DIY Equatorial Platform for Dobsonian

[Jasp05]

Hi guys,

After successfully building a barn door tracker, I thought I'd try my hand at building an EQ platform for my 8 inch dob.

I've been doing some research online, and there is bits and pieces of info around. I thought I'd ask here to see if anyone has had some "hands on" experience in building one.


The platform itself seems quite simple in theory, but how accurate do these things need to be to perform well?

I would like to use it for some basic astrophotography. Not expecting miracles from it, but a few shots of globs and brighter nebulae would be a nice starting point. Thinking anything up to say 30 sec exposures out of it would keep me happy for a while. Is this a reasonable expectation for such a platform?

But if anyone has any links to info or experience with a platform I'd like to here from you.

I may be able to make a build guide on the forum if it's successful.

Thanks in advance.

[billdan]

Hi Aaron,

I have no experience in the building of EQ platfroms. I do have these links you may want to look at.

This is the Stellafane links page.

https://stellafane.org/misc/links.html#EquatorialPlatforms

Here is a link to a water drip method of tracking (McCreary Fluid Mount), and it is claimed to be very accurate, there is no PE and it is accurate to 1 arcsec drift over 80 minutes.

http://subarcsec.com/index.html

All these platforms track in RA only, so you will need a really good polar alignment to stop DEC from drifting. DEC drifting will determine how long your sub exposures could be.

Cheers
Bill

[Rod]

Hi Aaron

I've built or helped build a few now. There are a lot of possible designs to choose from. At our local club we have built two designs. One that works well if you are building on your own is the one by Ed Jones. He has two videos that show you how to build it:

https://m.youtube.com/watch?v=YM9YCbeeGjI

https://m.youtube.com/watch?v=aIuF9bfbiW4

I would also suggest you join the yahoo group - eqplatforms:

https://groups.yahoo.com/neo/groups/eqplatforms/info

In the files section for the group you'll find a manual by Warren Peters and another by David Shouldice that explain how to build a platform. I find Warren's spreadsheet very helpful even if you are not using his design.

The thing I learnt from building mine is that using a jig to shape the sectors improves the performance significantly.

I have not tried photography but find an equatorial platform invaluable for public demonstrations and high power visual work.

Ive attached a photo of a platform I built with a friend 2 years ago. He made the electronics and I did the wood work.

Hope that helps,

Rod

[Jasp05]

Thanks Bill and Rod.

I'm still trying to work out which design will be the easiest to build.

Not sure if i want to try and make the conical shape for the north and south bearings, as that will take some ingenuity on my part to make them with the tools I have currently. Really wishing i had a table saw right now :(

However there are additional complications with going the VNS route (Vertical north segment, which has no conical shape. But it has to be mounted at a specific angle to compensate I believe).


Rod would you mind posting a pic of your platform showing the underside of the top board. I'm assuming you used the conical north & South bearings in your design?


Also does the stepper motor provide any unwanted vibrations? I know I have some vibration from the stepper in my barn door tracker but it is small enough to not be causing any issues for the widefield work I've been doing.

But at magnification this may become problematic?

[PCH]

There used to be a couple of peeps on here who viewed thru G-STAR cameras onto a PC screen. Such a camera was able to pick up heaps more light than our eyes, naturally, hence the image on the screen (like globs for eg) was way brighter than when viewed thru the EP.

I was just thinking, using any number of screen capture apps/progs, wouldn't a screen capture of your glob, or whatever, be a good substitute for proper AP?

Or is that just not capturing the essence of AP? Kind of like cheating?

Anyone tried that or is it just a daft suggestion? (Which is highly likely as I'm the first to admit I haven't tried it)

[Rod]

Hi Aaron

Attached is the photo you asked for. My platform used the same sectors as Ed Jones has. These are circular but the large sector is sanded so that it can ride on horizontally mounted rollers like Ed's does.

Ed Jones does this sanding with a circular saw sanding attachment. I used a jig mounted belt sander. The belt sander was cheap - I think around $40.

My first platform used the Warren Peters circle sector design. It worked but I found getting it to ride on 8 bearings very tedious. Ed's design and the VNS you mention are easier in that the platform top naturally sits on the 5 support bearings.

If you make a jig, a VNS is probably easier to build than a circle sector platform as there are less angled supports to cut.

