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DIY Dobsonian Tracking Advice

ATM DIY dob mount beginner astrophotography
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#1 gcwyatt

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Posted 02 May 2016 - 01:58 AM

Greetings fellow stargazers!  Please allow a humble noobie to seek your guidance.  I have scoured the Web searching for a way to turn my Dob into a GoTo/tracking scope and I'm just not finding all the advice I need.  I've been shooting photos of the Moon and sky for a while now, but so far I've been limited to adapting mirror lenses to my DSLR with less than satisfactory results.  Just this week I bought a Coulter Odyssey 1 telescope (the red version with the crap focuser) for $200.  I would like to use it for deep sky astrophotography.  I realize this is a tall order, especially is Los Angeles, but even if I can only get some descent images of Saturn I'll be OK with that.  

 

From my research I understand that I need to turn my scope's mount into a tracking mount that can hold a very precise position for at least ten minutes.  I've seen websites describe the accuracy as greater than 0.000478 degrees (http://www.codeproje...-Telescope-Part) and that's probably what I need.  I know I will need to stack images - no problem as I am an experienced photographer and Photoshopper.  I know I want GoTo capabilities and I have notebook computers I can use for that.

 

This thread was very helpful:

http://www.cloudynig...th-a-dobsonian/

But I'm really looking for specific examples of people that have automated their Dob and how they did it.  I'm a pretty good fabricator,so I'm not afraid of building what needs to be built be it structural or electronic.  On the other hand, I'm not so good with programming, so if I have to build an Arduino controller I might need some assistance with the code.  I do not know where to get proper motors (stepper or otherwise), worm gears (if they're what I should be looking into), and what focuser I should be looking into to replace the crap one the Coulter came with.  I'm really not interested in too much off the shelf stuff - I would like to build it myself if I can, not only to save money but also for the satisfaction of the ATM.

 

Essentially, has anyone done this and how?  Links to blogs or previous Cloudy Nights threads are all welcome, and thank you for your kind responses!

 

 



#2 RAC

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Posted 02 May 2016 - 02:11 AM

Onstep is what you want if you're interested in a low cost system.

 

This thread has a few pics of my cheap but very nice tracking setup. I've made a few improvements since then though.

http://www.cloudynig...ars-and-onstep/



#3 RAC

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Posted 02 May 2016 - 02:21 AM

I've got my OnStep now running on a Teensy 3.2 rather than a Arduino mega, that gives it about two time the speed for Goto's over the mega so long as the stepper motors can go that fast. The Teensy has a much higher clock speed.

 

Also my Az axis motor now runs a hard rubber strip around the outside of the ground board so very little force is needed to drive it.



#4 CoHPhasor

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Posted 02 May 2016 - 02:36 AM

I've got my OnStep now running on a Teensy 3.2 rather than a Arduino mega, that gives it about two time the speed for Goto's over the mega so long as the stepper motors can go that fast. The Teensy has a much higher clock speed.

 

Also my Az axis motor now runs a hard rubber strip around the outside of the ground board so very little force is needed to drive it.

 

     This is the thing that frustrates me about Beaglebone Black.

The Beaglebone has full micro controller capability, unlike others, as well as a full system.

The processor has a 200MHz clock, but to get to it is a huge PITA dealing directly with C, etc.

If it could be easily, readily accessible and coded for, it would crush so many dev-board competitors.



#5 RAC

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Posted 02 May 2016 - 02:51 AM

The Teensy 3.2 looks to be heaps fast enough for the job at 72mhz, looks like you can run them at 96mhz fine too. Most of the time the 16mhz Arduino mega would be fine also for most setups. I'm not changing microstep modes when slewing so I want all the speed the controller can do.

 

The Teensy's size makes it a bit fiddly and It would be nice if you could just run them off 12 volts. For powering mine I just added a usb socket to my scope right next to the controller.



#6 m. allan noah

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Posted 02 May 2016 - 07:16 AM

Skip the goto, build an equatorial platform.

 

allan



#7 Jon Isaacs

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Posted 02 May 2016 - 08:58 AM

Skip the goto, build an equatorial platform.

 

allan

 

 

:waytogo:

 

GOTO won't help for longer exposure photography anyway.. The scope needs to be equatorially mounted.  An equatorial platform is not so difficult to build..  It's a start anyway.

 

And Wyatt:

 

Hello and :welcome: to Cloudy Nights.

 

Jon



#8 tommm

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Posted 02 May 2016 - 10:03 AM

The issue with alt-az mount of the dob for astrophotography is the field of view rotates, making long exposures impossible without distorting the image.  You can do short exposures and stack them though as you mentioned.  Check the astrophotography group here and also QUIAG on Yahoo Groups - which specializes in using modified web cams, a cheap option.  There you take around 30 sec exposures and stack hundreds.

 

I second OnStep, also on Yahoo Groups. Arduino-based, simple and inexpensive, and probably accurate enough tracking for short exposures.  Long exposure astrophotography is another, much more expensive, ball game since it is far more demanding of the mount and tracking.



