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My homemade EQ fork mount


Vroobel

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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

Base2.jpeg

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Hi Tomasz, great project and I'm looking forward to following the progress.

Do you have a skectch of the entire mount to share? Are you intending to use the HD on the AR axis and input that with a smaller worm gear?

I suppose you want to do astro-photography with the mount? I'm sure you are aware that HD are virtually backlash-free but that comes at the cost of accuracy - almost inherently in their design. Having say that on the filed it might perform great

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19 minutes ago, Michele Scotti said:

Hi Tomasz, great project and I'm looking forward to following the progress.

Do you have a skectch of the entire mount to share? Are you intending to use the HD on the AR axis and input that with a smaller worm gear?

I suppose you want to do astro-photography with the mount? I'm sure you are aware that HD are virtually backlash-free but that comes at the cost of accuracy - almost inherently in their design. Having say that on the filed it might perform great

:) Thank you. 

You are right, I gonna use the small worm gear to drive the HD. Taking into account ratios of the HD and used worm gear, 200-400 stepper motor and its micro steps (LV8729) I can reach even 0.1 arc sec/step accuracy for the Ra axis. The Dec axis will have not so high accuracy, but sufficient enough. I want to use my earlier experience and make worm gear again, but this time I will use smaller fully aluminium blank. 

I have some sketches but excluding the fork I'm not sure if anything of my concept can be understood. It will be much easier to see that built step by step. 

Edited by Vroobel
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BTW, I bought an arc welder last week together with everything necessary to weld. I have 2 weeks till end of the June to learn welding enough to perform solid and good looking joints. Later it will be difficult as I come back to work. 

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C'mon, just a lil sketch ;)

I suppose you want to do astrophotography - if so the Dec has to be pretty accurate too. It won't carry as much load as the RA but it's crucial for corrections either guiding manually or with an autoguider. Try and fit the larger worm gear you can - thats the secret ;) ...my 2 cents. I saw you techinque for gears and it's quite inspirational.

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4 hours ago, Vroobel said:

BTW, I bought an arc welder last week together with everything necessary to weld. I have 2 weeks till end of the June to learn welding enough to perform solid and good looking joints. Later it will be difficult as I come back to work. 

Probably be better off with a MIG welder unless you're using 10mm plus steel plate.

Dave

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7 minutes ago, Davey-T said:

Probably be better off with a MIG welder unless you're using 10mm plus steel plate.

Dave

Probably you are right, as other people told me the same. They told also that cheap MIG welder is not good choice, but I don't have too much money to spend. I have to buy a good quality mitre saw (Evolution) and also high class bench drill press (Bosch). The welder is not only purchase related with welding. Years ago people didn't know MIG technology and used electrodes only and despite that they had not bad results. I think I could do it like many other, just have to be patient in learning. 

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2 minutes ago, Vroobel said:

Years ago people didn't know MIG technology and used electrodes only and despite that they had not bad results.

More likely Oxy' Acetylene for thin stuff but lots of distortion from heat, and expensive kit to operate as gas bottle rent is prohibitive for home use.

Mig welders can also be used for stainless steel and aluminium.

Dave

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  • 9 months later...

Hi guys, 

I just come back to the game. 

Presently I'm working on the EQ fork mount for my 10" Bresser Messier OTA, but if the project is successful I would consider moving towards something better, like the SCT 11.

I'd like to ask owners of that stuff with the original fork mount, doesn't matter what kind of type , what is the distance between mounts of the fork? What is the distance between most far points of the OTA mounts?

I'll appreciate your response. 

Tomasz 

Edited by Vroobel
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I guess dimensions would be similar to the existing Dob mount.

An SCT by design would be shorter but need allowance for the eyepiece being at the other end which can limit maximum elevation.

Dave

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Thanks, Dave. 

Unfortunately I cannot trust the "similar" size. I have opportunity to make it universal, so I prefer to choose the bigger size and make a kind of adapter to the smaller size. 

