Steve Bedair's Telescope Mounts
Longview, Texas   8-2002
 
 

 Building a DS Powered Telescope Mount ??
 
 

The biggest advantage of building a DS powered telescope mount is the ability to use Meade's Autostar controller. The
Autostar controller will automatically "goto" and track a selected object from it's huge database. This database can
easily be updated from the internet. To build a DS powered mount consist of adapting the DS motor assemblies to
drive a set of worm gears. The Autostar uses Alt / Az ratios ( these are just numbers ) to determine how far to move
or how much to turn the worm gears to place the selected object in the field of view of your eyepiece. These ratios
can easily be changed to allow for different gearing arrangements. Click Here to learn how to change the ratios
Please remember there are limitations on how well a DS powered mount can perform but with a good set of worms
and worm gears, a decent bearing system and a lot of patience a DS powered mount can be as accurate as an LX 90.
 
 

Parts Needed

2 DS Electronic Motors:     You don't need a whole DS telescope to get these. You can purchase a Meade 492 Electronic
                                         Control System for around $ 130. This kit includes 2 DS electronic motors , terminal block , 2-22
                                         tooth nylon gears that drive the worm shaft , and the 60 tooth worm and worm gears used on the
                                         DS mounts. Plus the kit includes a small hand controller with direction buttons. This is not the same
                                         as the Autostar controller.

Autostar Controller:           I use the 497 Autostar controller. The 495 will work fine also.
                                        ( Check out E-Bay for some good prices )
 

Worm Gears:
               Update added:  Here are some nice looking HDPE made by Andy Saulietis . I have not tried these
                                        gears yet but I plan to with my next project.
 
                                        This is the hard question!  I now use bronze gears from WM Berg . I have also
                                        used nylon worm gears from 12 volt automotive window motors on the smaller mounts.
 
 

Will the new ETX 60 AT  or ETX 70 AT work ??

I have been asked many times if the new ETX 60 AT or 70 AT will work for building a mount. I have never seen the insides of these scopes other than pictures posted at Mike Weasners web site. They are quite a bit different from the DS models.
Would take some work but I think it could be done ( If anyone wants to donate a AT  I'll be happy to see what I can do!! )
 
 

What size worm gears do I need ?

 The original Meade DS and ETX models use a very small 60 tooth 48 pitch worm gear with an OD of 1.25"
With such a small OD these gears are very hard to work with. Remember the larger the worm gear the better the accuracy
will be. This is because no matter how well the mount is built there will be slack in the gear train somewhere. Either from the worm gear not being perfectly centered or from the bearing system. With using small worm gears this "error factor" is
amplified as to with the larger worm gears it is not as noticeable. In theory a perfectly built mount with with no slack using 60 tooth gears would be as accurate as a mount with 180 tooth gears In other words one degree of error on a 60 tooth gear will show up 3 times worse than the same amount of error when using a 180 tooth gear.
   So what does all this mean ?  The larger and heavier the OTA the larger the gears need to be. Please note that as the
gears get larger the slower the slewing speeds will be. A mount using 120 tooth worm gears will slew at half the speed of
the original DS or ETX models. And 180 tooth gear will only slew at 1/3 rd the original speed. This also means a lot more battery power will be needed.

From my experiences here's what I would recommend:

Small mounts up to 4" OTA:   60 to 96 tooth worm gears

Medium 4" up to 8" OTA      96 to 120 tooth worm gears

Large 8" +  OTA                120 to 180 (or larger) tooth worm gears.

180 tooth worm gears are as largest gears I have used to date. These are some large gears that provide a lot of torque
but have very slow slewing speeds.
 
 

Mount Materials ?

All of my mounts are built from aluminum that I purchased from a local salvage yard. My larger Dob mount is a combination or
wood and aluminum.
The large aluminum pieces for the mounts were cut using a 10 radial arm saw and 60 tooth carbide tipped (woodworking) blade. Safety glasses and gloves are a must. By cutting very slowly (to avoid kickback) even thick aluminum can be cut easily. I also apply a lubricating spray (WD-40) to the aluminum piece and the blade before each cut. A jigsaw equipped with a metal cutting blade was used for cutting the smaller aluminum pieces and for the rounded cuts. A shot of lubricating spray applied every inch or so (depending on the thickness of the material being cut) while cutting will greatly increase cutting time and increase the blade life.

Another option for a DS powered mount is to do as Peter Wallner did.  Click Here for Peter's web site.
 
 

Still under construction so check back soon
                                                                              Thanks,
                                                                                       Steve Bedair
 
 

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 Copyright 2000 Steve Bedair