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Hi all.?
I¡¯m on the waiting list for a GM-8G, and a used opportunity has come my way. ?The mount was made pre-2011, had Gemini-1 and has been upgraded to Gemini-2. ?It¡¯s also been upgraded to OPWBs but they are not spring-loaded. ?Current owner does not know which motors are on the mount but says it slews as fast as any GOTO he¡¯s used. ?I¡¯ve attached a couple of pictures. ?It appears to have been well-maintained
I have three questions: ?
1. ?Can you tell which motors these are??
2. ?What material function and convenience would I give up choosing this mount over a new one? ?(I see these are not tucked-in motors and appreciate I¡¯ll need to watch for snags and bumps, and be extra careful moving the mount.)
3. ?Beyond the details of its features and what the seller knows about maintenance, what else should I be asking?
Thanks for your advice!
Jeff
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Hi
Jeff..
?
Motors
look like mine.. Hi Torque Servo..
See..
and
scroll down..
?
I
see on the above page the controller in your image is shown as a ¡°492¡±
controller.. And you said ¡°upgraded to Gemini II¡±.. No idea how the
upgrade would work ¨C someone here does ¨C but that is something to
look into.. It doesn¡¯t look like my controller..
?
I
bought my G11 / Gemini II used. I also live close to Michael
Herman (or too close depending on who you ask) and he was
nice enough to both explain the mount and it¡¯s operation, and install his
simple ¨C but very effective! ¨C upgrades.. That¡¯s a priceless
benefit for me, granted..
?
If
the price is right, I¡¯d buy it.. Those OPWs.. I do wish I had those
myself, but even without them, I get excellent tracking.. Again.. G11, but I,
for one, bought used and love it!
?
Derek
?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Jeff Rothstein
Sent: Friday, January 22, 2021
5:46 PM
To: [email protected]
Subject: [Losmandy_users_io]
Understanding a GM8 for Possible Purchase
?
Hi all.?
I¡¯m on the waiting list for a GM-8G, and a used opportunity has come my
way. ?The mount was made pre-2011, had Gemini-1 and has been upgraded to
Gemini-2. ?It¡¯s also been upgraded to OPWBs but they are not
spring-loaded. ?Current owner does not know which motors are on the mount
but says it slews as fast as any GOTO he¡¯s used. ?I¡¯ve
attached a couple of pictures. ?It appears to have been well-maintained
I have three questions: ?
1. ?Can you tell which motors these are??
2. ?What material function and convenience would I give up choosing this
mount over a new one? ?(I see these are not tucked-in motors and
appreciate I¡¯ll need to watch for snags and bumps, and be extra careful
moving the mount.)
3. ?Beyond the details of its features and what the seller knows about
maintenance, what else should I be asking?
Thanks for your advice!
Jeff
|
Hi Jeff
these look like the high torque servo motors. your seller should be able to confirm this
other than the tucked in motors, the big missing item is the spring-loaded worms, which are imo probably the most significant mount improvement in the last handful of years.? You won't have to think about east biasing your weight and it does a great job of minimizing backlash as well. Generally you won't need to reset your worm gears either.?
In this regard it's probably one-or-the-other choice - sending in a G8 for the upgrade is probably more $ than if you just bought a new mount.?
you would of course want to know the history of the mount upgrades, any issues the seller has had with it, has it been dropped or roughly handled, etc. look for unusual marks or scrapes. It does have the LW?tripod spreaders which are an additional accessory when buying new.?
HTH
Brian
Hi all.?
I¡¯m on the waiting list for a GM-8G, and a used opportunity has come my way.? The mount was made pre-2011, had Gemini-1 and has been upgraded to Gemini-2.? It¡¯s also been upgraded to OPWBs but they are not spring-loaded.? Current owner does not know which motors are on the mount but says it slews as fast as any GOTO he¡¯s used.? I¡¯ve attached a couple of pictures.? It appears to have been well-maintained
I have three questions: ?
1.? Can you tell which motors these are??
2.? What material function and convenience would I give up choosing this mount over a new one? ?(I see these are not tucked-in motors and appreciate I¡¯ll need to watch for snags and bumps, and be extra careful moving the mount.)
3.? Beyond the details of its features and what the seller knows about maintenance, what else should I be asking?
