The basic choice here is whether you want to build from
scratch or
purchase astronomical drive components and convert them to work with
your telescope mount. If you are a "purist" and want to start with only
basic components (stepper motors, optical encoders, self programmed
code, etc.), then I highly recommend visiting Mel Bartels'
Motorize Your Telescope Pages. This is a fantastic website
with a
wealth of information and links to related sites; there's lots
of
information regarding homemade gears and different drive
systems, that are
applicable to both a "build from scratch" or Autostar conversion
project. I
also highly recommend visiting Steve Bedair's GoTo
Telescope Mounts Pages; there is a lot of fantastic
information here regarding
the
Meade Autostar motors and making homemade worm gears and telescope
mounts. If you want to convert an equatorial mount, then
visit Christopher
Erikson's website. This site contains lots of great step by
step instructions and links to other telescope builder's sites.
I chose to purchase Meade components and convert them to work with my telescope mount. This was less involved than building from scratch, but still involved basic problems of reducing the Meade 492 motor gear ratios to an appropriate level and finding a way to connect the Meade components to a generic Alt-Az mount. An excellent site for all types of information on the Meade Autostar system is Mike Weasner's Meade Autostar Information Site.
There was a lot of trial and error during this process, and I will try to illustrate what didn't work as well as the final solutions. The remainder of this web page is a chronological description of what I tried and the results. The design that finally worked is described on the Friction Drive Page.
The nylon Autostar spur gears accept a tapered shaft (the tapered Autostar worm shaft is shown in the below photo to right). I experimented with different ways to make a straight shaft fit this tapered gear socket. I placed a M12 threaded rod in my drill press and rotated it against a metal file. This "poor mans" metal lath worked, but I couldn't turn down the threaded rod to accurately fit the tapered spur gear socket. I tried threading the turned down rod and tapping out the inside of the spur gear socket with the same thread, but this also failed. I made a few prototype worms, but they were all slightly off centered in the Autostar spur gear and didn't work (unfortunately my metal working skills are rather limited).
Following the instructions on Christopher Erikson's website, the first prototype shaft coupler worked fantastic; the threaded rod sits perfectly centered in the spur gear and the steel is a much stronger material than the brass Autostar worm. The Autostar spur gear is held in place by a 2.5 mm bolt. I didn't have a 2.5 mm tap, so I drilled a 2.5 mm hole and tapped it for a 3 mm bolt (this worked just fine).
I think that my initial problems in fabricating a shaft coupler were due to beginning with a M12 threaded rod. When I started with a M6 threaded rod, tapering the end required removal of very little metal and was both fast and easy. The problem of coupling a shaft to the Autostar spur gears is easily solved by just spinning a 6 mm diameter rod against a file, and the prototype and final fabrications only required about an hour each!
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I later took a spare Autostar worm and cut it into a hob. This hob cut much better than the M12 rod, but due to the limited length, there was difficulty cutting large gears; if the blank was too large, it rubbed against the power drill.
Hobbing nylon gears was very easy (and fun), however I couldn't control the hand drill with enough precision to cut uniform teeth. There were areas where the teeth moved away from center or were of uneven depth. It's quite necessary to have a jig to hold the cutting hob perfectly tangent to the gear blank edge and advance it into the blank with even pressure. Take a look at Martin Cibulski's site on making large gears from aluminum sheet metal for a nice photo of this type of jig.
After many attempts (and many cutting boards) I produced two satisfactory 330 tooth worm wheels, however they failed functional testing. The nylon was too soft and the altitude worm slipped repeatedly in the worm wheel as the OTA was elevated. The azimuth worm wheel seemed to function fine. These 330 teeth gears gave a lot of torque, but they turned very slowly. The slew speed was just too slow and I began to be impatient during testing. I finally abandoned cutting worm wheels.
An after note is that I later found 120 tooth worm wheels and worms available on eBay starting at about $35. I decided against belt and chain drives and eventually opted for a friction drive system (see the Friction Drive Page for the final design).
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The below photos shows the original band clamp and a close up of the worm and worm mount (left and right, respectively).
The band clamp was wrapped and glued to wood disk, creating a 280 tooth worm wheel (below photos). A rollerblade wheel bearing was installed in the worm wheel and it was secured to a scrap of pine with a M6 bolt.
