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My New Dob Tracking Platform

Discussion in 'Telescopes and Mounts' started by Ed D, May 4, 2022.

My New Dob Tracking Platform

Started by Ed D on May 4, 2022 at 8:48 AM

19 Replies 2507 Views 3 Likes

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  1. Ed D

    Ed D Well-Known Member

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    One of the four scopes I own is a 10" Skywatcher collapsible strut Dob. It was an early retirement gift from me to me which I have owned for 5 or 6 years now. At one point I accidentally chipped the secondary, which was replaced with a much better Antares mirror. The factory secondary was a Bow-Wow, no insult to dogs. Although the views through the Dob are very nice, I never really warmed up to the scope. The look-push-look-push at high power was a turn-off. Planetary imaging left a lot to be desired, too. I even tried to sell it at one point.

    I have always wanted some form of tracking for the big Dob. I considered buying one of the factory tracking mounts or an aftermarket kit, but the field rotation inherent in an Alt-Az design was a turn-off for the imaging I had in mind. I also looked at many tracking platforms. Although they are really nice, I couldn't bear spending up to 10 times as much (or more!) than what the Dob cost me. I even found one gorgeous tracking platform that had auto-guiding capability for imaging. I won't mention how many thousands that one cost.

    Browsing the web, I came across the North Star Systems tracking platforms, for under $300 US shipped. The website images show platforms that look nice and well made. The thought crossed my mind that I would probably be making small mods to the platform to make it perform how I want. Don't most of us do that with our precious Dobs?

    I contacted Peter, the owner, asking if the listed prices were current and if he could make a platform for 25.6 N latitude. He promptly replied, answering all my questions and giving me the time it would take to build and ship. I thought about it and placed my order. The tracking platform arrived on schedule.

    The components were shipped securely and well protected with bubble wrap:

    Dob Tracker 01.jpg
    Upper platform where the Dob sits

    Dob Tracker 02.jpg
    Bottom view of the upper platform

    Dob Tracker 03.jpg
    Ground board with box containing the motor drive and other parts

    These are the components:

    Dob Tracker 04.jpg
    Ground board - the instructions state the South bearings are designed to be offset

    Dob Tracker 05.jpg
    Closeup of the end-of-travel cut-off switch and motor mounting screw

    Dob Tracker 06.jpg
    The compass is a nice and useful touch

    Dob Tracker 07.jpg
    Motor, drive shaft, and assembly and use instruction sheets

    I put the platform together and tested it in the family room:

    Dob Tracker 08.jpg
    Testing the full range of travel - motor was set to fastest speed

    Dob Tracker 10.jpg
    The cut-off swith worked as intended

    After testing, I decided to put the wires together with a small connector:

    Dob Tracker Mod 01.jpg
    Drive assembly showing small connector I used - wires are soldered to the pins

    I could have simply soldered the wires or used wire nuts, but felt the connector was the better choice, especially if I need to take the assembly appart for any reason.

    I finally had a somewhat clear night and wanted to run the platform under the stars to see how it worked. I spent several minutes adjusting the motor speed on a random star. Once set, I aimed the Dob at the double star Castor in Gemini. I played around with different eyepieces, becoming immersed in the views. How nice not to have to look-bump-look-bump.

    I did not realize how much time had elapsed. The motor came to a halt. Oh no, I thought, what went wrong? Nothing at all. It was just the end-of travel cut-off switch doing its thing. I reset the platform and continued enjoying the views. I had intended to be outside only for about a half hour. I packed it up when I realized well over three hours had gone by and it was waaay past my bed time.

    So, am I happy with the tracking platform? You should see the big grin on my face. I will probably be doing a few mods to the platform in the future to make it suit me better, not because it needs it. This platform is not for everybody. If you want a Dob tracking platform that looks like a finely finished piece of furniture I suggest you look elsewhere. Likewise, if you want something that is made of metal, with fine welds that look indestructible, this platform is not for you. If you own a big custom Dob that cost you serious money don't even look at this one. But, if you have a production China-Dob and want a basic, no frills tracking platform then I suggest taking a look at the North Star platform. It works, period! Like your Dob, you will probably want to do mods to this platform to make it suit you, and have some fun in the process.

    Ed D
     
    Last edited: May 4, 2022
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  2. PXR-5

    PXR-5 Well-Known Member

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    Very nice Ed!

    Beautiful looking product, enjoy and let us know how it performs :)
     
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  3. Ed D

    Ed D Well-Known Member

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    Thanks, Jeff. My initial test was very positive. We are now in the rainy season here in South Florida, which makes it difficult to enjoy the night sky. But, I'm thinking of imaging lunar craters whenever it all comes together. Soon...

    Ed
     
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  4. Ed D

    Ed D Well-Known Member

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    On May 9th I finally gave the platform its initial imaging run on the moon. I spent some time adjusting the motor tracking speed and finally found the sweet spot. My East/West alignment was off, enough to cause a slow drift - a good thing when imaging planets and the moon. Being the initial run, I didn't mess with trying for accurate polar alignment, plus it was good enough for what I wanted to do.

