Motor drive for Dob

[Jackson42South]

Hi all,

How accurate are motor drives for large dobs?
Is the tracking good enough for short duration astrophotogaphy?
Any recommendations for a drive for a 12” dob?

Paul.

[iceman]

Hi Paul.

Did you want a drive or an EQ platform?

I use an EQ platform for my 10" dob, and is definitely accurate enough for lunar/planetary astrophotography. It would work just as well on a 12" dob.

Dave Pretorius uses dob driver II on his 10" dob, and again I think it would work just as well on a 12".

You can get Mel Bartel's, ServoCat or a number of other solutions for driving your dob. All of which would be accurate enough for planetary stuff.

[Astroman]

One of the biggest problems with the Dobs is they have really bad field rotation, that is the field rotates as the scope tracks the stars. Mel Bartels controller can be used to correct this but its quite fiddly, and unless you are mechanically minded it does get quite difficult to setup and install. The ServoCAT system is a great little add on for trus style dobs, could work with others I guess. Mainly designed for the Obsession style scopes this little unit attaches to the Alt/Az surfaces and drives it effortlessly, unfortunately you need the Argonavis DSC to do GOTO's and make it track, which is a real shame. But for simple movements across the sky its ideal, but it does not have field rotation motors. There are quite a few different systems to use, dob driver is an excellent alternative to mel bartels system.

Anyway check them all out.

http://www.bbastrodesigns.com - Mel Bartels Scope and Scope II

http://www.stellarcat.com/ - Home of ServoCAT.

http://homepages.accnorwalk.com/tddi/tech2000/ - Links to Dob Driver II and other stuff.

good luck.

[iceman]

Field rotation isn't really an issue for short exposure stuff, unless you plan to do an animation, then you'd need to rotate the images.

But I find I have to rotate to some degree anyway, as they're always slightly out even when I turn the camera to compensate for field rotation.

[Jackson42South]

Field rotation can be compensated for in the stacking software, so I am no too worried about that.
Sounds like an EQ platform is the way to go cost wise.
I am also toying with the idea of designing a fork mount for the Dob that would only need an RA drive. I have a stack of old stepper motors and small servo motors and it would be easy enough to make up a driver board.
I will need to build an observatory to permanently house it if I do the latter, but the platform is portable.

[netwolf]

Hi Jackson,

Lets just say i have been kicking tyers for a long time now going beetween, GEM, Eq Platform, Dob Driver (Bartel etc).

Here is a intresting site for Fork Design.
http://www.atmsite.org/contrib/Harbour/index.html
Specifically the Sector Drive technicque mentioned here
http://www.atmsite.org/contrib/Harbour/SectorDrive.html

I belive Asimov is using similar drive on his home made GEM.

Another Fork design (wedge really)
http://www.livingstonetelescopes.co.uk/K%20PAGE-2%20COM.htm
http://www.stellafane.com/scope_gallery/park.html

Alternative to Mel Bartel's Stepper and ServoCat sold by Mel Bartel.
http://www.siderealtechnology.com/

Standard Dob Customised base can be driven by Stepper or Servo.
http://4dw.net/svdgoto/custom.htm
this is a subsection of http://gototelescope.com/ Lenord's website mentioned on Mel Bartel site as well. Mel, Lenord, Dan (Inventor of Sideraltech) are easily accesable for discussion via the Yahoo Group http://groups.yahoo.com/group/scope-drive/messages.

For EqPlatforms there is but one place to go.
Everything is there from discussion to Files(plans), Photos of build systems. And access to discussion with the people at the leading edge of this method.
http://groups.yahoo.com/group/eqplatforms/

Regards
Netwolf.

[netwolf]

An Alternative is to use Meade Autostar and Motors.
Yahoo Group RoboScope
http://groups.yahoo.com/group/RoboScope/?yguid=102612404

Examples:

This site variety of scopes that have been converted to Autostar including a
DOB.
http://www.bedair.org/ScopeStuff.html

How a Cloudynights member converted his Dob
http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=749502&page=0&view=collapsed&sb=5&o=all&vc=1

[gary]

Hi Paul,

Good to see you on the forum here and I hope you have been well.
It's been about 3 years since we saw you last in Hobart.

