10” Equatorial Platform for Dummies

[PeterStudz]

2 hours ago, GasGiant said:

@Orange Smartie  Excellent ! So nice being able to get a good time on Jupiter without nudging every 20-30 seconds ! 🙂 

 

Even at low magnification, on the likes of nebulae, globulars & galaxies, you’ll be able to relax and let your eyes notice more details. At least that’s my experience.

Edited January 28 by PeterStudz

[westmarch]

3 hours ago, GasGiant said:

IT WORKS 🙂 

 

So, I get a very slight drift but I cant slow the motor down anymore.  

I have an idea what it is though. The two shafts instead of being 8mm are 15mm. I think the change in diameter has altered the 'gear' ratio.  If these shafts are smaller diameter then they will run slower on the wedge. I should then have more wiggle room with the speed controler.  I think 😁

I will whack em on the lathe and turn them down to 8MM

Hopefully shimming the shafts will sort it. The only other thing I can think of is that your design for wider arcs is distributing the weight of the rig more efficiently on the shafts and is leading to some slippage. 
 

John

[westmarch]

2 hours ago, Orange Smartie said:

I have joined the club! I had to go slightly off-piste with my top board, as the feet on my Stella Lyra 10" must be a bit wider apart than those on the plan. So my top board is a little wider than the base board, but it still feels very stable. I need to do a few little mods; I'll probably chop the ends off the ellipses as they serve no useful purpose as far as I can see - on my wedge, one side hits the stop way before the thin end is reached.

It also needs to be painted or varnished.

I managed to get a quick test on Jupiter this evening, before clouds set in. This design really works! Thanks to the OP for sharing, I think it will revolutionise my viewing.

Please ignore Mrs Smartie's foot, which has phot-bombed my pic.

Great piece of work.  I agree with you and Peter, the sharp ends are a bit superfluous and  a hazard. 
 

John

[Jimmy81]

So I’ve had a couple of nights to use my platform and have had mixed results. I get moments of tracking followed the dreaded drift. I have been tweaking the motor speed to try and eliminate this, but doesn’t seem to make much difference. I’m wondering that because I’m using a 6” Dob it’s not quite heavy enough and I’m getting slipping??

the only other difference to the design (from the original plans) is that I had to make the gap between the top platform and bottom platform 60mm because my motor drive had to mounted upside down due to the position of the driveshaft - would the bigger gap make any difference? My segments are still the correct curve for my location

[Mr Spock]

These motor drives can be variable in quality. I've got a spare that is next to useless. The speed varies so much it won't track effectively. 

[PeterStudz]

@Jimmy81 - the gap between my top & bottom board is 58mm (about the same) and I don’t have any issues, so I doubt it’s that.

I use mine with an 8” Dob, although my homemade base is “solid” and as such has some weight to it. 

I think that slipping is a possibility. Is your battery OK and have you tried a fresh one? The drives can go through these little 9v batteries quite fast. Mine would struggle as the battery drained. In the end I actually swapped mine and rigged a more substantial rechargeable unit. 

Edited January 29 by PeterStudz

[Jimmy81]

Just now, PeterStudz said:

@Jimmy81 - the gap between my top & bottom board is 58mm (about the same) and I don’t have any issues, so I doubt it’s that.

I use mine with an 8” Dob, although my homemade base is “solid” and as such has some weight to it. 

I think that slipping is a possibility. Is your battery OK and have you tried a fresh one? The drives can go through these little 9v batteries quite fast. Mine would struggle as the battery drained. In the end I actually change mine to a more substantial rechargeable unit. 

Thanks @PeterStudz I did buy a brand new 12v battery but when I was trying it all out it was freezing outside (literally) so the cold could have affected the battery voltage.

The first time I tried the platform I forgot to polar align (I was so excited to try it out!!) but second time I got  all lined up (pivot end to the south) made sure base platform is level, made sure the top platform is level, powered up, aimed at Jupiter with a fairly wide angle lens (18mm 60° BST) and at times along the tracking path it seemed to stay put for about 20 seconds or so,  then suddenly it would just start drifting again.
I’ve worked out that the speed of the drive needs to be around 50% or below, any faster and objects drift in the opposite direction but haven’t managed to find the sweet spot yet.  I will experiment a little more now that the weather is slightly warmer, but it’s baffling me. Maybe I should also invest in a more substantial power source. 

