DIY all-sky cam?

[Gina]

For moving a shutter I spose you could maybe try the head moving coil/magnet from the inside of an old laptop hard drive?

Or maybe a discarded DSLR mirror flip solenoid or DSLR shutter - of which I'm sure you have plenty of Gina

I've investigated or tried most of those   The mirror in a DSLR is controlled by the shutter mechanism which in turn is driven by a motor.  I found the motor got hot when running in "stalled" mode when enough power was used to move it.

The emanelled copper wire has just arrived and also the finest piano wire to make a spring.  So I might have a play with that.  But I shall be most interested in the "muscle wire" when it comes.

[Davey-T]

Don't laugh, but have you considered clockwork to power the shutter, no electricity needed and quite happy being stalled as that's how it is all the time.

Dave

[Stevp]

Now have the new casing and internal supports printed and the QHY5 and lens unit installed within, ready to put on the mast, except that there's no shutter control yet. I have the mast (AKA 1" ali tube) mounted on the NW corner of the obsy ready to take the camera, so I'm hoping to try it out tomorrow (oops later today ). It still needs weatherproofing around the dome.

Almost certainly I will need to reprint the internal framework later when I've worked out the shutter control. Unfortunately I don't expect to have the bits to do that until Tuesday.

All Sky Camera Unit 24.jpg

Gina, your projects never cease to amaze and inspire!

All sky cam on my to do list now

[Gina]

Don't laugh, but have you considered clockwork to power the shutter, no electricity needed and quite happy being stalled as that's how it is all the time.

Dave

I'm not quite sure what you mean here.  Do you mean using clockwork to set the time the shutter opens and closes?  If so there's the problem of the varying length of day/night.

[Gina]

I have just spent a happy hour or so dismantling an old VCR.  The mechanism in these is awsome!    Umpteen gears, levers, slides and springs of various types and sizes.  Two large multi-phase motors, one driving the mechanism with a small timing belt and the other the video head.  There is also a solenoid though rather large for the all-sky camera at 35mm x 17mm x 14mm.  It operated a lever and appeared to have about a 4 or 5mm stroke.  Curiously, the ribbon circuit that commects to it has 4 connections.  I can see two going to the coil but the other two are a mystery.  There are several springs that might be usable though  

There must be several sliprings within the video head mechanism - there's a 5 way ribbon cable going inside.  As I recall VCRs have 2 video heads within the cylinder and the latter spins at 25 rps (1500 rpm) for the PAL TV system so the slip rings must be hard wearing.  These could be useful for another of my projects (CCTV system).   Two BNC sockets are also useful.

[Gina]

Apart from the length-wise contraction of the muscle wire, I have another idea.  The material used has a memory - I believe it can be bent cold and when it is heated it will straighten out, returning to the bent state when it cools - but I could be wrong.  It may be that it needs pushing or pulling to the cold shape.  I read that the hot shape can be altered by heating the wire to 200C and shaping it before letting it cool while holding the shape.  This provide other options than just pulling it.

[Davey-T]

I'm not quite sure what you mean here.  Do you mean using clockwork to set the time the shutter opens and closes?  If so there's the problem of the varying length of day/night.

No I was thinking maybe a disc with a hole in mounted instead of clock hands but released and stopped by a solenoid controlled escapement, still working on the failsafe bit

Dave

[Gina]

No I was thinking maybe a disc with a hole in mounted instead of clock hands but released and stopped by a solenoid controlled escapement, still working on the failsafe bit

Dave

Ah, I see.  The return is not the problem - I have plenty of suitable springs - the problem is the solenoid (or whatever).

[NickK]

Can you use gravity a small weighted armature - then just use a small electromagnet to keep it from flipping?

The electromagnet could be a distance away from the camera.

[Gina]

I have the camera mounted on the corner of the obsy with the new casing.  Here are pics without and with new dome.  Of course conditions are changing all the time as clouds come and go so difficult to compare.  I'm trying to sort out some way to focus with the dome on as there is definitely a shift in focus.  Auto-exposure wouldn't work with the dome on.  But again, may be due to change in cloud cover.  The auto-exposure is somewhat hit and miss

[Davey-T]

Ah, I see.  The return is not the problem - I have plenty of suitable springs - the problem is the solenoid (or whatever).

I was thinking no return just keep rotating . Solenoid from old doorbell ?

Dave

[Gina]

I was thinking no return just keep rotating . Solenoid from old doorbell ?

Dave

The whole point is to provide a "failsafe" whereby the shutter goes to the sun protected daytime position in event of a power loss.

Doorbell solenoid would be too big I think.

