Rotator that won't break the bank

[stevepsheehan]

Hi all.

Due to disability following a stroke, I've spent the last 10 months or so establishing a fully remote controlled imaging rig, that I can control from a PC in a spare bedroom; so far, so good.

Now, it has become apparent, that if I want to get my target framing right, I'm going to need to fit a remote controlled rotator into the imaging train - nothing fancy, just something with 180 degrees of rotation, that can be controlled from NINA, via USB from the scope mounted NUC.

I have looked briefly, but they all seem SO over specified for the job I need to do, and SO expensive - initially, I thought the Pegassus one would be nice, and would match my Focuscube2, but at over £500, I figured it was time to re-think that 😉

So... does such a creature even exist? If so, can some kind soul please point me towards it?

Many thanks,

Steve

[andrew s]

They are all expensive. They need to be very well engineered to work well. I use the Optec Pyaxis LE.

Regards Andrew 

[pete_l]

35 minutes ago, stevepsheehan said:

they all seem SO over specified for the job I need to do

I get the impression that they are intended to compensate for field rotation in Alt-Az set ups. As such they need to track accurately much like an equatorial mount - though only with the weight of the camera attached and possibly not quite down to arc-second accuracy. That would explain their cost.
However, for simply framing an image it probably doesn't matter if that sort of rotator only has a resolution of a few degrees. It would be set once at the start of a session so that (for example) a long, thin DSO would be aligned with the long side of a camera. As long as it doesn't slip or have flop that moves the camera while tracking, it wouldn't need the engineering precision of the ones on sale.

Edited January 5, 2021 by pete_l

[andrew s]

8 minutes ago, pete_l said:

I get the impression that they are intended to compensate for field rotation in Alt-Az set ups. As such they need to track accurately much like an equatorial mount - though only with the weight of the camera attached and possibly not quite down to arc-second accuracy. That would explain their cost.
However, for simply framing an image it probably doesn't matter if that sort of rotator only has a resolution of a few degrees. It would be set once at the start of a session so that (for example) a long, thin DSO would be aligned with the long side of a camera. As long as it doesn't slip or have flop that moves the camera while tracking, it wouldn't need the engineering precision of the ones on sale.

The engineering needs to be be excellent to ensure no backlash or tilt, with possibly both heavy and off axis loads, independent of the position resolution.

I use mine to ensure my slitless spectra avoid field star and their spectra.

Regards Andrew. 

[stevepsheehan]

43 minutes ago, pete_l said:

 As long as it doesn't slip or have flop that moves the camera while tracking, it wouldn't need the engineering precision of the ones on sale.

Precisely - that's why I'm wondering if such a "basic" rotator exists... if not, then I reckon there's an opening there for a decent engineering company.

What's so frustrating for me, is that my scope has a perfectly adequate rotator bult in - loosen a thumbscrew, rotate as required, and re-tighten; simples. But there's no way to control it other than by hand 😞

Edited January 5, 2021 by stevepsheehan

[Stuart1971]

1 hour ago, stevepsheehan said:

Hi all.

Due to disability following a stroke, I've spent the last 10 months or so establishing a fully remote controlled imaging rig, that I can control from a PC in a spare bedroom; so far, so good.

Now, it has become apparent, that if I want to get my target framing right, I'm going to need to fit a remote controlled rotator into the imaging train - nothing fancy, just something with 180 degrees of rotation, that can be controlled from NINA, via USB from the scope mounted NUC.

I have looked briefly, but they all seem SO over specified for the job I need to do, and SO expensive - initially, I thought the Pegassus one would be nice, and would match my Focuscube2, but at over £500, I figured it was time to re-think that 😉

So... does such a creature even exist? If so, can some kind soul please point me towards it?

Many thanks,

Steve

The Pegasus one is very good, so I have heard, but it’s wwwaaaayyyyy overpriced, as all the Pegasus kit is...... 😮👍🏼

[newbie alert]

I have my camera set at a 90 degree camera angle.. other than the California neb I've yet to come across a target that lands awkward , I can rotate with the scopes manual rotator but I never do, not so far anyway

[Tomatobro]

As an aid to getting the two cameras aligned I added degree wheels to the capstan on a pair of Esprit 150's used on a dual rig. The protractors were printed off using Blocklayer. Best I can suggest as a low buck solution but it would mean a visit to the observatory to adjust

[SamAndrew]

Haha and there i was thinking the Pegassus one is reasonably priced compared to everything else on the market!

The problem is, they are so low volume, the price has to be high to cover the overheads. A rotator is the one item I haven't been able to DIY so far, as much as I've thought about it. 

An engineering company might be able to build the mechanical parts for less, but you also need the ascom drivers and software to go with it.

[stevepsheehan]

Well thanks for the comments guys - seems it was wishful thinking then 😉

However, it has got me thinking about a DIY idea. As my scope has a rotating option anyway, I'm thinking that a belt around that part, powered by a stepper motor (something like the way a belt driven focus motor would function) might be a cost effective option? Needs a bit more thought, but it's definately a route to explore I reckon.

Edited January 5, 2021 by stevepsheehan

[tomato]

The problem is the drive has to be robust enough to prevent slippage once you have moved it into the desired position, so a belt drive and motor would have to be quite hefty, especially if you have a heavy focuser, camera etc hanging off it.

[malc-c]

53 minutes ago, stevepsheehan said:

Well thanks for the comments guys - seems it was wishful thinking then 😉

However, it has got me thinking about a DIY idea. As my scope has a rotating option anyway, I'm thinking that a belt around that part, powered by a stepper motor (something like the way a belt driven focus motor would function) might be a cost effective option? Needs a bit more thought, but it's definately a route to explore I reckon.

