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Can I force a pier flip after slewing to a target?


Jeremy Parker
 

Hi All,


I'm wondering if any of you using CDC/POTH with the PMC-Eight ASCOM driver know of an easy way to force a pier flip after you've slewed to a target. The reason I would want to do this is if I was going to track/guide on an object that was just shy of passing the meridian, but would be imaged well past the meridian.


This happened the other night when I had initially tracked on M81/M82 before it passed over the meridian, and CDC slewed to it, putting the scope on the west side of the pier - as it should have. I had PHD2 guiding and an imaging session under way, and the CDC/POTH were not issued any subsequent slew commands, so the mount just tracked in RA. It tracked with the scope on the west side of the pier, past the meridian without a flip, and it would have crashed the camera into the tripod if I hadn't been paying attention.


What would have been great, is if I could have slewed to M81/M82, then issued a pier flip command. The scope would have been forced to the east side of the pier, with the counterweight bar slightly past horizontal, but it would have continued to track without needing intervention. The 'Flip' button in POTH doesn't seem to do anything, but are there some settings in the ASCOM setup or PMC-Eight driver that need to change from default? Or if this can't be done, wouldn't it be a useful feature?


Thanks,

Jeremy


Sunil Bhaskar Bhaskaran
 

I use sgp to force a meridian flip. I set the time up so that I can see when the target crosses meridian in cdc. I use a 12 inch Pier so I can track atleast a good hour or two past the meridian. Else I usually set up 15 min before or after the flip. Thr mount has gone upto 30minutes past meridian with no isssues.

Sunil

On Wed, Apr 11, 2018, 11:17 PM jrs1@... [ESPMC-Eight] <ESPMC-Eight@...> wrote:
 

Hi All,


I'm wondering if any of you using CDC/POTH with the PMC-Eight ASCOM driver know of an easy way to force a pier flip after you've slewed to a target. The reason I would want to do this is if I was going to track/guide on an object that was just shy of passing the meridian, but would be imaged well past the meridian.


This happened the other night when I had initially tracked on M81/M82 before it passed over the meridian, and CDC slewed to it, putting the scope on the west side of the pier - as it should have. I had PHD2 guiding and an imaging session under way, and the CDC/POTH were not issued any subsequent slew commands, so the mount just tracked in RA. It tracked with the scope on the west side of the pier, past the meridian without a flip, and it would have crashed the camera into the tripod if I hadn't been paying attention.


What would have been great, is if I could have slewed to M81/M82, then issued a pier flip command. The scope would have been forced to the east side of the pier, with the counterweight bar slightly past horizontal, but it would have continued to track without needing intervention. The 'Flip' button in POTH doesn't seem to do anything, but are there some settings in the ASCOM setup or PMC-Eight driver that need to change from default? Or if this can't be done, wouldn't it be a useful feature?


Thanks,

Jeremy


hubbell_jerry@...
 

This is try number two to respond to Jeremy. This is getting to be a PITA with the group.

Hi Jeremy,

The driver is designed for the user to be able to track past the meridian if he chooses and then it is a simple matter to just slew to the object again to force a pier flip. This is the design behavior of the driver and is typically the way that it is implemented in mount control systems. 

What you desire is a preemptive slew to object before it crosses the meridian so that you can start an imaging sequence without having to stop in the middle for the pier flip. I can think of really only one need for this. I understand the thinking is that if it is getting late, and the object location is still an hour or so before the meridian then you can start a sequence that would track for a few hours and you can get to bed earlier and let it do it's thing without worrying about getting up to do the pier flip.

This might be a compelling enough reason, but would take a bit of work to make sure it didn't screw anything else up in slewing to the next object, if you were to do that after it passed the meridian. I think I would implement it as a one-time action and any subsequent slew would be to the correct quadrant/side-of-pier.

Currently, the mount allows you to start a sequence of images when the object is in the east and then track continuously past the meridian until the sequence is completed as long as it is not too far past the meridian. You may be able to go up to an hour past the meridian, I have done this myself when imaging.  The specific time that you can track past the meridian is  very dependent on your mount and pier/tripod configuration of course. This is the same if you were to try and perform a preemptive pier flip in that you would only be able to point to an object only so far before the meridian, perhaps again, an hour or so.

