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Making an equatorial platform

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#26 Ed Jones

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Posted 30 July 2005 - 09:56 AM

The next step is the ground board. I cut two 3 X 32 inch boards with a 36 degree included angle. I made the block shown in this shot by first glueing two boards together and finishing one edge then gueing it to another cross grained. I cut the front side at 39 degreea and the side at 36 degrees to fit the angle of the bottom boards and glued these all together. The sharp point of the end will be rounded off and there will be a leveling screw here. This is where I am today.

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#27 Ed Jones

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Posted 30 July 2005 - 10:01 AM

This is the timing motor I plan to use, 1/25 RPM clockwise rotation and 3 watts. A machinist friend of mine made a stainless steel knurled roller .625 inch diameter which will drive it.

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#28 waynet

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Posted 30 July 2005 - 01:54 PM

Ed,
This is a great contribution!

thanks,
wayne

#29 Ed Jones

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Posted 31 July 2005 - 10:26 AM

Thanks Wayne, I want to get it finished ASAP. This would have been even easier to make out of baltic birch but I had the walnut and it'll look a bit nicer. I would always make the bearing out of hardwood though.

#30 Ed Jones

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Posted 03 August 2005 - 08:42 PM

I decided to glue a 2 inch wide board underneath the front board because it gives a stronger joint and I needed some room for leveling. It added another 3/4 inch to the height and it is now 4 inchs high. I used 3 ball bearings with 1/4 inch ID for the left roller.

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#31 Ed Jones

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Posted 03 August 2005 - 08:52 PM

I used Teflon blocks to hold the right roller. The motor shaft was press fit on the roller. I need a small block of wood to be glued on the base for one of the motor mounting screws. Both the left and right roller axis are aligned to the pivot point. I had to add a small shim to make the roller lay flat on the north bearing.

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#32 Ed Jones

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Posted 03 August 2005 - 08:59 PM

I used a 1/4-20 stainless cap screw for the south pivot with a Teflon washer between two steel washers. A 1/4-20 stainless carriage bolt is used for leveling with a T-nut underneath.

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#33 Ed Jones

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Posted 03 August 2005 - 09:10 PM

So here is the platform ready to go except for adding the Teflon pads and wiring up the motors. It'll need a limit switch, some rubber feet and a lock of some sort (details).

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#34 MrLunch

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Posted 03 August 2005 - 10:40 PM

Ed, I am stunned. I really couldn't tell what you were making at first. It's extremely elegant, especially the decl. solution. Will decl. be adjusted just with a hand paddle of some sort?

#35 MMICKELS

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Posted 03 August 2005 - 11:22 PM

Maybe I missed something. Are there two motors?

#36 Chriske

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Posted 04 August 2005 - 03:00 AM

Ed,

I don't see any screws , did you use dowels..?
I must admit, this concept is much more elegant than mine.

Marc, I asked miself the same question about these motors.

#37 Ed Jones

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Posted 04 August 2005 - 07:16 AM

Yes there are two motors, one for tracking the other uses a reversible AC motor driving the maple wedge for slow motion north and south (sort of). I used screws to attach the north bearing to the rails and the pivot plate. I used a ribbed nail to attach the cross piece for the rocker pivot. All other joints were face grain joints which are pretty strong.

#38 Stefan Rostyne

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Posted 04 August 2005 - 07:28 AM

Wonderfull piece of work! The second motor (at the far side) just drives the wooden wedge slider? The slider will get a teflon coat, as I read above, but how does this make sence as a slow motion controller? Does it slide immediately agains the rocker base board? It's a friction trick, for sure!

#39 Ed Jones

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Posted 04 August 2005 - 07:37 AM

Stefan,
Remember I glued the triangle that the wedge sit on at ~6 degree angle so when it is moved by the motor it moves uphill pushing the rocker box slightly. The top of the wedge is parallel to the bottom of the rocker box. I haven't tested this yet with my 12 inch but I'm pretty sure it'll work.

