EQ Platform for 12+" DOBs , easy .. includes 8,10". With plans & video

[AstralFields]

Two months ago I built my very first EQ platform (see bottom of this page) for my 8". Halfway through that process I decided to buy a 12".. so I needed a new platform.

As anybody who has ever built one, I discovered Reiner Vogel's website and further inspired myself by Westmarch's 10" platform topic on this forum.

I did make quite some changes along the way, so would like to put all of it here for future reference. The biggest difference from Reiner and Westmarch's designs is that I chose to forego the use of Aluminum whatsoever and I also chose to source everything (except the wood) from AliExpress, ensuring minimum cost and maximum convenience (they bring everything to my doorstep).

The cost for the 8" is around 90$ and the price for the 12" is around 120$

Another change I did was to add segments for latitudes like 49, 51, 53 etc.. and there was a mistake in one of the Reiner's segments for the 8" version I believe which I fixed.

You can check the detailed plans (they also include the 8" , 10" version at the bottom of the documents):

Libre Office Draw version to ensure printing at scale of the segments. 

EQ VNS 12 DOB.odg - Google Drive

Or you can try your luck with PDF and measure after printing to ensure scale:

EQ VNS 12 DOB.pdf - Google Drive

You can check the journey and video on it here:

The platform is tested and working for the 12" and I am sure it could handle a 16" Truss Tube.

And here is the part about the 8"

 

I am done building EQ platforms for a while. Must have spent a good 70 hours over the last couple of months. Spent more time building them than actually using them

Edited June 5 by AstralFields

[Ratlet]

I'm at work the now so struggling to get the video to work due to filter.

What is the name of the pivot you use for the south point?  I've struggled to find that specific part.

[AstralFields]

36 minutes ago, Ratlet said:

I'm at work the now so struggling to get the video to work due to filter.

What is the name of the pivot you use for the south point?  I've struggled to find that specific part.

2x 10mm M8 M6 Universal Boot Bonnet Gas Strut End Fitting Connector Ball Screw Bolt Pin Joint Valve for Spring Lift Supports (aliexpress.com)

This is the one I used. Simply drill a 4mm hole and screw it into the wood.. screws really nicely. I made a mistake and drilled a 5mm hole, had to replace the piece of wood.
edit: Or maybe it was 5mm and I made the mistake of drilling a 6mm.. shoot.. better to check.

It is inside the plans explained. Then all you gotta do is grind (with a small bit grinder, also can be ordered from Ali) a small hole on the other side in the wood.

6PCS Rotary File Cutter HSS Dremel Milling Rotating Burrs Grinding Head Wood Carving Knife Cutter Tools Engraving Accessories (aliexpress.com)

Edited June 5 by AstralFields

[Ratlet]

Perfecto!  Really appreciate that.  Love an AliExpress link for something that I need that costs next to nothing.  Gives me an excuse to order another £7 worth of stuff to get the free shipping 🤣

[AstralFields]

1 minute ago, Ratlet said:

Perfecto!  Really appreciate that.  Love an AliExpress link for something that I need that costs next to nothing.  Gives me an excuse to order another £7 worth of stuff to get the free shipping 🤣

Cool.. I don't put links in any guides because AliExpress links are quite temporary as products get rotated/sold out etc.

The best part is that the price is not the only win, I am a patient guy so I don't mind ordering a bunch of things and waiting three weeks for it, instead of hunting down small stuff in the local HW store. The added convenience is so much better. The postman hates me though .. he is visiting me every few days 😄

Btw , there is a ton of free shipping stores with even better prices without the limit, but they do tend to take a bit longer than the Ali Choice, sometimes quite a bit longer. I use them for stuff that is not a priority in any way... but yeah the Ali Choice free and fast shipping is great.

Unrelated to this topic, there is a big sale going on with coupons and stuff.. I just ordered a Max Vision 11mm 82 degrees for like 110$. Also the Sky Rover 30mm can be had for about 150$ after the 20$ coupon is used.

