Catching Light

Photography by

Dan Lessmann

Oklahoma City Clear Sky Clock

Cheddar Ranch Observatory Clear Sky Clock

Review of the Losmandy GM-8 German Equatorial Mount

I recently acquired a new GM-8 mount with the Gemini control system and have had the opportunity to work with it a bit.  What follows are my impressions of this mount as compared to other GEM mounts I own.  I should state a couple of points at the outset.

This review is nothing more than my opinions and perceptions based on my experiences with this one mount and compared to my experiences with other mounts I own. 

There are many other Losmandy mount owners that disagree with many of my perceptions and opinions and it appears that there is a rather wide variance of quality and performance with these mounts.  It is very possible and I think likely that my mount is perhaps a bit of a lemon.

Most importantly, this mount can work and good results can be had.  That said, and I think there would be general agreement on this, it is not a "plug-and-play" solution to accurate tracking and guiding.

My Goals

I should first describe what I was trying to accomplish with the GM-8 as my requirements are quite stringent and naturally influence my impressions. 

Portable and Quality Imaging Platform

I was looking for an easily portable, lightweight but quality mount for purposes of shorter focal length and hopefully unguided imaging.  The optics I intended to use on the long end are an Orion 80ED at 600mm.  On the short end this would typically be a 200mm prime or any number of other lenses all shorter than the 80ED.  Cameras would include any of my DSLRs or the SBIG ST-402ME; the latter to be used either for imaging or for guiding.

Overkill Load Capacities

I wanted a mount that would allow for future and heavier loads than my initial equipment usage demands.  I also intended to use a side-by-side dual mount dovetail saddle to be able to either image at two different focal lengths simultaneously or to guide on one saddle while imaging on the other.  This increases the load on the mount over and above the weight of a single optical train of course.

As an astrophotographer, I consider loads approaching 75% of design capacity to be about the max I would want to put on any mount.

Accurate Tracking

Since my goal was to generally image with this mount unguided, I needed a high quality and accurate mount with low periodic error (PE) and good periodic error correction (PEC).

Guiding Capable

I didn't truly expect to be able to image through the 80ED at 600mm focal length without guiding the mount as that's asking for quite a bit from a smaller, lighter mount in a portable environment.  So I needed a mount that was guiding capable using the SBIG ST-402ME.

Cost vs. Quality

Cost (within reason) was not a critical consideration as I'm willing to pay for quality.  But I do expect a reasonable bang for the buck and if I pay a premium cost I expect premium quality and design.

Diddle Free

While I'm mechanically inclined and certainly capable of tweaking equipment as needed this was not my goal.  Imaging is.  I was looking for equipment that, with perhaps an initial tune up, periodic maintenance and proper care, would just work.  Quality imaging time is a rare commodity and the last thing I wanted was some persnickety piece of equipment that required constant maintenance cutting into that commodity most especially while in the field.

ASCOM Compliant

Or more accurately, compatible with the software I already own.  One of the more costly aspects of this hobby is the software required to operate equipment and cameras.  I did not want to have to purchase a new suite of software to operate the mount.

Quality Customer Support and Documentation

This was a lesser concern but not by too much.  I expect timely replies to email and extensive information either in printed form or on line for a product as complex as a computerized mount.  Optimally, I expect to find the solution to my problem without the need to contact customer support at all but if I must, I expect very timely responses to my queries on preferably the same day or at least next day allowing for business hours of course.

Mounts I Considered

Generally in order of preference, I considered the following mounts:

Astro-Physics Mach I GTO

This was and is my first choice by far.  I have owned an AP-1200 for some years now and I have not one complaint.  If I were to complain, about the only negative with this mount is that it's not terribly portable.  This is not a design flaw of course but is instead a necessity for carrying the load capacities it can carry.  The Mach I on the other hand is a smaller, lighter mount with all of the advantages of the superb workmanship and design Astro-Physics puts into their products.  It also has the advantage of familiarity for me as it uses the same GTO control system as the 1200.

The only problem with the Mach I is its availability.  There is a waiting list for these mounts that is certainly months and probably years long.  I am on that waiting list and look forward to my name floating up to the top of the list.  Had this occurred earlier, no other mount would have been considered.

If it's not obvious already, yes, I am a loyal and enthusiastic fan of Astro-Physics mounts and quite frankly my AP-1200 has turned me into a spoiled brat when it comes to GEMs.  Please take that into consideration as you read the rest of my impressions.

Losmandy GM-8

With the latest release of the Gemini control system this mount became a possible.  Prior to that release, my understanding is that PEC data was not retained from session to session.  As I had no intention of reprogramming the PEC data for each session and intended to image unguided, this was a critical factor that kept me away from Losmandy until now.  Other than this one issue, I was of the opinion that Losmandy's reputation in the field for quality and accuracy would meet my other requirements.

