A new idea to track with a Dobsonian

[Pinwheel (Doug)]

While looking on the web at tracking platforms with a Dobsonian, I came up with a simpler idea. As the common GSO style dob has a rotating platform anyway, it occurred to me that if you attached a linear plastic gear strip around the base platform, it's just a matter of fitting a motor & matching pinon gear to track stars. I've found a manufacture of plastic gear strips in all sorts of configurations. So, how hard could this be? I am not an engineer so am I missing some important point, because this would be too damned easy.

[CJ (Chris)]

Wouldn't you need to have the Dob platform pivot bolt aligned with, as in pointed at, the celelstial pole?

[noeyedeer (Matt)]

it would need to move both alt and az axis .. good idea but moving the base alone won't track an object. if it was that easy it'd be made for cheap

matt

[Pinwheel (Doug)]

Originally Posted by CJ

Wouldn't you need to have the Dob platform pivot bolt aligned with, as in pointed at, the celelstial pole?

An adjustable platform wedge could fix this, Set the tilt at 36 deg ( or your latitude ) job done.

[CJ (Chris)]

Wouldn't that give you a rotation axis 36° from vertical. For your idea to work I think you need rotation about the axis 36° from horizontal. Much the same as with a correctly set up equatorial mount. I think.....
If I could sketch it I would but I'm hopeless outside of CAD software.

[astro744]

Just type in Poncet platform into Google and click on the drawing of the telescope (second image) and you will see what you need.

Note you can track with Alt-Az but you need to move both axis at the same time and at different rates. Stepper motors could do it with some sort of microprocessor. Note Alt-Az tracking causes field rotation that needs to be compensated if photographing.

A Poncet platform is an equatorial platform with tracking typically about 45 minutes before having to be reset. It is custom made to your latitude but adjustable versions are available. See http://www.equatorialplatforms.com/

[rustigsmed (Russell)]

http://www.optecinc.com/astronomy/ca...yxis/pyxis.htm

[Pinwheel (Doug)]

Originally Posted by astro744

Note you can track with Alt-Az but you need to move both axis at the same time and at different rates. Stepper motors could do it with some sort of microprocessor. Note Alt-Az tracking causes field rotation that needs to be compensated if photographing.

A Poncet platform is an equatorial platform with tracking typically about 45 minutes before having to be reset. It is custom made to your latitude but adjustable versions are available. See http://www.equatorialplatforms.com/

Ridiculously expensive product, I could buy an EQ8 mount & pier for similar money, converting the Dob completely.

[rustigsmed (Russell)]

Originally Posted by Pinwheel

Ridiculously expensive product, I could buy an EQ8 mount & pier for similar money, converting the Dob completely.

I think it makes more sense if you are getting into the 'real big' dob territory.

[astro744]

Originally Posted by Pinwheel

Ridiculously expensive product, I could buy an EQ8 mount & pier for similar money, converting the Dob completely.

Agreed. But if you want to do some astrophotography with your big Dob they are ideal.

If you have a big Dob and are mainly visual then I think the ServoCAT system offers far more especially when combined with Argo Navis. See http://www.stellarcat.com/ Also expensive but it and the EQ platform are the few practical ways of providing tracking for big Dob.

There used to be cheaper Poncet platforms available and maybe you can still source some although these days GOTO Alt-AZ tracking seems to be more popular.

[sharkbite]

I'm building one at the moment!

It is pretty easy.

The hardest bit is waiting for the parts to arrive!
If I was to start again i,'d get all the parts from servo city
As the local distributor does not stock them all.

Look up "ideas for motorising a dobsonian" on YouTube to see where I got the inspiration.

I have the altitude motorised and the gearing in place for the base,
Just need to mount the motor for azimuth control

I'll post pics when I'm done:-)