 

[Ratlet]

I dont want to take it too far off topic, but I keep my basket and wishlist full of cheap things that are nice to have and use them to round up when I need something.  I live rural and the local hardware store wouldn't be able to source much of what I need and the AliExpress things are the exact same as Amazon, only 1/2 the price.

I'm keeping well clear of the astronomy stuff right now.  There is a Gemini autofocusser on there for £60 and my willpower is being seriously tested.  Fortunately the solar guys on here are posting lovely reports and images and making me want to spend even more money of a Hershel wedge!

The EQ platform is my top priority right now though.  I'm going to use a stepper motor (nema 17 with a 1:100 planetary gearbox).  Not required over cheaper DC motor, but I wish to learn programming with an Arduino so it will be a good opportunity to learn.

I have already done the calculations for my sectors so with this ball joint (and some pillow bearings I have on order) I will be good to start.  You video has given me a major inspiration to get going as I've found the last part!

[PeterStudz]

Looks good! Although do you need 2 motors for your 12”? I know that @Mr Spock uses a commercially made EQ platform for his 12” Dob and it runs well with just the one - same motor. 

[AstralFields]

3 minutes ago, PeterStudz said:

Looks good! Although do you need 2 motors for your 12”? I know that @Mr Spock uses a commercially made EQ platform for his 12” Dob and it runs well with just the one - same motor. 

Yup .. watch the video ;). With one motor it was slipping at certain parts of the segments, especially the one where the motor has to work against the gravity and raise the whole telescope.

The main problem was not enough friction between the segment and the iron bar. The motor is more than capable of producing the torque necessary.

To get it to work with one motor it would've required coming up with ways on how to increase that friction and possibly spending more money and definitely a lot more time. Maybe grinding the bar so it is not as smooth or attaching some kind of a non-slip surface on the segment. The rubber that I originally put was torn to shreds as the weight of the telescope was too much and it was inducing minor wobble.

At this point I figured, I'd rather spend an extra 40$ on a second motor and have a completely reliable and accurate tracking. It also makes the resetting of the platform a lot easier as the less than perfect friction means I don't have to completely raise the telescope but simply raise it a bit and slide it back with the segments still touching the bars.

So yes, one motor is definitely doable with a 12". In fact it was mostly tracking well.. It just needs more work and testing.

[PeterStudz]

Indeed… I did watch the video  But I wasn’t sure if you’d tried anything else. Thinner segments would probably provide some more friction too. Might also depend on weight distribution and balance. Eg putting a 500g weight on one side of my EQ platform is enough to make it slip.

Edited June 5 by PeterStudz

[AstralFields]

11 minutes ago, PeterStudz said:

Indeed… I did watch the video  But I wasn’t sure if you’d tried anything else. Thinner segments would probably provide some more friction too. 

No I don't think so , the surface area touching the bar would be the same, actually maybe lower with the thinner segments. On the other hand the weight would be distributed on a smaller area.. at the end of the day it is mostly about the materials and their friction coefficients. 

What would help is grinding down the bars (they are pretty smooth and not exactly friction friendly) so that they are a lot more rough and then maybe putting some sand paper kind of material on the top of the segment. This material needs to be very sturdy.. the rubber was stretching a bit under the load and inducing all kinds of wobble at high magnifications.

It would also maybe help increasing the radius of the bars, maybe adding some rings over them.. this way the area of friction is increased. 

Another thing that would definitely help is simply shortening the segments, the tracking is most problematic towards the start of the segment as the motor is pulling up the whole telescope against the gravity. But this was a no-no as I love the fact it can now track for over an hour.

So.. at the end of the day, I just said to myself.. 40$ is fine.. especially given the fact I had already sold the platform and I didn't want to risk giving the guy a problematic platform. When the time came to build my own, again I said two motors seem like a much more comfortable solution with zero problems across the entire segment :). 

I am a family guy with a full time job, so at the end of the day I'd rather pay the extra money than spend another 10 hours troubleshooting and testing. Testing is particularly tricky as you have to do it at 600x+ zooms on the Moon to ensure maximum accuracy. Means getting the right time window where the weather is nice, I am free and then lug the whole thing to my balcony (lots of work!).