Losmandy GM-11

This mount was also a consideration with the release of the new Gemini version.  However, this mount was large and heavy enough that it was pushing my goal for a lightweight and ultra portable mount.  It did however have the advantage of substantially heavier load capacities than the GM-8.  I considered this a plus but not enough of a plus to forego portability as I'm perfectly equipped on the higher capacity end with the AP-1200.

Celestron CGE

I don't know much about this mount other than that it's comparable in size and weight to the GM-11.  And when I say I don't know much about this mount it's because there's not much advanced information for this mount on the Celestron website.  This was a rather critical vote against this mount in my opinion.  The CGE is touted as an imaging capable mount and if so, it should have a high degree of technical information available for imagers who are of necessity advanced users with advanced needs.

Comparative Mounts

I own two other German equatorial mounts; a Meade LXD-55 and as mentioned previously, an Astro-Physics AP-1200.  The LXD, in my opinion is a low end GEM while the AP is high end.  I expected the GM-8 to fall between these two mounts in quality and performance tending toward the AP-1200 as a higher end mount.  As these are to be used as a comparison to the GM-8, you should know some of my impressions of these mounts.

Meade LXD-55 w/ Autostar 497 Controller

Sorry Meade but as an imaging platform this mount is not acceptable.  It is not capable of adequately tracking at 600mm with the 80ED and really is pressed at focal lengths as short as 135mm.  That said and to be fair, this mount or the new model, the LXD-75 is not really intended for high accuracy imaging and as far as I know the only significant difference between the 55 and the 75 is the color of the paint and a newer model of controller.

This design intent is the key.  It's not an imaging platform and by design is not intended to be despite the advertising that comes out of Meade's marketing department.  This mount is fine for a visual only platform for light loads of say no more than a 4" refractor or maybe a 6" Newt or so though it's speced for quite a bit higher capacities than this equipment would demand.  It's a grab-and-go mount with a relatively easy to use and setup control system (I've always liked the Autostar controllers).  It is perfectly adequate for visual astronomy while providing moderate GOTO accuracy.  Just don't hang a camera on it as it is not and never will be a mount that can be termed "high precision".

Astro-Physics AP-1200 GTO-CP3

Oh man what a MOUNT!  As I said above, I have not one complaint and have never had a problem with this mount.  Nor have I ever needed to tweak it, tune it, or even pull a cover off a worm other than for routine maintenance.  IT JUST WORKS!  The GTO-CP3 control system is a dream to use and integration with all my software is flawless.  Its load capacities well exceed my current equipment loads and I've got longer term plans to put a 14" or maybe a 16" OTA on the critter and permanently mount it in an observatory.

Tracking is VERY accurate with about 1.5 arcsecond PE peak-to-peak when corrected by PEM (periodic error management).  I've not tried to further fine tune the PEM as I've never found the need.  The current PE curve allows unguided exposures of something approaching 3 minutes with a 2,500mm SCT and pretty much all night long with the 80ED.  That said, I do guide this mount to accommodate polar alignment error if nothing else and the guiding works like a dream using the ST-402ME generally through the piggybacked 80ED.

Using this mount is always a pleasure!

The GM-8

So what about the GM-8?  How does it stack up and what are my impressions of this mount and Losmandy overall?  As I said, this is a brand new mount (as opposed to used) and it's also still new to me having been around for about a week now and outside in the dark only once.  Nevertheless, I've been able to form some opinions and I'll also revise this review as my experience with the mount proceeds.  So let's start at the beginning.

Out of the Box

The GM-8 is a complete system including a tripod, counterweight shaft and 7lb counterweight and everything needed for the Gemini system, assuming the Gemini version is purchased, up to but not including the power supply of course.  This completeness is a point in Losmandy's favor as something like the AP Mach I is for the mount head only.  You must then purchase separately a tripod or pier plus mounting plate and these items are expensive.  You must also purchase separately a dovetail saddle, matching dovetail, counterweight shaft and counterweights again for quite a bit of dough.  In other words, the list price of the Mach I at $5,950 is only the beginning.  There will be at least $2,000 more or so in necessary accessories.

By comparison, the GM-8 is at least close to ready to go to work out of the box for $2,495.  That said, I did add on a few extras in the initial purchase, to wit, the tripod mounting knobs, the motor covers and a serial cable for computer control.  The knobs are fine and better than having to mess with an Allen wrench in the dark during setup and teardown but...

Surprise!  The motor covers won't work with the Gemini motors.  Apparently there is not a version of the motor covers that does and that's a shame because the motors definitely hang out there a bit and could use some protection.

Where's the Manual?!

Apparently there isn't one or at least not a printed one.  In fact, there was not a single piece of paper included in any of the packaging with the GM-8.  Okay fine, I'll get the manual off the web and that's okay. 