[Jimmy81]

Sorry meant 9v battery, not 12v. 

[Orange Smartie]

That's annoying. How good are your ellipse profiles? One could imagine that if you hadn't filed them smooth enough, any notch or bump might cause the platform to stop tracking. Not meaning to cast aspersions on your craftsmanship, just trying to rule that out as a possibility.

 

Edited January 30 by Orange Smartie
Stupid autocorrect

[westmarch]

5 hours ago, Jimmy81 said:

So I’ve had a couple of nights to use my platform and have had mixed results. I get moments of tracking followed the dreaded drift. I have been tweaking the motor speed to try and eliminate this, but doesn’t seem to make much difference. I’m wondering that because I’m using a 6” Dob it’s not quite heavy enough and I’m getting slipping??

the only other difference to the design (from the original plans) is that I had to make the gap between the top platform and bottom platform 60mm because my motor drive had to mounted upside down due to the position of the driveshaft - would the bigger gap make any difference? My segments are still the correct curve for my location

I agree that the gap is unlikely to be the problem and battery or motor is worth checking. 
 

Another thing to check is that the grub screws on the flexible link collar are tight and not allowing the shaft to slip inside. 
 

John

[PeterStudz]

1 hour ago, westmarch said:

Another thing to check is that the grub screws on the flexible link collar are tight and not allowing the shaft to slip inside. 
 

Good point which I’d forgotten. I had to do mine up very tight (and I needed to use two grub screws on each side of the flexible link) in order to ensure it didn’t slip.

[Jimmy81]

3 hours ago, Orange Smartie said:

That's annoying. How good are your ellipse profiles? One could imagine that if you hadn't filed them smooth enough, any notch or bump might cause the platform to stop tracking. Not meaning to cast aspirations on your craftsmanship, just trying to rule that out as a possibility.

 

I had initially made the ellipse profiles from sheet aluminium as per the plans, but I found it difficult to get them right with the tools I had, so I adapted the design to use ellipse segments like the Omegon (see attached image). I was able to cut and create the profiles very accurately. I will recheck the aluminium edge just to make sure it is notch free. 
thank you for your input, it all helps 😃

[Jimmy81]

3 hours ago, westmarch said:

I agree that the gap is unlikely to be the problem and battery or motor is worth checking. 
 

Another thing to check is that the grub screws on the flexible link collar are tight and not allowing the shaft to slip inside. 
 

John

Thanks @westmarch I’ll double check all the connecting parts and make sure they are as tight as they should be. 

[Orange Smartie]

19 minutes ago, Jimmy81 said:

I had initially made the ellipse profiles from sheet aluminium as per the plans, but I found it difficult to get them right with the tools I had, so I adapted the design to use ellipse segments like the Omegon (see attached image). I was able to cut and create the profiles very accurately. I will recheck the aluminium edge just to make sure it is notch free. 
thank you for your input, it all helps 😃

Doesn't sound like it will be too rough then. Perhaps the opposite is the case - if the aluminium is too smooth, it might be quite slippery. My edges are evenly filed down, but are quite grippy because of all the scratches from the file.

[PeterStudz]

If like the Omegon it’s also possible that they are too wide/thick for the weight of your Dob and are slipping. As @Orange Smartie my arcs are relatively grippy from all of the scratches from the filing. You could try and rough-up the surface with a fine file. 

[GasGiant]

On 28/01/2024 at 21:14, westmarch said:

Hopefully shimming the shafts will sort it. The only other thing I can think of is that your design for wider arcs is distributing the weight of the rig more efficiently on the shafts and is leading to some slippage. 
 

John

Ive turned down my shaft. unfortunately its been sper cloudy as usual so not tested the slight drift theory yet 🙂 

[PeterStudz]

It’s been a while since I “finished” my platform (about 18 months plus took a while to paint it) and it’s been superb. But I realised that I haven’t posted any pictures of the completed item, so here it is. 