But if somebody comes up with a solution with these big segments with one motor, I am very curious to see it here. 

Edited June 5 by AstralFields

[AstralFields]

12 minutes ago, PeterStudz said:

Indeed… I did watch the video  But I wasn’t sure if you’d tried anything else. Thinner segments would probably provide some more friction too. Might also depend on weight distribution and balance. Eg putting a 500g weight on one side of my EQ platform is enough to make it slip.

Yes .. adding counter weight balance fixed the problem, I tried with a 2kg exercise weight. But lugging a 2kg weight with me every time I am observing so I can avoid spending 40$ was not an option 😅

Also I tested it with the wheel on the platform.. it would've helped a bit had I put the telescope 'wood to wood' and lowering its center of gravity.. but I guess not by much. I was unaware at that moment that it is possible without cutting anything else.

[AstralFields]

Btw one more thing.. it also depends on the segment latitudes. For 52 , 54 , 56 .. they are a lot shallower.. so the work against the gravity is much less. I am willing to bet if you built the exact same platform at 56 , it would work with a single motor with no other modifications.

Once you get to 46 (I am 49), it becomes really problematic pulling that telescope out of the hole at the start of the segment.

[Mr Spock]

42 minutes ago, PeterStudz said:

Looks good! Although do you need 2 motors for your 12”? I know that @Mr Spock uses a commercially made EQ platform for his 12” Dob and it runs well with just the one - same motor. 

The shaft is covered in rubber. If you have a metal to metal surface you will have a lot less grip.

[PeterStudz]

5 minutes ago, AstralFields said:

Btw one more thing.. it also depends on the segment latitudes. For 52 , 54 , 56 .. they are a lot shallower.. so the work against the gravity is much less. I am willing to bet if you built the exact same platform at 56 , it would work with a single motor with no other modifications.

Once you get to 46 (I am 49), it becomes really problematic pulling that telescope out of the hole at the start of the segment.

Yes, that’s a good point. I use a segment for 52. Also a good point by @Mr Spock. Worth a try and it’s easy and cheap.

[AstralFields]

My main recommendation to anyone building one out there is to give it a try with a single motor and see how it goes. Increase the friction somehow.

 If it doesn't quite work, adding a second motor is very easy 😉

The type of rubber I used didn't work out, it was shredded after an hour.. but a lot better rubber should help.

 

[PeterStudz]

6 minutes ago, AstralFields said:

My main recommendation to anyone building one out there is to give it a try with a single motor and see how it goes. Increase the friction somehow.

 If it doesn't quite work, adding a second motor is very easy 😉

The type of rubber I used didn't work out, it was shredded after an hour.. but a lot better rubber should help.

 

I think it’s better over the shaft - as already mentioned - rather than the segment. Some silicone type tubing slightly smaller diameter than the shaft and pulled over tight would be what I’d try. I’m sure I’ve got some down the shed that was used for model aircraft fuel tubing. The stuff is tough.  Pure rubber will degrade over time. 

Edited June 5 by PeterStudz

[AstralFields]

3 minutes ago, PeterStudz said:

I think it’s better over the shaft - as already mentioned - rather than the segment. Some silicone type tubing slightly smaller diameter than the shaft and pulled over tight would be what I’d try. I’m sure I’ve got some down the shed that was used for model aircraft fuel tubing. The stuff is tough.  Pure rubber will degrade over time. 

Another tip I heard about is putting some cable isolation over the shaft. The type where you blow it with a hot air drier and it shrinks. I'd try that one .. I actually have some but not sure if over time the plywood segment would also not destroy it. Worth possibly a try. 

I did also try putting normal isolation tape over the shaft.. it did work initially but was also shredded within an hour as well. The 12" is seriously heavy when focused on such a small area

Edited June 5 by AstralFields

[LondonNeil]

I've read the other thread and just for interest pondered on the drive and inherent risk of slip with a friction drive. I came up with an idea,  it is entirely untested though.  I thought of a chain drive.  If you built a loop of chain that ran around the segment where it were pinned to it at the end,  then round a driven cog, then 3 free wheeling cogs, there works be no possibility of slip.

