Some questions about mounts

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turboscrew
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Some questions about mounts

#1

Post by turboscrew »


I haven't found any basic knowledge for beginners about mounts - even search fails, because "mount" is too common word. The basic forms (dobsonian, alt-az and equatorial) are discussed, but then...
Like, since OrionOptics dobson is a P.I.T.A. to motorize, I wondered, is there a better option for me, if I suddenly got really interested in AP.

Why can't I find any dobson mounts for sale in the shops? There are a lot of telescopes with dobson mounts for sale.

What kind of mount should I get for OrionOptics VX12 (20 kg tube) if I wanted an equatorial mount?
Are there such things? (Without their price also being astronomical.)

I've seen that people assemble their mounts from different parts. What are the parts called?
I guess, 'mount' usually refers to the part where the telescope is attached. Then there are tripods and poles and such?
What should the weight ratings be for a 20 kg tube? I saw somewhere that the rating should be about 3 times the actual weight of the telescope, to be steady enough.
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

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Re: Some questions about mounts

#2

Post by Refractordude »


I like to put an item I want into google images to see what is compatible. This is what I came up with. Forum members can best help you if they know your max budget. Congratulations on the new scope.



https://www.google.com/search?q=mount+f ... -1-d&hl=en
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Re: Some questions about mounts

#3

Post by Star Dad »


Well, I guess I'll jump in. You'll need at least twice the weight capacity of your scope and camera(s). So figure 20Kg scope + another 4Kg camera(s) etc. 25Kg is about 55 pounds carrying capacity. Double that and you are at 110 pounds capacity. I'm afraid with a 12" scope you'll need a pretty hefty mount and that won't be cheap. Here's an Orion solution: https://www.telescope.com/Orion/Orion-H ... ueIds=4517. You'll want the stability for that BIG scope. Hopefully others will chime in with suggestions.
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Re: Some questions about mounts

#4

Post by turboscrew »


Star Dad wrote: Sun Jul 05, 2020 3:16 pm Well, I guess I'll jump in. You'll need at least twice the weight capacity of your scope and camera(s). So figure 20Kg scope + another 4Kg camera(s) etc. 25Kg is about 55 pounds carrying capacity. Double that and you are at 110 pounds capacity. I'm afraid with a 12" scope you'll need a pretty hefty mount and that won't be cheap. Here's an Orion solution: https://www.telescope.com/Orion/Orion-H ... ueIds=4517. You'll want the stability for that BIG scope. Hopefully others will chime in with suggestions.
I kind of guessed... twice the price of the tube...
I think that's what is called 'mount'. And that needs to be attached to something else. Heavy-duty tripod?
I guess dobsons with axles and bearings might be cheaper...? If some shop sold them?
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

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Re: Some questions about mounts

#5

Post by Star Dad »


A lot of people make their own. You need some basic shop skills and, of course, the machinery. That mount I showed above includes the tripod. Yeah, technically the mount is just the "EQ Head", but in this case it's whole enchilada. mmm speaking of which, it's lunch time!

But a Dob is an altitude/azimuth mount and will not allow you to have longer exposures. Most dobs do not have tracking motors - they are used for visual observing.
"To be good is not enough when you dream of being great"

Orion 203mm/f4.9/1000mm, converted TASCO 114mm/f9/1000mm to steam punk, Meade 114mm/f9/1000, Coronado PST, Orion EQ-G, Ioptron Mini-Tower and iEQ30, Canon 70D, ASI120MM,ASI294MC, Ioptron SkyHunter
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Re: Some questions about mounts

#6

Post by Thefatkitty »


I was curious as to your scope, so I did a search on it and one of the first sites that came up was this:

https://www.orionoptics.co.uk/VX/vx12-12l.html

It lists at the bottom the mounts they provide for the scope, hopefully it's of some help. Very nice scope BTW; I'm envious!

All the best,
Mark

"The Hankmeister" Celestron 8SE, orange tube Vixen made C80, CG4 & AZ-EQ5 mounts.
Too much Towa glass/mirrors.

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Re: Some questions about mounts

#7

Post by turboscrew »


BTW, on astroshop pages it says Sky-Watcher EQ5 has "Max. additional load capacity" 10 kg.
What the heck is that supposed to mean?
And on Sky-Watcher's pages it says "Payload capacity 9.10 kg"
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Some questions about mounts

#8

Post by ARock »


AP needs very precise tracking of the scope on the mount. The heavier the scope+camera, the more difficult it is to track precisely, and therefore the more expensive the mount. With reflectors, be careful, as not all reflectors can reach focus with all cameras.

