10” Equatorial Platform for Dummies

[A P B]

Thanks John. I am redrawing everything to suit my small scope. I've hit a snag though. What is " 1/cos beta" ? I'm supposed to stretch my ellipse that will end up being my segments by 1/cos beta. I've attached the image. The calculation is to compensate for the angle of the segments. My segments will be angled 18 degrees. I got .951056 as the cos of 18. Just not sure what to do with the figure.

Adrian

[westmarch]

Hi Adrian,

the Dummies part of the title refers principally to me so I am the wrong person to ask about trigonometry.  I always ended up drawing out maths problems to find a solution so my suggestion is:

1.  Reduce all the platform plan dimensions by the same percentage on both the x and y axes to get an A frame that fits your scope base. e.g. if you only need a platform 50% as big, multiply all the plan dimensions by 0.5.

2. Using your printer software, reduce Reiner Vogel's 46 degree segment by the same percentage on both the x and y axes. Print it off and you should have a segment that fits your base. (You will, of course, have to reset the platform more often because you have reduced the circumference of your ellipse segment and therefore reduced its travel time).

This is my common sense theorem - not sure what Pythagoras would make of it. 🤨

Good Luck

John

Edited January 19, 2022 by westmarch

[aStone]

Finally managed to finish the platform! I also consider myself to be a dummy so this topic was perfect for me, thank you! 

For comfort, I added removable wooden legs, adjustable furniture feet are attached to them. That gives me the height of the small table I used before (can be seen in the background).

I could have drilled the holes for the stop bolts a bit closer to the edge of the arch but I'm going to replace one of the stop bolts with a micro switch so it should give me a few extra minutes.

Considering my skills, I'm quite happy with the result. After first test run I think I found the optimal speed of the motor, however there is still a small drift.  Acceptable for visual with wider FOV, I reckon, but noticable for imaging. Nevertheless, I believe it will improve my planetary imaging this season. I didn't expect it to use it for DSO but I tried anyway, 1-2 sec exposures are doable.

I have the EQ motor with the shaft coming out at the top. I found that the coupling screw supplied with the motor doesn't fit 8mm rod. So I had make the end of the rod thinner, about 6 mm. One could also get a different coupling screw or use a thinner rod but that would also require different size of bearings.

[westmarch]

Congrats on seeing the project through to its conclusion. I love how you have adapted it to your own circumstances - isn’t that the joy of a self build?

Good luck with imaging - if you recheck the platform with a spirit level, you may find it helps reduce the target drift. 
 

John

[Time Traveler]

On 31/01/2022 at 13:04, aStone said:

Finally managed to finish the platform! I also consider myself to be a dummy so this topic was perfect for me, thank you! 

For comfort, I added removable wooden legs, adjustable furniture feet are attached to them. That gives me the height of the small table I used before (can be seen in the background).

I could have drilled the holes for the stop bolts a bit closer to the edge of the arch but I'm going to replace one of the stop bolts with a micro switch so it should give me a few extra minutes.

Considering my skills, I'm quite happy with the result. After first test run I think I found the optimal speed of the motor, however there is still a small drift.  Acceptable for visual with wider FOV, I reckon, but noticable for imaging. Nevertheless, I believe it will improve my planetary imaging this season. I didn't expect it to use it for DSO but I tried anyway, 1-2 sec exposures are doable.

I have the EQ motor with the shaft coming out at the top. I found that the coupling screw supplied with the motor doesn't fit 8mm rod. So I had make the end of the rod thinner, about 6 mm. One could also get a different coupling screw or use a thinner rod but that would also require different size of bearings.

aStone: I like you skills!  I also made the same platform curiosity of Westmarch.  Great building instructions, yea?  Listen, I have to make a new modification after seeing your photo.  I like the idea of rubber band to hold battery!!!  This way you don't have to remove motor cover to replace battery!  Love that simple idea.  (Why didn't I think of that?)  I also made a few mods, if you care to think about. 1) I removed the extra aluminum at the points because I was afraid I might step into them at night.  That extra pointy part doesn't need to be there.  2) I put a micro switch to shut off power to motor at end of travel, in case I may miss the time ending the travel of platform.  I may be inside getting a drink! haha  3) I also cut off extra plywood in front of motor and the same on the other side.  Not needed and also cuts down on weight.   I really enjoyed building the platform.  It gave me a sense of accomplishment!  Good luck and clear skies!

[rojay]

This is super interesting, thanks all who've posted.

I have a question: the EQ1 motor presumably turns at 1 rev/day, but the bearing needs to go a lot faster. Did you need to do some modifications to the motor? Thanks!

[westmarch]

Hi there,

the EQ1 motor is specifically designed to turn your telescope on the RA axis once every sidereal day (23hr 56min 4sec) that equates to 1/4 degree per minute, you can adjust it slightly with a variable resistor knob on the motor and this is sufficient to compensate for any lag.  There is no modification to the motor required.

John

Edited February 13, 2022 by westmarch

[FrankRyanJr]

Looks great aStone! I love seeing how everyone is adapting the designs to suit their needs as John says above. 

[rojay]

Thanks John, but I'm still lost! I'd get it if the motor was connected to the south bearing, or otherwise directly moving the top board versus the bottom one, but if the motor is turning the pillow bearing, which has a much smaller circumference than the ellipse that the metal segments are part of, surely the motor would have to go many times faster than sidereal?

Maybe I should just get building and see for myself 🙂

[westmarch]

Hi there,

Sorry, I could have been clearer. The EQ1 motor is specifically designed to turn the RA part of an EQ mount at equatorial speeds.  It does turn faster but it is designed to work with a standard geared arrangement on an equatorial mount. It just so happens that, with the variable resistor knob,  this is within the rpm range that adequately drives a standard platform.