Where's the ADVANCED Manual?!

The web version of the manual for the GM-8 has all of the information needed to assemble and setup the mount and rather extensive information on aligning the mount to the celestial pole.  This latter information would be helpful to a beginner no doubt but I skimmed past that looking for what is missing.  That is a comprehensive set of instructions on how to tune, lubricate and maintain this mount.  As far as I can tell this simply does not exist and it turns out that it very much needs to exist as my later experiences taught me.

In contrast, the Gemini controller manual is quite good and extensive providing detailed information on all aspects of the control system. 

First Assembly

Let's take things a component at a time if you please.

The Tripod

This is a well built, yet lightweight and compact tripod that is very stable even when fully extended.  For my particular setup I don't need the full extension and the tripod is even more stable at the height I do use.  The only thing missing might be some sort of feet on the tripod legs or anti-vibration pads as standard equipment.  This is not because vibration is a problem but because the legs of the tripod are open square tubing on the ground end with some sharp edges.  They will I think have a tendency to sink into soft ground.  This is easily remedied of course.  My high-tech solution is three circles of half inch thick plywood under the legs.

Mounting the Mount to the Tripod

Mounting the mount to the tripod is simple and straightforward.  The mount simply slips into the top of the tripod and is secured with, in my case, the tripod knobs but in your case perhaps with Allen head bolts.  No problems here.  The only issue I have is that I believe the tripod knobs should also be standard.  A mount, any mount in my opinion, should not require the use of tools in the field and in the dark for typical assembly and setup.  This is the case with both my LXD-55 and AP-1200.  This too is minor in my opinion.

Leveling the Tripod and Mount

How nice!  Two bubble levels are built into the mount's base for leveling and are set well into the base for protection against any sort of impact.  They are both easily visible in the dark under red light.  This makes the leveling job a snap.

Installing the Gemini Control System

This involves installing the RA and DEC motors and hanging the control box on the tripod.  This is straightforward although, if you have the Gemini motor style and bought the motor covers this is where you find they don't fit.

At first I felt the cables running from the control box to the motors might present a snagging issue (most especially for the DEC axis) but this appears not to be the case.  I would say though that I prefer RJ type connectors for motors or some other type of cable connector that has a positive lock just to insure that the cables are secured well.  The same can also be said for the power cable.  I also prefer that the connectors for all connections be different if there's a chance of any sort of short damaging the equipment if it's plugged into the wrong port.  However, the connectors are well labeled and visible on the control box. 

The control box itself seems overly large but the way it's mounted to the tripod makes it unobtrusive so this too is minor.

Polar Alignment

There's no compass on the mount or tripod but one is not needed with the more than ample +/- 8.5 degree range of the azimuth adjuster.  I also very much like the single knob design of the azimuth adjuster and the wing-nut design of the azimuth lockdown bolts.

Altitude is also easily adjusted with the nice large altitude knob although wing-nuts would be nice for the altitude lockdown bolts.  These are instead Allen head bolts.  This too is relatively minor and replacement bolts are available from third party vendors.

I also use the polar alignment scope and can highly recommend it.  The only thing I find objectionable is that the LED illuminator is much too bright.  It needs either a much dimmer LED or better a pot to control the brightness.  I've used this polar scope before with the AP-1200 (which allows you to dim the illuminator through the GTO controller) and can easily achieve an alignment with it alone adequate for most imaging that I do as long as I guide out any residual alignment error.

After locking down the altitude and azimuth axes, the mount is nice and rigid with no apparent flex in either axis.

The Dovetail Saddle Plate

WARNING!  Make sure the first thing you look up in the Gemini manual is how to stop a slew that is underway.  To my surprise and disappointment I found that the clamp knob for the standard D-type saddle can collide with the RA motor.  For me this doesn't matter as I needed a V-type saddle for my equipment.  The narrower saddle clears the motor but this was a warning of things to come and my first indication that the motor mounting method leaves little to be desired.

That said, both saddles are nicely machined and very rigid.  Losmandy has long been known as the best for this sort of mounting hardware and I have no argument whatsoever with that sentiment.

DC Power Supply

Initially I used a 12v jump starter when I powered up the mount and this voltage proved to be a bit inadequate.  Things cleared up when I switched over to a variable voltage AC-DC power supply running at about 15v.  This means either that I'm tied to AC power requirements or must use a DC-DC converter to step up the voltage.  If this mount needs 15v power this is a bit disappointing as I wanted to be able to use this mount in the field away from AC power with simple 12v batteries. 

Follow up - This mount does indeed need more than 12v power.  I've since acquired a DC-DC 12v to 15v converter which does the job.  Anything less than 15v will cause motor lags in the RA axis.  See below for more details.