Thanks for your advice!
Jeff
-- Brian?
Brian Valente portfolio
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Hi!
The only motor that is clearly shown from side view is the RA motor, visible from your rear view photo.? That motor shows no "cooling fins" so that is an oldest version servo motor.? The latest HiTorque motor has about 6 cooling fins around the barrel, and I don't see any in that photo.? Photos of the various motor versions are at this website, so you can clearly tell the motor from counting the cooling fins:
But if the old motors work, there is nothing wrong with them.? You can increase motor torque by supplying say 17 to 18 volts to the Gemini DC power input instead of 12 volts to get proportionally higher motor torque.? If a motor does wear out, a replacement motor is about $225.? All the motors are interchangeable.? They all use the same stock gearbox from the company.? ??
Now...as you requested understanding.... here we go:
Autoguiding is essential and the Gemini-2 gives you that, but it is better if the autoguider needs as little corrections to do as possible.? So if you are looking to do deep sky imaging, then low PE is the factor of interest in any mount.? ?
It is pretty easy to tune this earlier style mount to low PE, as the RA drive has only got a few components (motor into gearbox into coupler into worm in worm bearings).? The OPW on the RA generally improves PE by holding the worm bearings in line, getting the best worm bearing behavior, and the OPW makes worm to ring gear space easier to adjust because it helps hold the worm bearings tight on the worm.??
The latest version "tucked" motor has its own OPW, and adds in two large transfer gears and another shaft to hold the inner transfer gear, and these add a few more elements to control for low PE.? ?The "spring loaded" version adds a spring and a back off bolt.??
Owners can improve these mounts by adding a Belleville spring washer to eliminate worm axial shift, and putting in higher quality RA worm bearings.? These are easy to do.? Perhaps this mount already has these elements.??
The GM8 has a 180 tooth ring gear on both RA and DEC, and a 480 second worm period.? The larger heavier G11 has 360 teeth in the ring gears and a 240 second worm period.? The smaller diameter GM8 ring gear would amplify the GM8 PE of the worm by 2X.? But the worm is only a part of the PE contributors.? The lineup of the Oldham coupler, perfection of the RA gearbox and worm bearings are important factors as well.? My own GM8 looks just like this one, and has about 1.6 arcsec RMS PE (about 4 arcsec peak to peak). I imaged with it using 5 inch or 6 inch refractor, and the GM8 was designed for up to 8 inch SCTs.?
The GM8 has 3 inch OD clutch disks, so if you are planning to image, you may want to install high friction disks, but these are inexpensive and easy to install.? The bigger G11 had 4.25 inch OD disks.??
This unit has also got a nice polar scope and latest illuminator.? That will help you get a good polar alignment.? It has a lightweight foldable tripod.? I have only heavier tripods, if you need a more beefy base there are other tripod options if you want one.??
The Gemini-2 is a good go-to controller.? This system shows some nice holders in the legs for the G-2 handset.?
I notice this particular GM8 has what looks like my DEC extension under the dovetail clamp.? That DEC extension allows the dovetail to rotate past the RA motor end, and gives the mount an ability to do a meridian flip.??
( Have I left anything out?! )
Have fun, Michael
On Fri, Jan 22, 2021, 7:59 PM Brian Valente < bvalente@...> wrote: Hi Jeff
these look like the high torque servo motors. your seller should be able to confirm this
other than the tucked in motors, the big missing item is the spring-loaded worms, which are imo probably the most significant mount improvement in the last handful of years.? You won't have to think about east biasing your weight and it does a great job of minimizing backlash as well. Generally you won't need to reset your worm gears either.?
In this regard it's probably one-or-the-other choice - sending in a G8 for the upgrade is probably more $ than if you just bought a new mount.?
you would of course want to know the history of the mount upgrades, any issues the seller has had with it, has it been dropped or roughly handled, etc. look for unusual marks or scrapes. It does have the LW?tripod spreaders which are an additional accessory when buying new.?
HTH
Brian
Hi all.?
I¡¯m on the waiting list for a GM-8G, and a used opportunity has come my way.? The mount was made pre-2011, had Gemini-1 and has been upgraded to Gemini-2.? It¡¯s also been upgraded to OPWBs but they are not spring-loaded.? Current owner does not know which motors are on the mount but says it slews as fast as any GOTO he¡¯s used.? I¡¯ve attached a couple of pictures.? It appears to have been well-maintained
I have three questions: ?