I don't notice any wobble with the stepper motor on this platform. I think it's because the allthread gives a high gear reduction ratio. The stepper circuit is the one described by Nils Olaf Carlin:

http://web.telia.com/~u41105032/Stepper/Stepper.htm

It has a number of nice features:

Automatic rewind
A beeper sounds before the rewind
Correction for the small error caused by a tangent drive
Warning beep if battery power is too low

My friend Geoff did the electronics and he sadly passed away last year so I can't answer many questions about how he build the circuit. If you are interested though, we both corresponded with Nils and he was extremely helpful so you could email him.

Hope that helps. PM me if you would like to arrange a phone conversation.

I think Equatorial Platforms are a great ATM project. You can get so much benefit from relatively little expense.

Rod.

[Rod]

Hi Aaron

Here is a photo of the jig we use at the ASV to shape platform sectors. I made a simpler one I used at home and can post a pic of that if it's helpful.

Rod.

[mswhin63]

I found rounding the drive flat instead of a more complex jig to make the angle. Instead U found it easier to make Motor Drive to be mounted on an angle.

I have some photos, but I don't know where they are. I am though going to build another EQ Platform as my other one use plywood that was too thin.

A good EQ platform can do really good Astrophotography as well. I did a lot of planetary from my google photo page, although i managed a good Deep Space version - https://goo.gl/photos/9P5Hsw8D8NbzfTpj8

I will try to locate the photos from the previous build.

[Jasp05]

Thanks for the replies everyone.

So if i go the circula segment route i dont necesarily have to do the whole jig to sand the bottom curve. This is only done so you dont have to mount the motor at an angle that compliments the bearing?


Ive not found a whole lot on how to work out what size and shape etc for the vns sectors.


Where are you guys located? Wondering if its possible to catch up and discuss some design plans or something. Im in rockhampton qld.

[Rod]

Hi Aaron

Unfortunately I live in Mt Martha, near Melbourne.

The jig makes sure everything is aligned, leading to better tracking accuracy. I made a platform with simple routed circle segments. It worked but was only accurate for a short period. However, if you have limited tools, then go for it.

We probably should be careful with the term VNS. I used it earlier but in the Southern Hemisphere it is a vertical south sector (VSS).

There is a description of vertical sector design in the files section of the yahoo group I referenced earlier. Or you can have a look here:

http://sawdustfactory.nfshost.com/eq%20platform/

Or here:

http://www.reinervogel.net/index_e.html Click on the equatorial platform link on the left.

Rod

[CognitiveBias]

Hi Aaron,

I built an eqp for my 12" dob about a year ago with alot of help from the net (don't know many people into this hobby let alone anyone with eqp build advice). I thought i'd try the "vns" design although at our latitude it'd be more appropriately dubbed "vss" i suppose :)
I found the calculations on reiner vogel's website (already mentioned in previous reply) very helpful for drawing up the vertical segments. I used micrsft publisher, or was it word i can't remember, to draw a circle then change its height/width using reiners formulae. I then printed actual size copies of the segments then glued them to 6mm aluminium flat bar and cut & shaped them with jigsaw and metal file. I spent a fair amount of time figuring it all out and doing it but that was basically it. I bought a stepper motor, speed controller etc online. Used a guitar slide for the vertical rollers - took the slide down to an engineering workshop to have cut and machined just a tiny bit to fit flanged 608 bearings in the ends. I designed and built a clutch mechanism for the interior of the drive roller to make it easy to return to the start position. Twist a knob to disengage the motor and it rolls freely. Not necessary - could just lift / drag it back to the start position if it isn't too heavy i suppose.
I'll link a few pics including some shots taken with a lodestar x2c camera. Although my exposures are generally 10sec or less with the lodestar, I've found 20-30 seconds is prob where image sharpness mostly seems to start its biggest decline.
I've since housed the electronics in a jaycar project box.

All the best
Nathan

http://i.imgur.com/y2Oeg6L.jpg
http://i.imgur.com/T2Hdyzi.jpg
http://i.imgur.com/8sHKgpC.jpg
http://i.imgur.com/JJcXITL.jpg
http://i.imgur.com/5q6iBNl.jpg

6 and 10 second stacked images using lodestar x2c:

http://i.imgur.com/QOhHuVZ.png
http://i.imgur.com/GBjV7IW.png