The Counterweight Shaft and Counterweight

There's nothing overly special here and both work fine.  I do like the Delrin tip on the counterweight lockdown bolt though.  This prevents the bolt from marring the counterweight shaft.  For my setup the standard 7 lb. counterweight is adequate.

Clutches

The DEC and RA axis clutches are not bad although they are not as secure as I might like.  This is especially evident in the RA clutch.  I did not purchase the optional clutch knobs.  I'm also told that I should not tighten the clutches excessively.  Yet for imaging, I would prefer to make sure there is no clutch slippage.  Nevertheless, with proper balance this doesn't appear to be a problem.  Losmandy claims this is to prevent possible damage to the gear trains allowing the clutches to slip in the event of impact with the tripod.  This is a valid point. 

I improved things somewhat by disassembling that axis and cleaning some excess grease off of the clutch friction plates but it's still too loose in my opinion.  I've not tried this yet but I believe a thin piece of  hard rubber cut to fit between the clutch plates could be a simple remedy for this problem as rubber would provide a bit more friction than do the standard nylon clutch plates.

Overall Fit and Finish

The Gemini Control System

Having used Autostar controllers and the AP GTO-CP controller I found initially that the Gemini controller was a bit cumbersome.  The menu structures aren't bad but the keypad and one line menu display leaves little to be desired.  It would at least be handy to have a 10-key pad including some hot keys to common catalogs and functions as part of the interface and a multiple line display would be better still.

However, after using it for a bit, I found the functionality to be acceptable.  One thing I do like is the ability to use the quick menu to do a meridian flip or to park the mount.

The keypad itself feels a bit cheesy and the buttons have an annoyingly loud click.  I'm wondering how well it will hold up over time but have neither heard nor read anything negative in this regard.

Gemini Startup

The Gemini startup was acceptable both for a cold start and for a warm restart.  The cold start would again have been easier with a 10-key pad on the controller but once the UTC time, mount type and location are set this is not much of an issue.

The alignment routines are quite good once one understands how they work.  This is perhaps the one place where the documentation for the Gemini fell short.  My problem was failing to understand that one has to first slew to a bright star and center it prior to requesting an additional alignment.  I expected the additional alignment option to function more or less as the original alignment where one requests that function and then selects and slews to a bright star.  Again this is not a big deal once one understands how it works. 

Building a T-point like model is a nice feature of the Gemini system especially for a less than accurate polar alignment in a portable environment.  I've found that with an alignment of three stars on one side of the meridian and one on the other one can achieve go to positions that are accurate enough to put the object of interest somewhere on an APS chip at 600mm.  I'm certain that this mount would be dead on accurate anywhere in the sky with more alignment stars especially if it was permanently pier mounted and drift aligned to the pole.

Gemini Use After Startup

Navigating the object menus is more or less as one would expect with the only room for improvement being a 10-key pad on the controller.  Manually slewing and centering the mount is straightforward using the diamond keys on the controller.  I'm not sure yet whether or not I like the method for controlling the speed of the slew.  One does this by momentarily pressing the opposite key to switch to slew at a faster speed.  Though convenient, I believe I prefer a more positive method of speed control as is the case with my other mounts' controllers to avoid inadvertent changes in speed.

Gemini Computer Interface and Control

This is a serial interface as is typical.  No problems have been encountered using my laptop running Windows XP SP2 with a serial port native to the laptop.  The Gemini ASCOM driver seems to work well and I was able to manage the mount just fine with The Sky 6, Starry Night Pro and MaximDL.

Slewing and Centering

The mount slews quickly and quietly in both axes.  In fact it's quite a bit quieter than my AP-1200 and way quieter than my LXD-55 or LX200 mounts.  Other than the annoying button clicks from the controller (minor at any distance), this mount is basically silent so one does not need to worry about disturbing one's neighbors at a star party.

Follow-up - Centering is straightforward with the controller using the four diamond keys on the keypad but my initial concerns regarding inadvertently switching slew speeds have proven to be correct.  It's convenient to use two thumbs on the pad to slew in both axes simultaneously and there is no tactile way to tell for certain which button your thumb is on.  Thus it's easy to be slightly off position and increase the slew speed by mistake.  What would be better is an additional button, say up in the upper right corner below the LED display that toggles through the various slew speeds available displaying the changes on the LED as they are made.

So Where Are We?

My initial impressions are more or less in line with what I expected.  This is not an AP mount but it is far superior to the LXD.  However...

PE and Backlash and Worms!  Oh My!

Here's where I ran into trouble and apparently this is not new trouble. 

PE

On my first night out I ran a PEMPro analysis on the mount and found 12.6 arcseconds peak-to-peak of uncorrected PE.  This is much more than I expected from this "precision" mount having read I think on the Losmandy web page for the Titan to expect something more along the lines of 5 seconds peak-to-peak.  I may have misread this or this specification is for the Titan only.

