Home Made Remote Controlled Filter Wheel

[1parsec]

Here's the drawing...

Lots of good work there :cool:

Your project is similar to a filter wheel I made to fit onto a Sbig camera.

I used a delrin gear blank for the carousel and drove this using a small stepping motor on the periphery.

The microcontroller used was Atmel AT90-2312 microcontroller and programmed in assembler.

I have a couple of photos of the mechanical bits if you're interested.

Dave.

[Gina]

Yes Dave - I would be - thank you

[1parsec]

Gina, here's my home brew CFW.

The main body is machined from 1 piece with a 6mm thick front cover plate. The body is 125mm diameter and 35mm overall thicknes with the cover plate fitted.

The cover plate was 'salvaged' and I machined the disc from it, hence the scratched black anodised coating.

The body is quite substantial, as I'd heard that the early SBig units had too thin front and back surfaces that

allowed a small amount of flex causing tilting of the focal plane. 6mm wall thickness eliminated this potential problem.

T2 threads were machined together directly through the body and cover plate for perfect centering.

T2 allows standard coupling and nose pieces to be fitted.

The delrin gear was bought fron HPC and the filter threads again, machined directly in to the face of the gear for the carousel.

A shaft was press fit through the centre and supported both ends in flanged miniature bearings fitted in to the body and cover plate.

My main reason for choosing a gear drive rather than a belt drive was for repeatability. I wasn't totally satisfied that a belt would not have

a small amount of back-lash. The teeth cut in to the pulleys are usually wider that those on the belt (for trapezoidal types any way).

This small 'float' could cause mis-alignment of the light frames with flats previously taken which would be a bit difficult to process out.

Check the specifications of the pulley / belts you intend to use and calculate what positioning error may be??

The little AT2313 on the vero board listens to the camera pulse position signal and translates this in to motor steps and filter position.

No serial comms or protocol to program

If I ever get time, I want to strip the whole thing down and get it all anodised. I'm just unsure what to do with the gear - matt black would be better

but I've not noticed any issues with it being white.

Dave.

[Gina]

WOW! Thats a wonderful job Dave - very nice indeed Unfortunately I don't have the machinery to do that.

[1parsec]

I an lucky to have access to a lathe and milling machine. Finding the time to do the 'home jobs' is another problem all together.

Dave.

[Gina]

I've modified the 36mm filter carousel to take the centre timing pulley and fitted it. Here are some photos.

[1parsec]

That looks great. Is the small phillips screw and fibre washer used to hold the filters in position ?

Dave.

[Gina]

Thank you Yes, that's right.

[Gina]

A redesign based on practical considerations. The approximate octagonal shape avoids sharp corners while still allowing straight wall sections. The walls of the casing to be cut from 30mm x 10mm aluminium bar and the side plates from 150mm square x 3mm aluminium sheet. The 30mm walls make the casing the right width for the focal reducer to sensor measurement. From the face of the reducer which sits flat against the FW casing we have 3mm + 30mm + 3mm + 5mm (T2 adapter) + 13.5 (face of camera to sensor) = 54.5mm plus 1mm to allow for filter comes to 55.5mm ie. just 0.5mm more than the specified 55mm. This will be good enough.

[Gina]

I'm not looking forward to sawing up the 30mm x 10mm bar by hand - maybe I should look into buying a router Alternatively, I could keep the square plates (orientated as a diamond shape) and just round off the corners. Then again, with a dual imaging rig I could just use a totally different system. I'm using just a simple filter tray for the widefield rig. Or I will be whenever we get some clear night skies! I'm getting to that stage again of wondering if I'm wasting my time and money trying to take pretty pictures of stars and glowing gas clouds - getting equipment ready in the desperate hope of the odd hour of clear night sky OK - yes - I like making things but I DO like to use the things I make.

[Gina]

Diamond shape with rounded corners.

[Gina]

Well, I've decided to go for the easier option of a diamond shape with rounded corners. I'm using two 150mm square plates and the 30mm x 10mm bars were 250mm long x 2 and I've cut them in half. That leaves 12.5mm gap at the end which I plan to fill with wooden quadrant to keep the dust out. Here's a photo showing the pieces of bar placed around the edge of one of the plates together with the carousel and the motor pulley. The latter has 24 teeth and the carousel pulley 48, so that gives a 2:1 reduction which makes it easy to calculate the number of steps per filter position.

