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Gina

All Sky Camera Revisited

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Posted (edited)

Captured image from shortly before dawn this morning at the time of the ISS passover.  Just visible in the SE.  Sun 05 May 2019 03:22:07 BST

Screenshot from 2019-05-05 08-34-08.png

Edited by Gina
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Posted (edited)

Sun 05 May 2019 03:36:36 BST

467432132_Screenshotfrom2019-05-0508-49-29.png.6819078768f8231c16763a330a34a3de.png

Edited by Gina
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Posted (edited)

Oh - I'm not seeing an image in the post above.  SGL seems slow and doing funny things this morning.

EDIT - Later - OK now.

Edited by Gina

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Daytime image just captured with minimum exposure.

1393651600_Screenshotfrom2019-05-0509-54-53.png.7b31bb83cef4831651f2d6122496c1b4.png

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Posted (edited)

Hmmm...  I'll try later...

Edited by Gina

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Posted (edited)

Lots of clouds coming over now and they're getting darker and darker!

311421679_Screenshotfrom2019-05-0510-27-07.png.ca85002823e5a0213060d480125b1f59.png

Edited by Gina

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Better now.

Connected a bicycle valve to a piece of tubing with heatshrink sleeving.  This then feeds the air reservoir.

1928683485_BicycleValve01.JPG.a695c07d8829f891900df249d4204419.JPG

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Connected up all the air pressuring stuff and pumped up the reservoir - have a leak somewhere - heard the pressure switches operate on pumping up then a few seconds later again as the air escaped.  Now I have to find where.  I also have the dew heater circuitry to check out and fix.  At least I achieved a good imaging run last night.  Probably need to take it a bit easy today.  Nothing's hurting.

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The electronics shouldn't take long to fix.  A few tests with the DMM should determine where the fault is.  The air pressure loss is another matter.  Guess I can test a few of the joints with soapy water.  Wonder if I can test the ASC without taking in down again.

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Posted (edited)

Went out to the observatory and painted the joints with soapy water.  The cap of the air reservoir bottle leaks but then I had a thought about the ASC itself and squeezed the tube to that to seal it and eliminate loss of air from the ASC and pressurised again.  This time it took a lot longer for the pressure to fall, so there is air loss somewhere in the ASC casing.  Guess I'll bring it back indoors for investigation.

Edited by Gina

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OK so it's back indoors!

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Posted (edited)

Found the leak - the main flange joint between casing top and base.  I shall have to improve that.  Silicone sealant doesn't stick to PETG.  I think I'll try a groove in the two parts filled with a TPU O ring.  A lot less messy than silicone sealant too.  OTOH the only perfectly flat surface possible on 3D printed parts is where they come off the glass print bed.  That is what there is currently between the flanges.  Maybe some closed cell foam rubber as a gasket.

Edited by Gina

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Posted (edited)

Decided to go for a flat gasket for the main flange.  But instead of using another flange on the mast coupling I'm going for a vertical joint with four horizontal screws to hold the ASC onto it.  The casing top is fine as it is but the base and mast coupling have been redesigned as shown below.

Underside of the base - top is flat.
1879337057_Screenshotfrom2019-05-0522-10-35.png.0739f5723d56cd390dab3a96f0f3fe33.png

1578714139_Screenshotfrom2019-05-0522-11-42.png.3132a6ae02ba8c713fc7899b48b00a7e.png

Edited by Gina
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Base printed successfully and now printing the conical mast coupling.

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Printed parts finished and tested for fit.  All the tubes and cables disconnected and separated from the previous base.

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I always used to coat any rubber gasket in petroleum jelly to avoid movement when tightening and its also a great moisture barrier.

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I thought petroleum jelly attacked rubber.

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Base and camera parts assembled and wired up.  USB cable sealed to base and camera tested.  Unfortunately, when I tried to test with the ASC control electronics I found a short on the supply.  Disconnected everything but the RPi and powered that separately but it didn't work - no red power light and no activity.  Seems to be dead.  Tried another RPi with the ASC SD card and the camera is working.  Because the RPi hardware is different the WiFi doesn't work (WiFi setup depends on the MAC address of the WiFi unit) so I'm using Ethernet.  I shall need to sort out what's wrong with the electronics otherwise I'm ready to bolt the top to the base using sealant and see if the casing is airtight.

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Bolted the casing top to the base - 8 M4 bolts and nuts through the flange with silicone sealant between.  I'll leave a while to set before applying pressure.  Yes, I did remember to include some silica gel bags (3).

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On 06/05/2019 at 21:48, Gina said:

I thought petroleum jelly attacked rubber.

Probably might attack natural rubber... which like myself you are much too young to remember.

But the synthetic "rubber" commonly used today is fine.

 

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Young???  Wish I was ?

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Been testing the ASC casing for leaks.  Still leaking from flange joint in spite of using a copious amount of silicone sealant!  ?  I'll try printing a gasket in TPU next.  I have some thick grease I can use with it.

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Have you tried annealing the printed parts? There are pros and cons, but it's the added strength and closer layers might help

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Posted (edited)

No, I haven't and can't see any advantage.  The printed parts are not leaking.  It's between the parts of the flanges.  The flange surfaces are perfectly flat from being printed on glass with good extrusion so that there are no grooves between filaments.  The mating surfaces are like a mirror.  Maybe just grease would work better that sealant.  Or perhaps a greased paper gasket - works for engines.

Edited by Gina

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