    2022 05-08 Moon.jpg
    Lunar craters Arzachel, Alphonsus and Ptolemaeus (center)

    One characteristic of the platform is that stiff gusts of wind do induce a little shake. The same thing happens when using my 6" Mak on the CG-4, so no surprise, and it's something I know how to deal with. It was not a good night for imaging with anything, but I really wanted to try out the platform. A small quirk I found was one spot during tracking that made the image jump a little, a bump. It turned out to be a small bit of wood finish buildup on the rear track, which was easy enough to rectify with a sharp knife in about 2 seconds.

    A small mod I made to the bracket that holds the drive shaft and cut-off switch was to drill the mounting holes one drill size larger. This gave me a bit of adjustment to align the motor and shaft perfectly, although it ran fine as it was. I also radiused the inside edge of the drive shaft head. I very sparingly used light lithiun grease on the bearing surfaces of the drive shaft and bracket. This thing purrs like a kitten and is smooth as a baby's behind throughout the travel.

    Ed
     
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  5. Orion25

    Orion25 Well-Known Member

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    Nice shot, Ed. Sweet platform for a sweet scope :)
     
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  6. Ed D

    Ed D Well-Known Member

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    I have had the platform for about a month now and have made a couple of mods. One mod was to glue a 3/8" wide strip of thin leather to the drive surface of the top plate:

    Dob Tracker Mod 02 Leather Strip.jpg
    Thin leather strip glued to drive surface

    A couple of nights ago I set up the platform, but the drive shaft didn't move the top plate - not enough traction. Tropical weather can be fickle and harsh, and can do weird things sometimes. I had the thin leather and glue in the garage. Within about two minutes I had the leather strip cut out and glued to the driving surface, which I let dry overnight.

    The other mod I made was to install a T-Level on the base:

    Dob Tracker Mod 03 T-Level.jpg
    Red T-Level added to base

    On a level interior floor the platform is spot on. However, the patio slab has to be angled to let the rain water run off. As soon as I placed the base on the patio slab I immediately saw the bubble was off, just as I had expected. A 1/8" piece of hobby plywood placed under the front feet leveled the base. I'm thinking about making adjustable front feet, but the small piece of plywood is so easy to use.

    Ed D
     
    Last edited: May 24, 2022
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  7. Orion25

    Orion25 Well-Known Member

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    Looking good, Ed. You've obviously done this before, lol!
     
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  8. Ed D

    Ed D Well-Known Member

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    I have been working on things and innovating since before I was ten.

    Ed
     
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  9. Orion25

    Orion25 Well-Known Member

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    Wow! That's impressive, Ed :D
     
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  10. Ed D

    Ed D Well-Known Member

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    Last night I set the scope and platform up, making sure the platform was level and polar aligned. The T-Level I added is a very useful addition. I tried it on a few stars in different parts of the sky and tracking was great. This morning I set it up in the family room and timed the platform travel. I'm getting 41 minutes of tracking time. This is plenty for my visual, and especially for lunar and planetary imaging, which takes only a scant few minutes.

    So far so good, but I'm needing more 9V batteries, and that's a good thing! :)

    Ed
     
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  11. Orion25

    Orion25 Well-Known Member

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    Great news, Ed. I'm glad everything's working well after all your effort :)
     
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  12. Nebula

    Nebula Well-Known Member

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    This is really motivating for me Ed D, to see a person with great success with an EQ platform like that. The design of that platform looks fairly simple also.

    I want to try to modelize a similar concept in CAD tomorrow. The front sectors, don't appear to have any special angles or anything.

    Everything is as simple as it can be.
     
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  13. Ed D

    Ed D Well-Known Member

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    UPDATE 10/16/2022: I kept having some issues with the platform drive, very annoying little glitches. I believe these platforms may be good for use with lighter 6" or 8" Dobs, but the weight of my 10" seems to be pushing it. The original drive system, although effective, was crude:

    Dob Tracker Mod 01 Connector.jpg
    Original motor drive - I installed the electrical connector.

    I thought about how to make a more refined drive system, one with a flexible coupler. The motor output shaft miked at 5mm, and the drive shaft 8mm. I found a 5mm/8mm coupler on eBay for a whopping $4.39 shipped to my mail box, the shipping costing more than the coupler. I used a nylon spacer I had in a junk drawer between the coupler and motor to prevent any possible binding:

    Motor Drive Mod 01.jpg
    Coupler and motor shown with nylon spacer.

    Motor Drive Mod 02.jpg
    Coupler installed on motor.

    I had a long stainless steel bolt with an 8mm shaft that I made the drive shaft out of. I purposely made it extra length and knurled it in the mid-section for better grip of the drive surface. The entire shaft was polished with 400 grit, including the knurling. I didn't want sharp knurling that would eat away the drive surface, only enough to afford a good grip:

    Motor Drive Mod 03.jpg
    Polished shaft in my very old Harbor Freight Mini-Lathe.

