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My homemade EQ fork mount


Vroobel
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😊

Thanks! I don't know what to say... Maybe, when finished, my mount may go on a date with your OTA? 😁

To be honest, I had not too many other real ideas how to build aluminium fork based on the flat harmonic gear. It must be strong and relatively easy to build at home. 

Edited by Vroobel
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  • 2 weeks later...

Hi, 

Next step is done: a main construction of the equatorial wedge. It's heavy, while isn't finished yet. Its weight will be nearly 40kg when finished. Some additional steel part will be welded and some ideas towards higher stability will be deployed. Soon. 

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Edited by Vroobel
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Hi, 

This time something not so effective, but it took me two days to perform. 

The wedge, even if heavy (around 40kg), after aiming on a polar with side bolts (soon) may move with any touch. After my friend, who shared the idea of the wedge with me, I'm gonna use vertical bolts and nuts with knobs for a better stability. The front arched holes are for this purpose. 12 degrees of the adjustment range should be enough. 

As the wedge is made using 6mm steel plate, when I hang the harmonic gear on it, and then the fork, OTA and accessories (around 50kg!) they will try to lift a rear side of the wedge. So the rear arched holes are there for preventing of that. 

There is a 16mm hole between the rear arched holes - it is for an Az axis. The 16mm treaded rod supported with two bearings under and over the plate will be there for the polar aiming purpose, but it will also partly hold the wedge on a base. 

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I finally made the wedge. It's not finished yet, but it's enough to begin working on it's base. I have to calculate a size of the base. 

Unfortunately it became very heavy. I knew it, the wedge and the base must be heavy, but I didn't predict that it is difficult to lift it and move. I hope Its stability will be the best award for the effort. 

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Edited by Vroobel
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Hi. 

3rd day in row: determining a centre of the mass. It's necessary for determining a size of the base platform. 

Finally I was able to hang my OTA without stress, but there was still needed some significant load to let it fall over. It should be really big guider with accessories. 

Now I know that I have to build a kind of trapeze-shape base platform around 80cm x 40cm, 110cm long. 

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Hi. 

I changed mind: I made the longest elements of the base 90cm long, the narrow side of the trapeze is 35 while the widest one is 80cm. It's long enough. The wedge weights 36.1kg, the base - 18.6, that means nearly 55kg together. Now I have to ask professional for welding. 

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On 25/07/2021 at 11:54, Vroobel said:

Hi. 

3rd day in row: determining a centre of the mass. It's necessary for determining a size of the base platform. 

Finally I was able to hang my OTA without stress, but there was still needed some significant load to let it fall over. It should be really big guider with accessories. 

Now I know that I have to build a kind of trapeze-shape base platform around 80cm x 40cm, 110cm long. 

IMG_20210724_210832__01.jpg

What would happen when you rotate the heavy metal wedge?  Like in this picture, the side with the red clamps under the ota. 

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12 hours ago, Vroobel said:

Up side down? It will still be wedge, but not equatorial and without possibility to fasten to the base. Is it what you mean? 

No, more like,

from this:D36CD60B-E6EA-4B70-98FE-9FF041CD2C44.jpeg.5fe3249c2d068e69a1e4a3dbe7615577.jpeg

 

to:

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will it tip over?  

Edited by Robindonne
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Ah, OK. I had this as plan on the beginning, but my (to be honest - not my) solution is better. In Liverpool latitude is over 53*, so I have lot of space under the top surface of the wedge for its jack and stepper motor. In your solution I would have only 37 degrees. Moreover, in present position the heavy harmonic drive, motor, fork and finally the OTA push the wedge down, which is natural situation for the car jack. In opposite position the jack should be pulled up, while I'm not sure if it's OK for it. 

To prevent it the wedge should be very heavy, much more than the present 36kg.

Edited by Vroobel
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47 minutes ago, Vroobel said:

Ah, OK. I had this as plan on the beginning, but my (to be honest - not my) solution is better. In Liverpool latitude is over 53*, so I have lot of space under the top surface of the wedge for its jack and stepper motor. In your solution I would have only 37 degrees. Moreover, in present position the heavy harmonic drive, motor, fork and finally the OTA push the wedge down, which is natural situation for the car jack. In opposite position the jack should be pulled up, while I'm not sure if it's OK for it. 

To prevent it the wedge should be very heavy, much more than the present 36kg.

Ah yes i see🙂. That might be true

Edited by Robindonne
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It's very close to finish. I mean the stage, when I can test it in action. There is still lot of work: grinding and painting. I have also to find a home for its electronic stuff. 

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Edited by Vroobel
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On 10/06/2020 at 17:53, Vroobel said:

Hi,

Usually I make my astro-toys, then make a video and show them on YouTube and astronomy forums. This time I will struggle with a subject whitch I am not familiar with, thus I have to ask You for help. Especially someone living not to far from Liverpool or Manchester.

I gonna make a bigger EQ fork mount for my 10" Bresser Messier (ES) reflector. I wouldn't even try to think about that without some very important and remarkably expensive part which I have bought as it is no longer able to be used at original environment. I mean a harmonic gear. My one is a little bit broken in area of one of many screw holes, but it is nothing as the fork mount is doing incomparable slower movements and operates with much lighter load.  The gear has 100:1 ratio and around 4.5 kg of weight. Here is link to the gear in action: 

 

 

 

The fork will be made using aluminium plate and profiles while the base has to be made of steel. An idea of the base is shown in the bottom. I hope I can design everything on my own, but the only thing that I can not perform is welding. Therefore I would like to ask mates living in Merseyside or Greater Manchester and familiar with welding for help. Its not urgent, but I would like to know if I can obtain the help or should I try other ways. I believe that the common passion gathers people having different experience. :)

Please don't hesitate to ask if anyone would like to know more details of my idea.