I made a few modifications most of which are personal choices. I did move a couple of the adjustable feet closer to the pillow bearings as it seemed to make it a tad more solid. Not that it was wobbly in the first place. I also added a micro switch to automatically shut it down when it reached the stop. And a chunky toggle switch to turn the whole thing on/off. It’s easier than fumbling for the little slider on the drive unit. Plus a decent sized knob on the variable potentiometer. I cut off the pointy ends of the arcs as they didn’t do anything and got in the way. There’s a “stop” at the southern end that makes it easier to slot-in the feet of my Dob when it’s dark.

To save batteries I’ve used a 12v rechargeable lead battery, knocked down to 9v with a cheap converter. There’s also a mini volt meter across the motor terminals so that I can easily and more accurately judge motor speed. It all gives a constant 9v to the drive unit which does makes the whole thing run smooth. Eg the little standard 9v starts to struggle when it gets cold - as I found out. The wiring could be tidied up, but it was originally done for my EQ1 on a tripod in those “early days”. I could replace the 12v lead battery with something more advanced, but I’ve had it for years and it just works. 
 

[GasGiant]

Very nice build, Peter.

I like the idea of fixing a larger thumb wheel for the potentiometer, an idea I will pinch 🙂 

[westmarch]

Excellent build. Love the artwork. 😎

John

[PeterStudz]

20 hours ago, westmarch said:

Excellent build. Love the artwork. 😎

John

Thanks John. The artwork was an afterthought - it just looked a bit empty especially after painting white. I based it off a design I saw online. Drawn on freehand with soft pencil and then painted freehand. Quite a relaxing thing to do on those far too many cloudy nights!

[pipiland]

I have been reading all the info about building the equatorial platform, and you guys are doing a great job. I have already collected many information, but Im holding construction because Im at latitude 39º, and Im still trying to figure out how to calculate my curves since Im very bad on those kind of things.

[AstralFields]

Hello 

Since I bought my telescope about one and half years ago, I have not missed much an EQ platform. Imaging was fine with the drift method and I was too busy hunting down the whole Messier catalog and also the weather has been pretty horrible and not much time with two pre-school kids to fiddle with anything. But now as I would like to go back to some more imaging I figured an EQ Platform would really help.

This topic is great, it shows a basic design which I can easily do. Already ordered the parts from Aliexpress for about 50$ including a rechargeable 9V battery for the EQ1 Motor. I actually already had a planetary motor made out of lego and gears, it worked, I tested it few times but that's another story.. it is not as small and convenient like the EQ1 motor for 37$.

Anyway .. went and looked at the plans by Reiner Vogel and of course, I am dead smack at 49 and the segments he provides are for 48 and 50. I know some of you said just choose 48 and 50.. and I was going to but for some reason that just didn't satisfy me .. at all. 

Went to his site and the logic behind creating the segments is not exactly rocket science. It is basically drawing a big circle (with a radius of about 45 centimeters for an 8" DOB) and then applying two basic trigonometry functions to the height and width of the circle.

a) The height is first reduced by the cos(lattitude) 

b) Then the width is stretched by the 1/cos(angle of the rods)

To help things out, I managed to import the segment plans into Libre Office Draw with the original circles and their dimensions that Reiner had designed. I took all his circle dimensions, put them into LibreOffice Calc (Excel for Linux) and discovered some inconsistencies for the segments for different lattitudes. Simply put, they didn't seem to be following Reiner's own formulas. Also for most of them it was clear he was calculating 15 degrees of angle for the rods instead of 20 as per his plan.

After some reverse engineering , the worst was segment 48. It needed an adjustment of about 4cm to the width of the circle which moved the resulting segment by few millimeters. The others were more or less fine.

After I understood the logic behind it and fixed the numbers a bit so they are more in line with his formulas, I was now able to draw and calculate my own segment for 49. I am actually at 49.1 and will be increasing the accuracy once I get to that stage. 

What you see below is the final result of 49 compared to the fixed 48 and 50. It is quite noticeable and does change things a bit.

What you see above is one huge ellipsis about 95 centimeters wide and 65 centimeters high .. simply overlaid over an A4 paper .. which gives us the final segment we need. 

You probably wouldn't notice an inaccuracy of about 2% over the course of 1 hour if like me you live at exactly a 49 or 51 or 53 etc.. but I am glad I eliminated it and now I can focus on the build part. This is very much at this point a work in progress so let me know if I am missing something here  This extra accuracy also helps with the fact that my segments will be made of wood and thicker, this will minimize the lateral movement during the working of the motor .. as per Reiner.

