Dob tracker, possibly one for Phil.

[Kaptain Klevtsov]

Been pondering this for a while now.

Plan is to make a guided Dob. stand, similar the the tracker ones that are out there but fancied up a bit. The plan is to have a three point support, one support being a ball and socket of some sort. The other two supports are electric motor driven nuts (linear actuators) which can be speed controlled. These are placed so that they form a right-angled triangle with the ball and socket being the 90 degree bit of the triangle.

Now for the clever bit. Normal guiding software gives pulses to the controller, so that a +DEC pulse would speed up one drive, and a -DEC pulse would slow it down. Similarly the RA + and - pulses would affect the drive speed of the other drive.

As I don't know much at all about guiding, but a little about feedback control systems, I think it might work OK.

First guess at a control would use the voltage across a capacitor to set the motor voltage using an OpAmp., with the output voltage being the same as the capacitor voltage and a feedback to the capacitor to maintain the charge voltage. The pulses would charge or drain the capacitor slightly thereby changing the output voltage and the drive speed.

It could work, it could be cheap and it could make big Dobs into hugely succesful imagers. Imaging a 20" Dob. with autoguiding!

Thoughts anybody?

Captain Chaos

[geppetto]

Thoughts anybody

Well yes, been pondering on how best to track the starGAZer 12 for a while now and

have been wading through heaps of info on the tinternet and making endless scribbles.

Your guiding idea sounds good CC and is worthy of some trials.

Imaging through a 12", now that would be something 8)

Have you done any scribbles yet?

[Kaptain Klevtsov]

Not yet Phil, not even got round to working out how fast the actuators need to go up and down.

Will do some sums now that nobody's said why it won't work.

Captain Chaos

[barkis]

Been pondering this for a while now.

Plan is to make a guided Dob. stand, similar the the tracker ones that are out there but fancied up a bit. The plan is to have a three point support, one support being a ball and socket of some sort. The other two supports are electric motor driven nuts (linear actuators) which can be speed controlled. These are placed so that they form a right-angled triangle with the ball and socket being the 90 degree bit of the triangle.

Now for the clever bit. Normal guiding software gives pulses to the controller, so that a +DEC pulse would speed up one drive, and a -DEC pulse would slow it down. Similarly the RA + and - pulses would affect the drive speed of the other drive.

As I don't know much at all about guiding, but a little about feedback control systems, I think it might work OK.

First guess at a control would use the voltage across a capacitor to set the motor voltage using an OpAmp., with the output voltage being the same as the capacitor voltage and a feedback to the capacitor to maintain the charge voltage. The pulses would charge or drain the capacitor slightly thereby changing the output voltage and the drive speed.

It could work, it could be cheap and it could make big Dobs into hugely succesful imagers. Imaging a 20" Dob. with autoguiding!

Thoughts anybody?

Captain Chaos

Are you meaning to drive in two planes CC ie Alt Az. I may have misinterpreted your plan, but my point is field de rotation. for long exposure images. You may slap my wrist if necessary.

[Kaptain Klevtsov]

Basically I wanted to think up something that you can polar align as roughly as you like, say +/- 10 degrees. Each screw jack acts so that the pivot axis runs through the other jack and the pixet pivot. The two jacks are arranged such that the two axes are orthogonal i.e. the screw jacks are at the pointy corners of a right angled triangle, the fixed pivot would be at the right angle.

When switched on the drive would actuate one jack up and one jack down at a default rate so that the top of the platform tips slowly.

The bit that I thought was clever :sign7: was to take inputs from a common or garden guiding system to modify the rate that each jack moves at.

Field rotation is going to be a problem for loooong exposures, unless I can take the same system and redesign the mechanics of it.

The reason that I posted it was that I'd not read of such a system, and if it's not patented, it now can't be. The concept is common knowledge as its been in the public domain, so there.

I'm going to trawl through some of Arthur's posts from a few months back when he discussed the tracking platform design as it currently is used to see if that would lend itself to some tweaking.

Captain Chaos

[barkis]

Basically I wanted to think up something that you can polar align as roughly as you like, say +/- 10 degrees. Each screw jack acts so that the pivot axis runs through the other jack and the pixet pivot. The two jacks are arranged such that the two axes are orthogonal i.e. the screw jacks are at the pointy corners of a right angled triangle, the fixed pivot would be at the right angle.

When switched on the drive would actuate one jack up and one jack down at a default rate so that the top of the platform tips slowly.

The bit that I thought was clever :sign7: was to take inputs from a common or garden guiding system to modify the rate that each jack moves at.

Field rotation is going to be a problem for loooong exposures, unless I can take the same system and redesign the mechanics of it.

The reason that I posted it was that I'd not read of such a system, and if it's not patented, it now can't be. The concept is common knowledge as its been in the public domain, so there.

I'm going to trawl through some of Arthur's posts from a few months back when he discussed the tracking platform design as it currently is used to see if that would lend itself to some tweaking.

Captain Chaos

Good Luck with it CC, Driven Dob design and developement was quite popular in the States, as I'm sure you know. Also, you will know of Mel Bartels, who was highly active in this particular area. I don't want to tread on your toes at all, you will be the best judge of where,and what, and whyfore. It is a challenging project.

[Astroman]

This sounds very much like an astrophotography guiding platform built by my friend, Professor Russel Nidey. I'm sure it's much larger than you had in mind, but it is essentially the same. His is built around a polar aligned truck differential, with a very large steel superstructure, similar to the triangle you mention. Think of an inverted, 4 sides pyramid, with one edge polar aligned and anchored such that the rest of the structure rotates about it. At one corner of the structure is a screw jack of large size and a guide scope. When I first encountered it, the jack was turned by hand, with the turner looking through the guide scope. Maximum exposures were 9 minutes, due to the length of the screw. Around the perimeter of the ~4 meter base of the pyramid were several dozen screw mounts for cameras. It was permanently connected and aligned.