A high capacity GOTO mount on a budget
...retrofitting the AutoStar and LXD55 servo motors to a Synta EQ6, or Orion Atlas mount


The Synta EQ6 mount

Background...

In the summer of 2001 a new mount from the Chinese manufacturer Synta, the Skywatcher EQ6, was making a relatively quiet debut. Talk of it on various internet newsgroups and mailing lists were both hopeful and pessimistic. Not surprisingly, the hopefuls were folks who really couldn't afford one of the heavy-duty high end mounts on the market. The folks who were pre-judging it were (again, not surprisingly) those who had already invested mega-bucks in well respected mounts from AstroPhysics, Losmandy, Takahashi, or William Optics. It was quite obvious that no cheap Chinese mount could come anywhere near the capability or refinement of those mounts, right?

Let's find out...

In the fall of 2001, I decided to place an order for an EQ6 from TeleHoon in Canada. The mount cost me just $695 USD. Shipping was another $90, bringing my total to about $785. This is not much less than what Orion is currently selling their version for. Very soon after receiving the EQ6, I totally dismantled it. The mechanical quality impressed me. Although it obviously was not of the same calibre as the $2500 to $4000+ mounts mentioned above, it was far better than the sleeve bushing CG-5's and other Chinese mounts that I'd inspected. The machining tolerances were reasonably tight, and the motion of each axis felt very good (especially after the adjustments done during re-assembly). Robust tapered roller bearings were used instead of the sloppy sleeve bushings I'd encountered in previous Chinese mounts. The worm shaft itself runs on small ball bearings, something the less expensive Chinese mounts also lack.

Under the Stars...

The first thing you notice is the weight. But the carrying capacity is quite obviously there. I've had both a C9.25 and 8" LXD55 SNT OTA on the mount and it is SOLID. It's far better than the LXD55 mount that came with my Meade 8" Schmidt-Newtonian.

The biggest weakness of the EQ6 became apparent the very first night I had it out. That weakness was the standard stepper motor drive system. The original EQ6 mounts were made with DC servo motors, but as I understand it, probably no western purchaser of an EQ6 ever got one of them. Rumor is that Synta had a problem with their servo motor design very early on, and all EQ6's were retrofitted with the stepper motor system before dealers actually sold many (if any) of them.

Unfortunately, it seems that the replacement stepper motor system wasn't quite perfect either. Many owners were noticing vibration problems which compromised medium and high power planetary viewing. Turning off the drive made a noticeable difference in the quality of the images. Not everyone reported this vibration problem though. Mounts loaded with heavier, or lighter scopes sometimes had no problems. There may have been (and still be) a mechanical resonance issue cropping up here which only happens under certain conditions.

Periodic Error...

Lots of folks who buy the EQ6 have aspirations of doing Astrophotography with it. That's what these big GEM's are for, right? If you are just going to use the scope visually, many people (myself included) find a Dobsonian much easier to setup and use.
My testing of periodic error was done using a small security video camera. By utilizing a special video monitor with a superimposed video cross-hair, I was able to accurately assess the PE of the mount in real time. The total P-P error was verified by putting Saturn on the cross-hairs. Over a period of 8 minutes, the drift proved to be about 18 arc/sec P-P, with no sudden jumps. Not bad - I can easy guide out that amount of error.

Note: Other folks doing early testing of the PE on their EQ6 mounts got comparable results. Strangely, I've heard of some recent cases where people are getting results of 40 to 60 arc/seconds, or even worse! This could be a quality control issue that may not be that unusual for Chinese made mounts. If someone has an EQ6 with this much PE, I'd strongly suggest that you return it to your dealer and get another one. They are not ALL like this!

New motors...