Edited March 20 by AstralFields

[westmarch]

well done, you make it all look so easy - unfortunately trig brings on my PTSD. 🤪  Stand by for the requests to compute segments for future builders. 😄

John

[AstralFields]

1 hour ago, westmarch said:

well done, you make it all look so easy - unfortunately trig brings on my PTSD. 🤪  Stand by for the requests to compute segments for future builders. 😄

John

At this point after I have spent about 7 hours thinking about this (I just couldn't get it out of my head and system until I figured it out). I have no problem producing segments for other builders with bigger accuracy than the 2 degrees or other latitudes (if it can be built practically).. as long as they don't blame me if it doesn't work for some reason in the end. I have built exactly zero platforms so far.. I am just a big nerd for physics, geometry and theory before doing anything. 😅. 

One more thing that is important is that the two segments must be placed from each other at the same distance as outlined on the big ellipsis (technically we are cutting one segment from each side). Or the other way around, once the exact distance of placement is known, the segments can be accurately chosen & cut from the bigger ellipsis. 

Based on Rainer's plans that is 244mm so this needs to be doublechecked on the big ellipsis if the end of the segment is really 122mm far away from the center.  Looking at it from the distance it does look like it. 

Edited March 20 by AstralFields

[AstralFields]

Update:

All the stuff I need arrived from AliExpress and I have initiated the planning phase. Spent about 2 hours fine tuning the Sector 49 degrees using Reiner Vogel's approximation method. The segment itself was easy but it was important to have it at the right dimensions on the A4 so that it fits with the plan I have that has the distance of the segments at 244. Everything needed to fit, and I had to ensure I can mount them to the board. I used Libre Office Draw to create a printable, at scale' segment I can easily copy on the wood without much hassle.

At the same time, I couldn't get off my mind the work HenkSB did here:

https://www.cloudynights.com/topic/916052-vns-platform-sector-calculations/

He is using a much more accurate projection and was claiming Reiner's projection is off by 1%. That is something, that was bothering me. So I installed SciLab (was really simple on Kubuntu from the app store) and ran his scripts for my latitude. The ellipse that was generated was a lot more compressed than the one I had calculated using Reiner's plans. 

So I asked him about it, I thought I was not using his stuff properly but in the end it was a simple oversight. He fixed the code and lo and behold in the end Reiner's projections are only 0.1 degrees for a 90 minute tracking off. That is something I can live with. My woodcutting will likely introduce a lot bigger errors. Either way, great work by HenkSB to confirm the accuracy of the segments. I don't think anybody had done this before.

He also made a nice animation that shows the movement of the segments in all three dimensions. They do move and this is something that should be taken into account when spacing the wheels. I am also skipping making the segments out of aluminum and doing them from the 18mm wooden board.  Omegon has gotten away with a lot thicker segments, so I am hoping this won't matter much as they do tilt on either side. I was originally going to use some aluminum at the bottom of the segments, but I will try to skip that part.. as long as I polish the wood after the cut, it should be fine.. I hope.

With the segments finally resolved. I put everything on the table for one final count that nothing is missing. Of course, stuff was missing, took me 30 minutes to figure out where I had put it and also had to locate a hex mini tool to tighten the wheels. 

After about an hour of some geometry fun with my daughter's coloring pencils, the board is ready for cutting.

I don't have a woodshop and I don't want to make a mess out of my apartment, so I am converting my cheap drill into a wood cutting machine. Will be doing the cutting sometime next week in my shared garage space. Hope I don't make too big of a mess. The cut of the segments will be a bit tricky but I did order some some polishing bits for the drill to make the final touches. 

I am documenting the whole thing for a video as stuff like this should be out there for future generations. Have not found any simple designs documented on YouTube.

The final price tag is right now at about 100$ , including the wood cutting adapter for my drill and some rechargeable batteries for the motor. The wood was pretty cheap, got it for 20$ including shipping as I couldn't find any good wood at our summer house. It is much more beautiful than some old worn-out wood. Maybe I will paint it white, or maybe not. We shall see. 

Edited April 13 by AstralFields