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CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
Meade LXD750 vs the Losmandy G11
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Early in 2001 I was getting back into astronomy after a pause of nearly 10 years. I bought a Klevstov 200K OTA which weighs about 12.5Kg and needed a mount to take me to the objects I wanted to see. Goto was essential. So I turned to Cloudy Nights for inspiration, like many would be purchasers of mounts before me I had narrowed down my search to the Losmandy G11 and the Meade LXD750. The used LXD750 with #1697 goto system seemed to be considerably cheaper than the G11 with Gemini and the review by Joe D certainly gave me no cause for concern. So when one came up around $1800 on Amart I bought it.
For the next two years I struggled to use the mount as an imaging platform, even with the Klevstov focal ratio reduced to 1500mm it was always a struggle for the guide camera to keep the 750 on target for long. Turn off the guide camera and whoooaa the 750 really lost the plot quickly if you just relied on pec. The main problem was the natural uncorrected pe of the 750 was 4 arc minutes (not seconds). Such bad pe gave the guider a really hard time. Compounding this was the erratic nature of the periodic error. I went thru the normal checks - swapped out some damaged bearings supporting the RA worm and re adjusted the end float tension. But the pe was coming from the worm and there was nothing I could do to reduce it.
Fine I thought I’ll get a new worm - hmmmm that’s when Meade’s policy of not supplying spares for the LXD750 first bit me. Don’t forget I live in Australia and the round trip to Meade costs an arm and a leg - around $600!! I called Meade and got the run around about who should deal with my enquiry. Finally I pinned someone down responsible for export sales only to be told that Meade don’t send out spares as this is their flagship mount and it would have to be returned for service. I protested that all I needed was a new RA worm which I could fit myself, but my protestations fell on deaf ears. The person I spoke to was unable to think for himself, “Oh I’ll have to ask my supervisor”, but the answer was always the same - send it back. So tempted by a Meade Factory upgrade for $200 I gave in and shipped it. 6 weeks later it came back - at my expense.
At first I was impressed that they had swapped out the whole electronics and fitted a new RA gearbox plus worm - all for $200 plus my big freight bill. Great I thought as two other problems the original system had seemed to be cleared up. Those problems were a tendency for the old software to lock up at random - well not really at random more a case of when I needed it to work most! The other condition was it would not start up above 27C - that’s a mild day here in OZ. So if you were into solar studies - you had to make sure you picked a really cool day. Anyway they’d fitted a new #1697 with new boards and software - great. Well the original lockups were much less but it still had random lockups which I could live with now. At least now I could finish an imaging run with the **** mount stopping dead.
The pe was also much better - only 50 arc seconds now down from the horrendous 4 arc minutes previously. Pec could now almost get a grip on the pe and I was able to get some runs down to 5 arc secs with pec alone - not good enough for imaging but better and with the guider invoked I did get a lot of imaging done and nearly got round stars - well more like ovals, there was still a struggle going on with pe and guiding.
A few months after I got the mount back disaster struck. The
mount stopped dead. Dead being the operative word. A call to Meade to get
help, warranty help, was met with the same response - send it back - but I’m
in Australia - sorry you’ll have to send it back. I felt like I was
having a conversation with Homer Simpson.
Stuff this I thought, I’ll have a look to see what’s wrong. It did not take long to track the fault to a pinched wire leading to one of the optical diodes reading the pulses on the RA servo. When Meade had reinstalled the new gearbox the clearance between the encoder leads and the case was insufficient and the insulation was finally squeezed thru and shorted out.
However the short caused internal damage on the circuit board besides killing the opto diode. I really did not want to go thru another expensive return trip to Meade so I fished around on the net and found some boards on Telescope warehouse for $250 - I also took a punt and ripped a diode out of a spare gearbox I had already bought on amart. Things were looking up. I got the boards only to find they were from an earlier vintage and nothing was compatible - or so I thought. In fact the Eeproms were compatible except that the number of pins on the chip was different plus a few extra wires were needed to be rerouted to make the chip go in the other board. From an electronic point of view this was the real reason Meade did not want to send out stuff in the field. If I was not an electronics person I would have got into deep trouble attempting to swap the boards. I did ask Meade for a circuit - you guessed it - send it back - doooaahhhh. I’m so cranky with Meade over this!