Still more disturbing to me was that the PE error did not seem to be consistent between rotations of the worm.  More research and careful analysis is required to confirm this but I'm wondering if there is the equivalent of the "76 second error" present with the GM-11 evident in the GM-8.  Regardless, this PE was causing seagull stars (yes I had some declination drift too) at 200mm focal length for 3 minutes.  Time will tell whether or not this can be tuned out with PEC.

Follow-Up 01/05/08

Yes it can or at least most of it can.  I've been able to program the PEC to achieve +/- 4 arcseconds of error.  This is adequate for most of my needs though not good enough to image with the 80ED unguided.  This is somewhat as expected but not what I'd hoped for.  However, as is noted in the following sections, PEC correction has to be programmed every time one adjusts the RA worm.  This somewhat eliminates the advantage of the Gemini 4's ability to retain PEC data from session to session.

Backlash

Something I did not check prior to first light was the backlash on the RA drive.  I assumed that a Losmandy would come tuned and ready to go and in fact this may have been the case.  After bringing the mount back inside I did the simplest thing to check for excessive backlash in RA by feeling for worm slop using the counterweight shaft.  I expected to feel nothing but was surprised to feel quite a lot, i.e., I could feel a definite clunk from side to side and could see that motion in the RA setting circle.  Even my LXD55 has much less backlash than this so based on my experience with my other mounts I felt this couldn't be right and that the RA worm needed tuning.

So how do you tune a worm on a Losmandy drive?  The PDF version of the instruction manual doesn't say but I did find a short paragraph on this in the HTML version on the Losmandy site. 

You remove the motor, the reduction gear case and the worm cover then loosen a bolt and press against the worm block with a finger and tighten the bolt.  Then you check the worm for resistance throughout a full turn of the worm and tighten or loosen the block accordingly.

The photo to the left shows the RA worm and the worm blocks that hold it (cover removed).  I was surprised when I took the cover off.  I expected to find a single integral unit for the worm and worm blocks as is the case even with my LXD mount.  Instead I found that the worm blocks are separate and can float relative to each other and to the worm.  There are also no thrust bearings here but only radial bearings.

This means the following conditions can be present all of which can affect backlash and resistance to worm rotation:

• The worm block spacing parallel to the worm axis can change.  This allows the worm to slide axially back and forth between the blocks within the radial bearings which obviously can drastically increase backlash and can cause yet more deviation at the Oldham coupler.

• The worm blocks can twist out of parallel to each other and the axis of the worm.  This places a binding load on the radial bearings and causes the RA motor to lag as well as introducing some odd ball deviations in the PE curve.

• The worm blocks can be misaligned parallel to the mount axis either alone or together.  Either causes a misalignment between the worm and the ring and can increase resistance to rotation.

• Since there are no thrust bearings there can be a resistance to rotation present from the worm shaft pressing into the bottom of the shaft hole in the outboard block.  This too I believe can cause a motor lag.

• There is no positive and quantitative way to adjust the worm mesh or the position of either block.  You loosen a bolt below the block away from the motor and finger push the block (and the worm) into the ring gear.  Too much and things bind.  Too little and there's too much slop.  While doing this you must also push that same block toward the opposite block and must also attempt to keep the block's axis plumb to the worm axis and must then retighten the bolt securing the block.  This takes four or five hands.

As I said, even my LXD-55 mount has a better arrangements for mounting and tuning the worms and that mount's worms and blocks are mounted as a single integrated unit.

But okay I'll give it a shot.  I removed the motor, reduction gear case and the cover.   Then I loosened the bolt holding the outboard worm block (the one away from the motor or the right one in the photo) and pressed the worm into the ring gear while wiggling the counterweight shaft to allow the teeth of the worm to fully engage in the teeth of the ring.  I could feel the backlash reducing down to essentially nothing while doing this as I expected. 

I retightened the bolt holding the block while keeping pressure on the block to prevent it from slipping back.  Then I manually rotated the worm feeling for any resistance.  I felt none and actually believed that the worm was probably not tight enough at that point.  But the clunk was gone so I decided to give the motor a try.  I reattached the reduction gears and motor and powered up the mount.

The mount slewed just fine with no excessive noise from the RA drive so I left the mount powered and watched a bit for indications of sidereal tracking.  Up pops a message on the controller, "RA Motor Lags!"  Not good.  This isn't documented anywhere that I can find but I rightly assumed this indicates the RA drive motor is having to work too hard at tracking speeds.  I shut down the mount to avoid any possible damage to the motor.

This could be caused either by the worm binding or because I had an out of balance load on the mount.  I double checked the balance in both DEC and RA and found the mount was balanced in both axes.  So back to the worm.  I once again removed the motor and the gear box and loosened the bolt securing the worm block while applying slight pressure to the worm block and gently jiggled the counterweight shaft to allow the block and worm to slip back from the ring gear just a bit.  I tightened the bolt when I could feel just the slightest backlash in the worm. 