[Gina]

Latest diagram.

[Gina]

Made some progress today. Marked out the side panels and drilled holes to attach them to the 30mm x 10mm side pieces/spacers. Also pilot holes for the light path and carousel axle. Then I cut the holes for the ED80 focal reducer 48mm thread and the adapter to attach the camera to. Having lost the cutter of my trepanning tool and being unable to buy any right size hole cutters, I made the 48mm and 60mm diameter holes by drilling a ring of holes, breaking out the middle and then filing out to size. Rather a tedious job but it's done now.

Here are some photos :-

1. Focal reducer fitted to side panel - side view.
   
2. FR side of panel.
   
3. Fixing ring taken from 48mm to EOS adapter holds the FR.
   
4. Camera side showing adapter for camera fitting.
   
5. Inside of camera side showing adapter fitted into 60mm hole.
   

[Gina]

Tomorrow I plan to drill and tap holes in the side bars to take M4 Allen bolts. Then a hole to take the stepper motor. I have to drill out the hole in the motor pulley from 4mm to 5mm to take the motor shaft too.

[JAS]

Looking good Gina, I like the idea of using the fitting from the EOS adaptor.

Jason.

[Gina]

Thank you Jason Not up to your standards but I think it will work

[Gina]

A bit more progress today. I didn't drill the 30mm x 10mm spacer bars because the material turned out to be a very hard aluminium variant so I'm not keen to drill and tap holes as I had intended - I'll do something else. Instead I sorted out the stepper motor fixing. The motor is screwed to an ali plate which in turn is attached to the FW side plate with 3 allen head screws into tapped holes in the motor plate. These go through elongated holes to provide timing belt tension adjustment.

[1parsec]

That is progressing nicely Gina.

I usually use 6082 aluminium (HE30) for 95% of the bits I make which is good for general machining, drilling and tapping.

Sometimes I go for 7075 which is a bit harder but machines to a superb finish, but quite a bit more expensive.

Dave.

[Gina]

That is progressing nicely Gina.

I usually use 6082 aluminium (HE30) for 95% of the bits I make which is good for general machining, drilling and tapping.

Sometimes I go for 7075 which is a bit harder but machines to a superb finish, but quite a bit more expensive.

Dave.

Thank you Dave I usually get whatever is available on ebay as I rarely want big pieces. Thanks for the grade info

[Gina]

Progress has stopped for a few days as I need some extra bits which are now on order. I tried to open out the centre hole in the aluminium motor pulley from 4mm to 5mm to fit the stepper motor but I was a miserable failure However motionco now have the plastic timing pulleys that are a nice tight fit on the stepper motor shaft so I've ordered more of those. Ony thing is they only had the 20 tooth ones in - the 24 tooth are out of stock. So slight variation on the design but don't think it'll be any problem.

For the spacing between the side plates I have ordered some 30mm x M4 hex pillars. To dust proof I plan to use something flexible to put round the edge, perhaps with some draught excluder. There could be two advantages of this new approach - less weight and I can have any shape by cutting and filing the side plates.

[Gina]

Should be able to get back on the FW today as the pillars and timing pulleys have arrived. When it's done I shall be able to have the Baader 36mm Ha and SII filters in it. Probably not as good as the Astrodon 5nm filters but won't need adapters. For LRGB imaging I can use the Astronomik CLS CCD clip filter as Luminance filter and use the EFW2 for RGB on the other scope. I have checked and found the clip filter will fit nicely between the 36mm fixing holes/screws without modification. It will fit flat against the carousel rather than dropping into a stepped hole as with the 36mm unmounted filters.

[1parsec]

Nice to see the filters mounted.

[Gina]

Actually they're just placed in position but I does show how they will look except for the screws and fibre washers that will hold the filters in place.

[Gina]

Been doing some more work on the filter wheel. Here are some photos. I've put it together roughly to show the construction. I'm using a 5mm bolt as wheel axle ATM but that will be replaced with a piece of 5mm diameter SS rod. I shall also cut the aluminium plates to a suitable roundish shape and fill in the sides to keep dust out.