Parking a Temma 2 vbscript

[troypiggo (Troy)]

I'm writing a script to park my EM200 back to Dec=-90 and RA exist vertical, because the mount has no home position. Normally at the end of a session I just release the clutches and move by hand.

Just want to check my theory. I was thinking it would be as simple as connecting and slewing to Dec=-90 and RA=LST. The script works on the ASCOM simulator in that it connects and skews to Dec=-90, but the RA doesn't slew to LST as RA.

I'll post the script when I get back on computer, but for now just checking not missing something in the theory that RA=LST should give counterweight shaft down position.

[Dennis]

Hi Troy

I think that you are correct as I believe that the Right Ascension of the Zenith at your location is the same as your Local Sidereal Time.

See screen print from The Sky X Pro.

Cheers

Dennis

[Dennis]

Hi Troy

Here is a screen print from the now defunct Pegasus 21 Manual. Note the horizontal CW shaft.

Cheers

Dennis

[RobF (Rob)]

I think Dennis is right Troy. You will need to use LST in your calcs, but RA=LST would be orientated so the scope is overhead (and DEC=Latitude).

Its probably going to be LST+6hrs?

[Dennis]

From memory, whenever I have synced my EM200 with e.g. The Sky X Pro or SNP, I think the program has always “assumed” that the OTA is positioned on the West of the mount, pointing to the East, based upon my settings for the Southern Latitude of Brisbane.

After having polar aligned the mount, I then find a bright star in the East and sync on that. I have never started in the Tak “Initial Position”.

Cheers

Dennis

[troypiggo (Troy)]

Thanks so much guys. You're right, the answer was to set RA=(LST-6hrs). Assume it would be plus 6hrs if Northern Hemisphere, and Dec should be 90 instead of -90.

Here's the very basic script. Please excuse any odd coding practices - I'm not a programmer. Test it first yourself with finger on the mount control "all stop" button at the ready, just in case. It worked for me tonight, but LST was more than 6. I just added the little if/then in case less than 6 to avoid negative RA, but that bit is untested.

' ####################
' temma_park.vbs
' Script to park at RA=(LST-6), DEC=-90
' by Troy Piggins
' #########################

Option Explicit

' #########################
Dim objChooser,objScope,strScopeProgID
Set objChooser=WScript.CreateObject("ASCOM.Utilities.Chooser")
objChooser.DeviceType="Telescope"
strScopeProgID=objChooser.Choose(strScopeProgID)
' connect to ASCOM, unpark, and start tracking
Set objScope=WScript.CreateObject(strScopeProgID)
objScope.Connected=True

If objScope.AtPark Then
  objScope.Unpark
End If

If Not objScope.Tracking Then
  objScope.Tracking=True
End If

Dim hmsLST,hmsRAPark,degDecPark

hmsLST=objScope.SiderealTime
if hmsLST<6 then
  hmsLST=hmsLST+24
end if

hmsRAPark=hmsLST-6
degDecPark=-90

objScope.SlewToCoordinates hmsRAPark,degDecPark
objScope.Tracking=False
objScope.Park
objScope.Connected=False
WScript.Echo "Done."

[RobF (Rob)]

Looks good Troy. Success in the end by the sounds of it. LST-6 makes more sense for S hemisphere.

[Dennis]

The now defunct SW (Pegasus 21) that came with my Tak EM200 mount expected the OTA to be pointing at the Zenith with the CW horizontal for the initial alignment.

However, reading The Sky X Pro’s User Manual for the Temma II mount, it writes:

“When the Temma mount is powered off, then on, the Temma control system’s right ascension/declination coordinates are always 0.0, 0.0.”

If I understand this correctly, RA=0 and DEC=0 are the coordinates of the Vernal Equinox.

If this is the case, then at certain times/dates, the EM200 would expect the OTA to be pointing up, down, E or W depending on when you set up and connect, as the VE “moves” (rises, culminates, sets, etc.) within a 24 hour period due to the earth’s rotation as well as during the year as a result of the earth orbiting the sun.

Just something I hadn’t really thought about until Troy’s post.

Cheers

Dennis

[troypiggo (Troy)]

Thanks for following up on this, Dennis. Makes sense in explaining where it's starting from when powered on and you try to slew before syncing.