#9 gcwyatt

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Posted 04 May 2016 - 01:15 AM

Thank you all for your answers, but I was afraid this would happen.  My research indicates that there is some *disagreement* in the astrophotography community about the usability of an alt-az tracking mount.  Plus, I really, really want GoTo capabilities.  Go ahead, call me lazy, but I'm not fond of the idea of hunting for deep sky objects.  And while I'm not opposed to building a equatorial platform for my Dob, wouldn't that make any GoTo functionality unusable?  

 

So my specific question is, has anyone built or seen in use a Dobsonian with GoTo and tracking, and if so what was it and how well did it work?



#10 RAC

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Posted 04 May 2016 - 01:57 AM

A Dobsonian with GoTo and tracking is very doable but using it for deep sky long exposures is not really going to happen. It will however be able to to planetary imaging.



#11 Tom M

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Posted 04 May 2016 - 07:57 AM

A Dobsonian with GoTo and tracking is very doable but using it for deep sky long exposures is not really going to happen. It will however be able to to planetary imaging.

 

It could also most certainly be used for EAA, which can result in some very good images if one isn't after the perfection of true long-exposure astrophotography, so long as the tracking is fairly decent.


Edited by Tom M, 04 May 2016 - 07:57 AM.


#12 S.Boerner

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Posted 04 May 2016 - 06:08 PM

Read "Field Rotation in Altitude over Azimuth Mounts and Its Effect on CCD Imaging – What is the Maximum Exposure?"  by Bill Keicher:

http://autostarsuite...rotation v3.pdf  It will answer many of the Alt/Az related problems.

 

Yes, you can image with an Alt/Az but your exposure time will vary depending on where in the sky the object is (East/West, North/South, straight up, etc.)

 

No matter where the object is, Alt/Az exposures are going to be relatively short to prevent field rotation (15s-90 sec) vs. what auto-guided equatorial mounts can do (10+minutes).  Alt/Az exposures don't go as deep in terms of magnitudes.  Software like Deep Sky Stacker can correct for rotation between images, but nothing, other than a shorter exposure, can correct for rotation within an image...the center will be sharp and the stars on the edges streaked.

 

I do have a 12" tracking, GOTO SkyWatcher SynScan collapsible dob.  I love the scope, it is easy to align and use.  Views are great and I used it to see the H400.  I might use it to image the planets or Moon, but would never think of using it for a DSO...too much focal length, too heavy, too much scope (for me).

 

If you can settle for push to rather than GOTO, Dave Ek digital setting circles are pretty easy to construct, fairly cheap to build ($100 or so) and it wouldn't be very hard to install on your Coulter: http://eksfiles.net/...etting-circles/  You would need a computer to use them but only a cheap laptop.

 

If you want tracking the "cheap" way as mentioned above would be a platform and they are not cheap to buy and take some DIY skill to make.  It would be an either/or deal...either goto/push to OR tracking, not both at the same session.

 

For GOTO and tracking at the same time you're going to need something like a StellarCat.  They can really run you and and in my book, need advanced DIY skills to work well.

 

If you've got your heart set on imaging with the Coulter realize you are going to be limited and go for it. 



#13 gcwyatt

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Posted 05 May 2016 - 12:08 AM

S. Boerner - thank you for some very useful advice.  This is exactly what I was hoping for - someone to help me avoid the pitfalls and dead ends of ATM and Astrophotography.  

 

So, if I understand this correctly, Deep Sky is just out of my reach for the time being.  A 10" Dob just isn't up to the task.  But like you, I should be able to see the entire Herschel 400, right?  I could live with that for now and maybe upgrade someday if it turns out I really like this hobby.

 

Second, Push To sounds like a great alternative.  Pushing a button and having the scope do all the work is a nifty idea, but considering the cost/feasibility matrix I can live with computer assisted pushing.

 

Third, once I've locked onto a planet or H400 object I want to take a photo of, what's stopping me from using an equatorial platform to keep it aligned for a few minutes?  As long as I return the platform to center before using the push to to move to the next object wouldn't it work?  And if there is a reason it wouldn't work, what option do I have for a few minutes of tracking?

 

And thanks again.  It's very kind of your to share your experience.



#14 Jon Isaacs

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Posted 05 May 2016 - 12:37 AM

If you want tracking the "cheap" way as mentioned above would be a platform and they are not cheap to buy and take some DIY skill to make.  It would be an either/or deal...either goto/push to OR tracking, not both at the same session. 

 

 

I believe many DSCs can be used with a tracking mount like an EQ platform. In the simplest form, one could align the mount, start the tracking but leave the clock off in the DSCs..  Realign would be necessary each time the mount reaches then end of it travel and is reset.