Thanks for the suggestions anyway

[Gina]

I now have a form of focus control that can be used with the dome in place.  It's manual and local and relies on turning the dome ring on the casing.  A printed part glued to the inside of the rim has a notch which couples with the focus lever on the lens so that turning the rim moves the focus lever.  The following pics should make it clearer.

Image of the part for printing

The part glued (using acetone) to the dome rim and engaging with the lens focus lever.

[Gina]

It works   There's a considerable focus shift with and without the dome but I can focus with the dome on now.  This image is still with the shutter in "safe" position with solar film in the optical path hebce the rather long exposure - the sky is getting darker and darker

[Gina]

Now the sun's come out and shining on the trees   I'm currently changing exposure by hand as the PHD2 auto-exposure doesn't work in this application.  I could do with finding software with working auto-exposure.  I guess PHD2 will be OK for nighttime as the exposure could be left at 15s but the light value varies enormously in the daytime.

[Gina]

So that seems to be the focus problem sorted out

I've also been playing with solenoids.  The ready made unit from the VCR would be a possibility though it's a bit big.  It does give a reasonable pull at 5v though.

I laso tried making my own with the 26 gauge enamelled copper wound on a printed bobbin.  I got a few dozen turns on the bobbin.  However, on it's own with a nail offered into the hole, the pull was miniscule even with 2A flowing through the coil.  At this current it started getting hot.  I think an iron frame would be needed as well as many more turns.  TBH I think the ready made solenoid looks a better bet.  At least until I get the muscle wire.

Here's my bobbin print and test coil.

[Gina]

What I need to decide now is do I try to make the solenoid work or wait until the muscle wire arrives

[Davey-T]

From memory (not very reliable nowadays) the wire looks a bit thick.

Dave

[Gina]

From memory (not very reliable nowadays) the wire looks a bit thick.

Dave

Yes, I agree, I could only get about a metre length on that small bobbin and just a few dozen turns.  I think the thinner wire might be better though not really suitable for winding by hand.  I've wound coils for transformers etc. in the past using a winding machine my father made but no idea what happened to it.  I guess I could make a winding machine from ABS   Unfortunately, I haven't come across any magnetic printable plastic   I would need to fabricate an iron yoke. Maybe an iron (or mild steel) tube might do.  Hmmm...

[DIYASTRO]

Gina,

As I posted the other day, I too have made my own coils.... I know how painful it is!!!

To save time and effort would you like me to send you those coils I described in my last post on this thread.... A 5/6volt dc read relay / 5volt stepper motor coils?

I am sure one or other would do the trick.

An alternative till your 'muscle' stuff arrives and may equally prove to be no use.

Kind regards

Boyd

[Gina]

Gina,

As I posted the other day, I too have made my own coils.... I know how painful it is!!!

To save time and effort would you like me to send you those coils I described in my last post on this thread.... A 5/6volt dc read relay / 5volt stepper motor coils?

I am sure one or other would do the trick.

An alternative till your 'muscle' stuff arrives and may equally prove to be no use.

Kind regards

Boyd

Thank you for your kind offer but I think I will go with my ready made complete solenoid until I get the muscle wire

[Gina]

I have an idea of what I might do to use the solenoid from the VCR.  Here's a photo of the solenoid and a screenshot from SketchUp of a design for connecting the solenoid to the shutter.  Return would be with a spring.  This could be torsional, extension or compression.

[Gina]

Some calculations...

Stroke of solenoid = 4mm

Angle for shutter = 40 degrees

Solenoid centre to edge = 8mm

Add 6mm to tooth pitch centre so solenoid centre the pitch centre = 14mm

Lever centre to tooth pitch circle = 50mm (this may be cahange depending on how the overall size works out)

Lever centre to solenoid centre = 50 - 14 = 34mm

Lever ratio = 50/34 = 1.47 (near enough 1.5) thus movement of lever gear teeth = 4 x 1.5 = 6mm

(Takes breath )

Circumference of pinion = 2 x pi x r mm for 360 degrees ie. distance at tooth pitch for pinion 2 x pi x r x 40 / 360

Now the variable we are looking for is r (the tooth pitch radius) and the distance has been calculated as 6mm. 

Therefore, 6mm = 2 x pi x r  / 9 = pi x r / 4.5  and r = 6 x 4.5 / pi = 27 / pi = 8.6mm

Phew!

Using a pitch radius to no. of teeth ratio of 3, this gives 25.8 or 25 to the nearest whole number below giving slightly more travel than needed.  So pitch radius = 25 / 3 = 8.33mm.

[Gina]

Here's how all those calculations turn into a design.

Don't need the whole pinion - just a segment.

[Gina]

Photos of the printed parts.