The band clamp worm was removed and nailed to a scrap of pine; top and side views are shown in the below left and right photos, respectively.
The worm was pushed against the band clamp worm wheel and clamped to the same pine board as the worm wheel (below left photo). The below right photo shows a close up of the worm and worm wheel. A variable speed power drill supplied the rotational motion.
This gear system functioned surprisingly well. The main problem seemed to be the worm mount. Since a band clamp is designed for other purposes, the worm mount is not too precisely formed. There was a fair amount of worm wobble and friction/heating of the worm mount. Substitution of a better worm and worm mount would drastically improve the results. My major concern with this worm wheel was backlash error. The band clamp teeth are a bit wide and may introduce significant backlash into this system; I will leave this for someone else to test and evaluate.
I only constructed this gear to satisfy my curiosity about the feasibility of using a band clamp to make an inexpensive and easy worm wheel. I am not planning any further testing of this system. If anyone successfully applies this gear to a project, please send me an e mail and let me know how it turns out. I highly recommend substitution of a better worm and worm mount.
I chose to purchase Meade components and convert them to work with my telescope mount. This was less involved than building from scratch, but still involved basic problems of reducing the Meade 492 motor gear ratios to an appropriate level and finding a way to connect the Meade components to a generic Alt-Az mount. An excellent site for all types of information on the Meade Autostar system is Mike Weasner's Meade Autostar Information Site.
There was a lot of trial and error during this process, and I will try to illustrate what didn't work as well as the final solutions. The remainder of this web page is a chronological description of what I tried and the results. The design that finally worked is described on the Friction Drive Page.
Unsuccessful Drive Prototypes
There are many different drive choices (metal worm gears, nylon threaded rod gears, friction drives, belt drives, etc.) and I have seen fine examples of home built GoTo telescopes with all of these drive systems. I have chosen a drive system which worked for me with regard to my construction skills, available materials, what I could make work, and ultimately what I liked. I'm adding this so that I don't receive a flood of hate e mail from telescope builders employing alternative drive types.Threaded Rod Gears
I started by looking over the links on Mel Bartel's Mechanical Aspects of the Drive Page, and selected a few drive types for testing. I first tried making worm gears by wrapping threaded rod around a circle. I couldn't locate threaded nylon rod, so I experimented with threaded M6 steel rod. After making a jig to bend the rod, I was able to bend a pretty good circle, however pretty good wasn't good enough (left photo). There were small imperfection in the bent rod and I couldn't get the gear to rotate smoothly. I eventually abandoned steel threaded rod and finally located some M6 threaded nylon rod. I made a prototype gear that was much better than those using threaded steel rod (right photo).
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Autostar Shaft Coupler
Gears made from threaded nylon rod looked promising, however the next problem was a shaft coupler to connect the worm with the Autostar spur gears. A good site dealing with Autostar shaft couplers is Christopher Erikson's website; here you will find ideas for shaft couplers and diagrams that can be taken to a machine shop for fabrication. Unfortunately I didn't find this web site until after I abandoned this type of drive mechanism.The nylon Autostar spur gears accept a tapered shaft (the tapered Autostar worm shaft is shown in the below photo to right). I experimented with different ways to make a straight shaft fit this tapered gear socket. I placed a M12 threaded rod in my drill press and rotated it against a metal file. This "poor mans" metal lath worked, but I couldn't turn down the threaded rod to accurately fit the tapered spur gear socket. I tried threading the turned down rod and tapping out the inside of the spur gear socket with the same thread, but this also failed. I made a few prototype worms, but they were all slightly off centered in the Autostar spur gear and didn't work (unfortunately my metal working skills are rather limited).
- Make a shaft coupler by taking a piece of aluminum block and drilling a 7 mm pilot hole through the block. Then using the pilot hole as a precise guide, drill a larger hole half way through the block, tap it to the thread on the worm rod, and install set screws. Then cut off the tapered end of the Autostar worm and install it into the 7 mm side of the shaft coupler.
- An alternative is to turn down the Autostar worm to a shaft and then thread it to match the worm wheel thread-but it seems a shame to do this to such a nice worm.