#40 Stefan Rostyne

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Posted 04 August 2005 - 09:18 AM

Aha! So if I'm right, the second motor is not meant to work all the time, but only for slight corrections on the guiding? Off course that will work, a clever, clean and easy solution!

#41 Ed Jones

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Posted 07 August 2005 - 10:32 PM

Final report: How does it work?
It was very hazy tonight and I could hardly see Arcturus but I could test my platform out. With a 6 mm eyepiece in my 12 inch f/5 Arcturus stayed steady in the field with no slipping until it slowly drifted north (my polar alignment wasn't perfect). The north/south motor worked but with more periodicity than I'd like, it would speed up and slow down. I'll have to check into that and it needs limit switches too. The only other criticism I have is that the tracking motor is a bit noisy. A timing motor should be very quiet but perhaps I did something to it when I pressed it into the knurled shaft. I'll replace it and they're not very expensive anyway. All in all not so bad though, I spent about $15 on hardware and now another $20 for a tracking motor. My goal here was to show that it's not so difficult to build one of these.

#42 Chriske

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Posted 08 August 2005 - 01:33 AM

Ed,

On the RA driving motor, you did not mention if there where ballbearings to support the knurled schaft. Are there any..?

Chris

#43 Beri

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Posted 08 August 2005 - 05:23 AM

Thank you Ed for this thread, it will help me a lot in building my own platform for my 300mm F5 :)

#44 Ed Jones

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Posted 08 August 2005 - 06:57 AM

Chriske,
I used teflon blocks to support the knurled shaft. This is the same method I used on my first platform and the motors on it were quiet as a mouse (as they should be).

#45 rnabholz

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Posted 08 August 2005 - 10:26 AM

Congratulations on a very nice project. Your approach using hardwood instead of plywood made for a very elegant looking finished product. I would almost hate to take it out and expose it to the elements.

Thanks again for documenting this for our benefit.

#46 Ed Jones

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Posted 08 August 2005 - 12:17 PM

Thanks. I'm not too concerned about the elements though. I have 2 coats of urethane varnish on it but it won't get a lot of dew being under the rocker box. Making it out of baltic birch would have been easier and probably looked just as good. I just used what I had on hand.

#47 Ed Jones

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Posted 07 October 2006 - 09:03 AM

Here is an update. I replaced this motor and added two 4 RPH motors from Herbach and Rademan using 3.8 inch SS shafts that were knurled. I tried this out last night and it worked to perfection, 2 motors is the way to go. Two motors will prevent slipping that I would sometimes get when using another scope with a CG higher than was designed for this platform. These motors ran pretty hot to touch I thought so I added 2 1/2 watt 2.2K resistors to each motor to limit the current since they will run off my car battery. Even so they still had plenty of torque and couldn't be stalled.
Ed Jones

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#48 netwolf

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Posted 07 October 2006 - 11:53 AM

Ed, I just realised how that north south motor works, thats brilliant. The motor moves the wedge up and down an incline to give you find Dec adjustments. Most designs I have seen require the replacement of the grond board to achive this, with your design you can just put the whole dob on top. Brilliant. I wonder if one could adapt the autoguding circuitry being discussed in the eqplatforms yahoo group to work with this setup.

Regards

#49 Chriske

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Posted 07 October 2006 - 02:13 PM

Ed, I just realised how that north south motor works, thats brilliant. The motor moves the wedge up and down an incline to give you find Dec adjustments......

Regards


The correction made by that motor is there to correct the 'polar axis' direction. No correction in decl. is made with that motor at all. If one is observing with this mount say on the western horizon and correcting with that so called declination correction motor, it is turning completely wrong, that is 90° on the supposed decl. (altitude) movement.
Only when observing south one *could* correct in declination with that motor.
Or did I misunderstood the whole consept, Ed...?

Nice mount btw.... :bow:

#50 Ed Jones

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Posted 07 October 2006 - 03:37 PM

Chriske you are correct it moves it north south but it doesn't align with the celestial coordinate direction. It's a good compromise though. Actually it didn't work as smoothly as I'd hoped, I'm thinking about a redesign if I get serious about photography.
Ed


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