Neq6 , Automatic Flip

[kenny k]

During a great couple of hours viewing earlier I entered the double cluster into goto,which was pretty much overhead at the time and after slewing to near off center it suddenly stopped then reversed from west side of mount to east side.I was amazed when it centered double cluster back in view.

I've read about the meridian flip a fews years back so I pressume this was what occurred.

Has anyone else had this happen,I wasn't aware of this on these mounts.

Kenny

[Steve 1962]

Yup - that's a Meridian Flip..and it's a real pain if it occurs while you're imaging!

[kenny k]

Good shout,that would not be good.only scratching at AP at the moment so that's least of my worries in mean time.

Although I was impressed with accuracy of mount doin a flip and coming good,only had it

6 months and loving it.

[Patrice Lanteigne]

It's always interesting to watch that happen!

[laser_jock99]

Yup - that's a Meridian Flip..and it's a real pain if it occurs while you're imaging!

I find that PHD guiding software needs re-calibarating once the scope has flipped over. It should only take 5 mins, but still a pain.

[Steve 1962]

"I find that PHD guiding software needs re-calibarating once the scope has flipped over. It should only take 5 mins, but still a pain. "

LaserJock is correct - I'm currently trialing Sequence Generator Pro (SGP) (well - it's sat on my laptop waiting for some clear skies anyway). If it works - they say this software can carry out a meridian flip, do a platesolve (using Elbrus or Pinpoint), re-sync the scope if necessary and flip the PHD calibration data. Should be great if it works!

Steve

[kirkster501]

Meridian Flip? Define please? Ok, I know what the meridian is but what's this flip business all about and why should we care? I noticed this as well and wondered was going on....

Thanks, Steve

[Patrice Lanteigne]

To understand why just unclutch your mount and manually try to track the scope through the meridian. You'll soon notice the counter-weigths getting higher than the scope which if they slipped would be disastrous to say the least.

[Steve 1962]

"Meridian Flip? Define please?"

Picture a German Equatorial Mount tracking an object as it rises across the sky from the eastern horizon - the scope will be on the "top" (west side) of the mount with the weights "down" on the east side. As the object crosses the meridian, the weight bar will be horizontal..and from there onwards the mount will be weights "up"...and if it's left going long enough, the scope will be at risk of colliding with the mount.

To avoid this risk of collision, many GEM mounts can be set to perform a "Meridian Flip" at a predetermined limit point. This flip "flips" the mount so that the scope is on the east side with the weights down on the west side and with the scope pointing at the same object again .

This is great but the problem is that, if you're imaging, the image in now upside down and, if you're guiding, the calibration data is flipped too.

Does that make sense?

Steve

[laser_jock99]

Another thing to be aware of when Meridian Flip is likely is your cabling arrangements. I nearly had a laptop dragged off it's table and onto the crazy paving once.......luckily I was on hand to avert a disaster.

[r3i]

Yup - that's a Meridian Flip..and it's a real pain if it occurs while you're imaging!

If you are using EQMOD you can pre-empt meridian flips. See Chris Shillito's excellent tutorial on YouTube:

[IanL]

EQMOD has settings to permit automatic meridian flips, but I seem to recall it is disabled by default for safety; once the mount tracks a bit past the meridian it will park to the home position and wait for the operator to intervene.

If you route the cabling properly and attach it to the right places on the mount then you should be able to perform a meridian flip safely, but I always keep a close eye on things. A long tail of cables straight from the camera(s)/mount base to the laptop, etc. is asking for disaster; it will invariably snag on something (e.g. the altitude bolts are a good bet).

If you fix the cable loom to the non-moving part of the mount base near the tripod first, then route everything to the control panel and fix it again, you can easily work out how much of a loop of cable to leave between the two points to allow the RA Axis to rotate through a normal range of motion (bear in mind that using a PA routine, the mount may actually go weights up so it will be more than you think). Then any cables that need to go to the ends of the scope (e.g. dew heaters and cameras) are fed by a second loop from the fixing point on the control panel. Again it is easy to work out how much slack you need to allow a full rotation of the Dec axis.

Why is that a good thing? Because you have now separated the loops of cable that needs to accommodate rotation in each axis and it is easier to monitor/predict how they will behave. You don't end up with one giant cable loom that can snag all over the place unpredictably and that also drags on the cameras and OTA which is also not a great idea! It can still snag even so, and I would always recommend doing meridian flips attended, with your red light on and with one hand on the emergency stop button!

Just reversing the PHD settings won't necessarily work after a meridian flip. For one thing you need to adjust the counterweights (when the weights are on the east side, you move them down the shaft so that side is a bit heavier and the gears stay engaged by going uphill). After the flip you need to move the weights up the bar a bit so the scope side (now on the east) is a bit heavier, again keeping the gears engaged. For another, the flip changes the side the RA worm gear rides on the gear and also you have to change the balance deliberately. That could easily be enough to require a recalibration of PHD's parameters (reversing them may work for you, but if it doesn't then this is why it didn't).

[Steve 1962]

Just reversing the PHD settings won't necessarily work after a meridian flip. For one thing you need to adjust the counterweights (when the weights are on the east side, you move them down the shaft so that side is a bit heavier and the gears stay engaged by going uphill). After the flip you need to move the weights up the bar a bit so the scope side (now on the east) is a bit heavier, again keeping the gears engaged. For another, the flip changes the side the RA worm gear rides on the gear and also you have to change the balance deliberately. That could easily be enough to require a recalibration of PHD's parameters (reversing them may work for you, but if it doesn't then this is why it didn't).

Good point - I must admit that I run with EQMOD limits disabled and do a manual flip - normally way past the meridian, but one of the features of SGP is that it flips PHD calibration data.

[martin_h]

You can flip guiding data within PHD, but as stated above if you move the weights(as I do) reversing the data wont work...I know, I've tried, but re-calibrating is no big deal.

I have auto flip turned off, but I do check when my target will cross the meridian and check that the scope/camera is going to miss the mount, there is nothing worse than having to abandon a 20 min sub at 80% finished, if it looks like that is going to happen I slew to a star just the other side of the meridian at the same altitude as my target, re-calibrate PHD and wait for the target to cross then line up and fire away, or if its close to the meridian I will manually slew the mount to pickup the target from the "wrong" side and image from there.

[laser_jock99]

If you route the cabling properly and attach it to the right places on the mount then you should be able to perform a meridian flip safely, but I always keep a close eye on things. A long tail of cables straight from the camera(s)/mount base to the laptop, etc. is asking for disaster; it will invariably snag on something (e.g. the altitude bolts are a good bet).

Fixing cables is a good idea in a permanent set up, but not that practical on a rig that has to be dismantled daily.

[IanL]

Fixing cables is a good idea in a permanent set up, but not that practical on a rig that has to be dismantled daily.

I dismantle mine every time, and it works fine. I will dig out some pictures and show you how when I get a chance.