 

Jon



#15 RAC

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Posted 05 May 2016 - 12:37 AM

You Can have Goto and tracking if you use OnStep and it's cheap, I have done this on my 20" dob and it works great. You could even use an OnStep setup to power an equatorial platform that would be more suitable for deep sky photos but your motors and tracking hardware will need to be very good for smooth operation.



#16 gcwyatt

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Posted 05 May 2016 - 12:43 AM

RAC: Sounds like you disagree with Boerner, which doesn't surprise me.  Like I said, there's a lot of disagreement on int 'Net about this.  Can you recommend some website where I can research and lean to build what I need?



#17 RAC

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Posted 05 May 2016 - 01:07 AM

No I do agree with him, with everything he has said. But StellarCat is not the only option, there is a great free option called OnStep so long as you do the work, it will give you tracking and GoTo on a Dob scope. It works great, I know this because I use it. Everything he has said about using an alt/az scope for imaging is true.

 

http://www.stellarjo...quipment_onstep



#18 S.Boerner

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Posted 05 May 2016 - 07:55 AM

And I agree with RAC :) .  I said something like StellarCat, not that it was the only way to go. 

 

One thing that I'd add is that I really love controlling my various scopes with SkySafari on iOS or Android.  When investigating the various control possibilities check to see if SkySafari plays well with the system.



#19 RAC

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Posted 05 May 2016 - 01:43 PM

SkySafari works very well with OnStep with bluetooth.

#20 tranquockhue

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Posted 27 June 2016 - 12:10 PM

RAC. Have you tried with servos? I believe with digital encoders, servos can be give better performance than stepper motors (stepper motors require microstep, while digital encoders give pulse, and microstep may requires more processing power from microcontrollers), and with my try, stepper motors make more vibration than servos.
Btw, your OnStep is really nice :D I will turn over your code.
Ah, I read a post about using Celestron Nexstar mount to computerize Dobson. I wonder if I buy a used Meade LX90 or LX200, or Nexstar 8SE, then mod with a new frame, new gears, and maybe replace motors (in case original motors can't produce enough torque), is it possible? 



#21 gregj888

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Posted 27 June 2016 - 01:41 PM

The only amateur deep sky long exposure imaging with  Alt-Az (they are not Dobs)  scopes I've seen results from have field derotators and Sitech controllers.  All the new big professional scopes do this, we know how.   Look at the SiTech web site for examples.

 

I'm not advocating this as a solution for the OP's scope, each encoder used costs several times the OP's scope, but it shows how to do it.

 

I also agree with the On-Step as a way to get started.  Then add a DYI field derotator or Equ platform.  The other alternative is to mount the tube on an equatorial mount.

 

OR

 

Use a On-Step and image with a CMOS camera.  Keep sub-exposures short (<10s)and stack.  You'll need to be careful about the camera choice- a 290, 178, 224 or the ASI1600 then stack and derotate in Software.  The TDN (read noise) need to be really low <2e or stacking to 20 minutes will bite you.  The first 3 cameras listed all have TDN < 1.2e and QEs >80% so effectively photon count...   Also look at AstroLive... 

 

JMHO...



#22 RAC

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Posted 27 June 2016 - 01:50 PM

RAC. Have you tried with servos? I believe with digital encoders, servos can be give better performance than stepper motors (stepper motors require microstep, while digital encoders give pulse, and microstep may requires more processing power from microcontrollers), and with my try, stepper motors make more vibration than servos.
Btw, your OnStep is really nice :D I will turn over your code.
Ah, I read a post about using Celestron Nexstar mount to computerize Dobson. I wonder if I buy a used Meade LX90 or LX200, or Nexstar 8SE, then mod with a new frame, new gears, and maybe replace motors (in case original motors can't produce enough torque), is it possible?


I now use tmc2100 stepper drivers and they are as smooth as silk with zero vibration. Stepper motors don't run like stepper motors with these drivers, they turn like servos.

#23 gregj888

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Posted 28 June 2016 - 10:53 AM

Raymond, running stepper smoothly is usually done by micro-stepping.  On-Step also micro-steps.  Smooth motion is the reason for micro-stepping and doesn't help with Micro-positioning (unless the same encoders used with a servo are used).

 

The real advantage with servos is dynamic range.  Steppers typically can't go faster than a few thousand full steps per second.  Servos that would be used on a scope can typically go from zero to a few thousand revolutions per second and some much faster.  This show up when you have enough resolution to track, then want to do a fast slew.  Both systems can track beautifully.



#24 RAC

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Posted 28 June 2016 - 02:02 PM

I've tried a few different drivers and all sorts of micro steps from 8 to 32 but no driver out there can come close to what the trinamic's can do. Vibration is always there even when microstepping but not with the Trinamic drivers.
I run my stepper motors at 40volts with these and I get very good slewing speeds.

#25 TonyStar

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Posted 30 August 2016 - 09:46 AM

 

I now use tmc2100 stepper drivers and they are as smooth as silk with zero vibration. 

 

Hi Ray, with the Arduino, do you drive the tmc2100 using only the STEP/DIR pins? 




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