Bicycle chain cogs are cheap,  it would add a bit of added complexity though.

[PeterStudz]

4 minutes ago, AstralFields said:

Another tip I heard about is putting some cable isolation over the shaft. The type where you blow it with a hot air drier and it shrinks. I'd try that one .. I actually have some but not sure if over time the plywood segment would also not destroy it. Worth possibly a try. 

I did also try putting normal isolation tape over the shaft.. it did work initially but was also shredded within an hour as well. The 12" is seriously heavy when focused on such a small area

It would be worth a try. Heat shrink tubing is cheap as chips and is to useful for a whole range of tasks. I’ve had a supply since I was a teenager - every household should have some

[PeterStudz]

16 minutes ago, LondonNeil said:

I've read the other thread and just for interest pondered on the drive and inherent risk of slip with a friction drive. I came up with an idea,  it is entirely untested though.  I thought of a chain drive.  If you built a loop of chain that ran around the segment where it were pinned to it at the end,  then round a driven cog, then 3 free wheeling cogs, there works be no possibility of slip.

Bicycle chain cogs are cheap,  it would add a bit of added complexity though.

I don’t have a slipping issue, although it’s for a smaller Dob. For me the friction drive works perfectly. The thing here is the “bit of added complexity”. 

There are a whole host of different ways and methods of making an EQ platform. The beauty of this one it’s so simple, cheap, easy to make and can literally be constructed on a kitchen table. With really basic tools too. I haven’t seen another EQ platform that comes close. 

And that’s the whole point and beauty of a Dob - It’s simplicity itself. Once you make things too complicated it’s no longer a Dobsonian. At that point you may as well stick it on a massive, expensive heavy tripod with an equally massive, expensive and heavy EQ mount.

Edited June 5 by PeterStudz

[LondonNeil]

I agree,  simple is beautiful, so if the friction drive works that's great.  If you're struggling with it and a 12" or bigger dob is going to test it, a second motor or 3 freewheeling cogs and a foot or two of bike chain are probably pretty simple alterations. 

[AstralFields]

1 hour ago, LondonNeil said:

I agree,  simple is beautiful, so if the friction drive works that's great.  If you're struggling with it and a 12" or bigger dob is going to test it, a second motor or 3 freewheeling cogs and a foot or two of bike chain are probably pretty simple alterations. 

There are several benefits of the friction drive.

- Very easy to separate the top and bottom parts of the platform for storage.

- Easy to reset the platform without even fully lifting the telescope (which for the 12" is a very nice benefit). Just alleviate a bit of the weight and slide it back.

- Zero Maintenance. 

- Easy to design and build. 

But yes, there are many variations of the drive system out there. There are a couple of guys I've seen that went as far as to implement guiding into their EQ platform allowing them for DSO exposures up to 300 seconds etc. They guy said he invested north of 500$ to make it happen.. and hundreds of hours of time

[LondonNeil]

For some the fun is the complexity of the problem and finding your own solution!

Just on your 4 points though,  a chaon driven solution could still separate (the chain would just be resting/running around the segment and the pin by which it pulls could be just that,  a pin that sits in a link)   reset still easy,  just flick a switch and motor back to the start (the chain needs to be a loop to facilitate this and allow it to pull in both directions). Maintenance just as simple as chains are very durable and robust.  Design and build yes. I'm not sure it's really any harder but the friction design had been done already so use it,  unless you need to change because you've hit a problem. 

[bosun21]

My EQ platform made by the late David Lukehurst only used one motor. It was his larger size platform for my 12" SL dobsonian. The shaft was belt driven and used a knurled brass shaft which provided ample traction. I never experienced any slippage whatsoever whilst in use.

[bosun21]

The South pivot point is far better if it is metal to metal as metal to wood will introduce a degree of stiction. David used a male pin on the top and a female recessed part on the bottom. They were bought as a pair but I have no idea what they are called.