I will do some initial investigating and see how I might implement this change and make it available. I am a bit cautious about this because it raises the possibility of causing some unintended behavior thus the need to make it a one-time action. 

Thanks for the suggestion.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.



---In ESPMC-Eight@..., <jrs1@...> wrote :

Hi All,


I'm wondering if any of you using CDC/POTH with the PMC-Eight ASCOM driver know of an easy way to force a pier flip after you've slewed to a target. The reason I would want to do this is if I was going to track/guide on an object that was just shy of passing the meridian, but would be imaged well past the meridian.


This happened the other night when I had initially tracked on M81/M82 before it passed over the meridian, and CDC slewed to it, putting the scope on the west side of the pier - as it should have. I had PHD2 guiding and an imaging session under way, and the CDC/POTH were not issued any subsequent slew commands, so the mount just tracked in RA. It tracked with the scope on the west side of the pier, past the meridian without a flip, and it would have crashed the camera into the tripod if I hadn't been paying attention.


What would have been great, is if I could have slewed to M81/M82, then issued a pier flip command. The scope would have been forced to the east side of the pier, with the counterweight bar slightly past horizontal, but it would have continued to track without needing intervention. The 'Flip' button in POTH doesn't seem to do anything, but are there some settings in the ASCOM setup or PMC-Eight driver that need to change from default? Or if this can't be done, wouldn't it be a useful feature?


Thanks,

Jeremy


Jeremy Parker
 

Hi Sunil, Jerry,

Thanks for the responses. I don't have SGP yet, but maybe down the line I'll get into that when I upgrade my camera. In the meantime, I suppose that I could slew to an object on the west side of the meridian from my intended object, but at about the same DEC. Then I could use the POTH RA control to manually slew the scope back across the meridian and use CDC as a visual guide for aligning my object.

So yes, I think this would be really valuable if you know the meridian flip is coming soon. In some cases, depending on DEC, I think could image for a while pre-meridian cross, not just an hour.

Jerry, I totally understand the concern about forcing such an operation. But if you were there and could watch the mount, you could abort the slew if needed. If it would avoid the crash that would otherwise occur later on had the mount just continued to slew past the meridian, maybe it would be worth the risk. If this feature was added, maybe it would just put up a 'Are You Sure?' warning dialog box to confirm that you were at the mount and could abort the flip operation if needed.

This has me thinking about another possibly simple feature to add, for safety. If using CDC and knowing our mount/scope physical limitations, you could predict when the scope would crash the mount, could there be a 'stop tracking after xx hours' field? This way the scope would simply just stop moving after a certain time, so if you went to bed and had an imaging session going, you would be sure that nothing bad would happen. Just a timer to stop all mount movements.

I have another idea which would be a lot more work, but maybe another valuable feature?...If everybody has a different scope and mount configuration, with different physical limitations on the movement before crashes/interference, could there be some routine for the PMC-Eight driver to 'learn the prohibited scope positions'? So in terms of altitude and azimuth on each side of the pier, maybe there could be some kind of learning routine that asks the user to manually move the scope around to determine the safe area of operation. Then any slew commands from CDC/POTH would have to meet this criteria or otherwise be rejected, and RA tracking would automatically stop if the ALT/AZ position on the particular side of the pier crossed the safe area.

Thanks for your thoughts and feedback.

Regards,
Jeremy


Mike Leemhuis
 

My preference would be to have several options concerning a meridian flip.  ie:

1) Perform flip only when manually requested
2) Stop tracking when crossing meridian
3) Perform flip when crossing meridian and continue tracking
4) Stop tracking at x minutes to meridian flip

This would let you sleep through the night and not worry about a pier crash etc.

Just my 2 cents.

Mike


hubbell_jerry@...
 

Hi Mike,

These options are typically provided in the ASCOM Client program, not in the driver. Jeremy's suggested behaviour would be a one time selection in the driver dialog box, which typically is not an active open windows interface. The driver dialog is really only for configuring the driver. ASCOM Client programs typically provide the functions that are needed to operate the mount. Maxim DL is an example of a client that performs the functions you describe above. I would not be inclined to implement these functions at the driver level.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.