Who had the thread about equatorialising a Dob?

[The Warthog]

Here's a site that not only explains the function of a dob tracking platform in terms even I, a Social Science graduate, can understand. It also gives instructions for building one that I am pretty sure I could follow successfully.

http://www.budgetastronomer.ca/index.php?page=eq-platform-pt-ii

[Ant]

This one?

http://stargazerslounge.com/index.php/topic,31514.0.html

Ant

[The Warthog]

It was a rhetorical question. Whatever that means.

[EA2007]

In the words of Jim Carey.....it was me!!!!

Yeh, I looked at that page ages ago, before I was even into the whole idea.

I must say that for a DIY job which on the face of it looked like it might never work...it turned out to be blindingly brilliant. I used the scope the other night and it tracks brilliantly and that was even with a rough polar alignment. The rotation is smooth and quiet and the mount is sturdy. There are no issues with balancing when its in different positions (I have yet to try a camera on it), all in all a very good job.

I have to point out that, I think Lightbucket stated that larger dobs could be used, something which I agreed with at first. But having re-looked at the way large dobs work then I have a few reservations with the weight on the forks and also the balancing. Meade and Skywatcher dobs are balanced at the base of the OTA not in the middle like the Celestron ones. Therefore I think that if one with a large dob wanted to EQ it then they would need to make somekind of metal fork system and cut spherical holes in it whereby the rollers can sit. (If that makes sense).

[The Warthog]

Well, your system is a fork mounted Newtonian, like the 200 inch at Palomar, but they don't have to worry about ep position. You could solve the ep problem by making the top of the tube rotate, but that's another whole world of pain.

Of course, the other thing you could do is stick a camera in the hole...

[GazOC]

Or swap out the secondary flat for a concave mirror, drill a hole in the primary and use it as a Cassegrain...

[Sam]

Imagine drilling a hole in your primary mirror!... eeek!

To EQ my lightbridge the pivot point would have to be moved the tube about three inches to get it to balance, or add some weights to the base - I would imagine that it could be done but it take quite a bit of modification. The whole concept is basically a fork mount with a wedge as mentioned.

Sam

[Astronut]

I'd always wondered how those platforms work and why the 'scope doesn't tip over at the platform limits - thanks for the link WH.

The theory is back one page from the link posted.

[EA2007]

In my opinion its a very simple (and cost effective) way of making your dob equatorial. Don't get me wrong, the tracking may be worse than a proper EQ mount and there are no electronics. But if you have the know-how I am sure someone could russell up a motor driven goto version.

[The Warthog]

There are goto and push-to systems for Dobs, but they work in Alt-az mode. I think it would be difficult, if not imporssible to make a tracking platform part of a goto system.