SCT modifications:- filter wheel/camera rotate and focus

[DIYASTRO]

I have just posted a request for info on copper clad boards.

this is to help finish of this project .... so.....

Thought I would start a new thread for some of the modifications that I have been doing to my 10" SCT and some plans for future additions etc.

You will see from the pics that I have made another version of twin 2" filter wheel. The first has now found a permanent home on my multi lens astro camera.

This version that I figure here was far simpler to build and since I had most of the bits from left overs from other builds came together quite quickly.

Still more time in the planning and marking out stages though to ensure that it will all fit together in the correct place and work!

It is quite basic since I didn't put steppers on this version simply dc motors a gears boxes.

you will see that each wheel is independant driven and that these drives are on the rear of the contraption which nestle in to the SCT since the screw threads on the Meade are quite forward in position to the main casing.

The third motor/gearbox is for the main mirror focus so that can be used to give the coarser focusing reqirements.

The front plate supports the camera rotation gearing and its motor gearbox drive/ Crayford focuser and motor gearbox for the fine focus on the Crayford.

Just need some time now to solder the connections on the 25pin d skt, limit switches for filter position / recognition, motors etc etc.

[Horwig]

I take my cap off to you sir, that is proper engineering.

In Awe

Huw

[DIYASTRO]

Horwig/Huw

Many thanks for that.

Not quite finished, since I think I can reduce the width of the unit by another 10mm, thus reducing the distance to focal plane.

I have made many many astro bits over the last few years and at some point must find the time to post up photos of some of them.

My need at the moment is to begin a concentrated effort to get some sort of obsy constructed since the various projects have grown arms and legs and have filled all available spaces at home, I post pic of our so called living room which my wife says enough is enough and I either get something built outdoors or start looking for a flat! My own room is so full I cant get in it!

[Horwig]

He He, I can see why you'r wife might have grounds for being a bit miffed, looks as if you are preparing for a three camera OB.

Huw

[DIYASTRO]

Horwig,

Yes, at least a three unit scope set up. although mine will be a 10" SCT with two multi lens cameras for different ranges of wide field/ lunar / solar.

you will see from first pic the three units, the two multi lens cameras have to get covered yet.

Coming back to the original SCT mod. topic, the other two pics are of the non filter focus Crayford design that I built some time ago.

Again a separate motor/gearbox for the main mirror and a fine drive for the Crayford. pics show it with eyepiece but have tried it with cameras also and works fine.

The whole thing is fixed to the SCT via a mounting ring with three grub screws and takes about 2 mins to attach or remove.

will try to complete the electronic conections to the filter wheel unit this week and finish the parts for its sibling smaller 1.25" version and post results then.

by the way I am beginning to think that wife is getting serious about looking for a flat, I only hope I can find one she likes!

[ChrisLX200]

Whilst I am impressed with the engineering and quality of construction I'm at a bit of a loss to understand the advantages of using a pair of wheels to hold the 2" filters rather than a single larger one? The footprint would not be any larger and the construction/operation far more simple? Also, there would be no issues with some filters being at a different distance from the sensor (which, apart from affecting focus point can also result in slight mis-registration of frames in the final image). I do like the idea of a camera rotator and it's something I must make at some point, commercial units are very expensive.

ChrisH

[Davey-T]

Hope Olly doesn't see all those wedge mounted forks, he'll have a fit 

Dave

[DIYASTRO]

Just home from work, which plays havoc with my hobby!

firstly in answer to Chris H.

Thanks for your reply and kind comments.

If you work out that the two 5 station filter wheels each carry four filters leaving a blank space in each so as to allow no filteration of light source then a single wheel would need to be at least 9 station, allowing the 8 required filters with one blank position.

Now, if you make a single 2" filter wheel of 9 holes then the minimum diameter of that is around 230mm.

