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Re: G11 survival kit
Very good question! (Oh oh... Another lightning rod question... off the deep end I go.? Apologies again!? My first blunder of 2020!) ... survival...and maintenance... Firstly: The G11 mounts have been tested by Periodic Error ("PE") tests to get to as low as about 0.9 arcsec RMS.? Those used the new version "high precision brass" worm (these vary individually) and also had some slight mount mods (added a Belleville spring washer under the far end worm bearing).? Stock G11 mounts vary.? The stock Titan used to be stated to have PE below 2 arcsec, and that has twice the ring gear size of the G11.? That would translate to about 4 arcsec on a G11 (G11 has no stated PE spec).? So the basic mount design is capable of fabulous performance.? I think all G11 units should get under 2 arcsec RMS if properly tuned up. I'll talk about the issues below.? ? _____ Your question about "survival" then has to do with how to make adjustments, how to recognize what adjustments to make, and other maintenance issues that might some day arise.? Here is a list of common issues this group has encountered, though frankly many folks have never had any issues at all.? Your sensitivity to issues really depends on what optical equipment you are using... could be a light short refractor or long 65lb Newtonian... or a long FL SCT.? So here goes....? ______ Tools: To adjust the drive gears, required from time to time, you should have these tools: 1. US fractional sized hex key ("Allen") wrenches.? Get two types: ? ? ?a.? straight end (use these if you have straight-on access) ? ? ?b. ball end (these allow you to get to bolts where you have no straight-on access).? That occurs for the critical large bolts below the worm blocks mounting flange (on the GM8, those bolts are accessible at an angle, on the G11, it's tight from straight on) 2. Good lubricants for the needle bearings.?? ? ?a. WD-40 ? ?b. A lubricant recommend by many is the Superlube type with teflon.? ? ________ Maintenance: _______ Gemini units: The Gemini units have an internal "coin" battery, nominally 3 volts.? Keep a spare of the required size battery for replacement, about once per year or 2 years.?? Preventing Gemini damage: To prevent internal corrosion, protect the unit from weather (i.e. rain!) and to protect it from electrical shock (like lightning), just unplug it's power and comm lines when you are done using it.? I find it's ok to keep the motor cables plugged in if the system is enclosed or totally covered up. *** Label your motor cables and motor and Gemini connections ***? The connectors on the motor cables are round ("DIN") and have 6 pins and a "detent" metal notch.? But the pins are rather equally distributed around in a circle.? And the notch is not very deep. It has been know to happen that an owner forced a motor cable into the socket when it was mis-rotated.? ?If you were to mistakenly rotate the motor connection you will damage either the Gemini or the motor...costly repairs or costly replacement.? Easiest to use a label-maker and keep the connections very clear.? Also the DEC cable is longer than the RA cable, because the cable must travel around with the mount head.?? _______ Mount head parts: Pertains to?non-tucked motor type drives:??older G11 and all GM8 type designs (DEC axis of GM811): Of course, don't drop the mount head(!) and when transporting, be sure to protect the motor end that is only attached to the gearbox, if your G(11 or M811 or M8) if it is exposed. The newer tucked motor design protects the motor and gearbox by metal flanges. The plastic gearbox cases have been known to break.? The gearboxes do not break under normal operation.? You can force grease into the internal plastic gears from the motor shaft side, but these gearboxes do not come apart.? ?Of course, over decades, the plastic becomes brittle and can break down.?? Therefore, some folks recommend having a spare gearbox! (About $35?from Losmandy). That's inexpensive insurance. (On the strsight-out motor version, people have replaced the plastic gearbox with a metal precision one.? McLennan has a model that can be made to fit ...needs some handiwork to fit one in.? I've done this on one GM811, and plan to do that on a G11 and CG11, but those are still working great with the plastic gearboxes.) _____ AZ hold down bolts You will be using the AZ and Elevation adjusters to polar align your RA axis.? (Strongly advised to drift align... and the PHD2 software has a nice feature for this.) There are two side hold down, T handle top AZ bolts that clamp the mount vertical rotation axis.?? I find the mount gets too slack when I loosen my 2 bolts.? So I add in Belleville spring washers to adjustably take up the slack.? Adding these also needs slightly longer bolts.? Contact me off line if you want these parts.? I have caps in Red, Yellow, Black.? I find the colored ones help me in near darkness.? See attached photo of this mod.? _______ All G11, and GM8 and GM811 (and Titan) Clutch disks issues and options: The clutch disks are plastic donut shaped pads, and they gently couple the driven bottom plate (driven by the worm gear) to the upper plate (holding the scope if DEC or holding the DEC axis if RA).? These plastic stock pads were designed to slip, so that