ETX TECHNICAL TIPS Last updated: 16 February 2004

Using DS mount with ETX-90RA

Convert your older ETX (or other small scope) into GOTO capability.....

Its been some time since I had made a post here on Weasner's ETX site; with the wet and cloudy nights here in South Florida all summer long, my scopes have been collecting alot of dust. With the arrival of the new ETX EC on the market place just 6 months after I had purchased my standard ETX, I've been looking for a way to produce a GOTO mount or some sort of digital setting circle system to help locate objects in my light polluted backyard.

Well, it is now fully automated AND with better GOTO accuracy than the ETX EC for under $400.

Our local Service Merchandise store had the Meade DS-60 series scope on sale for $225.00. For those of you who don't know, the Meade DS Series are the cheapest motorized scopes available with GOTO capabilities, but with questionable quality. I purchased one to see if can be (the mount only) converted to handle my ETX tube assembly. After a complete tear down of the system, I can now say that the DS does not stand for Department Store quality as many of us backyard astronomers have affectionately named this series of scopes. The mount is cast aluminum with the axis pivot points made of 1/2 inch shafts mounted in what appears to be bronze bushings. This makes for a very smooth and solid movement. The tripod legs are extruded aluminum and very ridged, but the hardware (leg ends and locks) are of plastic and therefore somewhat flexible. The scope itself (60mm refractor) never came out of the box (definitely "first scope" quality). The mount and tripod are well able to handle the ETX, so, with some aluminum plate and a little work I was able to attach the ETX (removed from it's own fork mount) firmly in place using the two holes and flat base under the tube assembly.

The real question was the quality and accuracy of those drive units(one for each axis) that is the heart of any GOTO system. On close inspection I had found these units to use DC motors coupled to an optical timing disk and followed up with a gear reduction drive train. Quality parts were used throughout. Fine tooth gears from the motor to the timing disk help eliminate gear slop and improve timing. Moving up the gear train, each was progressively larger and stronger with the final output gear almost 1/2 inch thick. The motor is rubber mounted within the gear housing to reduce noise and vibration common with a DC pulse motor system. The entire gear housing is then rubber mounted to the outside casing. A single circuit board of good quality contains several ICs and a large quartz crystal used for the accurate timing and control required in this type of system. Final output is to a worm and ring gear with the ring gear attached to the main mount axis shafts via a hand tightened clutch assembly (so you can unlock the drive motors to swing the scope manually). My concern was with the very small ring gears used, about the diameter of a quarter. Many computerized GOTO mounts use ring gears of 5 to 6 inches or more in diameter coupled to stepper motors, but, with the extreme power of this DC motor through a large gear reduction system, you can literally lift a brick tied to the end of the scope with power to spare. There are a couple of adjustments for these two gears to reduce backlash and it works very well when adjusted properly. Unlike the ETX EC, there is virtually no backslash felt when trying to move the mounted scope by hand. I was also amazed at how jiggle free, when viewing through the eyepiece, the scope was during handling and focusing as compared to my original ETX mounted on a Bogan 2080 tripod. The light weight tripod legs of the DS system seemed to absorb vibrations very well. The original plastic ETX fork mount (no longer being used) were most of my ETX's jitter problems anyway.

After I was satisfied with the quality and steadiness of the new mount, I purchased the Autostar controller #497 (with it's larger 12,000 database as compared to the #495 with 1200 object database. Only $50 Difference) which will work with both the ETX EC or the DS series base which I now have. The autostar is probably one of the best values in the astronomy industry. With a 12,000 object database, scrolling object information screens, back lighted keypad with red utility light, downloadable updates and the ability to be controlled by your laptop computer, all for $149.00, it just can't be beat. But most importantly, it's built in drive training program almost completely removes the effects of gear backlash and axis slop found in low end mounts. Unlike my tests with the ETX EC, the new mount hit is targets almost dead on 95% of the time, due mostly to the all metal mount and large axis shafts. Using the Tour mode, I have found more deepsky objects in 30 minuets then what use to take me hours using the setting circles on the old ETX base. That is if I could find enough stars in my bright night skies to use as a guide. The entire system with legs, battery pack and scope is very light and can be lifted and moved with one hand. I have no doubt that this DS mount can handle heavier scopes tubes like the 5" C5+ with no problem.

The cheap Meade DS-60 had breath new life into my older ETX and with the included Meade Star Finder software (canned version of their EPOCH program) in my laptop (Sky Map Pro and SkyChart will also work with the Autostar), I have an excellent fully computerized scope with point and click operation. Since it is said that the DS Series will be appearing in department and catalog stores you will no doubt find one discounted from the $299.00 list price as I have. I will send a post soon on how I made the metal plate which attaches to the DS mount and holds the ETX in place.

I have received many EMAILS on my DS mount setup for the ETX since you have posted it on your site. Attached is a rather lengthy description and setup instructions with a mechanical drawing for those interested in trying this.

Anyone interested in a mechanical drawing plus instructions on building, setup and alignment of the DS mount conversion can EMAIL me at: strburst@mindspring.com. Just ask for the DS mount conversion and I will EMAIL the information to you.

Thank You
Paul

Subject:	ETX-90 RA on DS-70 mounting - warning!
Sent:	Thursday, May 9, 2002 6:56:54
From:	tede@tede.freeserve.co.uk (Stephen O'Leary)
This is a magnificent site, Mike, and an example of the Internet at its
best.  I got one of the first ETX-90's to arrive in the UK, and your
site has been very helpful.  I like your ETX book, too!

Having bought in too early to join the ETX-EC revolution, I have always
wanted an upgrade path, so when I saw the articles on your site about
putting an ETX-90 onto a DS-70 mount, I immediately ordered a DS-70.  My
12-year-old daughter can play with the new scope , and I'll have the
mounting.

BUT...

..warn your readers to beware!  Although I thought I had ordered a
DS-70, what arrived was a different model called the DS-2070. 
Fortunately the supplier still had one (that's ONE) DS-70 left, so I was
able to exchange.

The bad news is that the DS-70 appears to be going out of production in
favour of the newer DS-2070.  The 2070 has a cradle/ring mounting like a
Celestron, instead of the fork mount provided with the DS-70.  As far as
I can see, there's no way you can get the ETX-90 tube into the 70mm ring
of the DS-2070.  The DS-2070 also appears to be less solidly
constructed, although I must admit I didn't try opening up the mounting
base to make sure.

So if anyone is thinking of putting an ETX on a DS-70 mounting, it looks
like they will need to get their DS-70 pretty soon.

Steve O'Leary
Leeds, UK

Subject: Update for ds_mount.html to note new Meade DSX series scopes...
Date: 2/12/04, 17:39
From: Mark Warren (mark.warren@oracle.com)
I just purchased a new ETX-90EC and I have to add my voice to the choir
praising your superb web site.

Hopefully, I can make a small contribution to http://www.weasner.com/etx/techtips/ds_mount.html

I recently saw the Meade DSX90-AT and DSX-125AT for sale at my local
Brookstone (also online at www.meade.com/brookstone/dsx125at.html)
Meade's product designers seem to like the ds_mount idea as well. More
details are available in the Meade DSX manual at
http://www.meade.com/manuals/index.html .

Mark

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