Following the instructions on Christopher Erikson's website, the first prototype shaft coupler worked fantastic; the threaded rod sits perfectly centered in the spur gear and the steel is a much stronger material than the brass Autostar worm. The Autostar spur gear is held in place by a 2.5 mm bolt. I didn't have a 2.5 mm tap, so I drilled a 2.5 mm hole and tapped it for a 3 mm bolt (this worked just fine).
I think that my initial problems in fabricating a shaft coupler were due to beginning with a M12 threaded rod. When I started with a M6 threaded rod, tapering the end required removal of very little metal and was both fast and easy. The problem of coupling a shaft to the Autostar spur gears is easily solved by just spinning a 6 mm diameter rod against a file, and the prototype and final fabrications only required about an hour each!
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Moulded Gears
I also considered making molded worm gears. I made a prototype using hot glue and was very pleased with the threading. Hot glue was only suitable for testing the idea and would not be strong enough for the actual worm wheels. Unfortunately I couldn't locate a suitable polymer patching material or resin, so this idea never got beyond the initial test stage.Back To Top
Hobbing Nylon Gears
I next returned to my first drive choice: worm wheels. I decided to try hobbing (cutting) nylon worm wheels with a power drill. I bought several nylon cutting boards, cut them to circular gear blanks, and built a jig to hold them perpendicular to my work bench. The first test hob was made by using a hobby saw to cut a groove into a piece of M12 threaded rod.I later took a spare Autostar worm and cut it into a hob. This hob cut much better than the M12 rod, but due to the limited length, there was difficulty cutting large gears; if the blank was too large, it rubbed against the power drill.
Hobbing nylon gears was very easy (and fun), however I couldn't control the hand drill with enough precision to cut uniform teeth. There were areas where the teeth moved away from center or were of uneven depth. It's quite necessary to have a jig to hold the cutting hob perfectly tangent to the gear blank edge and advance it into the blank with even pressure. Take a look at Martin Cibulski's site on making large gears from aluminum sheet metal for a nice photo of this type of jig.
After many attempts (and many cutting boards) I produced two satisfactory 330 tooth worm wheels, however they failed functional testing. The nylon was too soft and the altitude worm slipped repeatedly in the worm wheel as the OTA was elevated. The azimuth worm wheel seemed to function fine. These 330 teeth gears gave a lot of torque, but they turned very slowly. The slew speed was just too slow and I began to be impatient during testing. I finally abandoned cutting worm wheels.
An after note is that I later found 120 tooth worm wheels and worms available on eBay starting at about $35. I decided against belt and chain drives and eventually opted for a friction drive system (see the Friction Drive Page for the final design).
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Band Clamp Gears
A band clamp is just a flexible worm wheel (band) that is tightened around an object and held in place by tensioning the worm (screw). An idea that I recently had was to test if a band clamp could be wrapped around a cylinder to make a worm wheel. If successful, this would be a very easy and inexpensive way to make a worm wheel. I found a large band clamp in the furnace ducting section of the local hardware store and made a test mock up of the system.The below photos shows the original band clamp and a close up of the worm and worm mount (left and right, respectively).
The band clamp was wrapped and glued to wood disk, creating a 280 tooth worm wheel (below photos). A rollerblade wheel bearing was installed in the worm wheel and it was secured to a scrap of pine with a M6 bolt.
The band clamp worm was removed and nailed to a scrap of pine; top and side views are shown in the below left and right photos, respectively.
The worm was pushed against the band clamp worm wheel and clamped to the same pine board as the worm wheel (below left photo). The below right photo shows a close up of the worm and worm wheel. A variable speed power drill supplied the rotational motion.
This gear system functioned surprisingly well. The main problem seemed to be the worm mount. Since a band clamp is designed for other purposes, the worm mount is not too precisely formed. There was a fair amount of worm wobble and friction/heating of the worm mount. Substitution of a better worm and worm mount would drastically improve the results. My major concern with this worm wheel was backlash error. The band clamp teeth are a bit wide and may introduce significant backlash into this system; I will leave this for someone else to test and evaluate.
I only constructed this gear to satisfy my curiosity about the feasibility of using a band clamp to make an inexpensive and easy worm wheel. I am not planning any further testing of this system. If anyone successfully applies this gear to a project, please send me an e mail and let me know how it turns out. I highly recommend substitution of a better worm and worm mount.