an observer could easily push the scope to see something desired, and then gently grab to be again driven by the RA worm clock drive.? But in our age of 8 deep sky imaging, or the real world of bumps, a slippery clutch is a troublesome hazard.? So...let's talk about the clutches... The clutch pads can wear out...but should not.? They fail (slipping, won't hold position) because oils eventually creep on to the flat surfaces from the lubricated bearings.? Once oils creep into that area of the flat clutch pad, capillary action pulls the oils across the whole surface.? They are cleanable.? You can rather easily (no scope or counter weights!) undo and bag the rear clutch knob and it's flat needle bearings, and flat race washers, and lift off the axis shaft. Then de-grease the clutch metal faces, and clean the plastic clutch pad. The clutch pad and mating surfaces might come clean with just isopropyl alcohol.? The clutch disk can be replaced by a new plastic one, but the problem will eventually recurr.? I make up a special clutch disk that resists water and oils, and has a higher friction than the slippery stock clutch disks.? If you are planning to image, these replacement pads will help protect against bumps and also reduce the rear knob force needed to lock the axes in position.?? _______ Degreasing and re-lubing the bearings: When replacing the clutch disks, this is a great time to re-lube all the internal needle bearings.? The needles are very thin hardened steel rods, and they are supposed to be oiled or greased to work properly. The needles should be free to revolve. When you pull out the 1.25 inch axis shaft, you can reach in to touch the top needle bearing rollers. See if they are moving easily or are gummed up.?? ?If (when) old lubricant loses its fluid light oil part, it can congeal into a gummy tar, and the axis will not rotate freely.? There is a very strong toxic auto parts cleaner called Berryman B-12 that will totally de-grease the internal bearings...just stuff a rag into the bottom of the shaft opening, and spray in this de-greaser solvent.? Of course, use protective?gear (air mask and rubber gloves, etc) and do this outside.? Once cleaned out if old grease, you must re-lube those internal cylindrical needle bearings.?? If you don't want to de-grease, try WD-40 to free up the needle bearings.? Then add in a Superlube or perhaps a lithium based grease.?? (Superlube makes several formulations. There is a general purpose PTFE gease that says "< 2%" separation and there is a dielectric grease that has 0% separation (also acts as a vacuum grease).? Both are good from -45F to very high temperature.? I'm not sure which is best for lubing the G11 needle bearings...) ______ The Oldham coupler. There is a special mechanical coupler called an Oldham coupler.?? On the strsight-out drive, that critically links the gearbox drive output to the worm gear drive shaft.? On the Tucked Motor version, the coupler attaches the inner transfer gear shaft to the worm drive shaft.?? The metal ends are held on their metal shafts with tiny setscrews, and these can work loose over time and temperature.? When one end gets loose, the drive will either have a time lag, or spin without driving anything.?? Each metal end has an attached polished metal rod. The rods insert into perpendicular grooves on the two sides of a molded plastic center part.? It is a rare but known problem that the 2 tiny allen-head setscrews in the metal Oldham ends can work loose. Then the Oldham coupler might either fully spin, or partly spin.? When that happens, you will have a large time lag (hysteresis) when you reverse axis direction (or the motor spins and the axis does not move!).? Always check both of the Oldham coupler ends grip first when you have time-Iags in your RA or DEC drive.?? The metal rods on each metal end of the Oldham coupler can slide in it's plastic center part groove.? The rods can also pivot. This ingenious coupler design allows a drive shaft (the gearbox) to be offset and at an angle to the worm driven shaft...it will still drive 360 degrees at the same rotation time!? But...just rotating at perfect 4 minute 360 degree intervals is not good enough for precise Astro imaging!? The rotation has to have the same drive speed throughout the 360 degree rotation.? So beware: you don't want the coupler ends to either pivot, or to slide!? If those mechanical movements occur, the worm will have either a slight glitch? or periodic error !? You will see these on?your Astro image!? And in a frequency ("FFT") evaluation, the error from the Oldham coupler will look like it's at the worm period (looks like a bad worm) or at 2x the worm speed (half the period)...looks like a worm with a secondary harmonic.? It's all possibly from a misaligned Oldham coupler.? People have tried other coupler designs (Ruland) but none work as well as a properly aligned Oldham coupler.?? So it is important to look at the Oldham coupler behavior as you fast-slew the motor.? Note: On the older straight-out motor design, you can easily see and adjust the Oldham coupler.? On the newer tucked motor design, the Oldham coupler is totally hidden under the worm drive, so it's impossible to get to.? You'd have to consult Losmandy on how to adjust or fix that case. Probably you'd have to remove the worm drive