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DIY GOTO


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DIY GOTO

 

Most amateurs these days seem to want a goto scope, and those of us who are into ccd imaging all lust after the AP 1200’s and the Paramounts of the world, however not all of us have the budget for these sort of modern computerized scopes. Many of us would love to try our hand at a wide variety of astronomical pursuits, but envy the people with expensive software corrected tracking systems that can be set up to compensate for almost everything.

 

Some of us also just like doing things ourselves. Building a scope is an important part of the hobby for us, trying to build the elusive perfect scope for our needs.

 

Yet others worry about what may happen a few years down the track when that scope that we saved so hard for, breaks down and manufacturers no longer stock spares – how many people had a big name computerized scope that stopped working properly due to the y2k bug?

 

Well the holy grail is here, and has been around for years……The DIY Bartels Goto system.

 

How would you like a drive that could be used as a goto system on any of the following:

 

Dob or other altaz scope configuration.

 

And / or

 

Virtually any form of equatorial mount (german, fork or split ring, siderostat for example)

 

What about

  • the ability to utilize one set of electronics with any scope just by changing a configuration file, or having ten versions of the driver program for 10 different scopes – but only one set of electronics to be built?
  • had electronics that you could build yourself or buy inexpensively already completed?
  • Have access to a support group http://tech.groups.yahoo.com/group/scope-drive that has 2,400 members?

 

Mel Bartels is a well known amateur telescope maker who, for nearly a decade, has provided a DOS based computer control program and electronics plans/boards for self build drive systems.  He also has a commercial program that controls servo motors, but this is article is refers only to the free stepper version – which is in no way inferior.

 

He wrote a program called “scope.exe” to run on low end dos based computers  that uses simple electronics to control stepper motors to drive telescopes via a parallel port.. Over the years the program has been added to at the suggestion of users until it currently has no peer as a scope control system. Importantly the source code is available freely……

 

I have used it to drive a dobsonian (home built), an 8”newt EQ-5 combo, a Vixen Super Polaris/C8 combo, and currently a 10” Newt/EQ6 combo. All of which have performed superbly.

 

It is impossible in a brief article to fully describe the system, so I’ll simply outline some of its capabilities.

 

Essentially the program consists of 3 main parts;

 

  • the scope.exe program executable
  • a file called config.dat that contains sets of parameters that govern how the drive performs (set up by the user)
  • sets of data files that contain the locations of objects that you want to form your object database.

 

The program MUST run in a pure dos environment, it will NOT work in a Windows dos box due to timing issues. People are successfully running the program on old 486 machines, but my experience has been that things work much better on Pentium class machines – I use a 400mhz Pentium and it works superbly.

 

The program uses the computer’s parallel port to control a simple box of electronics that in turn drives stepper motors of your choice to control your telescope. The software drives the motors in 2 modes – full step mode for slewing, microstep mode for tracking. How many microsteps per full step you use is determined by the gear ratio your drive uses. My EQ-6 has a 180:1 worm wheel, fed by a 1:5 belt drive from a 200 full step per turn stepper motor with each full step divided into 20 microsteps. Hence each microstep moves the scope:

1,296,000 (seconds per day)

Divided by 180

Divided by 5

Divided by 200

Divided by 20

= 0.36 arc secs.

 

My scope slews at 1.5 degrees per second between objects, and no movement in the eyepiece is visible at high magnification due to microstepping.

 

 

 

 

 

 

My scope converted to belt drive

 

The system allows for the following:

 

  • Drive dobsonians as well as Equatorials.

 

  • With a dob you simply align on two stars and the system will allow you to goto an object, and automatically track it – and use field derotation if you have built the hardware.

 

  • An equatorial scope that is well polar aligned can simply align on one star and then track, if not well aligned then a 2 star alignment can be performed.

 

  • The software incorporates a sync function.

 

  • Backlash (adjustable on the fly) on both axis

 

  • PEC on both axis, the program can save guiding/autoguiding corrections, automatically subtract drift from them, generate pec correction files, allow you to average the files, perform a median smooth on the resulting file, save the pec file, reload it and continue tracking without loosing track of where it is pointing!

 

  • Motor focuser control including autofocusing using Maxim and Focusmax through control of a motor focuser driven by either a stepper or DC motor (software configurable for speed of focus etc).

 

  • Error correction for mount fabrication errors (orthogonality etc)

 

  • Dome control

 

  • LX200 command compatibility (can be connected to planetarium programs)

 

  • Autoguiding using LX200 serial commands from all the main ccd/guiding programs via the ASCOM interface

 

  • Drift correction – imagine you have a german eq not quite polar aligned, (or a dob not precisely set up and initialized) simply guide to keep a star centered for a minute or so, and the program will alter drive rates automatically to keep the object centered.

 

  • Automatically flips a GEM (allows manual flips if you wish)

 

  • Has a Polar alignment routing that simplifies setting up an equatorial scope.

 

  • Create/ edit data files to create custom lists of objects.

