Preventing Meridian Flip on EQMod

[Gib007]

So I'm imaging away for hours and hours, slewing through mosaic segments via EQMosaic and then later on it crosses the Meridian and my next segment slew flips the telescope. I don't know about you but I hate that forceful flip. I have limits disabled all the time and despise lack of control and I consider the mount deciding it needs to flip from one segment to the next to be a lack of said control.

Is there any viable way to disable this? I'm imaging with my small Borg 77mm refractor and collision with the mount is impossible for my current target (Orion Constellation). I'd love to do something that will allow the mount to slew from segment to segment with zero consideration for Meridian. Thank you!

[earth titan]

I think there a setting somewhere to disable it. I'll have a look later as I haven't got EQMOD on my MAC.

[chrisshillito]

EQMOSAIC itself can be set warn you that you that your next goto is about to cross the meridian. The colouring for the grid squares also provides information on the meridian line so that you can best plan you mosaic sequencing so as to avoid crosses. If mosaicing an object spanning the meridian it is best to start with the most westerly panes so that by the time you've captured them the easterly panes may have actually crossed the meridian

If a goto across the meridian cannot be avoided then there is an option in EQMOD to force a what we term a 'flipped goto' - i.e. one that breaks the standard EQ mount control convention of always maintaining a the counterweights down orientation. Because this is an 'abnormal' condition that can lead to mount collisions the checkbox used to force this type of goto is automatically cleared after the goto is performed - so the user has to make the decision to override the goto mode for every 'flipped' goto they wish to make. Another factor you have to take into consideration when initiating a flipped gotos is that the goto accuracy itself my suffer as alignment model points created in the  'counterweights down' orientation cannot reliably be used to compensate for counterweights up goto's.

All in all it is much simpler if you just carefully plan your targets to avoid meridian crosses.

Chris.

[Gib007]

Thanks for the replies on this topic - I forgot I had posted this!

I'm aware of EQMod's "Force Flipped Goto" checkbox that makes the next goto command given avoid flipping the meridian if already past it (or forcing it to flip if not yet past it). What I find annoying is not being aware that indeed the mount has already crossed the meridian and then asking EQMosaic to slew to the next segment and being surprised by the telescope slewing all over the place to perform a meridian flip. Ideally, EQMod would never, ever flip the meridian on any kind of goto UNLESS ASKED to do so. Is there no such setting?

[Gib007]

I have much love for the ASCOM simulator...it has taught me so much! I answered my own question with 15 minutes of playing around. For anyone that reads this, here it is.

When you use EQMosaic, your telescope's current position is saved when you click "Get Position". Anyway, this sets F6, the central segment, as your current and starting position. If you are close to the meridian, there will be segments with yellow squares and segments with white squares. If you are currently on a white square, slewing to a yellow square involves crossing the meridian, and vice versa. EQMosaic will warn of meridian crossings in this scenario and to prevent the flip, you can check "Force Flipped Goto" in EQMod. This sends the mount to the meridian and then back to your target segment, preventing the flip entirely. However, you are now in an odd position. Say you are on a yellow square (having come from a white one). If your next segment is also on a yellow square, you will need to check "Force Flipped Goto" in EQMod once again so that when slewing to the next segment in the mosaic, indeed a meridian flip doesn't occur. This has to be done each and every time you stay within your newly coloured squares (yellow if coming from white or white if coming from yellow). This is of course if you want to prevent a meridian flip at all. If you're on a yellow square, having come from a white square and forcing the flipped goto, and you are now intending on going back to a white square, you need not check "Force Flipped Goto" because your mount is already in the correct position for the white squares (since you came from there and had to force flipped goto only to cross into the yellow squares). 

Hope that makes some sense to anyone who reads it, otherwise please do feel free to ask, if you are even bothered by meridian flips!

[chrisshillito]

Thanks for the replies on this topic - I forgot I had posted this!

I'm aware of EQMod's "Force Flipped Goto" checkbox that makes the next goto command given avoid flipping the meridian if already past it (or forcing it to flip if not yet past it). What I find annoying is not being aware that indeed the mount has already crossed the meridian and then asking EQMosaic to slew to the next segment and being surprised by the telescope slewing all over the place to perform a meridian flip. Ideally, EQMod would never, ever flip the meridian on any kind of goto UNLESS ASKED to do so. Is there no such setting?

The standard way of moving an GEM is to always keep the counterweights down - this is certainly how the synscan moves the skywatcher mount and I suspect the same is true for most other mount controllers. For most user setups this represents safest method of mount movement with regard to potential pier/mount collisions. Very early on in EQMOD's development the decision was made to follow the synscan's methods of mount control for gotos and EQMOD's entire alignment/goto model based upon the assumption that the mount moves in this way. So from EQMOD's perspective counterweight down movement is considered the norm - I personally would not wish to change something so fundamental to the operation of EQMOD - but others are welcome to try it .

The only setting that can make the mount move in an abnormal way is the 'flipped goto' checkbox. This actually represents my best attempt at providing a counterweights up movement option without 'breaking' EQMOD. However, Anyone choosing to use this mode needs to appreciate they are moving in an unnatural way for EQMOD, the goto model / limits may not work correctly and collisions are more likely - i.e. it should only be used with caution, never remotely, and with a finger poised on onte emergency stop/power button!. Because of the potential dangers of conterweights up  movement the 'fliped goto' mechanism is deliberately designed to be a bit of a pain to use and automatically clears itself on goto  completion to restore the default of counterweight down movement at the earliest opportunity.

Managing and understanding a mounts movement in respect to the meridian is a fundamental skill that GEM owners have to master - its really not that hard. You are the person initaiting the slew, you should know roughly where in the sky your mount is currently pointing (if not use a planetarium) and if its near the meridian then you really have to ask yourself the question - "what's likely to happen next?". EQMOD itself isn't going to warn you directly if a flip is going to occur (ASCOM frown on drivers that interrupt automation), its job is simply to do what the higher level applications demands of it (and if it can't then return an error message). The higher level applications controlling the mount via EQMOD may well be able to warn you  - for instance EQMOSAIC has a pop up message you can enable if you choose.

Chris.

[Gib007]

Thanks for the reply. I'm aware of the optimun and safe nature of counterweights down but when imaging for just one hour over the meridian when your telescope is tiny is not unsafe and I hate the idea of the mount flipping despite it being ok for an hour more. I just don't want large slews to cause the telescope to end up in a different part of the sky than intended and thus avoiding meridian flipping seems like a good idea for my large mosaic.

[Stub Mandrel]

I know this is a 5 year old thread, but I was pointed here for advice.

It was also suggested I look at mount limits. The EQMod manual says:

Quote

Meridian.
This detects when the scope has moved past the meridian (usually through tracking) and has
been a part of EQASCOM since V1.07. By default the limit is set to trigger when the RA axis is
horizontal but most folks will want to allow some degree of tracking past the meridian. To set the
limits simply slew the scope to the limit position and click the “add” button. You will need to do this
for both East and West sides of the pier.
As these limits use encoder positions they can only be applied properly if the mount is parked and
unparked. On start-up the default ‘horizontal’ limits are applied and on unparking any user
specified limits are restored.
The default ‘horizontal’ limit can be restored by pressing the “Defaults” button.
Meridian limits can be removed altogether by pressing the delete button.

So there is now clearly a mechanism for overriding  flips or simply 'moving' the meridian.