Found this

Linked post on another forum http://www.iceinspace.com.au/forum/showthread.php?t=142002

Seems to use a belt, stepper and an arduino so shouldn't break the bank.... can't' vouch for how well it performs, or how easy it would be to integrate with NINA etc as this proved too hard for the OP

Personally, you might have to bite the bullet and opt for a commercial offering as whilst the hardware side of things is straightforward, the software / ASCOM stuff will be the hard part

[stevepsheehan]

Thanks Malcolm, yes that's the sort of thing I was imagining. A stepper motor from something already ASCOM supported would be the easiest option I suppose, though no idea what that might be at the moment. Time for some thinking.

Cheers,

Steve

[malc-c]

Steve, I presume all you want to do is to be able to rotate the camera in the focuser  to frame the shot, rather than a device that counteracts the field rotation when imaging with an ALT/AZ mount ?

Ifd so then one option you could look at would be to simply use a wifi enabled stepper controller.  You could then have a simple web page to send the position to an ESP8266 enabled device that can then drive the motor.  This guy had a crowdfunding project to do this

https://youtu.be/3CSEmAAK7VM

The crowdfunding link is https://www.crowdsupply.com/good-robotics/wi-fi-stepper  

At $110 plus $20 worldwide shipping for the board, software, Nema 17 motor and PSU it could make for a cheap option...  Or if you wanted to go DIY

https://climbers.net/sbc/esp-wifi-stepper-motors-controller-revb/

£20 for the kit... but you would need to purchase the Stepper motor and PSU.... and of course you would still need to fabricate the rotation part (belt / pulley / bracket etc)

You could then use your phone or web browser to rotate the camera.  Not sure if the £20 kit has the option to keep the motor powered so it holds position or not - The more expensive complete kit does have this feature, so once the position is set it won't move due to gravity

Hope that helps

 

[Whirlwind]

I don't think it has been mentioned but another reason for a high quality rotator is to allow you to position accurately for flat if you image multiple targets over a night.  This can be more or less pronounced dependent on where the rotator is located and the optical arrangement of the telescope.  Otherwise you would have to fix the position at the beginning of the night and then leave it there regardless of what objects you image for that night (so you maintain the same rotation for the flats before/after the imaging run.

[Xsubmariner]

Stuart1971 “The Pegasus one is very good, so I have heard, but it’s wwwaaaayyyyy overpriced, as all the Pegasus kit is...”

A review of rotators that are available today shows the Pegasus falcon is reasonably priced. Any commercial rotator has to be a precision instrument to support the necessary accuracy and strength criteria associated with the Astro imaging demands. Ultimately any failings in these areas will degrade the final image.

Currently in the process of fitting a falcon rotator in my imaging system, thinking about rip offs in this community what about threaded adapters. I had to pay £145.79 for 4 x treaded adapters to fit the rotator, that’s a rip off. 

Edited January 6, 2021 by Xsubmariner

[malc-c]

1 hour ago, Whirlwind said:

I don't think it has been mentioned but another reason for a high quality rotator is to allow you to position accurately for flat if you image multiple targets over a night.  This can be more or less pronounced dependent on where the rotator is located and the optical arrangement of the telescope.  Otherwise you would have to fix the position at the beginning of the night and then leave it there regardless of what objects you image for that night (so you maintain the same rotation for the flats before/after the imaging run.

I think Steve needs to clarify what he intends to use the rotator for.  If it's simply to rotate the camera to frame the target, then do an image run, along with any flats etc then the DIY options might be all that is needed.  If he wants to compensate field rotation due to an ALT/AZ mount, or take multiple targets etc then one of the professional rotators would be needed, and he should forget about a DIY option

[SamAndrew]

2 hours ago, Xsubmariner said:

Currently in the process of fitting a falcon rotator in my imaging system, thinking about rip offs in this community what about threaded adapters. I had to pay £145.79 for 4 x treaded adapters to fit the rotator, that’s a rip off. 

Agreed! I've got about £150 worth of adaptors to fit my Riccardi reducer to my Esprit, already balking at the idea of having to change the setup to add a rotator.

 

1 hour ago, malc-c said:

I think Steve needs to clarify what he intends to use the rotator for. 

Steve said in the first post it's for target framing.

[Whirlwind]

3 hours ago, SamAndrew said:

Steve said in the first post it's for target framing.

Still, if you need to align it properly for flats after you have imaged then you still need one that is accurate (otherwise dust bunnies will be in different places for the flats etc).

[stevepsheehan]

Thanks all - some interesting food for thought here. I hadn't considered the effect this would have on taking flats for each different target and rotation. My intention was to "simplify" framing over a full night's imaging, but the potential drawbacks re flats is making me rethink this now. Maybe back to basics, set the camera rotation up manually once, and just choose targets for that night that fit that rotation adequately. It's never simple, is it?

[DaveS]

I have my cameras set to 90 deg (ie straight up and down). The only target I can think of that would need anything else is Markarian's Chain at 0 deg. I'm following Olly's advice regarding keeping everything orthogonal to avoid diagonal cuts after meridian flip.

[AngryDonkey]

38 minutes ago, DaveS said:

I'm following Olly's advice regarding keeping everything orthogonal to avoid diagonal cuts after meridian flip.

Not something I have heard of, can you elaborate? Thanks!

[DaveS]

I think (And according to Olly) if your sensor isn't orthogonal to RA / Dec, then after a meridian flip your subs won't align, and you get diagonal cuts along the edges. in the extreme you can get stacks that are octagons.