 

  • Create custom “scrollfiles” that allow you to creat a guided tour for an evening

 

  • A sample “dat” file for the first 10 Messier objects:

 

05 34 48 +22 01 11 M1 Pl Crab

21 33 45 +00 50 20 M2 Gb

13 42 26 +28 21 30 M3 Gb

16 23 54 -26 32 41 M4 Gb

15 18 51 +02 03 55 M5 Gb

17 40 26 -32 13 09 M6 OC

17 54 20 -34 49 03 M7 OC

18 04 06 -24 22 58 M8 Nb Lagoon

17 19 30 -18 31 18 M9 Gb

16 57 22 -04 06 27 M10 Gb

 

 

  • Has full pointing model correction through

backlash
PEC
refraction
drift
Z1 (axis misalign)
Z2 (az offset)
Z3 (alt offset)

 

  • Home position for scope parking

 

 

The program is easy to drive via a mouse or keyboard inputs. I personally find the keyboard inputs to be incredibly effective and quick to use following is a list:

 

Shot of the screen

 

Shortcut keys:

 

'1' selects 'move to equat'

'2' selects 'track on/off'

'3' saves current equatorial coordinates

'4' retrieve saved equatorial coordinates into the input fields

'5' saves current #2 equatorial coordinates

'6' retrieves saved #2 equatorial coordinates into the input fields

'7' read slew file from Guide

'8' write slew file to Guide

'9' input altaz

'0' reset to input altaz

'a' adds in the altitude offset to all initialization altitudes, adds in the altitude offset to the current altitude, and re-initializes

'b' begins an already loaded scroll file, and once started, 'l' continues onto the next scroll action, simulating a leftkey press of the handpaddle

'c' displays PEC graphically

'd' selects 'data file' menu item

'e' averages PEC analysis files and displays results graphically for the altitude axis

'f' averages PEC analysis files and displays results graphically for the azimuth axis

'g' selects menu item 'Guide.bat' (which calls Wguide.exe, passing it the current scope coordinates, the DOS 32 bit version of Guide)

'h' selects menu item hand paddle, toggling through handpad modes

'H' selects a hand paddle mode from a selection palette

'i' displays the initializations

'k' kills the inits

'l' reloads pec.dat file (when scrollfile is underway, 'l' simulates the handpad's leftkey press)

'm' selects microstepping speed

'n' slews to input altazimuth coordinates

'o' reset to input altazimuth coordinates

'p' selects PEC

'q' quits the program

'r' resets to input equat coord

's' selects scroll file

't' toggles tracking on/off

'u' altitude axis: graphically displays guiding efforts with respect to pec - gives options to save and update pec

'v' azimuth axis: graphically displays guiding efforts with respect to pec - gives options to save and update pec

'y' zeroes out the altitude pec array (does not save PEC.DAT)

'z' zeroes out the azimuth pec array (does not save PEC.DAT)

F1-F4 moves the scope with microstepping: F1 up, F2 down, F3 CCW, F4 CW 

'`' (the left apostrophe key in the upper left of most keyboards) selects the menu item 'Guide.bat'

'$' or '[' or '{' gem meridian flip

'?' input equatorial coordinates

'<' handpad mode left key

'>' handpad mode right key

'&' restart scroll file

'@' toggle right handpad mode to reset equatorial in grand tour

'%' zero out backlash

'*' do a three star polar alignment

 

How does it perform in practice?

 

Gotos routinely put an object in the field of view at 500x when properly set up.

I can image unguided for 2 minutes at a 1200mm focal length and get 100% keepers – a result of pec correction, precise polar alignment, and minor drift rate correction – all done in software.

 

Virtually every error that a scope has can be corrected in the software

 

Guided imaging is unlimited – on a night of good seeing corrections are trivial – rms guiding values can be less than ¼ of an arc sec. (12 month old EQ6 raw PE around 15 arc secs. total)

 

Examples of people using the system

 

Small dobs eg http://www.geocities.com/CapeCa naveral/9601/compudob.htm

Medium dobs eg http://users.adelphia.net/~greg_gran/bi gdob.html

Small EQ’s eg http://home.sc.rr.com/thomiwancio/Scop e_Drive.htm

Convert other eq’s  eg http://es.geocities.com/astrohyperi on/losmandy_i.htm

 

Have a look at the Webring – almost any commercial scope has been converted, and any homebuilt scope can be too. Cost could be anywhere from a couple of hundred dollars up depending upon how much you build or buy, and whether you have an old computer around. Join the Yahoo group and ask questions – it’s full of helpful people. Homebrew is alive and well and gives nothing away to any commercial system…………………No wonder Mel Bartels had an asteroid named after him (17823 Bartels) in recognition of his services to amateur astronomy

 

Webring

http://u.webring.com/hub?ring=scopedrive

 

Mel Bartels website http://ww w.bbastrodesigns.com/BBAstroDesigns.html#Computer_Operated_Telescopes

 

A commercial supplier of bits to adapt your scope (I have no affiliation )

http://www.gototelescopes.com/

 

Excerpts from the Scope Drive List http://ben.davies.net/scopemanual.htm

 

 

There are so many possibilities with this system, that no short article could do it justice, join the Yahoo group and ask questions. If any readers decide to build a system then writing this article was worth the effort…..

 

Cheers

Gary McKenzie




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