New type of Dobsonian tracking platform?
Full Name:
I recently had an idea for a tracking platform for Dobsonians. It seems
like it would be very cheap and easy to build. I'd be interested to know
whether it has been done before. The closest I've seen in principle are
the existing equatorial platforms for Dobsonian mounts but this is quite
different in design from those. It doesn't require the roller track -
instead it simply hangs from two ball joints.
I don't have time to build or test one yet, but I did some Lego mock-ups
(see link) and they seem to validate the principle. I'm curious to know
whether this idea would work and whether it's practical:
http://cluton.googlepages.com/equatorialcradle
Cheers,
C. Luton
'200704' at the following domain:
luton.id.au
wsne...@hotmail.com
It might work, but it doesn't seem very compact or portable.
Mark F.
<wsne...@hotmail.com> wrote in message
news:1176043471.7...@e65g2000hsc.googlegroups.com...
Alan French
news:pan.2007.04.08....@notreal.blah...
It looks like you've essentially turned a cross axis mount into an
equatorial platform. I can't see how this gives you any advantages. You
might as well just make a cross axis mount or perhaps a yoke mount, and
leave it at that.
Clear skies, Alan
Shawn
Where do you put the ladder? My dob only has 90 deg or so of alt travel
which I think is fairly typical of big truss tube dobs. If I were to
use such a device, I would only be able to look east or west without
rotating the secondary and recollimating. I think the equatorial wedge
is a more elegant solution. However, a simple, portable mount for
typical big dob "OTA's" (from the alt bearings up), that could turn them
into photographic scopes would be really interesting IMO.
Shawn
Full Name:
>
> It looks like you've essentially turned a cross axis mount into an
> equatorial platform. I can't see how this gives you any advantages. You
> might as well just make a cross axis mount or perhaps a yoke mount, and
> leave it at that.
>
> Clear skies, Alan
Yes, I think you're right - it is just a cross axis mount. Thanks for
pointing that out.
I guess the difference here is that there's no shaft between the pivots -
which would allow the use of a platform to sit a Dob on. And the Dob can
sit directly between the pivots.
I still think it should be possible to build a fairly compact version to
sit a Dob on - it only needs to turn through 15-30 degrees. Won't know
whether it's actually practical though - until (unless) I build one though.
Cheers.
Full Name:
>>
>> It might work, but it doesn't seem very compact or portable.
>>
I 'photoshopped' an image to give an idea of size with a real Dob:
http://cluton.googlepages.com/gimpshopped.jpg
It would certainly be larger than the existing equatorial platforms, but
it wouldn't be huge.
George
"Full Name:" <thisis...@notreal.blah> wrote in message
So what would be the benefit of building and using something like this
over, say, a poncet mount?
George
Full Name:
> So what would be the benefit of building and using something like this
> over, say, a poncet mount?
>
> George
I'm not sure - there might not be any benefit at all. It's just guesswork
until I try building one (or someone else does ;-)).
It seems to me like it would be much easier to build than the Poncent
mounts (my carpentry skills and equipment are limited ;-)). There's no
need to cut and assemble pieces at the correct angles and no need to cut
the proper arcs for the rollers.
In comparison, it's just a matter of bolting a couple of ball joints to a
supporting structure and hanging the platform from the joints. As long as
the axis formed by the ball joints is pointing at the pole then I think it
should give the correct motion. It might be harder to motorise and/or
balance though - I'm not sure.
I wonder whether 2 ball joints (or spherical bearings) would give smoother
motion than a track on rollers? I'm not enough of an engineer to know.
But smoother motion would obviously be better for long exposure
photography.
wsne...@hotmail.com
You will need to get the telescope's center of gravity located on the
line connecting the ball joints or just slightly below that line, and/
or add some counterweights, or else the scope will tip over.
Also the right-angle connection of the platform with the upright
section that connects with the upper ball joint will need to be very
strong and rigid, although extra structural material here could
provide some of the counterweight.
What size truck do you own? <grin>
Ernie Dunbar
> Yes, I think you're right - it is just a cross axis mount. Thanks for
> pointing that out.
>
> I guess the difference here is that there's no shaft between the pivots -
> which would allow the use of a platform to sit a Dob on. And the Dob can
> sit directly between the pivots.
>
> I still think it should be possible to build a fairly compact version to
> sit a Dob on - it only needs to turn through 15-30 degrees. Won't know
> whether it's actually practical though - until (unless) I build one though.
What I would do, (especially if you have a mass-market dob, like I do)
would be to build an english mount permanently somewhere. The OTA can
be put in there when you're at home, and you can take it out again and
put it in the dob base when you want to take it to star parties.