So what you can do, is first decide your mount budget. Then come up with a mount, that fits in that budget. Then decide on a scope+camera+guider thats fits within the payload of the mount (AP payload is roughly 1/2 visual payload). Ask for opinions on the overall setup and if you dont like it, increase the mount budget and repeat the procedure. Another way to evaluate a setup is to search astrobin.com (an astro pic site) and see what kind of pictures people get with similar setups.

One way to cut costs, is to buy a manual mount, and motorize it yourself. Since you are an embedded software engineer, this might well be in a familiar area for you. Look at https://onstep.groups.io/g/main/wiki/3860 for inspiration.
Last edited by ARock on Sun Jul 05, 2020 3:48 pm, edited 1 time in total.
AR
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Re: Some questions about mounts

#9

Post by turboscrew »


Star Dad wrote: Sun Jul 05, 2020 3:32 pm A lot of people make their own. You need some basic shop skills and, of course, the machinery. That mount I showed above includes the tripod. Yeah, technically the mount is just the "EQ Head", but in this case it's whole enchilada. mmm speaking of which, it's lunch time!

But a Dob is an altitude/azimuth mount and will not allow you to have longer exposures. Most dobs do not have tracking motors - they are used for visual observing.
Well, at least some motorized dobsonians exist: https://www.astroshop.eu/telescopes/sky ... to/p,21051
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Some questions about mounts

#10

Post by Lady Fraktor »


turboscrew wrote: Sun Jul 05, 2020 2:29 pm I haven't found any basic knowledge for beginners about mounts - even search fails, because "mount" is too common word. The basic forms (dobsonian, alt-az and equatorial) are discussed, but then...
Like, since OrionOptics dobson is a P.I.T.A. to motorize, I wondered, is there a better option for me, if I suddenly got really interested in AP.

Why can't I find any dobson mounts for sale in the shops? There are a lot of telescopes with dobson mounts for sale.

What kind of mount should I get for OrionOptics VX12 (20 kg tube) if I wanted an equatorial mount?
Are there such things? (Without their price also being astronomical.)

I've seen that people assemble their mounts from different parts. What are the parts called?
I guess, 'mount' usually refers to the part where the telescope is attached. Then there are tripods and poles and such?
What should the weight ratings be for a 20 kg tube? I saw somewhere that the rating should be about 3 times the actual weight of the telescope, to be steady enough.
turboscrew wrote: Sun Jul 05, 2020 2:29 pm I haven't found any basic knowledge for beginners about mounts - even search fails, because "mount" is too common word. The basic forms (dobsonian, alt-az and equatorial) are discussed, but then...
Like, since OrionOptics dobson is a P.I.T.A. to motorize, I wondered, is there a better option for me, if I suddenly got really interested in AP.

Why can't I find any dobson mounts for sale in the shops? There are a lot of telescopes with dobson mounts for sale.

What kind of mount should I get for OrionOptics VX12 (20 kg tube) if I wanted an equatorial mount?
Are there such things? (Without their price also being astronomical.)

I've seen that people assemble their mounts from different parts. What are the parts called?
I guess, 'mount' usually refers to the part where the telescope is attached. Then there are tripods and poles and such?
What should the weight ratings be for a 20 kg tube? I saw somewhere that the rating should be about 3 times the actual weight of the telescope, to be steady enough.
1. For AP dobsonian mounts are not very useful, you could build what is called a barndoor tracker but your tracking time is limited.
A goto az/ alt mount will let you do some AP but it does not compensate for the rotation of an object as it moves across the sky so limited in exposure times.
Equatorial mounts once polar aligned track with the arc a object makes as it travels across the skies so longer exposures are achieved.

2. To size the mount you add the weight of all of your equipment (telescope, camera, filter wheel, and such) then double it. This is the mount capacity to look for.
You will want your equipment weight to be 50-60% of the maximum capacity of the mount. Cost goes up as capacity increases.
The mount is more important than the telescope when doing AP.

