Meridian flips with Skywatcher mounts and EQMOD

I am posting this in a separate thread to another users request so that it might appear in searches when Skywatcher users have issues with meridian flips and it will hopefully save Leo a question being asked.

I will limit what I am posting to EQMOD users though most of this would apply to other mount software as well and most of the mechanical considerations are the same no matter what mount you have.

After some initial teething problems, I have found meridian flips to be very reliable, my only failed flips now are due to passing cloud stopping plate solving after the flip, if that is the case you are probably not going to be getting useful data anyway…

A few items below to check and it should be possible to have reliable flips with the Skywatcher and EQMOD combination.

I will put in the usual caveat that you must be sure of how your equipment behaves and accept the risk of a pier crash if you want flips to be unattended. I would advise observing a number of automated flips at various declinations to make sure nothing untoward is happening. The risk is always on the user here and if you can’t accept the risk of a crash, you should not allow automated flips.

Mechanical considerations:

    1. Your cable management needs to be good. The aim of meridian flips should be for them to be able to occur safely. Your telescope needs to be able to point at the horizon in any direction without cable tangles. The bonus of this is you will not have to worry about cables when you start the night, or worry that you will come out in the middle of the night to find damaged ports from a cable snag, or your laptop on the ground with a broken screen.
    1. Your mount needs to be able to track well past the meridian at any declination without an equipment crash. An hour past the meridian should be plenty.

Software considerations outside Voyager:

    1. You should use the mount limits in EQMOD (Or any other mount control software) as a defence against your mount tracking too far through the meridian and causing a crash. How close is up to you, I am comfortable so long as I can put my hand between the camera (The first thing which will crash in my setup) and the pier/tripod but you need to make your own mind up.
    1. in EQMOD, you need to set your mount limits to permit the mount to track through the meridian in the “West, pointing east” configuration and only stop the mount when it is approaching a crash. If your mount limits (Physical or software) do not allow the mount to track far enough past the meridian you will have errors that could stop your night. For ease, it is best to set the “East, pointing west” limit to allow it to point somewhat east of the meridian, but it does not need to be very far, perhaps half an hour east.

Voyager setup:

This is the critical part, it is critical not because of Voyager, but because of how EQMOD behaves. All mounts will have some amount of cone error and other pointing errors so when you carry out a meridian flip (Which is simply a new Goto command sent to the mount, after the target has passed the meridian) the mount will almost certainly NOT land on the target in the first iteration due to the combination of all errors in the setup, most of which are mechanical.

You need to determine the amount of pointing error in your setup. In my case after the flip the errors combined to have the telescope pointed about 12 minutes (Hour angle) east of the intended target. If your pointing errors combine to have the telescope pointed east of the meridian after the flip, the sync after the initial plate solve will be rejected by EQMOD and your flip will fail. If you do not know exactly what your error will be (Cone error for instance will probably be different every time you mount the telescope) then you only need an approximate value.

Voyager Settings:

    1. In the mount tab of the setup form, the time in “Do flip after mount passing meridian by” MUST be greater than your pointing errors. This allows the mount to track through the meridian far enough that when the flip is performed, the telescope is always pointed west of the meridian. The default time is 10 minutes, my mount errors seem to be about 12 minutes, I set Voyager to flip after 20 minutes. This value MUST be lower than the time past the meridian which will cause EQMOD to stop the mount.
    1. In your sequence file (I have not looked yet as to how to manage this if you image by calling exposures directly in a dragscript rather than calling a sequence or research/Mosaic file) you should, in the meridian flip tab, set the “Force meridian flip” flag and set this time to something longer than your flip time in the mount setup tab, this must still be less than the hour angle after the meridian at which EQMOD will stop the mount. This will permit a running exposure to be completed if there is time to do so without risking an equipment crash. This is the best bit of the sky to image through, so you don’t want to waste a 20 minute sub by flipping at the 15 minute mark if your equipment can safely keep going.

Once I sorted out the settings above, I have had no issues with flips, attended or unattended. My setup has carried out at least 20 automated flips without issue. The only problems I have are from cloud preventing successful plate solving.


Thank you so much for your report and info … really useful

All the best

Always happy to help other users if I can. If something trips me up it will probably trip others up as well sooner or later.