 

Base1.jpeg

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You are a genius!

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Nearly done. Three days of drilling, welding, grinding, I'm really tired.

The 36.5kg of the wedge can be easily moved in the Az axis using one finger on the knob. But the wedge + harmonic drive and stepper motor + fork + OTA and its accessories will weigh around 80kg together, so I expect some slight resistance. I'll check it very soon.

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The Az adjustment looks nice and smooth in your video. I wonder if Teflon pads would help it out it if got stiff under the full load?

Do you have a method for locking out the car jack once the Alt is set?  I would be a little concerned about it creeping down but I guess the weight acting on it will be a fraction of what it is designed for so maybe no issue there after all. 

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Hi Craig,

Thanks for your advice. I am ready to lock it in both Az and Alt axes. The Az is physically done while the Alt is partly performed. I'll finish the Alt one later or immediately if needed. I considered it rather against wobbling, but 4 hinges and the top plate supported on sides should make it solid. The car jack can lift and hold at least a half of the 1 ton car, so I think the 80kg shouldn't be a problem. 

I'll consider the Teflon instead of brass or bronze. 

As long as the weather is not good enough for test I have to focus on something else. 

Edited by Vroobel
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Ok, so last several days I was very busy and productive. I designed and printed many knobs for different bolts and nuts and also adapter for 1.25" ASI 120MM mini camera which will work with SW 8x50 finderscope as cheap guider. I finished slides to be able to move the wedge in the Az axis with minimal friction, so the base is ready in general. Thanks to advice another friend from the Polish forum I also replaced most of M6 threaded rods with short stainless steel bolts, spring washers and nuts. The fork is much stronger now. And finally I finished all the mount enough to test it in action. Now all the setup is at home as I have to prepare some box for electronic stuff. There is still lot of work to do, but the most important work is done. 

I had a plan to build a mount able to hold 30+ kg equipment. Accidentally I made a 70+ kg one... 😳 I confirmed it hanging myself on the tops of the fork - the mount didn't move at all. 

I am very tired, but happy! 😁

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Edited by Vroobel
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It looks really solid.  How is that harmonic gear under the load of the scope?   Is the fork directly attached, and the weight of the fork/ota combo hanging on the harmonic drive?

Edited by Robindonne
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Yes, it is! 😁

 

This kind of harmonic drives work in a joint of industrial robot arms without a counterbalance. The arms are very heavy itself, while they are much more efficient than my mount. 😊

I see, that the fork is OK, when OTA is aimed somehow forwards or backwards, but I expect some bents, when the fork will rotate more left or right. That's why I have to consider welding, even if the profile and bolts are strong, they aren't strong enough to hold themselves and the fully equipped OTA. I'll check it as soon as the electronic stuff is ready and the weather allows.

Edited by Vroobel
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Hi, 

I have pleasure to present a first GoTo test: Polaris -> Deneb -> Polaris, performed at home because of rain. 😒

It's made with some stress included. I invested lot of money in fantastic high performance TMC5160 drivers, they are so nice, silent, but not working... After several seconds of work, in random moment they move into disabled mode, steppers stop while an application (the APT) still works. This is very confusing and generates big mess. I tried to find solution looking at forums, but people don't know why it happen, even if it's known problem. 

I still have some other drivers: A4988, DRV8825 and LV8729. The A4988 offers 16 micro steps while I need at least 64. It's current is not big enough as well. The DRV8825 offers 32 micro steps and also low current. There is big friction in the axes, the Ra needs 3A in GoTo mode, the Dec one needs around 2.5A. The LV8729 is quite good, it offers 128 micro steps, while the 2A of current cause that I can boil eggs... But it works fine for a while. And the poor TMC5160 ones... 

I told sorry to my DM556 industrial drivers which I bought several months ago. They offer 128 micro steps and 5.6A current! 😳. I set the LV8729 mode and connected everything with wires. It looks odd, I know, but it works perfectly. At home... 

 

 

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Edited by Vroobel
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Hi. 

Around one month ago I downloaded and installed the Astroberry on my new RPi4. I like the idea of everything in one place. But as my mount isn't entirely ready I decided to use temporarily the APT application, especially that more people use the Windows and ASCOM compatible software. I should take it into account when I need a support if any problem appears. And indeed, some problems appeared. Just for reminding, I use OnStep @ MKS Gen-L v2.1. 

One is about parking in wrong position. But at this stage it's acceptable. 

Second problem is more annoying, because every Park or Unpark command finishes with a crash of the Ekos-KStars. After several days of looking whether it's caused by the OnStep firmware or the MKS hardware I finally found a solution: the Ekos at 3.4.3 version had a conflict with the INDI driver for the OnStep. 

After updating and full-upgrading the Astroberry the  problem of crashes disappeared at all. 

https://onstep.groups.io/g/main/topic/75830899?p=,,,20,0,0,0::,,,0,0,0,75830899

 

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Hi. 

I still struggle with some parking issue: sometimes the mount stops much earlier than it suppose to do.

But instead of wasting the time and looking for a solution, I improve the mount. I move step by step towards the maximal ease of assembly outside. 

Recently i worked on a way of arranging the electronic stuff and cables. Finally I figured out how to avoid tangling and hooking on obstacles like leveling knobs. The electronics found home inside one side of the road he fork. Its temporarily fastened on an MDF board, but I think that is a good place to it. 

I try to finish building this modular setup before clear nights begin. 

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Edited by Vroobel
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