Re: ES G11 / ExploreStars issues

Jeremy Parker

Hi Chris,

I was planning on putting something together like this, time-permitting, but in some ways I'm still working on the solution! I'd say my RA error is manageable by the installation of the Ruland coupler, careful adjustment of the worm block, and predictive PEC in PHD2. The RA axis friction (and ability to balance) is fixed by the wavy washer, as you've also confirmed. My DEC axis backlash oscillations in guiding is somewhat managed by reducing DEC aggressiveness. But the ultimate overall solution to perhaps both RA periodic error AND DEC backlash will be the spring-loaded one-piece worm block design that I'm hoping to start work on fairly soon, if Losmandy doesn't happen to come out with it sooner. I'll post something more on that when I have a decent drawing to share.

On the software/communications side of things, the main lesson is to make sure that your RA rate is set to 53.33, and not some other number, when using the G11. I haven't mentioned this next discovery on the forums yet, but early on I did notice another issue that may or may not be related to some intermittent communications issues on the wired-serial connection to the PMC-Eight. I had my hand on the counterweight shaft and felt an AC voltage 'tingling'. It’s the first time I guess I noticed that, so I measured the PMC eight chassis ground compared to earth ground. Sure enough there was 59VAC rms on my meter. Since none of the power supplies in my setup (laptop, camera, PMC, usb-hub) are IEC class I, there is no earth ground anywhere in the system. And these universal switching AC-to-DC supplies, like the one for the PMC-Eight, have higher leakage current to neutral than the older style linear power supplies (transformer-based). So these systems can float at some relatively high AC voltages, which is what I measured for the PMC-Eight by itself (no other equipment hooked up). So then when you’re sitting outside, and you go to touch your laptop or anything else semi-conductive connected to the 'system ground', you could provide somewhat of a short to earth ground. This can cause the system ground to ‘bounce’, and I now wonder if this could explain the weird intermittent communication dropouts/errors with my system. So I added a earth ground jumper between the power strip and one of the serial cable housings, and I haven't really had any issues since then.

I do agree that a concise summary of my problems / solutions would be helpful.


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