The 10" SCT has a maximum fork width of 320mm or so at the base where the filter wheel and rotator etc has to pass though, or in real terms only 160mm from the rear of the scope where the visual bit in the centre is located. So a single large 9 station could not pass though the fork gap even if you placed it so the top of the wheels assembly was 'at the top of the scope' it interferes with the guidescope finder access etc and will only pass with difficulty in construction by offsetting the wheel in the assembly.

I live with the refocus situation quite well since the 'exotics' (narrowband) live in the lower filter and the solar continuum ND types and other live on the other filter and refocus is not too much of a problem when you have such fine adjustment on the motorised Crayford.

Alignment is as you say quite crucial hence the wheels are run on bearings and are well aligned with the optical path.

I have seen some camera rotators and cannot understand why they are so expensive, some of them are not even gear mechanisms. I decided to make my own for comparative cheapness ( though not cheap!) but really for accuracy as well, mine take some weight!

Dave: not too sure if 'OLLY' is a fork man or not from your comments! I have a few!!! 8 in total and I like them when I have converted the electronics and drive systems to stepper motors and good solid gears. Most of my fork mounts are now 'converted' and several are also fully goto.

[DIYASTRO]

managed to get a pick up board etched and soldered to try out the problem with the focus motor assembly.

In doing so inadvertently discovered a potential solution to the tracks being so thin.

Coat them with solder!

I have done this with the pick up board, roughly!

I am sure that if I could get some other boards etched out and send them to a professional  pcb soldering outfit who would be able to 'dip' the board the finish would be even enough for the eventual carbon brush pick ups.

I have used a simple solution here, a couple of spring loaded baynet lamp connectors.

Anyway, tested this contraption out and it works like a dream!

Will try and solder up the 25 pin d connections in a couple of days and run it to the control panel to put it through its paces!

Boyd

[Gina]

I'm thinking about a rotating connection for CCTV cameras where I want the camera to be capable of 360 degrees.  I shall want 4 connections - Gnd, +12v, video and control (for pan and tilt).  One possibility I considered was a 4 way jack and plug, I remembered I had a telephone jack/plug from way back when companies had telephones that could be moved from office to office.  That was in the days of the GPO.  If it could be done with 3 wires a stereo jack and plug would suffice.

I guess I could use a radio link for the control - video has a bandwidth problem.

[DIYASTRO]

Gina,

I have tried this without much success, using exactly the type of plug / skt you mention. (Ex; telex machine!)

When I was etching the copper plate I was going to put extra tracks on to try a carbon pick up arrangement to see if I could use the video out function on the Canon. Perhaps I will get another plate and give that a go. Was wondering if a ferrite core around the cable might help.

The present system would lend itself to powering the canon its the usb and video that I am not too sure about.

I have made a multi rotation connector years ago for a microscope stage rotation and heating / cooling platform, no bandwidth problems with that!

Boyd

[Gina]

Thanks Boyd   I'll think again then   Good luck with your slip rings   A ferrite ring is always worth trying.

[DIYASTRO]

Finally decided to wire up the filter wheel unit!

Only a temp for trials since the cable looms should go in some tubing / trunking but after testing all the drives, independently and all running together at the same time, it all appears to work just fine.

Only things left to do are to 'notch' out the filter wheels to allow the limit switches to 'locate' each position...and then start building the control panel and the associated electronic pcbs etc!

Since starting this project I have been thinking about the way in which I will construct the much smaller 1.25" filter wheel / rotator. Making a double 5" type twice now! has given lots of practice and enabled some problem solving which I find difficult unless I have something 'physical' to look at and work on.

(old age that!)

Not sure when I will get the time to finish the control panels but will post that up when ready.

Boyd

[DIYASTRO]

Its been a while....took me ages to find my thread!

Have been busy with the smaller 1.25" filter wheel/rotator and posting some pics to show progress and finished article.

will post up some explanations on build sequence etc a little latter, just wanted to get these uploaded first!

[DIYASTRO]

Thought I had better offer some verbal description for my last post.