I tried several things to fix the stepper motor vibration issue. No amount of adjusting of worm gear clearance, or "soft" mounting of the steppers helped. I came to the conclusion that only a completely different set of motors was going to fix the problem. I looked at my options. They all seemed very expensive, with most of them costing MORE than I paid for the EQ6! Some of these retrofits are available from the following companies:

  1. AWR Technology
  2. AstroMeccanica
  3. DynoStar (Boxdoerfer Elektronik)
  4. Skysensor 2000

The Skysensor 2000 retrofit seems to be gaining popularity recently. It also seems to offer the most capability for the lowest price. Note that an SS2K retrofit of an EQ6 will definitely cost you well over $1000 USD - still higher than the cost of the EQ6 itself! The SS2K was the approach I was most seriously considering before finding a source of the LXD55 motors. Once I located them, it was not a hard decision on which approach to take. The LXD55 motors can be bought for $45 each, and the AutoStar 495 (easily software upgradable to a 497) control unit can be bought for around $40! Although the motors are not available in large quanities, they can typically be purchased from either from Bill Vorce at The Telescope Warehouse or Gary Russell of Russell Optics. That means you can buy all the electronics and motors for under $150 USD! (NOTE: You will probably have to email Bill or Gary privately about getting these motors, because they don't currently have them listed on their webpages)

Seems to good to be true...

OK, right up front I'll tell you that there is one capability in the AutoStar retrofit that is missing. It may be important to you, and it may not. The capability I'm referring to is PEC (periodic error correction). The Meade AutoStar does not currently offer that capability in its firmware. It's possible it could be added at a later date, but I would not count on it. If the periodic error of your EQ6 is low, and has no sudden jumpiness, you may find that you can guide just fine without PEC. It is possible to autoguide any dual axis driven mount with external software if the device has a communications port. There are programs available that WILL allow autoguiding of an AutoStar mount, and adding the capability to record and playback a PEC file within one of these programs shouldn't be that difficult if someone decided to do it.

Now, as for what it DOES DO, you need to read up on the capabilities of the AutoStar. Most importantly, it solved the vibration problem on my EQ6 - no more high magnification jitters! For such an inexpensive system, the AutoStar is quite impressive. It has numerous features that you won't find in any other Goto controller. The slew speeds with the EQ6 are quite rapid. In fast slew mode, it moves the scope at 800x the sidereal rate! Unlike the Meade LXD55 mount, the EQ6 mount fitted with these motors really isn't that loud. For some examples of how an EQ6 mount sounds with the LXD55 motors installed, visit my VAL AutoStar control software page. Click on the 'Sound Bytes' on the left side to hear me TALKING TO THE SCOPE and the scope slewing quietly in response to my commands.

OK, I want to do this...

In order to make the retrofit easy, it would be ideal if you could purchase a pre-fabricated bracket kit to allow allow a quick bolt-up of the LXD55 motors in the belly of the EQ6. My retrofit required a lot of machining on the original LXD55 motor brackets. What is really needed is a set of custom made brackets designed specifically for the task. I am investigating the idea of having them made by someone who has a better equipped machine shop than mine. I'm very busy developing the Equatrak right now, so I don't currently have the time to devote to this myself.

Here are a few pictures that I took of the completed retrofit that may help to guide you..

 

FrontPanel
...The new front panel...

RA Motor
...View of the RA motor...


DEC Motor & Servo Board
...Closeup view of the DEC motor and servo board...


RA Motor Closeup
...Closeup view of the RA motor...


The AutoStar EQ6
...View of the completed mount...


If you have any trouble figuring out how to get around the clearance problems, send me an email and I'll be glad to help you figure it out.

The correct gear ratio to input into the AutoStar when the EQ6 retrofit is completed is 4.02858. The stock LXD55 ratio should be 2.53715.

One final bit of advice. Remove the metal encoder wheels from the LXD55 motors before you start handling them. If I recall correctly, it takes a 1.5mm allen key to remove the setscrew. The wheels are very thin and very easily bent.


Please visit my VAL AutoStar control software page.

CLEAR SKIES AND SMOOTH SLEWING !