Designing a Rotator

[Earl]

If you were designing a Rotator for  your scope what would you like it to have?

Currently im looking at one on the end of my 106 Draw tube and have a maximum optical lenght of 20mm with the reducer going direct onto it this will avoid any light path issues.

Any thoughts?

[DIYASTRO]

Earl,

Are we talking about a camera / eyepiece rotator with 360 deg rotation ?

I have been working on some ideas for rotating camera in combo with a filter wheel.

I am particularly interested in analogue control, keep wondering what other people use when imaging without laptop or PC using standalone autoguiding.

Most of the filter wheels and rotators appear to be USB / ascom controlled.

Most of my home made stuff is now designed to have independent analogue control, getting away from the dependency of PC.

Just wondered if this is what you are describing.

Boyd

[Earl]

In this instance it would connect to the Drawtube, putting it at the very start of the chain meaning its going to have to support all the weight of reducer filterwheel, oag, guide and ccd (QSI so all in one box) and at the same time be no more than 20mm optical lenght.

Also it has to have ascom and manual control, for which it would need a handset for the degree display etc.

[callump]

Hi Earl,

I presume you're interested in using this for framing rather than field de-rotating?

(though no doubt the mechanics could be used for either purpose..)

I'd have thought the main problem would be finding some sort of 2 or 3 inch i/d bearings, that will induce minimal flop as the imaging assembly rotates. Then a similar sized i/d worm wheel, or could be driven by belt...

Could be done in 20mm, but it might be tight...

Callum

[Earl]

Hi Earl,

I presume you're interested in using this for framing rather than field de-rotating?

(though no doubt the mechanics could be used for either purpose..)

I'd have thought the main problem would be finding some sort of 2 or 3 inch i/d bearings, that will induce minimal flop as the imaging assembly rotates. Then a similar sized i/d worm wheel, or could be driven by belt...

Could be done in 20mm, but it might be tight...

Callum

Yes Callum framing is what im looking at. If a fixed plate was attached to the scope and the rotating part was on the outer side, if there where ball bearigs inbetween the too plates every cm or so aroud the diameter I wounder if that would be enough?

Belt drive does seem to be the way to go.

[callump]

Hi Earl,

no, I was thinking something more like:

http://www.bearingboys.co.uk/6010_2RS_Budget_Sealed_Ball_Bearing-1873-p

Or maybe larger diameter.

You might get away with one, but I expect you would need two, otherwise there will be a tendency to tip.

Fix the outside of the bearings on one part, and put a tube through the bearings and secure with grub screws.

You can probably source better bearings (maybe thinner), this was just the first example I found.

Cheers, Callum

[ChrisLX200]

Hi Earl,

no, I was thinking something more like:

http://www.bearingboys.co.uk/6010_2RS_Budget_Sealed_Ball_Bearing-1873-p

Or maybe larger diameter.

You might get away with one, but I expect you would need two, otherwise there will be a tendency to tip.

Fix the outside of the bearings on one part, and put a tube through the bearings and secure with grub screws.

You can probably source better bearings (maybe thinner), this was just the first example I found.

Cheers, Callum

I don't think that will work. All bearings must have some clearances to work and that is the one thing you cannot have between camera and scope. Perhaps using an OAG you could get around it, but using a guidescope that clearance would show up.

ChrisH

[DIYASTRO]

When building my rotator, I tried needle roller thrust bearings, ( only 3mm thick) they work well but require two and quite expensive.

I resorted in the end to making sure the plates where very flat and using .5mm Teflon sheet between the large gear and front plate and another Teflon 'washer' the other side of that plate.

No problems with rotation or 'play' in the assembly.

I was using a large diameter gear wheel though (200mm) so the Teflon covers a large surface area.

Boyd

[NickK]

This is the sort of thing you could use a small harmonic drive for - making the two plates large, then with the hole in the middle and having the harmonic drive on the outter edge of the plates. You should get very little play as harmonics drives have multiple teeth engaged. Or.. you could use a small direct drive.. but I'd be worried about the magnetic field inducing currents in the camera electrics close by.