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By Michele Scotti
i'd like to share with you the design, making and progress of a project my astro club endeavoring to. I'll post here relevant info in a run-up to where we got to so far.
Here is the mission: 800mm in diameter. That's it. A lot of inspiration out there but it needs to be able to do science. So it's a relatively fast Newtonian capable of tracking for tens of minutes.
So we realized that we were facing 2 projects in one. The mirror on one side and the mount on the other. Shall we start with the mount? What's the best compromise in terms of ease to build and cheap components and the chance to have a stiff yet light structure. An alt-az, like the biggest telescope! - or rather a glorified dobsonian in this case.
Any comment/suggestion is welcome!
As my GoTo is successfully finished (some cosmetic issues remain) I shoud focus my attention on planets' positions. I have proper source of information: fantastic book "Astronomical Algorithms" by Jean Meeus, thus I will sort the planets soon. But planets are not a challenge for me at this moment, they are just something obvious to do in my list.
I have another idea and ambitious plan for next project within the year: locating and tracking the ISS to be able to make a video of its fly, not only transition.
Similarly to other objects, I need some equations. I'm pretty sure they are available somewhere, because plenty websites or apps offer showing current position of the ISS.
I will use this topic for sharing a progress ot the project.
I'm trying to balance my AZ-EQ5 as perfectly as I can, all was going well (all 3 axes) until I added the Polemaster. As this is off-axis it applies torque to the RA causing the axis to rotate until the Polemaster is hanging at the lowest point.
I need to couterbalance this, any ideas how?
Do I need to counterbalance this? Am I being too picky?
I have considered taking the arm off and gluing the Polemaster onto the on-axis point of the top cover, but again, is this overkill?
I have some sad news, sad for me anyway, but unfortunately during the final night of imaging my last DSO, the Fighting Dragons in Ara, my CGEM blew up.
At about 4 am, I went outside to check on the imaging progress and decided to dim the laptop screen but accidentally hit the "sleep" button instead of the "DIM" button. Usually this shouldn't be a problem.... but when I "woke" the computer up, the CGEM stopped tracking. Not thinking like it's a big deal, I tried to re-center the object and guide star and this is when I realized that there is something seriously wrong as the mount was not responding to my computer or hand controller commands.
When I power cycled the mount and hit a RA button, the mount moved, it moved at full speed until the OTA and camera almost hit the peir.... the only way to stop it was to cut power to the mount.
Power cycling it a few times did not change anything except that the mount stopped responding in RA completely.... note that the DEC function works as normal.
The hand controller is working normally and not reporting any NO RESPONSE error messages either.
I went on a fault finding mission and tried a different Hand controller with no change than I opened the CGEM and swapped the RA and DEC motors on the main motor control PCB to determine whether I burned out the motor.
With the motor connectors swapped the mount moved in the RA axis and worked properly by pressing the DEC buttons but now the mount is not moving in DEC, so I knew that the motor is not burned out, but the Motor Control board is faulty, possibly the RA encoder/controller chip.
I tried to re-flash the MC Board firmware, hoping that it's possibly just a corrupted data in the EPROM, but after a successful firmware flash, that did not change the situation.
With is information, I need to get a replacement motor control board, and this might take a while to arrive from the USA... so until that moment I will have to return good old observational astronomy using my 14" Dob and imaging will have to wait for the future.
I guess I'm lucky in a way that the failure happened toward the end of imaging my last image, in that last hours, instead of in the middle of it, so at least I ended up with an image.
My theory why this has happened:
I don't think that accidentally sleeping the laptop caused the mount to fail, at least not the act itself... of course, there is a possibility that it's just long term use and eventually everything fails, since I had the mount for 9 years, and it did do a lot of tracking hours... BUT than again it did work flawlessly for all of this time until soon after I started experimenting with PEC, and I had PEC running when this happened.
Could it be that PEC in the mount was trying to move the RA axis in one way, and PHD2/GPUSB tried to move the mount in the opposite way, causing some kind of conflict, or short circuit like/excessive current drain event? perhaps not in general use with quick pulse commands, but when I did sleep the laptop, could it be that GPUSB was stuck in nudging the mount in one direction, and than PEC tried to move it in the opposite direction and that state was held for long enough to burn out the encoder or controller IC?
Either way, comparing PEC programmed mount on PHD2 guiding accuracy to no PEC accuracy, the results are so close that PEC might not even be worth the hassle, and PEC is more useful for unguided imaging?
I think that when I fix my CGEM, I might stick to NON PEC autoguiding since, like I found, PEC is no, or very little, improvement, such a small improvement that the reason can be caused by just the atmosphere becoming slightly more still within the comparison time... accuracy difference of only 0.02-0.05" arc sec RMS.
Thanks for reading and of course thoughts, opinions and experiences welcome.
By Cosmic Geoff
I have had an issue with the mount of my CPC800. I have noted that sometimes when slewing through a large angle in azimuth the note of the gear noise changes. Also once or twice the target image has taken off to the left while I was preparing to image and even motor speed 3 would not hold it on screen. Also I have once or twice left it unattended for several minutes and returned to discover that I needed to use the optical finder to recover the target. This makes me wonder if something is binding.
It still works far better than the 6/8 SE mount, so I am reluctant to send it for repair or open it up without a clear pointer to the nature of the problem and likely fix. It would be a more serious issue for long exposures/deep space imaging.