1.? Can you tell which motors these are??
2.? What material function and convenience would I give up choosing this mount over a new one? ?(I see these are not tucked-in motors and appreciate I¡¯ll need to watch for snags and bumps, and be extra careful moving the mount.)
3.? Beyond the details of its features and what the seller knows about maintenance, what else should I be asking?
Thanks for your advice!
Jeff
--
Brian?
Brian Valente portfolio
|
This is great information. ?Thanks, all. ?I will follow up with the seller on a couple of the points you raise.
Interesting question, Derek, about the hand controller. ?Since it has 4 buttons on its face it does not look like the Gemini-2 hand controller Losmandy now offers as part of the Gemini-2 Upgrade package, here:?? Michael, Brian, others¡ªdoes that reduce functionality at all, or otherwise present an issue?
I¡¯m by no means a mechanical wizard but I believe I can handle the sorts of tinkering you describe.?
Do any of you care to hazard a guess as to what it¡¯d cost to ship this from the E Coast to Arizona?
Kind regards,
Jeff
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On Fri, Jan 22, 2021 at 05:47 PM, Jeff Rothstein wrote:
Hi all.?
I¡¯m on the waiting list for a GM-8G, and a used opportunity has come my way. ?The mount was made pre-2011, had Gemini-1 and has been upgraded to Gemini-2. ?It¡¯s also been upgraded to OPWBs but they are not spring-loaded. ?Current owner does not know which motors are on the mount but says it slews as fast as any GOTO he¡¯s used. ?I¡¯ve attached a couple of pictures. ?It appears to have been well-maintained
I have three questions: ?
1. ?Can you tell which motors these are??
2. ?What material function and convenience would I give up choosing this mount over a new one? ?(I see these are not tucked-in motors and appreciate I¡¯ll need to watch for snags and bumps, and be extra careful moving the mount.)
3. ?Beyond the details of its features and what the seller knows about maintenance, what else should I be asking?
Thanks for your advice!
Jeff
Hi Jeff, As a long time Losmandy user who just recently sold a valued old friend in my classic GM8 Gemini and bought a new GM8G mount after upgrading my G11 to a G11G 3 years ago my advice is buy the new mount. It will save you a.lot of trouble chasing the problems of an old mount and trying to update during a time when Losmandy is running full bore and cannot spend the time to do basically custom work while his production falls behind. Buy the new mount, it will save you time getting to where you want to be.? ? -- Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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>>>
?Since it has 4 buttons on its face it does not look like the Gemini-2 hand controller
i'm fairly certain that is the current Gemini-2 hand controller
We don't really offer an option of a hand controller with no touchscreen that is Gemini-2 compatible.
But you can ask the seller for a picture of the other side to confirm
This is great information.? Thanks, all.? I will follow up with the seller on a couple of the points you raise.
Interesting question, Derek, about the hand controller.? Since it has 4 buttons on its face it does not look like the Gemini-2 hand controller Losmandy now offers as part of the Gemini-2 Upgrade package, here:?? Michael, Brian, others¡ªdoes that reduce functionality at all, or otherwise present an issue?
I¡¯m by no means a mechanical wizard but I believe I can handle the sorts of tinkering you describe.?
Do any of you care to hazard a guess as to what it¡¯d cost to ship this from the E Coast to Arizona?
Kind regards,
Jeff
-- Brian?
Brian Valente portfolio
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Thanks. ?Could you help me understand a bit more what sorts of trouble chasing problems I¡¯d typically encounter with an old mount? ?And even more important, do you prefer to addressed as Chip or Louie?
Best,
Jeff
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I'm in the "buy new, don't inherit do-do" camp.
I'm not saying the used mount isn't a great value, it may very well be great.
But it might also have some very frustrating quirks, or wear and tear, to work around. Things you can't possibly know ahead of the actual purchase and use.
I bought new with the faith anything I encountered would be attended to.
So far, Golden! And no troubles foreseeable.
Buying new also assures one that everything is exactly as Scott Losmandy intended it to be.
Not a Chevy with a Ford water pump installed. ;^)
Your Mileage May Vary....