The advice about place of focuser became significant. To be honest, how to observe (not astrophoto) objects close to the Polaris? 🤔

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  • 1 month later...

Hello again,

I'd like to share with you what I already performed.

First of all I have made a plywood model of a wedge to avoid expensive mistakes. As another ATM maker from Poland suggested, I used a car jack for its elevation. It's strong enough to hold a one ton load. I have bought thick aluminium C-profiles and performed proper hinges for the jack. Four other high quality hinges (keeping dimensions) placed on edge will provide stability, so the wedge will not be wobbly. During performing the wedge I figured out that it will be better to weld the harmonic drive wall downwards instead of upwards, so the eyepiece - if I wish to observe - will be around 300mm lower. That is a significant difference.

When some aluminium parts arrived I began working on the fork and fixing of the OTA. Several points of the mount at the same time.

An aluminium base plate, 600x300x12mm with a big central hole and 16 small ones around for the harmonic drive, two round 600x30mm pillars in the middle of each side of the fork, two "tables" holding axes fixings. And here I have to explain my idea. I'm gonna use two high quality worm gears dedicated for CNC as axes holders. One of them - ratio 80:1 - will be driven by a Nema 23 stepper motor. I will remove the worm from another one with a 25:1 ratio, which I already had, so it will work as the axis holder only. I have designed and performed a kind of saddles holding my 10" OTA, which is 17kg load, without accessories. They will allow you to easily seat the OTA on the fork.

I wrote it down very briefly, but it took me several months to get it done, mainly because of the waiting for the material. The sellers on eBay are now scammers and swindlers who use COVID and delays to sell goods they don't have in stock. I waited over one month for aluminium square and rectangular profiles and finally eBay gave me a refund for them. Now I wait again for the same stuff, but not from an eBay seller. I hope it will arrive on Monday, 7th June.

In the meantime I have made some steel elements of the wedge. Supported by my friend I decided to fix the harmonic drive and its stepper motor to the fork permanently. This is because the fork base must be screwed to the harmonic drive using 16 bolts. It would be simply annoying to screw and unscrew it every time when I want to use the mount and finally the threads would be damaged. So the harmonic drive is attached to a 400x200x8mm steel plate. This plate will be put on the wedge top plate and screwed using eight welded M8 bolts. I expect that the steel wedge with the car jack will be heavy enough even without the harmonic drive, so the drive can be a part of quite light aluminium fork. The wedge top plate has a 90mm hole in the middle to let the stepper motor attached to the fork and the harmonic drive pass through. Using a 500x200x6mm steel plate I have made supporting triangles which will be welded on both sides of the wedge.

It sounds complicated, but believe me, it will be very easy to assemble. All mount will be assembled using three parts: an "A" shape steel base, the wedge and the fork. I have 4m of 50x50x5mm steel square profiles for the "A" shape base. But this is the future...

Regarding the mentioned earlier other OTAs, I'm gonna use a kind of shelf on the 300x30x30 aluminium bars (parts of the saddles) and screw it to them using M8 bolts. My idea is to install a rail in one of the existing standards to the shelf to be able to attach any OTA smaller and lighter thern my 10" Newtonian one.

Tomasz

01 wedge 1.jpg

02 wedge 2.jpg

03 wedge 3.jpg

04 alu base 1.jpg

05 alu base 2.jpg

06 pillar 1.jpg

07 pillar 2.jpg

08 axis table 1.jpg

09 axis table 2.jpg

10 saddles 1.jpg

11 saddles 2.jpg

12 saddles 3.jpg

13 wedge top plate.jpg

14 fork bottom plate.jpg

15 supporting triangles.jpg

16 fork 1.jpg

17 fork 2.jpg

18 fork 3.jpg

19 steel base profile.jpg

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  • 2 weeks later...

Looks like the mount is coming along well.