Note that at this point I was introducing backlash when my goal was to at least minimize and preferably eliminate backlash.  I didn't like the fact that I was adjusting things such that I could actually feel backlash as that would be excessive in my book.  Regardless, my initial adjustment was not truly tight so I had no choice but to loosen things up a bit.  So be it.

I once again checked the worm through a full rotation for any resistance.  The worm turned easily for a full rotation in both directions.  I reassembled the gearbox and motor, turned the mount back on slewed the scope over to the east side of the mount and let it track for a bit. 

"RA Motor Lags!"  I was really surprised.  I had introduced noticeable and significant backlash in the worm and was still getting a warning for a motor working too hard.  Worse, the RA motor was now warm to the touch and I was concerned I was going to burn out that motor.  With no documentation and with no real way to determine just how tight or loose is tight or loose enough short of actually damaging that motor...  I was now truly concerned.

Okay I shut the mount down and once again loosened the worm block bolt and basically let it float while jiggling the weight shaft.  I could noticeably feel the backlash increasing and I was not liking that at all!   But the mount was then able to track without a motor lag warning.

I have attempted a number of times to adjust the worm to eliminate this excessive backlash without a motor lag and have not been successful.  I've come to the conclusion and confirmed this on the Losmandy Yahoo discussion group that it is necessary to leave as one put it,  "a clunk amount of backlash" in the RA axis.  This is quite disappointing.  My impression is that the worm and motor mounting needs to be completely redesigned and the motors need more torque as they seem a bit underpowered.  If I can easily turn the worm by hand, the motor especially through the reduction gearing should be able to easily turn it as well even at the low torque of tracking speeds.  The fact that it could not and apparently lags is a mystery to me.

Compare this to my AP-1200 mount.  I firmly believe one could pull a truck out of a ditch using the RA axis as a wench, albeit it would take a few days at sidereal speeds.  I never expect any sort of motor issues with the AP-1200 and I in fact have never had any unless there's a power drop below 12v.  The motors on this mount appear to me to be way over speced for what they are intended to do.  That's very good in my book and is part of the forget about the mount and just image aspect of the mount that I love so much.  But of course the AP-1200 is much more expensive than the GM-8.

Okay compare this to my LXD-55.  Basically the same thing as the AP-1200.  I've never had an issue with the motors on the LXD-55.  While backlash certainly is a problem with this mount this is due to the out of true, less than precision worm.  Unless one just goes nuts with cinching down the worm to the ring, there is no issue of an overloaded motor with this mount either.

Consider the ramifications of this design flaw in the worm mounting and the under powered motors:

• In addition to the rigidity of the mounting, the crux of a good imaging mount is the mount's ability to track and/or guide well and consistently.  Adding backlash to the mount means the tracking and guiding will at least potentially be less accurate than when backlash is minimized or eliminated.  That is, by accommodating the poor design of the worm mounting and under powered motors, we are introducing a source of error in guiding and tracking when we want to do everything we can to eliminate all sources of error.

• With such backlash present in the RA axis of the mount it becomes necessary to intentionally imbalance the RA axis with a bias to the east so that the mount has to push the scope (or counterweight depending on which side the scope is on) up hill slightly.  This keeps the RA worm loaded so that contact with the ring gear is always on the same side of the worm gear tooth and prevents the mount from chattering its way downhill.  This is somewhat standard practice for any GEM.  However, this increases the load on the motors as they must push the RA axis up hill against that imbalance.  If the motors are not powerful enough to accommodate the imbalance, it may not be possible to bias to the east enough to overcome the amount of backlash the mount requires. 

Since this imbalance acts through a moment arm perpendicular to the vertical vector of gravity, the amount of east bias changes with the position of the RA axis with the least amount of bias present when the counterweight shaft is vertical (no bias) to the most when the counterweight shaft is horizontal.  This is because the length of the moment arm, with respect to gravity, changes with the position of the RA axis.  If one is going to image anywhere near the meridian in all declinations (the optimal place to image) one must make sure there's enough east bias in the axis to provide an adequate load to keep the gears in contact when the counterweight shaft is near but not at vertical.  That slight bias will be multiplied as the moment arm lengthens as the mount tracks from near vertical to horizontal and the bias may end up being so great that it will cause a motor lag, motor stall or even motor damage.

• While perhaps not considered normal procedure, one would optimally like to be able to track right through the meridian when imaging.  This is not possible with the GM-8 given the excessive amount of backlash that must be left in the RA axis.  This requires a meridian flip and also requires a readjustment of the counterweight to make sure the balance with an east bias is maintained when  the scope is flipped to the other side of the mount.  This is problematic for operating this mount in a remote observatory.