--
SonnyE
(I suggest viewed in full screen)
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Hi Jeff,
My name is Chip, Louie is my surname.
The main issue is the value proposition of buying a used Losmandy mount for imaging that lacks Gemini 2 and spring loaded worms. If you don't have these two key features on the mount you will not have an easy time imaging. The older mounts can always be updated but that costs time and money. The time issue is the real problem right now as Scott has no time for doing upgrades because the Losmandy shop is running day and night to keep up due to the Covid-19 surge powered interest in our hobby. This is not going to change for maybe another year is my guess. Several years ago now my old G11 was fully updated to the latest and greatest with all the doodads but those were different times without the Covid-19 rush and it still took a few months to get me scheduled for an update slot. The other issue is that it costs money to have the updates done which is an easy calculation, add up all the features the used mount lacks and subtract that cost from the cost of a new bare mount sans tripod. If you do this you will see that unless you acquired the mount for an very low price or have owned it for several years may or may not be cost effective to upgrade. I had a mint condition G11 and I had it for a while and it was purchased at a price that allowed me to update the mount for less than buying a new one would have cost. Plus it was a valued companion so I waited and updated. My GM8 was a similar situation but I had already been waiting when Covid-19 hit so I figured out the update was just not going to ever come up for an upgrade. So I sold my trusted observing companion GM8 and bought a new GM8G to make new adventures with so now both of my mounts are current version mounts.?
Trust me, as an imager you NEED the spring loaded one pieces worm blocks. This means based on my explainatin above you basically will be buying a new Losmandy mount. If you are not an imager and have zero plans to image my advice is to buy a used Losmandy mount in the best possible condition as cheaply as possible. This means if possible no Gemini but a #492 digital drive and then spend the money for an Astro Devices Nexus DSC and use the Losmandy mount as they were designed to be used, well balanced with fairly loose clutch settings and using two fingers PUSHED-TO your destinatin using the Porter Slip Clutches with the DSC to guide you there.? ?
--
Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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Chip nice writeup
It's getting better at the shop but it's still quite a few weeks lead time right now
when are you coming back to finish your mount? :)
On Sun, Jan 24, 2021 at 2:20 PM Chip Louie < chiplouie@...> wrote: Hi Jeff,
My name is Chip, Louie is my surname.
The main issue is the value proposition of buying a used Losmandy mount for imaging that lacks Gemini 2 and spring loaded worms. If you don't have these two key features on the mount you will not have an easy time imaging. The older mounts can always be updated but that costs time and money. The time issue is the real problem right now as Scott has no time for doing upgrades because the Losmandy shop is running day and night to keep up due to the Covid-19 surge powered interest in our hobby. This is not going to change for maybe another year is my guess. Several years ago now my old G11 was fully updated to the latest and greatest with all the doodads but those were different times without the Covid-19 rush and it still took a few months to get me scheduled for an update slot. The other issue is that it costs money to have the updates done which is an easy calculation, add up all the features the used mount lacks and subtract that cost from the cost of a new bare mount sans tripod. If you do this you will see that unless you acquired the mount for an very low price or have owned it for several years may or may not be cost effective to upgrade. I had a mint condition G11 and I had it for a while and it was purchased at a price that allowed me to update the mount for less than buying a new one would have cost. Plus it was a valued companion so I waited and updated. My GM8 was a similar situation but I had already been waiting when Covid-19 hit so I figured out the update was just not going to ever come up for an upgrade. So I sold my trusted observing companion GM8 and bought a new GM8G to make new adventures with so now both of my mounts are current version mounts.?
Trust me, as an imager you NEED the spring loaded one pieces worm blocks. This means based on my explainatin above you basically will be buying a new Losmandy mount. If you are not an imager and have zero plans to image my advice is to buy a used Losmandy mount in the best possible condition as cheaply as possible. This means if possible no Gemini but a #492 digital drive and then spend the money for an Astro Devices Nexus DSC and use the Losmandy mount as they were designed to be used, well balanced with fairly loose clutch settings and using two fingers PUSHED-TO your destinatin using the Porter Slip Clutches with the DSC to guide you there.? ?
--
Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
-- Brian?
Brian Valente portfolio
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Michael Herman
Chip Louie