The unit that I have made was simply to combine a motorised 1.25" filter wheel with a camera rotate facility since I have not seen such a unit for sale from any of the major manufacturers / dealers.

I have also designed it so that it is possible to use the dc motor controllers from high tech astro and Shoestring astronomy so that if desired, it is possible to control the unit via a pc.

I personally prefer a 'stand alone' controller so as not to 'overload' the pc with unnecessary functions.

The controller that I have built gives filter wheel position via the 'led bank' you simply depress the push to make switch and hold until the led changes position and then release the switch and it has indexed to the next position.

the filter wheel only operates in clockwise direction to make the electronic circuit simpler but it also has a pulse width modulation speed control so complete rotation can be done in a few seconds. the filter wheel as you can see from pics, is belt driven powered by a small metal geared modified  servo motor.

The camera rotation is a 190tooth .5mod gear driven by a high torque metal geared servo motor which has been modified somewhat in order to fit the unit. Again, it has a pulse width modulation speed control and a reversing switch allowing full 360 degree rotation in clockwise or anticlockwise direction.

the rear of the unit has threaded plate allowing connection options. It has a male 77mm thread and a female 58mm which holds the 58mm to t thread so a 2" or 1.25" adapter can be screwed in and then fits in the Crayford focuser.

The front of the unit with the rotation gear has  a 46mm female thread which takes the 46-female t thread adaptor allowing camera connection.

I am at present thinking of building a mould for casting resin to make a 'ring' to go between the plates so as to make it light tight.

When complete will post up results with some pics.

Boyd

[DIYASTRO]

Made a start on the resin mould for the filter wheel and rotator.

Decided to make from copper clad board and brass strip this time to allow easy removal of the cast resin.

Need to make up the internal 'block' so that the cast is just over 18mm thick / deep, and incorporates the 4 hex brass support stand offs which is what the secures the front and rear aluminium plates together.

Will surface grind the cast for its final 18mm depth to maintain accurate plane for rear and front plates.

Have had some response on this, not only from members of this forum but emails from 'other' astro people and would just like to say thankyou to all for your interest.

It seems that others have looked around for a combo filterwheel/camera rotator and I am not the only one who couldn't find one!

Its been very rewarding to work on this particular contraption! A bit of a challenge for some accuracy and working out how to fit it all together. Took quite a few attempts on the old drawing board!

will post up the progress of the mould and eventually the black resin cast.

Have also to find a place to send all the aluminium bits for anodising, any suggestions welcome!

Boyd

[DIYASTRO]

I mentioned in an earlier post, that DIY is not perhaps as inexpensive as we like to think!

I have been asked to send someone who has shown great interest in buying one of the filter wheel / rotators that I have made, a list of what is within the construction and how much it cost!

I thought it would be useful to post that list within my thread.

I havnt started to plough through the old invoices yet but suspect I am in for a shock!  Its a good thing that I enjoy making my own equipment since I don't think on a costings basis I should!

Component costs have really increased over the last few years and although many people have asked me to make things for them they simply don't understand just how much work and the cost of the materials .

I shall post my findings when I have completed the invoice search, and hope that my wife doesn't get hold of the 'classified'  information!

Boyd

[DIYASTRO]

Short update,

Have not had the time that I had planned for this last few days but have basically completed my trio of driven filter wheels and rotators.

Decided to 'assemble' one of them with acrylic front and rear plates to enable a clearer idea of what is inside.

Will re-assemble this with the aluminium ones when I get around to sending away loads of bits to get them anodised black. I also want to make a short video of the 'transparent' example to show how the filter wheel and camera rotation actually do their stuff.

Most of the control electronics are assembled, but the actual wiring up may have to wait till next weekend.

What is useful, is by keeping the assemblies identical, the one control box that is complete can be used to test the others, pleased to report that all three rotate really well and filter alignment is nice and accurate.

Will update progress.

Boyd