3. Many people have built mounts out of piping and fittings though I doubt these would be good enough for more than a few seconds of imaging.
A typical equatorial mount consists of a tripod with 2" stainless steel legs as a minimum or a pier which can have legs like a tripod or be permanently installed in the ground.
The actual mount sits on top of the tripod/ pier and contains all of the moving parts. It will either accept what is called a Vixen or Losmandy style mounting plate/ dovetail/ prism rail or some of the newer ones are capable of using both styles to attach the telescope to the mount.

A dobsonian is slightly different from a newtonian in the dobsonian has bearing surfaces mounted on the side of the tube for support which a newtonian does not have.
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Re: Some questions about mounts

#11

Post by KathyNS »


To be honest, I think it is a mistake to try to use your 12" scope for AP. It will have a focal length that is too long for most DSOs, too short for planetary, and it is too big to mount on a reasonable equatorial mount. As noted, a dobsonian mount is alt-az, and therefore unsuitable for long exposure AP, even if it is motorized.

Get a more affordable EQ mount, and a small refractor.
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Re: Some questions about mounts

#12

Post by turboscrew »


ARock wrote: Sun Jul 05, 2020 3:41 pm AP needs very precise tracking of the scope on the mount. The heavier the scope+camera, the more difficult it is to track precisely, and therefore the more expensive the mount. With reflectors, be careful, as not all reflectors can reach focus with all cameras.
It seems that I need 50 mm extension tube to be able to focus for visual use. (Tried outside in day time - tried to see a tree top far away.)
So what you can do, is first decide your mount budget. Then come up with a mount, that fits in that budget. Then decide on a scope+camera+guider thats fits within the payload of the mount (AP payload is roughly 1/2 visual payload). Ask for opinions on the overall setup and if you dont like it, increase the mount budget and repeat the procedure. Another way to evaluate a setup is to search astrobin.com (an astro pic site) and see what kind of pictures people get with similar setups.

One way to cut costs, is to buy a manual mount, and motorize it yourself. Since you are an embedded software engineer, this might well be in a familiar area for you. Look at https://onstep.groups.io/g/main/wiki/3860 for inspiration.
I was, actually, thinking about that. I was first planning to put motor controls and camera reader plus a TFT-touchscreen all in one Raspberry Pi (bare metal, no operating system), but I realized that there were not enough pins. Probably some STM32 board is needed as a slave - those boards don't have nearly enough memory to be used alone.
The shortage of pins comes partly from the fact that the MIPI-CSI-interface (and especially how it's handled via the GPU) is sooo secret, and the MIPI-DSI is too. I'd probably have to settle with parallel 8- or 16-bit bus (well, SPI might do with TFT). Handling the parallel bus camera looks pretty much the same as the TFT handling, except the direction of the data (what I could tell from the data sheets). :-)

The main problem for me is the mechanics. I don't have the tools, nor surgeon's hands.

And one thing I haven't even looked into yet, is the stepping resolution. Good enough tracking might cause the directing (is it called "slew"?) to take ages.
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Some questions about mounts

#13

Post by turboscrew »


Lady Fraktor wrote: Sun Jul 05, 2020 4:06 pm
1. For AP dobsonian mounts are not very useful, you could build what is called a barndoor tracker but your tracking time is limited.
A goto az/ alt mount will let you do some AP but it does not compensate for the rotation of an object as it moves across the sky so limited in exposure times.
What do you mean by "the rotation of an object as it moves across the sky"?
Equatorial mounts once polar aligned track with the arc a object makes as it travels across the skies so longer exposures are achieved.

2. To size the mount you add the weight of all of your equipment (telescope, camera, filter wheel, and such) then double it. This is the mount capacity to look for.
You will want your equipment weight to be 50-60% of the maximum capacity of the mount. Cost goes up as capacity increases.
Yes, I've noted the prices...

The mount is more important than the telescope when doing AP.
I've begun to realize...
3. Many people have built mounts out of piping and fittings though I doubt these would be good enough for more than a few seconds of imaging.
A typical equatorial mount consists of a tripod with 2" stainless steel legs as a minimum or a pier which can have legs like a tripod or be permanently installed in the ground.
The actual mount sits on top of the tripod/ pier and contains all of the moving parts. It will either accept what is called a Vixen or Losmandy style mounting plate/ dovetail/ prism rail or some of the newer ones are capable of using both styles to attach the telescope to the mount.

