On Tue, Aug 27, 2024 at 06:07 PM, Paul Buckley wrote:
Chip, interesting comment.? I habitually readjust worm?block spacing outdoors every October and March (or thereabouts) because of the seasonal changes here in?WNY. I may have had this RA spiking issue all along but it was always masked by the "bigger holes in the sieve" problems, so to speak. As I've become more technically proficient and have better mastered the mount, other sources of error have fallen away or are controlled to the point that these RA spikes are next on my list of issues to resolve.??
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Except for a few experiments I have never stalled the mount, at least not during an observing session.? I will incrementally back off the worm blocks next time the skies are clear.? My current RMS errors are generally right around 0.5" so my goal will be to keep them in that range without those occasional spikes.
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Paul
On Tue, Aug 27, 2024 at 06:37 AM, Paul Buckley wrote:
UPDATE on my RA spike issue:? I swapped RA and DEC motors but the spikes stayed with RA, so I've ruled out the motors.? There are no more clear nights for the time being, but my next experiment will be to back off the RA worm blocks a couple hundredths of a millimeter at a time to see what that does.? I'm?pretty?confident that it will make a difference, just not sure about the resulting backlash.? My last resort will be to bite the bullet and degrease/relube the worm/ring gears and use John Kmetz' suggested in house HGM lubricant.? I'm currently using Stalube?Synthetic Brake & Caliper Grease (Moly?+ PTFE?+ graphite).
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Paul
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Wait, before you bother to strip the mount think about what the mount is doing as it gets cold acclimated.? Your classic Losmandy 2-piece worm drive system mount will never have as low backlash as the newer spring loaded OPWs. This is a fact and nothing is going to change that.? That said backlash on the classic Losmandy drivetrains is your friend in the dark especially as the night air gets colder and the winter moves in.? The thing to know is that with the classic drivetrain Losmandy GM8 and G11 mounts backlash shrinks as the air temp drops. If your mount has minimal backlash in a warm room it will stall once it shrinks in cold air. Ideally you should set your backlash up on a fully cold acclimated mount. Once it warms up it will seem to have a ton of backlash but that's okay because you don't use it to capture images when it is warm. There is no grease made that can overcome the sliding friction of a worm with no backlash with the low level of torque the Gemini drive systems produces. You MUST have some backlash or stall the drivetrain.?
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
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With an average PE in the 0.5" RMS range and lower the spikes are not likely from worm to worm gear backlash. Have you checked your worm axial end play? This one is easily resolved in the old 2-piece worm blocks by adding Bellvue disc springs which minimize worm shaft end play and also prevents the bearing balls from.causimg the start / stop bumps in tracking error. Michel Herman and I worked on this and he wrote a nice note about the problem, it's here someplace. Just Google Michael Herman and how to improve Losmandy mount or something like.it.?
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This issue could also be contamination in the drivetrain or axel bearings, it could be anywhere. Servo pinion, hearboxes, loose or missing set screws to Oldham couplers (there should be 2 per coupler), Oldham parts, worm or worm gear faces etc.?
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It sounds wacky but have you lubed your Oldham couplers to see if this has any impact??
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Being desperate early in my Losmandy ownership more than a few moons ago discovered that using heavy grease on the Oldham couplers can sometimes have a positive effect on PE smoothness. I don't know if they were just dirty, worn out, had some kind of a hitch or damage in the plastic sliding piece or just made them move easier smoother or what but it helped my PE curve. I have only done it twice and only saw an improvement on one mount.
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I replaced the Oldhams on that GM8 mount and it was not an issue anymore but then I sold it. I still put a tiny toothpick daub of Superlube with Teflon on the Oldhams after cleaning them when I reassemble Losmandy mounts. Just sort of a religious thing as I can't proove one way or another if it really works or not LOL.?
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Chip Louie Chief Daydreamer Imagination Hardware?
Astrospheric Forecast - South Pasadena, CA?
Chip Louie