Polar Alignment

 
polefocus:
 
A simple program to assist with polar alignment using Astrotortilla ...or any other method of quantifying the amount of polar misalignment.  Simply connect to an ASCOM mount, enter the polar alignment error in arcminutes for both Alt and Azm, center and sync on a reference star, then push 'slew to offset'.  The program will slew to the calculated offset using the method published by Frank Barrett.    Star Offset Positioning for Polar Axis Alignment - 2nd Edition 2/19/2010 .  Finally, use the mount Alt and Azm adjustments to bring the star back to the center of the eyepiece/camera FOV and you're aligned.   If too far off, start by centering in your finder, then use eyepeice or camera frame and focus.
 
To install, download from bottom of this webpage (click arrow bottom/right).  Unzip (anywhere) and double click setup.exe.  You will find a shortcut in the startup menu under scopefocus.  Tested only on windows (should work XP through 8).  Requires ASCOM platform 6
 
This is VERY alpha, there is very little error handling and no logging at this point.  Eventaully I may have the error fields automatically populate from astrotortilla...for now easy to manually enter. 
 
 
Screenshot:
 
 
 
 
Center and sync a reference star: (click on pic for full size - readable) 
 
 
 
Slew to calculated offset then recenter with Alt/Azm adjustments on Mount.  (In this case I wasn't off by much to start with)
 
 
 
 
 Download from files below..
 
 
 
 
Early work toward remote/automatic polar alignment of the CGEM :
NOTE:   Put on back burner....It is promising but the motors stick out too far and tend to catch cables...with some re-engineering I fully intend to someday continue this project. 
 
 
Altitude:
 

Altitude Control

 
 
 
 
Azimuth:
 

Azimuth

 
PHOTOS:
 
I had originally just drill and 1/4-20 tapped the top of the square peg, leaving it loose to rotate.  This worked but was too 'sloppy' and eventually would have likely damaged the threads that secure it to the mount base.   I decided to use a tie rod end that could be tightly fixed to the mount base and still allow rotation.   
 
Tie rod end used for coupling.  McMaster-Carr (#59935K84) M10x1.5  29mm ID ball with 1/4-20 thread insert (#97191A230) in ball.  The thread insert needs to be ground down a bit to fit.  I cooled it in ice/salt water prior to pounding in, also used locktight.   
 
 
 
 
 
A small cut-off disc on dremel tool was used to cut the grove in the ball. 
 
 
 
 
 
To achieve linear motion, the ball must not be allowed to rotate (only swivel in 1 plane) .  A small hole is drilled in the side of the tie rod end and tapped for a set-screw.  CAUTION: small tap = high risk for breaking...mine did but serendipitously there was a perfect amount of the tap protruding which worked just as good (if not better since hardened) than a set screw.
(the slot (below) was just part of an unsuccessful attempt at removing the broken tap)    
 
 
 
 
 
 Tie rod end replaces square peg on base of mount.   The north side flattened to fit.
  
 
 
 
The Azimuth drive shaft is a 1/4 - 20 threaded rod.  It fits through the Azm adjustment bolt holes but is too close to fit any sort of a spacer between the rod and the bolt hole threads.  I did not want to damage those threads so decided I needed the shaft to be smaller where it goes through the mount hole so I ground it down to about 5mm leaving about 2" of 1/4-20 threads. 
 
The motor is mounted w/ 1" x 1/8" aluminum.  I originally just used the opposite Azm bolt hole but there was too much play.  Since the drive shaft was smaller I decided to make stabilize the stepper on this side as well,  a 5/16" aluminum spacer is the perfect diameter to cut 8mm threads, from both directions(~1/8 in the middles without threads)   The ID was drilled to match the ~5mm shaft.   A right angle bracket then attaches to the stepper mount.   The shaft is coupled to the stepper threaded rod coupler drilled out to match shaft diameters with set screws on each end.  Additional aluminum spacer was used as an adapter from the 5mm shaft to the larger coupler ID, set screw goes all the way through. (more pictures pending)  
 
 
 
(Click to enlarge and see the details)
 
  
 
 
Altitude Mount
 
 



CGEM ASPA:

Example of a single iteration of CGEM All-Star Polar alignment routine.  PA error determined by PHDLab using PHD guide data shows polar alignment error of 0.24 arcmin



Download polefocus from below:

Current Version 1.0.0.4
--allows comma for decimal separator 
 
 
ċ
polefocus1004.zip
(214k)
Kevin Sipprell,
Oct 19, 2014, 8:40 AM
Comments