I built a fork mount some years ago, mine also had hinges at the base of the polar wedge. They proved not to be up to the task, there was play that resulted in pointing inaccuracy when the OTA was swung.

I've now put triangular side plates to fix the wedge after polar aligning, problem went away.

 

Huw

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Thanks for that, I'll consider it when (if) my ones will do same. But it seems to be aimed in fixed position. 

 

Edit:

I have got a clever advice from another ATM creator: two steel flat bars with long hole along, one end screwed at the bottom of the wedge, second end screwed in position given by the angle. That should fix the wedge in the position enough. 

Edited by Vroobel
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On 19/06/2021 at 23:10, Vroobel said:

ChamferTool.jpg

Aside from getting my vote for the most novel use of a scissor jack since they were invented (even putting it ahead of my own use of one in an apple press), I'd like to ask: what is the above tool in the drill chuck.  I think I can honestly say that I've never seen one before.

James

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😁

As I wrote earlier, the jack is not my idea. If it can hold a weight of a half average car lifted, why not to use it for around 40kg load? 

The item in pics is a chamfer tool for any round rod, including threaded ones. I have made 48 x M6 rods that means 96 round edges to chamfer. This tool does it quickly and smoothly. 

Edited by Vroobel
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1 hour ago, Merlin66 said:

Back in the 1970's I built a Disk Fork mount for my 12.5" f5 reflector.

It could easily handle 100Kg load and worked very well.

 

canopus320_1small.jpg

Canopus320_2s.jpg

canopus320_1984.jpg

It's very impressive! Today we have laptops, Raspberry PIs, Arduino, but I see you had to make your own controller.

The construction must be very accurate. Are you still using it? 

Amazing job! 

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Hi, 

I have to rest a bit from the manufacturing, so it's good time to think about hardware and software. In the beginning I had a plan to rebuild my own software written for my previous mount, motorised Dobsonian one. But my friend, another astronomer amateur and DIY enthusiast encouraged me to look at the AstroEQ or the OnStep software which together with the EQMOD or EKOS can work perfectly in my setup. 

Thus lest start with the Arduino Mega 2560 with the AstroEQ. I'll try to work on the EQMOD on Windows 7 laptop (I have spare one) - just to be familiar with that.

I know that the Arduino Mega is the worst solution as it is not accurate, so I ordered the MKS Gen-L v2.1 which will work with the OnStep. It's the best mobo for the mount and works wireless. 

Finally I'm gonna install the Astroberry and EKOS on my Raspberry Pi 4 8GB. 

IMG_20210622_223556.jpg

IMG_20210622_223642.jpg

IMG_20210622_235217.jpg

IMG_20210622_235321.jpg

Screenshot_20210623-071910.jpg

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  • 2 weeks later...

Hi, 

After some attempts with the Arduino Mega 2560 and AstroEQ firmware I had to leave it. I asked its author for access to higher number of micro steps, but they didn't response. 32 micro steps mode gives me 2 arcsec accuracy in Ra axis and 2.5 in Dec one. It's not acceptable for me. 

I focused then on the OnStep @ MKS Gen-L v2.1. As I use Nema 23 stepper motors, I chose the Trinamic TMC5160 drivers, because they have external MOSFETs onboard and can give really high current with small amount of heat. 

As an author of the OnStep firmware warned, I had to cut a CLK pin. I am possibly a second person who had to solder it to GND (in GoTo slew randomly Ra or Dec didn't work, now is OK)...

It doesn't work with the EQMOD, because it's compatible with Meade standard. Instead of that I used the APT app and of course the ASCOM Platform. 

I am amazed... 😳 It's so silent! I recorded a Sirius-Polaris-Sirius slew as sample, just to share it on the YouTube. You can hear the mouse click louder than the stepper motors. 

Special thanks for my friend Sebastian from our Polish astro forum. He shared his knowledge and experience with me and patiently answers all my questions. 

 

 

 

Edited by Vroobel
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