@FrankRyanJr is the man to talk to if you want to get into the details. He has a thread on cloudy nights relating to this:

https://www.cloudynights.com/topic/778667-celestron-eq-motor-drive-speed-question/

Hope that helps

John

[rojay]

Indeed it does, and that's a useful link too. Thank you!

[FrankRyanJr]

Hey guys. To give context, when I was checking out what others had done, I noted that everyone who had used the Celestron drive and either a 6 or 8mm bar was able to tweak the speed setting to find the right rotation rate.
My intention was to use off the shelf parts so knowing that it would be a case of trial and error. I reckoned that it was worth the punt on the EQ drive to test. (I got 2 cheaply on Wish before they added import duties). 
The biggest obstacle I had and still do is weight really putting these drives to work. If everything is balanced properly and the pivot point turns as smoothly as possible, then gravity and the right resistance between the bar and the arc means it's ok to track. It actually works fine with just a single drive on the downward but just before it levels out I have to switch on the second drive. 
This is a pain for 2 reasons. One, I have to set a timer to remind me to do it or else I'll be mid observation and suddenly everything starts drifting out of the FOV. Two,  I have to adjust the rotation speed for each when the 2 drives are working in tandem. Don't ask why lol. I've given up trying to figure out what's happening but I reckon it's the extra weight on the upward is requiring more torque so... yeah... not very scientific I know but hey.. I'm more of a practical problem solver. 

Having used the platform for a good while now. I have to say I'd never be without it. I do want to replace the 2 drive system with a single Nema Stepper motor to simplify things and because I'm just waiting for the night the other two fall on their swords and go to tracking drive heaven for a well earned rest. 

 

 

Edited February 15, 2022 by FrankRyanJr

[westmarch]

Frank, I think you are in motor bike engine territory with your scope.  😄
 

John

[nordwald]

Hey guys,

thanks so much for all that information and help here, this is extremely useful

I am about to build an EQ platform myself as well and was wondering about the skywatcher EQ1 vs EQ2 motor, which one to get? Do they share the same characteristics / speed and just have different fittings?
On the Nick Hill design you can see an EQ2 motor, in here I found the EQ1 being mentioned a few times. So is there a difference / recommendation?

Thanks a lot!

Michael

[westmarch]

Hi Michael,

The design posted requires a basic EQ1 motor.  This is has been tested by many of us and found perfectly adequate for a 10 inch dob platform.  Somewhat confusingly, EQ2 mounts can be driven by an EQ1 motor. Skywatcher also markets another motor called an EQ2 motor with multi speed capabilities - you don’t need this for the equatorial platform.

BW

John

[nordwald]

Thanks a lot for the quick reply

I guess the thing that confuses me is the image on reinervogel.net showing the EQ2 motor. Also in the Online Shop both EQ1 and EQ2 motors look exactly the same and also cost exactly the same...

 

[westmarch]

Hi Michael,

It is confusing 🙄  As far as I can make out, Skywatcher  branded their lightest German Equatorial Mount as EQ1: it has a payload capacity of 3.2kg. The EQ2 has a heavier payload of 4.1kg.  The motor drive for both is identical and it is only Skywatcher who term their motor drives as EQ2.(with variable speed or without).

Having looked at a number of them, the only thing that differentiates them is the writing on the box, sometimes the orientation of the motor/ attachment bracket and of course the cost. I think they all use the same components and may even come from the same factory.

John 

[nordwald]

Thanks a lot, it’s really amazing how you keep helping people in here after so much time, I wonder how many star gazers have build their platform based on your instructions. I will post pics of mine once I (hopefully) finish it. 

One more thing I am wondering about: the southern pivot in the back - do you think the pivot should ideally be as close as possible to the bottom board, the top board or right in the middle between them? Cause that will change the exact rotation axis of the whole platform quite a bit I would assume? 

Michael

Edited March 26, 2022 by nordwald

[westmarch]

Hi Michael,

You might be falling into the trap of thinking too deeply about this. The whole centre of gravity thing and building a motor from scratch put me off initially. Sometimes, like Frank, you just give it a go and are pleasantly surprised or improvise. 
 

It’s important to keep the top board parallel with the bottom, the south pívot works as a bolt in a depression in the underside of the top board.  For visual observation, this works. 
 

Good luck with the build. 
 

John
 

 

Edited March 27, 2022 by westmarch

[rojay]

Here's my build so far. I don't think there's a straight cut on it, apart from the original edges of the board... But I reckon it's going to work! 

[westmarch]

Its coming on nicely! 👍

John

[rojay]

In order to wrap my head round the geometry of these platforms, I enlisted a couple of helpers! The pirate is holding his boathook at an angle of 52 degrees (roughly), with the bottom end pointing to the south bearing, while his Viking colleague is holding his pointer vertically.

Moving the platform across its range of travel, the polar-aligned boathook is stationary, while everything else moves...

Not sure if that shows up on the pictures, but it's a pretty convincing demonstration in real life 🙂.

Ooh, and Snapseed lets you combine photos, that does the trick! 

[westmarch]

Just as well you picked seafarers then. Cowboys would have been useless at geometry!

John

 

[rojay]

But after all my geometry efforts, I took it outside last night, put the telescope on it, and only after not understanding what was going on, realised I'd carefully put the south bearing due north! 🤔

[Stu]

5 minutes ago, rojay said:

But after all my geometry efforts, I took it outside last night, put the telescope on it, and only after not understanding what was going on, realised I'd carefully put the south bearing due north! 🤔

Been there, done that, felt silly 🤣