One of the perpetuating myths that appears on various forums is that you can't
perform deep-space CCD photography on a Dob without a hardware field-derotator,
platform, adaptive optics, etc, etc.

To the contrary, a growing number of enthusiasts are performing deep-sky
imagining on motor-driven Dobsonian mounts, often with stunning
results.

For example, consider these images by Johannes Brachtendorf in Germany -
http://homepages.uni-tuebingen.de/johannes.brachtendorf/Kinder/Galaxies.htm
http://homepages.uni-tuebingen.de/johannes.brachtendorf/Kinder/Nebulae.htm
http://homepages.uni-tuebingen.de/johannes.brachtendorf/Kinder/new.htm

All of these images were made on a truss-pole Dob using a ServoCAT
and Argo Navis. The ServoCAT includes an ST-4 compatible auto-guider
port for fine correction. Derotation was performed in software.



The ServoCAT and ServoCAT Jr. have been fitted to a large variety of mounts,
not just truss pole Dobs. The Jr. is optimized for 8" to 14" mounts. Some
ServoCATs are even installed on equatorial mounts. Both the ServoCAT
units and the Sidereal Technology units can be connected to an Argo Navis
DTC, in which case the Argo Navis performs all the object offset and
tracking rate calculations in real-time. When configured in this way,
full GOTO operation is suppported. However, these units can also
track without an Argo Navis being connected. The ServoCAT system that
provides this feature is referred to as "EasyTrack".

Servo motors systems provide numerous advantages over stepper motor
systems on telescope drive applications. Avoid stepper motor systems if
considering astrophotography. A system that provides autoguider
support is highly recommended.

Hope the above is helpful.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au

[Jackson42South]

Hi Gary,

It was at NACAA, Easter 2004. Good to hear from you again.
I well remember your presentation and looking seriously looking at an Argo Navis for my then 10" Meade SCT, but I ended up selling the scope and buying something smaller and more portable - 6" Intes Makustov.
Now I miss the light gathering power of the 10" and have decided to sell the Intes and buy a 12" Dob. to tide me over until I retire and can afford a 12" or 14" LX90 or, if I can afford it (Read: If the wife will let me), an LX200 SCT.
Trouble is that I now can't stop myself from looking at drive systems for the Dob. – Astronomers are never satisfied.

I would not have thought that those images by Johannes Brachtendorf, were possible with a Dob. Wow.

Regards
Paul.

[Astroman]

Thanks Gary for clearing that up, obviously got my wires crossed when I read up about it. :) I will also slap myself in the face for forgetting about software fixes for field rotation. God I am losing it.

[darkskybondi]

Hi guys - sorry to revive this old thread BUT:

I'm about to pick up a skywatcher 10-12" dob. At this point I don't want to image but would like the option in the future. More importantly, would love to have a simple system for controlling my scope using my laptop. I looked at the stellarcat website but it all is a bit overwhelming. And frankly for a newbie, some of the jargon you fellas use is a bit impenetrable at this point! :newbie:

My question is: if I want to retrofit a motordrive onto the dob in the future, and control it using a software package from my laptop (presumably this saves $$$ buying a separate Goto computer system), can this be done fairly easily/cheaply? Can you give me a basic idea of the sorts of options and expense and difficulty I'd be looking at?

Best,
DSB :)

[netwolf]

DSB,

You can not directly control the motors from your laptop, you will need a stepper or servo driver to interface with the motors. A relatively cheap and good system is this one

http://www.siderealtechnology.com/
user group on yahoo
http://tech.groups.yahoo.com/group/sitechservo/

I am using this system for my G-11 mount. Other than a computer you can also use a Argo Navis DSC to control the Servo system.

The stellercat system called the Servocat is also tried and tested system, but i think the Sitech is every bit as good if not better.

[Ian Robinson]

Depends on what you want it to be able to do.

An option may be be Bartellise the scope - Bartel came up circuitry to control dual axis drives , http://www.bbastrodesigns.com/BBAstroDesigns.html may be a way to go that wont cost you a fortune.