• Guiding becomes problematic with backlash most especially in the DEC axis where the guiding must accommodate the backlash as it needs to reverse direction from the north to the south or vice versa.  This is less of a problem with the RA axis where guiding is done by changing the tracking speed fractionally either over or under sidereal rate.  That is, the RA axis never needs to reverse direction but simply adjusts its speed under or over sidereal rate by some fraction of that rate.

• Since the worm must essentially free float with respect to the ring gear, temperature fluctuations from season to season can change the amount of backlash present in the gear train due to thermal expansion of the components.  This will I imagine require rather continuous adjustments of the backlash of both axes to achieve consistent backlash correction and guiding from session to session.

• Every adjustment of backlash to the RA axis changes the characteristics of the periodic error for that axis.  This means that the adjustment renders the PE correction curve invalid and PE must be reprogrammed after every adjustment.

This design deficiency is apparently not new and has plagued users so much and for so long that they actually submitted a petition to Mr. Losmandy asking him to address this issue.  It will be interesting to see what comes of this and hopefully a retrofit kit will be made available to remedy the deficiency. 

Follow-Up 12/3/2007

Here is a summation of the design deficiencies on a point by point basis including a few new ones that have come to light since my initial evaluation:

1. The worm blocks are not a single integral unit.  This allows the blocks to float relative to each other causing binding that overloads and potentially destroys the tracking motors.  Avoiding this condition requires that excessive backlash be left in the drive trains far beyond anything that might be considered optimal and requiring constant tweaking of the mount.

2. There is no quantitative way to adjust the worm block run out (spacing between the worm blocks).  This allows the worm to potentially slide axially within the radial bearing bushings drastically increasing backlash and affecting the Oldham coupler connection.

3. There are no thrust bearings in the worm block design.  This introduces the potential for metal to metal friction between the worm shaft and the bottom of the worm block which can cause a motor lag and potential damage to the motors.

4. There is no quantitative way to adjust the worm to ring mesh to minimize backlash.  Meshing the worms snugly (that's the best term I can use since this can't be measured) causes an RA motor lag and potential stall.  This requires that a "clunk" amount of backlash be left in both drives which introduces all sorts of potential problems for accurate PE correction and guiding.

5. The drive motors are under powered at tracking speeds and burnouts are common enough that it's actually recommended by some Losmandy users that one keep some spares on hand for this eventuality.

6. The drive motors are mounted in such a way that they are potential snag points for cabling and impact points for the scope.  The mounting method for the motors and the reduction gear housings is not robust enough to withstand either without damage requiring replacement.  The motors should be flipped 180 degrees to be mounted in front of the axis rather than hanging out excessively to one side.  This would require a new design of the reduction gear housing and the motor mounting overall.

7. The reduction gear housing is made of plastic yet the motor is mounted to that housing which in turn is mounted to the mount assembly.  In the event of an impact, the cover of the housing can break loose from the main gear box allowing the motor to wobble against the broken plastic or to come loose entirely.  There is no obvious way to repair this short of purchasing a new reduction gear box which will have the same design of course.

8. Of less import but still irritating, the worm covers are secured by set screws that tighten against the worm block.  Tightening the cover's set screws can cause aluminum shavings to be flaked off of the worm blocks and, with tear down and setup those shavings could easily end up in the worm gear.  Under normal circumstances this wouldn't be much of a problem but the necessity to constantly adjust the backlash means the covers have to be removed and replaced quite often increasing the likelihood of a sliver making its way into the worm and ring.

In short, the design of the drive trains for these mounts could easily be improved and is in fact substantially inferior to the drive trains of even my LXD-55 mount in design if not in tolerances.  I feel certain the worm and ring gears are machined and finished adequately to do a good job but the way the worms and motors are mounted renders those accuracies moot.  This is a critical aspect of a precision mount being used for astrophotography or other precision applications. 

Customer Support

After encountering these issues I sent an email to Mr. Losmandy which outlined the difficulties I was encountering and asked him for advice on how to remedy this.  As of this writing, it's been four business days since I sent the message, I've yet to receive a response or even an acknowledgment of receipt with a promised follow-up.  I know the email was delivered because I was asked to confirm my email address by Losmandy's SPAM filter.  I have not as yet tried to telephone and doubt I will as I've determined the cause of the problem and have determined there is no solution short of a redesign and retrofit.

Email is a convenient means of communicating both for the customer and for the vendor.  I should not have to call for support when email is more convenient for both parties.

Given that this condition is not new, this should have been documented on the Losmandy site along with any workaround procedures that are available and in truth, the design should have been corrected years ago in my opinion.  I don't expect a quality company to be mistake free.  I do however expect a company, when a mistake is made, to have the integrity to admit the mistake and do everything it can to remedy the mistake. 

