New type of Dobsonian tracking platform.

[eqcradle]

Hi Folks,

I started a thread over in sci.astro.amateur about an idea I had for a
tracking platform for Dobs:
http://groups.google.com/group/sci.astro.amateur/browse_thread/thread/6964d717edd7cb66/?hl=en#

And then another thread in the Yahoo Eqplatforms group:
http://tech.groups.yahoo.com/group/eqplatforms/
(I think you'd need to be a Yahoo member to read these ones.)

I put my (evolving) thoughts (including Lego mockups!) on a page at:
http://cluton.googlepages.com/equatorialcradle

Going by some of the discussion in the Yahoo group, it seems like the idea may have some uses. It wouldn't be as compact as I was hoping, but one might be useful as a permanent structure (eg. in the backyard).

In summary, it uses 2 ball joints to form an axis - but variations
could use spherical bearings, plain bearings or even a shaft through a
block. It eliminates the roller-arc of the existing platforms I've seen
(which I think would make it much easier to fabricate). I suspect it would be smoother too.

Cheers,

Chris.

[rmcpb]

You have essentially reinvented a version of the horseshoe mount. No reason why it should not work but you are right in that it will be bulkier than a twin cylinder version.

Cheers

[ving]

looks good. i used to have space lego too :D

[Escortitis]

Hey Chris,

Reinvented the wheel myself not to long ago. I used the two pivot point idea in a dob mount and it worked really well, but..................... With the distance between the two pivot points, you will find that the twist between these points will give you big stability problems. it will be great right up to the time when you need to refocus, cough, burp or breathe. You can search 'escortitis', or 'dob mount cheap, cheap, cheap' and you can see pictures of the one i tried (this site). As i said, it works really well but the wobble will drive you mad at 100x and above. I still use it for planet/ lunar stuff, but now im in the process of building one of those platforn trackers using the roller blade wheels driving an arc. They look to be much more stable, by not actually have any pivot points.

None the less, i love watching people think

Keep it up.

George:D

[eqcradle]

Ha, yes I think it is the same principle. It seems to be analagous to the 'extreme' one on my page - ie. everything sitting above the polar axis. And the axis of rotation appears to be the short axle at the bottom? I'm assuming it isn't hanging/pivoting from the tall arm - ie. the tall arm is a lever for rotation? And the pivot is at the bottom where the tall arm joins the short axle?

The guys on the Yahoo Eqplatforms group pointed out some of the centre of gravity issues. If you can arrange it so that the COG is below the polar axis, then it should be self-righting (ie it won't dump the scope). Someone suggested physically restraining it - which looks exactly like what you've done with the lever.

Using the ball joints allows the scope to sit in the middle of the polar axis and even cross it.

With yours, I think you could raise the back of the platform so that it sat level to the ground. I don't think that affects the tracking motion of anything sitting on it. I suspect you could even then extend the platform out in front of your front pivot?

Cheers.

[eqcradle]

Yeah, I like it. I photoshopped a version of it with an image of a real scope: http://cluton.googlepages.com/escortitis.jpg Pretty much the same as yours I think. And if the lever goes back at an angle, it wouldn't inhibit movement of the scope at all. Cheers, Chris

[davidpretorius]

great ideas....