[darkskybondi]

I see I need to do some research into the various required components. At this point it sounds like I require a motor drive, servo, and computer to drive it.

Ian - I just want to have the option of relatively cheaply adding tracking capability (mainly for convenience while I view visually) and also for finding objects of interest more quickly using the computer. The option to image using this system later on would be nice, but principally I just want to have an idea about what I'll need in future for a 10 or 12" dob to enable a basic tracking/"go-to" system (using my laptop as the computer control). I wouldn't have imagined it would be tooooooo complicated but I am trying to gauge the rough costs and complexities of doing it cheap and nasty!

DSB

[netwolf]

DSB, you might want to consider JMI solution Train-and-Track
http://www.jimsmobile.com/buy_acc_lightbridge.htm

[Ian Robinson]

Bartelling it looks like the go for you then , can add fancy features later (goto, etc through coding them up if you want them).
The problem with a dob and imaging is Field Rotation. That's fixable and I may be wrong but I think Bartel tackles that too (a three axis system).

[darkskybondi]

Cheers for this - looking at http://www.bbastrodesigns.com/BBAstroDesigns.html it seems that it would cost US$145 for the circuit board, $50 for the handpad and $40 for the motor... but I am confused. Why do you need both a handpad and a laptop for control? I have scope controlling software on my computer already... so what I'm looking for is a way to retrofit a motor to a dob that responds to the software...

Can you set me straight? Maybe I'm misunderstanding.

- DSB

[Ian Robinson]

Not sure .... guessing it comes down to how the interfacing works . The handpad is probably redundant but would be helpful for observing at the eyepiece - a lot of dobs and newts on equatorials using a Bartel System will be big and it'd be pain in butt and hazardous going up and down ladders to key in something on the lappy , while the handpad can be kept handy making the whole thing more convenient - I suppose it's a convenience thing for than anything.

Maybe someone who has a Bartelised scope can give you the good juice on this.

you know you can actually make your own handpad using easy to find chips and capacitors and other components and need only buy his PCB to solder things onto ? That would likely cost next to nothing.
I think there is a chat room too for those who have and are considering Bartelising their scopes.

[darkskybondi]

Cheers Ian et al - will definitely look into it!

[netwolf]

DSB,

The bartel stepper system needs the Bartel Stepper control software to make it work. This software is limited in that it needs to be run on a the older MS-DOS Operating system. Most people just buy a very old laptop to run DOS and run the Bartel control software. The hand pad is only for Slew and Track operation. Its like a Left, Right, Up, Down control very basic.

The Servo control software from Bartel was developed for Windows and can work with various PICServo controllers. Dan Gray developed the Sitech Servo controller and intially the Bartel Servo software was used to interface with it. However Dan has since developed a ASCOM driver for his controller, so the Bartel Servo control software is no longer needed. Mel and Dan are good mates but the two systems are often confused and written off as Bartel's servo system. Mel's system is actually his Software which can work with other more generic PICServo Cotrollers like the JKerr PICSErvo. This PICSErvo like Mel's Stepper circuit does not have any intelgence of its own.

Dan a mate of Mel's decided to Simulate a PICServo like controller inside a Microprocessor and give it some local intelegence. So it can be computer controller for Goto or DSC controller for Goto. Or it can work stand alone (With some pre configuration from a PC) for simple Track and Slew mode. Then Dan released his own ASCOM Driver that makes the system a full GOTO system (with the aid of a computer). The Sitech also has a simple handpad control.

Often people confuse Handpad with the notion of a Meade Autostar or Celestron nexstar handpad. These hand pads actually are self contained computers with a database of stars and objects in they sky. One other option as I mentioned in a much ealrier post is called RoboScope. This is the name given to a Telescope mount not made by Meade that has been converted to a Autostar control. Essentially people have ripped out a Autostar and its motors from a Meade Telescope and retrofitted it to another telescope mount.



Regards
Fahim

[darkskybondi]

Thanks Fahim - very useful advice. Appreciate it.

- DSB