entirely to get to the coupler hidden inside. That's like the strsight-out OPW design where the Oldham coupler is inside the drive housing.? If you can observe the coupler in action, you will see if the Oldham coupler parts are totally lined up or not.? It is my view that you must try and adjust out as much (ideally all) of the Oldham coupler movement other than pure rotation.?? How can you do that?? The worm is fixed because it is forced fairly tight against the ring gear that is driving the axis.? So the only way (on a straight out drive) you can adjust the Oldham coupler is at the gearbox, where it is mounted.? If that gearbox does not have enough manouver room, you have to enlarge or slot? it's mounting holes to get the optimal position.? (On the tucked motor version you would adjust the inner transfer gear position, though I did not see how to do that on the unit I examined.? It is probably lined up by design at the factory. ) _________ Adjusting the worm gear spacing: The only critical gear spacing was originally thought to be the worm to ring gear spacing.? On newer drives (Spring Loaded Worm), this is automatically done by a spring mechanism.? On the older straight-out drives, you had to adjust this spacing by hand.? The adjustment provided was to loosen the two bottom worm block bolt fasteners, then nudge the worm into the ring gear, then tighten down the worm blocks again.?? _____ Improving worm and bearing performance... Even with the worm gear tight to the ring gear, sometimes there still remained a wiggle in the drive....? many people worked to trace this down.? Finally, it was recognized that the wiggle was coming from a problem that can occur: worm side to side movement.? That is, the worm is only confined by the two blocks on either side, holding the worm bearings (R4ZZ type).? If the blocks are not pressed together at assembly, or loosen up over time and temperature, the worm can move laterally in the gap.? That gap shows up as a time lag in reversing direction, thus can affect autoguiding.?? Moreover, the bearings performance is improved when the bearing is under axial compression.? There is no provision for consistent compression in the stock design.? Earlier mounts like the Meade LXD-55 used a heavy brass bolt to drive the worm axis...but that had no bearing.? So I recommend on older straight out drives to install a R4 size Belleville spring washer.? I have a PDF describing how to do that, but it is not a stock feature.?? I think that ends my list of maintenance and improvements and tools and issues to look for.? ?I'll attach some photos and notes of the newer Tucked Motor and Spring Loaded Worm systems below.?? Have fun with your new mount... ! Michael Photos: Older CG11 worm showing how it drives the large ring gear.? The Oldham coupler is visible at the far end of the worm, with the gearbox.? The AZ hold down bolts go totally slack when you loosen the T handle to do polar (drift) alignment. I find better performance by adding Belleville spring washers under the T handle.? I make the bolts longer and with color caps to be easier to find in near darkness.?? The clutch pad goes at the far end if the 1.25 inch drive shaft.? This photo shows a replacement clutch pad in place. The original pads are milk white.?? This is the Spring Loaded Worm spring mechanism.? The big radial spring pushes the worm down into the ring gear. For this to work properly, the worm must be able to pivot on the left side mounting bolt (not shown in this picture), and the right side hold down bolt must allow the pivoting.? If the bolt pressing the radial spring down is driving too tight, the worm can get stuck (too much friction), so the spring bolt must be loosened up.? The smaller bolt on the left of the spring, when driven in, lifts the worm away from the ring gear.?? This photo shows the two transfer gears of the Tucked Motor drive.? These should have no gap. You adjust the space between these gears by adjusting the gearbox position.? The gearbox is attached to the back of the bottom transfer gear, in this photo.?? On Wed, Jan 1, 2020, 12:29 AM Deric Caselli <JethroStCyr@...> wrote: What spare parts do I need to stock up on to keep the G11 going?? |
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Re: Almost a new owner....
Hi Sonny,
Hey welcome, almost! Anyway if you are already happy using the tools you already have there is no reason to change really. The Gemini will need to be started using the touchpad hand controller and once the Gemini is running you can go inside and get comfy. To do this most people are using ASCOM to allow running all of the good software under Windows on a PC such as you have.So here is a short list of links to the basic programs you need to download and install to get your Gemini 2 talking to the computer, find objects in the planetarium Stellarium, autoguide for your existing other apps used to capture and store the data. Post capture processing is up to you, whatever you are using will still work fine. ? Whatever camera control and capture program currently used as long as it is ASCOM compatible. This will get you started.? There is also a fantastic resource for Losmandy users, go and read it over and over: .? ? Enjoy and ask questions! -- Chip Louie - Chief Daydreamer Imagination Hardware |
Michael Herman
Chip Louie