A dobsonian is slightly different from a newtonian in the dobsonian has bearing surfaces mounted on the side of the tube for support which a newtonian does not have.
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Some questions about mounts

#14

Post by turboscrew »


KathyNS wrote: Sun Jul 05, 2020 4:14 pm To be honest, I think it is a mistake to try to use your 12" scope for AP. It will have a focal length that is too long for most DSOs, too short for planetary, and it is too big to mount on a reasonable equatorial mount. As noted, a dobsonian mount is alt-az, and therefore unsuitable for long exposure AP, even if it is motorized.

Get a more affordable EQ mount, and a small refractor.
Too long focal length for DSOs?
Please educate the ignorant?
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Some questions about mounts

#15

Post by ARock »


turboscrew wrote: Sun Jul 05, 2020 4:16 pm The main problem for me is the mechanics. I don't have the tools, nor surgeon's hands.

And one thing I haven't even looked into yet, is the stepping resolution. Good enough tracking might cause the directing (is it called "slew"?) to take ages.
Look at the ONSTEP showcase page, https://onstep.groups.io/g/main/wiki/4414 , there are some motorized Dobsonian examples. Some of them use 3D printed parts, and you could go that route for the mechanics. The Slew/Track problem is indeed an issue, which can be somewhat solved by changing microstepping modes on the stepper motor.

As Kathy mentions, using the Dob for long exposure AP may not be the best way to start. A small refractor on a stable GEM is usually a good place to start AP.

However some people get decent results using goto Dobs by stacking a lot of very short exposures.

https://www.cloudynights.com/topic/6334 ... ?p=8940551
AR
Scopes: Zhumell Z8, Meade Adventure 80mm, Bushnell 1300x100 Goto Mak.
Mount: ES EXOS Nano EQ Mount, DIY Arduino+Stepper drives.
AP: 50mm guidescope, AR0130 based guidecam, Canon T3i, UHC filter.
EPs: ES82 18,11,6.7mm, Zhumell 30,9mm FJ Ortho 9mm, assorted plossls, Meade 2x S-F Barlow, DGM NPB filter.
Binos: Celestron Skymaster 15x70 (Albott tripod/monopod), Nikon Naturalist 7x35.
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Re: Some questions about mounts

#16

Post by SkyHiker »


The price of a suitable mount will make the price of your VX12 Dob look like pocket change. You need a 100 lbs. capacity mount such as the Paramount MX+ ($9K), AP-100GTO ($8K), well the Orion HDX110 is cheap compared to them at $3.3K. Regardless of what software solution you choose, that's what you need if you want to go that route. But that scope is not an astrograph so it won't come to focus without you having to do some modifications. Even then, the secondary mirror size is not optimal for AP so you may need to replace it. And Kathy is right that it is not suitable for the larger DSOs that everyone wants to image.

Someone suggested an EQ platform; trouble is, the cheap DIY ones are single axis and not accurate enough. Osypowski sells high end dual axis EQ platforms but they cost quite a bit. They make sense for scopes 20" and up.

I would like to understand why you want to implement a bare metal Pi. When people use a small embedded computer it is usually Linux based and not powerful enough to take care of everything so the client ends up being on a separate PC. It still means that the Pi will have to run several threads or processes for motor control, autoguiding and image storage or transfer (assuming no DSLR with flash). So you still need to run multiple threads, why reinvent the wheel by going bare metal if there is Linux? The only time critical thing is motor control. For that you can add two Teensy's (one for RA, one for DEC) that you can control over a serial line from a Pi that runs Linux. But is it even realistic to assume that you have to build the controller from scratch? If you have to buy one of those high end mounts, they definitely have Goto and come with their own controllers so there is no need for real time control.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Some questions about mounts

#17

Post by turboscrew »


ARock wrote: Sun Jul 05, 2020 5:12 pm
turboscrew wrote: Sun Jul 05, 2020 4:16 pm The main problem for me is the mechanics. I don't have the tools, nor surgeon's hands.

And one thing I haven't even looked into yet, is the stepping resolution. Good enough tracking might cause the directing (is it called "slew"?) to take ages.
Look at the ONSTEP showcase page, https://onstep.groups.io/g/main/wiki/4414 , there are some motorized Dobsonian examples. Some of them use 3D printed parts, and you could go that route for the mechanics. The Slew/Track problem is indeed an issue, which can be somewhat solved by changing microstepping modes on the stepper motor.

As Kathy mentions, using the Dob for long exposure AP may not be the best way to start. A small refractor on a stable GEM is usually a good place to start AP.