Regardless, no response at all doesn't qualify as quality customer support although one incident is not a fair evaluation for customer support overall.

Follow-Up 12/3/2007

After a month there has still been no response to my email and I'm sure there never will be.  Nor have I called as there's no point.

However, there has been some speculation on the Losmandy Yahoo group regarding Mr. Losmandy's response to the customer petition asking for a design retrofit to this problem.  I repeat that this is speculation but in absence of any official word from Losmandy that will have to do.  Apparently Losmandy is of the opinion that the tolerances required to remedy this issue are so fine that the machining costs of a kit would be beyond the cost that any customer would be willing to pay for the kit. 

However, several viable solutions have actually been recommended and even built and documented on the Losmandy Yahoo group.  These solutions apparently do not require any excessively fine tolerances and eliminate completely the backlash issues present in the native design.  I am not a machinist but if I had a mill available, I'm quite certain that I could manufacture on my own any number of the solutions recommended.  The consensus opinion of that group appears to me to be that Losmandy simply does not want to mess with this issue.

I repeat yet again, this is speculation but there is no official word from Losmandy and silence from the company tends to (at least in my mind) give credence to that speculation.

Summing Up

I know it is possible to image with this mount and to produce very high quality images at that.  But let's see how well this mount addresses my goals:

• Portable and Quality Imaging Platform -- This mount is indeed easily portable and lightweight but I'm afraid the "quality" moniker cannot apply given these deficiencies in the worm block design.  This could be remedied with a redesign and retrofit at which point I believe this mount would qualify.

• Overkill Load Capacities -- I would certainly not be comfortable with loading this mount up to capacity given what appear to be the rather frail motors.  As it is, the mere 7 lbs I have on it currently are not excessive.

• Guiding Capable -- In theory this mount qualifies.  In practice I believe it will be a necessity regardless of focal length.  Whether or not the PE can be smoothed to an extent to allow for unguided imaging at shorter focal lengths I have yet to determine.  Regardless, I feel certain guiding will be problematic and less than optimal given the excessive amount of backlash that must be left in the drive trains; most especially in declination.

• Cost vs. Quality -- This mount is nowhere near the cost of a Mach I.  Whether or not I'm going to come to the conclusion that there's an acceptable bang for the buck here I don't know as much of this depends on what Losmandy does regarding the worm mounting.  If that is solved at a reasonable price, then yes I'd say this mount is a good value.  If not...  no probably not given the requirements astrophotography demands.

• Diddle Free -- No I don't think this mount qualifies.  I believe it will be necessary to constantly adjust the worms from season to season and I believe the actual use of the mount will require continual diddling if for no other reason then to balance the mount to accommodate backlash on either side of the meridian.  I believe it easily could qualify if the worm design was changed.

• ASCOM Compliant -- Here I think the answer is yes this mount qualifies.

• Quality Customer Support and Documentation -- No and no.  But the good news is that the Losmandy group on Yahoo is quite active and includes many experienced and knowledgeable users.  That will most likely suffice in lieu of support from the company.

So what have we got here? 

Well, for a visual mount the GM-8 will work very well indeed.  So will my LXD-55 at much less cost or many other options from Orion, Meade, Celestron, etc. all for substantially less money so there's certainly no reason to spend the money for a Losmandy for visual use. 

As an imaging platform it can work and good results can be obtained but only at the cost of putting up with constant tweaking and less than optimal guiding and tracking.  But it can work with good results.  Whether or not the cost in irritation and frustration, lost imaging time, etc. versus the price is too high or not is subjective of course. 

But for me, I want to forget about the mount and concentrate on catching photons.  The GM-8 does not allow this.  My AP-1200 does and I am certain a Mach I would as well.  So I'm on the waiting list for a Mach I and as things currently stand I'll take advantage of that when my name comes up as a replacement for the GM-8.  In the meantime, I believe the GM-8 is barely a reasonable compromise.  Given the difference in price that's somewhat to be expected but after delving into these design flaw issues this mount came within a whisker of being returned. 

Now here's the sad part.

This could all change with a retrofit for the worm blocks and frail motors.  What I mean is this mount has everything going for it that I want assuming the worm mounting and under power motor issues were resolved.  The other mount components are obviously of a quality that there should be no excessive need for support and with proper tracking and guiding through that retrofit I'm convinced it would be a great imaging platform at a very reasonable price.  Hopefully this will come to pass as provided by Losmandy.  If not, I'll figure out a way to do it through a custom machine shop or will remedy the situation by replacing it with a Mach I.

I've always felt that one of the best measures of the quality of a company and its products is an existing customer's inclination toward becoming a repeat customer.  Would I buy another Losmandy mount as currently designed and supported?  As I said, I'm a spoiled AP brat but sorry Losmandy.  Not a chance.