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Equatorial platform type 'BM'


Chriske

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I think there is a problem with the power supply as I have used the same 5v for the arduino and the stepper driver. I had noticed that an analogue input changed depending on if the motor was running so there is a problem. I will modify the power supply to make the motor run from an independent 5v supply.  I was trying to cut corners which proved to be the wrong strategy.

I have received the 8mm 3d printer threaded rod and brass nut this morning. Its much easier to turn  and I think it will be a big improvement. 

Robin

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This threaded rod and brass nut will give you a far better result.
If you have the complete set, you should have received a three part nut. The nut itself a counterpart and a spring. This is to get rid of play between rod and nut.
If these two parts are not present, you could always add a spring or a rubber band a the end of the board, to do just the same. It will give you a smoother action while tracking.
If there's enough load on top of the plank no need to add that extra tension.
You must also consider that spring or rubber band in case there's to much friction on the hinge.

In my case, using it as a eq. platform for telescopes, it will not be an issue of course. There's always more then enough load.
As matter of fact if the load on top of my board is to high I need to just the opposite. In a few of my earlier BM's I've added an pressure pump (out of the backdoor of a car) to get rid of the load sitting on top of it.
But this time this new BM only 65mm high I have to come up with another solution because there's not enough room to add a  pressure pump between the two sheets of multiply. The rod and nut are no match at all for the weight of my 14" DarkStar.

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Have you decided how to drive the plywood circle?  I assume that the pressure pump is what I would call a gas spring.  Could the assisting pressure pump  be mounted flat to push the top disc round rather than lift it?

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  • 3 weeks later...

Still at it...

Busy making a smaller BM. It was used to drive a big binocular manually.
I will now use this one to support and drive a folded refractor I'm working on.

Bleu : polar axis at 51°
Red  : Bracket + stepper
black : threaded rod
Angled gliding blocks cut at 39°
Poulies and belt not in drawing yet.

image.thumb.png.58efe540cc9abda4a8f0da70f79d9244.png

image.png.ff44a3a96387dc8b69200c3079eac4b1.png

 

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Are the guiding blocks  39 degrees and flat.?  It looks very simple which is good. Lots of other eq platforms seem to have complicated guide profiles.

Will you need to pivot the motor to match the angle of the threaded rod as it moves? I know you will not run for long so maybe the belt can just twist a small amount.

I am very interested as I have been wanting to make a platform for about 4 years but other projects have got in the way and I am very slow.

Robin

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In my case indeed the gliding blocks are flat and at 39 degree angle(I live at 51°N). There's no need for these complicated guiding profiles, indeed.
And no the motor does pivot at all because the other pulley, driving the threaded rod, is stationary too.
Almost done building this platform, I'll post some detailed pictures soon.

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Last night first test for the laser position. And with success.
The laser was collimated in it's aluminium tube, was done in a lathe.
The two holes, for polar axis and laser unit were printed parallel.
Mounting the laser in its unit and aiming it toward the exact north. I had no aid to do that, so eyeballing. But with the knowledge that North was about 0.5° from Polaris and in the direction of beta Umi, I was very close. Aiming the laser was done by adjusting the mount of course.

I was so close in fact that I could track a star at the equator for about 25minutes without the need for correction in declination at all(at 125x). I was a bit surprised as a matter of fact.
Yesterday's tracking was done manually, now the only thing to do is connecting the stepper to the RAMPS.

image.png.f265e658cc7d5115328980f9d96fc4a1.png

Edited by Chriske
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  • 2 weeks later...

I have now remade my barn door tracker to use the 8mm 3D printer threaded rod that you suggested May 22. It works much smoother and is the correct part to use. I found one that moves 2mm for every revolution which was twice as much as my original M6 threaded rod but it will not be difficult to change the software to suit. 

Thank you for your very helpful idea.

Robin

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Digging in an old box filled with spare parts I found a little polaraxis-scope from an old Vixen mount.
The eyepiece  has a reticle on board marking the distance between the exact North and polaris.
I also found on the net the correct value distance Polaris-TN : 40'37"

The only thing I  need to do is add a red LED to illuminate that reticle.

1975824545_Vixenpolarscope.thumb.png.cb16250abc4a6750ed7d0b140fb2e8ae.png

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  • 2 weeks later...

This was a rather simple solution.
I thought the perimeter of that white part would reflect just enough light homogeneously from the LED onto the reticle, not...🙄
So I pointed the LED directly toward the polar-scope's lens ...et voila... Works just perfect. I have in fact to much light now, but I can adjust to the right amount with the potentiometer.

 

image.png.3ee0f1bab6edea727e9ef69cc321538c.png

Edited by Chriske
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  • 2 weeks later...

Last night first test with the running stepper (Arduino/RAMPS) and it worked flawless. I only used a moderate magnification and only tracked for about 8 minutes or so.

Today I'll make a proper fork to support that new refractor and will test later on this evening using a higher magnification.
Need to find that old illuminated eyepiece, it has a reticle on board. So I'll end up with a far more accurate test.

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Yes, it does work very good as a matter of fact.

Next thing to do is work on the polar-laser to see if it is absolutely 100% parallel with the polaraxis.
I don't want to spent to many time tuning the mount before I can start taking pictures with it.
I did adjust the laser in its aluminium tube using a lathe, remember. But that doesn't mean the laser-unit is correctly installed in the mount. I know it is very near, very near, as I already tested it. These printed parts are very accurate, but that doesn't mean I can start using it as is.

Next last step : pointing the polar axis toward the true north, as I described before, with the aid of the laser. Then I'll start tracking a star using the drift method. At this point I ignore the laser completely. During tracking I (probably/maybe) need to fine tune the polar axis by very gently moving the mount. It'll take some time to do this because the drift method is rather time consuming.
When I can track stars over a long period, using very high magnifications and the star does not drift at all in the field of view, I know at this point the polaraxis  is pointing perfectly toward the true North.
The very final step to do is correcting the Polar-laser in its aluminium holder toward the true North using that little tool I made.

To be clear : These correction as I describe here needs to be done only once of course.
Next time I use the laser to adjust the polaraxis to it's proper position I know it is pointing toward the correct spot in the sky.

That said, pointing the laser to polaris and move it just a little bit(less then 1°) toward beta UMi by eyeballing is more then enough for visual observing.

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