Anyway I did the reverse board mod and the new boards worked and the mount was off and running again. At that point, I decided that before it gave any more trouble I would sell it. So I got it out of my hair on Amart.
In with the G11.
I landed a G11 with a Ramona Goto cheap on Amart.
There are issues with Ramona in the southern hemisphere - the software won’t flip and the RA wont run in reverse, but for the price of a G11 alone the Ramona was thrown in free. After the Meade experience how bad could it be? Before I could use it I had to reverse the RA motor plate on the G11 so I did not have to run the motor in reverse and I just lived with the lack of flip. Oh boy what a difference. Pe was only 10 arc seconds without pec and with the guider working I got the most brilliant images.
THE G11 KILLS THE MEADE LXD750. I was stunned.
These are not two similar mounts. The 750 is so substandard compared to the G11 it should never rate in any ones consideration when selecting a mount. It is a visual mount only and should be used only with very light and very short length OTA’s.
I was so impressed with the G11 that I bought a second G11 for my other OTA a 7" Intes Maksutov - this time a new one with the Losmandy digital drive, it had the new improved worm which oddly has twice the pe - 22 arc seconds, but the pe is so smooth that I knew it would be a synch to guide out and that’s how it proved in practice.
Now the G11 is not perfect, I could point to the poor system for holding the worm bearings and the crude method of adjusting worm and wheel spacing. But these things can be fixed if you like to fiddle and at least if you need a new worm you can buy spares from Losmandy. Adjusting the Meade 750 for polar alignment was easy once I got rid of the thin nylon disc between the head and the base - I think it was intended to be a dry lubricating disc to enable the head to slide in azimuth but in fact it causes the head to stick, so I removed the disc and greased the two surfaces - then the head could turn with ease, but Oh dear the altitude adjuster is just a piece of threaded steel rod with handle on the end pushing against a part of the aluminum casting which forms the head. There is a serious problem of the steel rod biting into the aluminum.
On it’s own the rod cannot lift the head with an OTA fitted, the rod just chews into the aluminum. So you need to hold some of the weight off the adjuster manually whilst you crank up the elevation. Then pinch up the elevation lock - that big dumbbell shaped thing on the side of the mount - problem is you can’t get enough pressure with the lock nut to hold the head, so you end up with a combination of the steel adjustment rod and the pinch lock trying to hold the head up. I can tell you that I was continually having to apply a little more pressure over the months and years I had the mount, as the head would keep dropping - more like chew deeper into the aluminum.
Now the Losmandy is bad in this area too, the azimuth adjuster is really not good, on both my mounts the brass central pillar against which you adjust the azimuth is loose, I have a friend who also has a new G11 and he has the same problem. I have to conclude it’s inadequate design. Compounding this is the gear ratio of the azimuth adjuster - much too coarse, when you want to make a fractional arc second adjustment what you get is at best arc minutes of shift with the smallest of tweaks of the adjuster knob. This results in the need to reverse direction when you (most often) overshoot where you want to be, problem is the loose central pillar introduces so much backlash that you need the patience of a saint to fiddle on before you can get that “perfect” polar alignment. The altitude adjuster of the Losmandy is fine and does what it should do.
I got rid of the Ramona goto system back to the northern hemisphere as it had other issues down here, that left me with no drive system at all on one G11 and a digital drive on the other. No problem I thought I’m an electronic person I’ll design a better goto system. Well two years later I have a much better goto system capable of long unguided imaging based on pec alone. But in that time I’ve come to be impressed with the simple design of the G11 - yes it has shortcomings, but it’s a mount “you can work on” and you can buy all the bits for it as spares. The 750 is not a tinkerers mount with it’s totally enclosed slot car motors and worms which are not much better than wood screws.
In summary the G11 is by far and away the mount to go for. It’s motor burnouts can be overcome by improvements to the worm adjustment system - I’ve fitted a simple brace which keeps both bearing blocks parallel to each other. Also my goto system has a current detector which trips if current to either motor exceeds 1.5 amps. Motor burnouts cannot happen. I also suspect that the Swiss motors in the Gemini are much less robust than the American Pittman motors I use in my goto system.
So overall if you are in the market for a mount then go for the G11. Too many issues with Meade’s LXD750.
- magic-man likes this