However some people get decent results using goto Dobs by stacking a lot of very short exposures.

https://www.cloudynights.com/topic/6334 ... ?p=8940551
Yes, the stacking is probably necessary.
Any yes, the microstepping mode change depends mostly on the stepper motor driver chip, but even running full steps may be slow if, say 1/32 step moves the tube about half an arc second (close to the limit of the tube resolution). I guess 200 rpm from a stepper motor is hard to get - the torque tends to fall short.

Also the microsteps won't work (they are kind of cumulative) unless the driver chip can feed enough current to the motor.
Also, the smaller microsteps the more inaccurate the steps are.
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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Re: Some questions about mounts

#18

Post by ARock »


turboscrew wrote: Sun Jul 05, 2020 4:16 pm I was first planning to put motor controls and camera reader plus a TFT-touchscreen all in one Raspberry Pi (bare metal, no operating system), but I realized that there were not enough pins. Probably some STM32 board is needed as a slave - those boards don't have nearly enough memory to be used alone.
The common way to do this, is to have an Arduino like microcontroller for the Real Time stuff like controlling steppers (tracking), and a raspberry pi/laptop talking to it for the higher level software like slewing, guiding, interacting with a planetarium app, plate solving, camera, display etc, all of which need some OS support.
AR
Scopes: Zhumell Z8, Meade Adventure 80mm, Bushnell 1300x100 Goto Mak.
Mount: ES EXOS Nano EQ Mount, DIY Arduino+Stepper drives.
AP: 50mm guidescope, AR0130 based guidecam, Canon T3i, UHC filter.
EPs: ES82 18,11,6.7mm, Zhumell 30,9mm FJ Ortho 9mm, assorted plossls, Meade 2x S-F Barlow, DGM NPB filter.
Binos: Celestron Skymaster 15x70 (Albott tripod/monopod), Nikon Naturalist 7x35.
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Re: Some questions about mounts

#19

Post by Refractordude »


If I wanted to get into AP, this is what I would get. These two combined will cost less than a mount for your 12" newt. Post processing of the images can correct color using an achromatic.

https://www.telescope.com/Telescopes/Re ... goryId=337

https://www.telescope.com/Orion/Orion-S ... /24709.uts

https://computerphysicslab.wordpress.co ... refractor/
Last edited by Refractordude on Sun Jul 05, 2020 5:34 pm, edited 1 time in total.
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Re: Some questions about mounts

#20

Post by turboscrew »


SkyHiker wrote: Sun Jul 05, 2020 5:22 pm The price of a suitable mount will make the price of your VX12 Dob look like pocket change. You need a 100 lbs. capacity mount such as the Paramount MX+ ($9K), AP-100GTO ($8K), well the Orion HDX110 is cheap compared to them at $3.3K. Regardless of what software solution you choose, that's what you need if you want to go that route. But that scope is not an astrograph so it won't come to focus without you having to do some modifications. Even then, the secondary mirror size is not optimal for AP so you may need to replace it. And Kathy is right that it is not suitable for the larger DSOs that everyone wants to image.

Someone suggested an EQ platform; trouble is, the cheap DIY ones are single axis and not accurate enough. Osypowski sells high end dual axis EQ platforms but they cost quite a bit. They make sense for scopes 20" and up.

I would like to understand why you want to implement a bare metal Pi. When people use a small embedded computer it is usually Linux based and not powerful enough to take care of everything so the client ends up being on a separate PC. It still means that the Pi will have to run several threads or processes for motor control, autoguiding and image storage or transfer (assuming no DSLR with flash). So you still need to run multiple threads, why reinvent the wheel by going bare metal if there is Linux? The only time critical thing is motor control. For that you can add two Teensy's (one for RA, one for DEC) that you can control over a serial line from a Pi that runs Linux. But is it even realistic to assume that you have to build the controller from scratch? If you have to buy one of those high end mounts, they definitely have Goto and come with their own controllers so there is no need for real time control.
"I would like to understand why you want to implement a bare metal Pi. When people use a small embedded computer it is usually Linux based and not powerful enough to take care of everything"
That's why. Linux, being pretty much general OS has quite an overhead. And it's not real-time - not even with the "real-time extensions".
And I've already written a bare metal GDB-agent for RPi2B. :-D
https://github.com/turboscrew/rpi_stub
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

I don't suffer from insanity. I'm enjoying every minute of it.

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