iterative process, adjust, tighten, inspect, loosen slightly, adjust, tighten, inspect… It usually consumes half a clear night’s session.

How about these?  https://www.cromwell.co.uk/shop/spindle-nose-and-workholding/fixing-components/fc25-17mm-bore-2pc-spherical-washer-set/p/IND4252860G?gclid=CjwKCAjw1JeJBhB9EiwAV612ywuGB3-wUoFeLSvyLeIvLvuv9H-fFkqIHwGNrCVVmAzJX7PMlg6tmxoC6NgQAvD_BwE

They were spotted by Mark on the other thread.

Olly

[StevieDvd]

1 hour ago, ollypenrice said:

How about these?  https://www.cromwell.co.uk/shop/spindle-nose-and-workholding/fixing-components/fc25-17mm-bore-2pc-spherical-washer-set/p/IND4252860G?gclid=CjwKCAjw1JeJBhB9EiwAV612ywuGB3-wUoFeLSvyLeIvLvuv9H-fFkqIHwGNrCVVmAzJX7PMlg6tmxoC6NgQAvD_BwE

They were spotted by Mark on the other thread.

Olly

Posted in other thread first but these any good?

 

[ollypenrice]

9 minutes ago, StevieDvd said:

Posted in other thread first but these any good?

 

Certainly the right principle but I think the washers may be made of something soft to avoid cracking the porcelain.

Olly

[tomato]

Thanks for the links, certainly worth a try.

[gorann]

Interesting discussion here about bracing arms. I will consider it if I notice flexure. After @Sp@ce_d here pointed out that the max imaging weight of the CEM70 is stated to be 21 kg I decided that I will move the rig to my Mesu 200. That mount is also sitting in an obsy with more floor space which will make everything more comfortable. I will be traveling for the next week so it will take a while before I can give the rig a try, skies permitting.

[ollypenrice]

52 minutes ago, gorann said:

Interesting discussion here about bracing arms. I will consider it if I notice flexure. After @Sp@ce_d here pointed out that the max imaging weight of the CEM70 is stated to be 21 kg I decided that I will move the rig to my Mesu 200. That mount is also sitting in an obsy with more floor space which will make everything more comfortable. I will be traveling for the next week so it will take a while before I can give the rig a try, skies permitting.

My guess is that the RASAs will prove mechanically stiff, the only question being primary mirror stability.

Olly

[gorann]

56 minutes ago, ollypenrice said:

My guess is that the RASAs will prove mechanically stiff, the only question being primary mirror stability.

Olly

Would that be more problematic in a dual rig? In any case I never noticed any primary mirror movement before, such as loss of focus or image drift/shift. The RASA is claimed to have a different and more stable mirror holding mechanism than the ordinary SCT. 

[wimvb]

An f/2 system is more sensitive to internal movement than an f/10 system, so another solution for the mirror is probably needed. Unless the mirrors move in opposite directions (which is unlikely), I wouldn’t expect this to be more problematic in a dual scope system than in a single scope system

[thomasv]

Hi Gorann,

Cool setup, good luck. A side question, how did you connect the FD lens to the ZWO camera, do you know where to get the adapter from?

Thank you.

 

[Jessun]

Hej gorann,

I have shelved what little I have left of a triple rig and I am no longer an active imager - if that is even a word...

My view from experience is that once aligned, the OTAs should be left alone. By that I mean that after painstakingly aligning two or more OTAs, a new attachment point will just create more issues.

I doubt that a bar can be secured without upsetting the initial alignment, or introduce another thermal expansion issue. You will most certainly end up confused as to which bolts to adjust, much like trying to cut the four legs of a chair dead even, in order to prevent the chair from behaving like a metronome.

I shimmed my first triple rig to decent alignment, and for my second triple setup, with heavier OTAs, I used two of the saddles that you use. I found that the OTAs behaved in a similar way and there was no individual flexing worth noting. They all seemed to warp in unison.

I never ran multiple reflectors though, so I would tend to agree with the comments that focus on the mirrors, rather than the mounting hardware.

Good luck with the mission!

/Jessun

 

 

[gorann]

13 hours ago, Jessun said:

Hej gorann,

I have shelved what little I have left of a triple rig and I am no longer an active imager - if that is even a word...

My view from experience is that once aligned, the OTAs should be left alone. By that I mean that after painstakingly aligning two or more OTAs, a new attachment point will just create more issues.

I doubt that a bar can be secured without upsetting the initial alignment, or introduce another thermal expansion issue. You will most certainly end up confused as to which bolts to adjust, much like trying to cut the four legs of a chair dead even, in order to prevent the chair from behaving like a metronome.

I shimmed my first triple rig to decent alignment, and for my second triple setup, with heavier OTAs, I used two of the saddles that you use. I found that the OTAs behaved in a similar way and there was no individual flexing worth noting. They all seemed to warp in unison.

I never ran multiple reflectors though, so I would tend to agree with the comments that focus on the mirrors, rather than the mounting hardware.

Good luck with the mission!

/Jessun

 

 

Thanks for the encouragement Jessun.

[gorann]

15 hours ago, thomasv said:

Hi Gorann,

Cool setup, good luck. A side question, how did you connect the FD lens to the ZWO camera, do you know where to get the adapter from?

Thank you.

 

Hi Thomas,

I could not find anyone selling such an adapter so I made one by taking apart an EOS-FD adapter from ebay (image below) and attaching it to this adapter from FLO:

https://www.firstlightoptics.com/adapters/astro-essentials-samyang-lens-to-m48-adapter.html

Had to drill three holes and put it together with three M1.6 screws and nuts.

Cheers, Göran

 

 

Edited August 29, 2021 by gorann

[ollypenrice]

On 26/08/2021 at 09:49, gorann said:

Would that be more problematic in a dual rig? In any case I never noticed any primary mirror movement before, such as loss of focus or image drift/shift. The RASA is claimed to have a different and more stable mirror holding mechanism than the ordinary SCT. 

I don't think it would because, if there is no flexure between guidescope and main scope (and there isn't) the mirror must be stable.

I think what I might try on our troublesome TEC dual rig is a flat plate bridging between all four tube rings and attached to them at four points using the self adjusting cup washers in the earlier link. I would then mount the guidescope on this plate, so it is equally connected to both tubes. This might make both scopes trail, or neither! 

Olly

[thomasv]

3 hours ago, gorann said:

Hi Thomas,

I could not find anyone selling such an adapter so I made one by taking apart an EOS-FD adapter from ebay (image below) and attaching it to this adapter from FLO:

https://www.firstlightoptics.com/adapters/astro-essentials-samyang-lens-to-m48-adapter.html

Had to drill three holes and put it together with three M1.6 screws and nuts.

Cheers, Göran

Thank you very much for the reply, I shall attempt the same. Regards.

[gorann]

On 29/08/2021 at 12:22, thomasv said:

Thank you very much for the reply, I shall attempt the same. Regards.

Here are two pics of my adapter that may help you. The holes I drilled was in the FLO adapter to fit the holes in the FD-EOS adapter (after I unscrewed the EOS part). You also see a M48 to T2 adapter and a distance ring in the pics (adding 14 mm) screwed on to get the right distance. Lens flange to chip distance for FD lenses is 42 mm, and the chip distance in the ASI2600 is 17.5 mm. The adapter I made was 10.5 mm thick so I had to add 14 mm to get to 42mm.

Cheers, Göran

Edited August 30, 2021 by gorann

[gorann]

Moved the rig over to the Mesu. New season so I started with polar alignment tonight but then clouds decided to cover the whole sky... Will give it another try tomorrow.