FAQs - Miscellaneous

FAQs - Miscellaneous

RA offset Diff and DEC offset Diff

Q: If I start an alignment and goto a star and accept (without any adjustment) the position, the DEC offset is always 0 (as expected) but the RA offset is not 0.

Mon: That is the difference in microsteps from the computed ra/dec ring counter values of the alignment star goto using the ra/dec equatorial catalog coordinates and the ring counters that is read on the simulator. Ideally the discrepancy should be less than 50 if you are using the physical mount (crystal based counter) than the simulator (pc based sidereal counter).

EQMOD Connection Issues

Q: When I try connecting my planetarium program to EQMOD the connection fails. If I attempt to connect to a non-existent serial port (say, COM9), the EQMOD config window pops up very briefly and disappears. When I attempt to connect to the correct port (verified through Windows XP's HW manager), the window pops up, but only displays its outline… hangs there for some time and then disappears. What's happening.

A: When you see the EQASCOM “ghost” interface appearing, it means that EQASCOM has found a valid COM port and is trying (in vain) to contact the mount. When you try with an invalid com port EQASCOM quickly detects this so can close much quicker (no comms timeouts or retries etc). So, it would appear that you do not have a com connection to the mount or you have not used the correct port settings… typically 9600, 8-1-N, no flow control.

How do you use the function "Drift Compensation"

Drift compensation is needed for the motor control boards V1.06 or later. For some reason these boards do not track accurately when issued the same commands as earlier boards and so this additional parameter was introduced. There is a “driftmeter” application

[[http://tech.groups.yahoo.com/group/EQMOD/files/A%20EQMOD%20Release/EQASCOM/RA%20Drift%20Meter/|http://tech.groups.yahoo.com/group/EQMOD/files/A EQMOD Release/EQASCOM/RA Drift Meter/]]

that allows you to measure any tracking drift but others have found that for V1.06 boards a figure of 3 is required, for earlier & later boards set the compensation to 0.

The tracking must be stopped and restarted for the compensation value to take effect. This is because the compensation is applied directly to the message used to start tracking.

What is the purpose of the “Auto RA Sync” setting?

The Auto RA Sync check box (located in the “Drift Compensation” panel)is actually rather important . If checked then EQASCOM will periodically resynch its position based upon a poll of the the motor position. If Left unchecked then such a resynch only occurs on slew completion and, while the mount is tracking, EQASCOM calculates its own 'emulated' position.

If you want to test for RA drift then you must have the Auto RA Sync check box checked. You are advised to always leave the Auto RA Sync box checked.

There was once a theory that polling the mount for motor position could itself lead to a tracking error and this why the option to remove polling by via the checkbox was added. In fact this polling/tracking problem is likely just a red herring with the real problem being the drift associated with V1.06 boards. This option has to do with how EQASCOM determines the stepper motor positions while tracking. If it is unchecked EQASCOM simply estimates the position based upon the last known position (as read following a slew or goto) and the elapsed time. With the option checked EQASCOM will regularly poll the mount for the current position and between polls estimate the position.

How do I determine the board version in my mount?

Once EQMOD has been connected to the mount click the [Display +] button located just below the ASCOM logo. The message centre will appear. Clicking the [Display +] button repeatedly cycles through several displays but you want the message centre for the version information.
The information displayed may be something like
EQ Modded Mount found at COM1: 9600
Mount Version : 000601 DLL Version: 000204
The mount version is displayed in reversed order. In the above example the mount version is 1.06.00

GPS time question and Daylight Saving (Summer Time)

The PC's clock may advance but the underlying windows UTC time is not adjusted when you move into daylight saving or summer time. EQASCOM only ever uses the PC's UTC time + any GPS delta correction. Irrespective of any GMT/BST changes EQASCOM and the GPS will continue to work in UTC.

What does camera aligned orthogonally mean?

“orthogonally” is the adverb from the root verb “orthogonal”. http://m.dictionary.com/d/?q=orthogonal&o=0&l=dir

The camera should be aligned such that mount movement in RA should result in an image shift to the left/right along row of sensor pixels whereas mount movement in DEC should result in an up/down image shift along a column of sensor pixels.

The DxSA/DxSB data fields

These data fields display the offset data in stepper steps for the SYNC Command. They show the discrepancy from the current stepper value computed Catalog coordinates (planetarium database coordinates converted to Stepper data) vs the one that was read currently on the stepper motors.

/home/welshdra/public_html/eqmod/data/pages/faqs_-_miscellaneous.txt · Last modified: 2012/07/14 16:47 by jon
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