    I didn't like the little wood screw used to mount the motor to the platform. I drilled the hole all the way through and used a longer bolt and nut to mount the motor. The bolt doesn't have to be tight, snug works best. I put everything together, aligned it and snugged it down:

    Motor Drive Mod 04.jpg
    Motor assembly with new drive shaft and coupler.

    As you can see in the above picture, I modded the motor for use with a six AA cell holder. The battery is held on the platform with velcro, which I stapled on with an upholstery stapler.

    Weather has not been cooperating, so I tested the drive in my family room:

    Motor Drive Mod 05.jpg
    Testing the modded drive.

    I'm glad I tested it because it revealed that the battery cable had to be routed to the right of the motor to avoid pinching as the platform moves. No big deal to screw in a small wood eyelet and Ty-Wrap the cable to it:

    Motor Drive Mod 06.jpg
    Picture of battery cable securing method.

    In my limited testing indoors the platform appears to be tracking very smoothly now. The glitch spots seem to be gone. I'm anxious for a clear night so I can test my platform under the stars.

    Just like mass produced Dobs, this platform has been a work in progress. Like I said previously, I think this platform is better suited for 6" and 8" Dobs. My 10" is really pushing it, and I would say it's a bit undermounted.

    The Dob and the platform are works in progress. Stay tuned.

    Ed D
     
  14. Orion25

    Orion25 Well-Known Member

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    Nice work. Can't wait to hear your report from the field, Ed!
     
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  15. Nebula

    Nebula Well-Known Member

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    Cool quality upgrade, I like your knurled mid section on the shaft too, it's a good idea, well made!

    For the battery I bought this 12v 1.5AH lead acid battery with a voltage step up and down circuit board. It's possible to adjust from I think from 2v to 24v however the amount of amps is variable but it's good for small circuits consuming not much current. it's possible to set the voltage a bit higher like +-9.2v so when the load is applied there is a voltage drop at 9v precise and stable.

    [​IMG]

    That's what I was told to do.

    The larger battery is rechargeable, very inexpensive compared to Duracell and Energizer AAs.

    ***
    Not sure I am attracted to the platform anymore especially with the weight issue you talk about...
     
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  16. Ed D

    Ed D Well-Known Member

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    Very nice. I'm guessing you're powering up a 9V motor drive for a GEM and/or heater strips? Years ago I installed a Celestron 9V drive on the RA of my CG4 mount to track planets. The 9v batteries used on these motors don't have much amperage, especially for the load, and internal battery heat builds up enough to affect performance. The high environmental temperatures down here don't help. A larger capacity 9V battery runs cooler and output is stable.

    The reason I use AA cells is because I make sure I have an ample supply in my hurricane prep kit for the lanterns, radio, etc. They eventually expire and I'm too cheap and ecologically sound to toss them out unused. I also have a couple of Harbor Freight portable jump starters that I keep charged for reserve hurricane power, which do double duty to power my astro dew strips, fan, etc.

    Ed
     
    Last edited: Oct 16, 2022
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  17. Nebula

    Nebula Well-Known Member

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    @Ed D It was to power my equatorial platform, but the design was a total failure, I used it to power 3v leds and now it's useless. For my EQ5 mount I use D batteries in the original controller power pack :D I also have a bunch of them from Amazon. But for the EQ5, 4xD batteries will last 6 months of observation with the quality Duracell, now I don't know about the Amazon brand, how long these will last.

    Initially the step up and down board was really for the Celestron drive! I found that only 1x 9v battery was too small for the purpose.

    My dew strips are powered by a standard 12v Lead acid 7AH battery, but my DIY controller works directly on 12v, it will draw about 0.8A @12v with 4 straps operating at the same time but I always use only 2 straps at the same time when I get the scope inside then put the battery on the charger directly.

    I understand your concept now! good idea to use these batteries instead of losing them.
     
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  18. Ed D

    Ed D Well-Known Member

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    UPDATE 10/23/2022: Finally got the platform and 10" Dob out under the night sky. I observed Jupiter at medium-high power, tracking through three full cycles and a few partial cycles. I'm happy to report that the platform tracks smoothly without any issues. Although the 10" Dob is undermounted, the platform settles down in reasonable time after focusing or touching the scope. Also, the six AA cell battery works so much better and consistent than the 9V 'transistor' battery.

    The only other mod I want to make to the platform is installing adjustable feet to make leveling easier. Currently I'm using a thin piece of hobby plywood under the North feet - Crude, but effective. I will report and post pictures whenever I get around to doing the mod.

    Ed
     
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  19. Nebula

    Nebula Well-Known Member

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    Good! Glad your platform improved after you've made your modifications to the "ok" original engineering!

    Did you see white oval storms on Jupiter so far?( in the SS Temperate belt)

    I use small pieces of plywood to adjust the height of my Dobson base currently, they are kind of fast to install! (But i rarely get a precise 100% level)
     
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  20. Orion25

    Orion25 Well-Known Member

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    With bated breath, Ed! ;)
     
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