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Gina

All Sky Camera Revisited

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I'm also using small layers of 0.2mm.  Still printing ATM.  I'll report back when I have some new test results.  At least the ASC enclosure looks good.

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Posted (edited)

The tube coupler was better but still leaked so I smeared silicone sealant on it and put the tubes back on.  The sealant squeezed out the end and a water test showed no leaks.  However, there's still a leak and I found one on the base of the ASC enclosure.  Maybe I'll print another with higher extrusion rate and thicker or maybe just with solid fill.

Later :- went for lots of extrusion and solid fill.

Edited by Gina

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Posted (edited)

Taken the existing base off the enclosure top/dome and tested the top & dome under the water for air leaks and there weren't any with a water pressure of 6-7", so that confirms the soapy water result.  New base over 80% done and 15m left.

Edited by Gina

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Base finished and pipes & cable fed through.  This is quite a lot heavier part than the previous base so I think it will be waterproof/airtight and I'm wondering if I can risk it being alright and go on and continue the whole assembly.  There's some clear sky forecast for tonight, tomorrow night and Saturday night.

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Posted (edited)

Having worked out a way of pressurising the ASC enclosure with dry air and sorted out the sealing, I'm having second thoughts about having the RPi etc. up in the ASC casing.  A few things really, perhaps the worst is that having the RPi+HAT in the ASC casing means that any alterations to either wiring or firmware would entail taking the whole rig indoors and breaking the main seal to gain access.  Cooling the RPi and other electronics to cope with a possible summer heatwave, with the unit in the full heat of the sun, meant adding a heatsink to cool the air and hence the electronics, to keep it working.  Also, I would like to keep the volume of air inside the enclosure to a minimum.

The reason for having the RPi and other electronics in the ASC casing was to reduce the wiring etc. passing through the sealed bulkhead, particularly the awkward USB cable with a plug on each end, as well as all the other wiring (apart from power and pressure switch).  I guess the problem of the USB cable could be got round by cutting the cable and rejoining it after passing through a grommet in the base - otherwise some printed parts to clamp together round the cable like I had before.

I would appreciate any thoughts on this.

Edited by Gina

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Posted (edited)

Bicycle valves have just arrived.

Edited by Gina

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As mentioned before I'm using the waterproof USB connectors which work well but cost 25 USD for one with a 5m cable.

I'm also experimenting with USB to ethernet adapters to be able to increase the distance between camera and computer. These adapter pairs are also not cheap and need additional space but it's easy to run and splice an Ethernet cable.

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I have some 7 core low voltage (automotive/marine) round cable I can use for the ASC if I put the RPi etc. in the observatory which can be used for the focus motor (4 wires), camera cooling and dew heater.  Red, blue, green & black are the standard stepper motor colours leaving brown, yellow and white which can be Common, Camera-Cooler and Dew-Heater.  That would just leave the USB.

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Posted (edited)

I can seal the cable part of the USB lead with a hole for the plug and a block on the fixed base and a "plastic plug" to cover the base round the hole where silicone sealant is placed.  Bolts hold it all together.

746191647_Screenshotfrom2019-05-0121-13-41.png.8887187ca2dffcf479c9e75340be0c22.png

 

Edited by Gina

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3 hours ago, Gina said:

Having worked out a way of pressurising the ASC enclosure with dry air and sorted out the sealing, I'm having second thoughts about having the RPi etc. up in the ASC casing.  A few things really, perhaps the worst is that having the RPi+HAT in the ASC casing means that any alterations to either wiring or firmware would entail taking the whole rig indoors and breaking the main seal to gain access.  Cooling the RPi and other electronics to cope with a possible summer heatwave, with the unit in the full heat of the sun, meant adding a heatsink to cool the air and hence the electronics, to keep it working.  Also, I would like to keep the volume of air inside the enclosure to a minimum.

The reason for having the RPi and other electronics in the ASC casing was to reduce the wiring etc. passing through the sealed bulkhead, particularly the awkward USB cable with a plug on each end, as well as all the other wiring (apart from power and pressure switch).  I guess the problem of the USB cable could be got round by cutting the cable and rejoining it after passing through a grommet in the base - otherwise some printed parts to clamp together round the cable like I had before.

I would appreciate any thoughts on this.

Good result on the leaktesting and snagging of the leaks I/D'ed by that Gina! Its not altogether reassuring that the silicone didn't stick well to the PETG, but provided the joints are lightly compressed all may be well when they see rain and condensate. Given the work it took to address environmental sealing, you have earned the karma for leak-related problems to recede!

Re location of the electronics: you are right. The proper place for electronics, given a choice,  is in controls enclosures. Which implies properly sealed field wiring to sensors and devices is needed. The machine-build world has lots of high cost elegant solutions to this which I'm sure you are well familiar with.  One idea you could consider is a 5m USB 3 cable run up the pylon to the ZWO camera  (you might want the extra bandwidth in a later ASC incarnation) and seal this using a tight-fitting sleeved rubber grommet lubricated with Hellerine (or olive oil!) and stretched over the connector at one end of the cable. Maybe this one: https://ie.rs-online.com/web/p/rubber-grommets/1366294/ which is polychloroprene rubber and is stretchy with good recovery. A cable tie around the sleeve to seal off the cable entry. Print the ASC enclosure base to take the (expanded) grommet diameter once this can be measured. No need to cut anything. How much force to stretch this I dont know. Warming it would help. There is an electronic technician's loom-making tool for stretching grommets and heat shrink sleeves but I dont know if it would be strong enough...

 

Tony

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Thank you for confirming my thoughts Tony ?  I shall now start turning out new designs.  A nice big reel of white PETG filament has arrived and I shall be using that.  A better colour, I think, for a unit that will be in full sunshine (when we get it).

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Busy printing the new parts.  Well my Mini printer is - I'm busy designing them.  (And watching Countdown ? )

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Blimey you've put some work into this Gina. Well done. Sorry I'm a bit late to this thread, but some of the images you've captured looked good. You could see the milky way clearly in some.

Good stuff.

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Slight rearrangement of component required for the latest dew heater and camera cooling circuit.  Originally, the dew heater used an N channel power MOSFET with the heater in the power side.  I wanted the camera cooler to work at two different levels of cooling - LOW to just keep the camera from overheating in daytime and HIGH for low noise at night.  This was achieved by running on 5V for LOW and 12v (13.8v) for HIGH so the -ve had to be connected to power Gnd.  +5v power was provided by a diode and HIGH by pulling up to 12v with a P channel power MOSFET.  As a result the dew heater and camera cooler needed 4 wires altogether.  +12v & dew heater and Gnd & camera cooler.

To allow for only having 3 wires for both features I needed to arrange that they both used Gnd as Common with the dew heater in the Gnd side of the circuit.  At first I thought of changing the circuit to a P channel MOSFET for the dew heater like the cooler but I don't seem to have any more.  However, one advantage of using optocouplers id that the voltage between the driver and receptor can be up to 5000v so the standard N channel MOSFET circuit can simply have the load in the negative (Gnd) side.  The optocoupler transistor emitter will be going from 0v to 12v as the dew heater is switch on and off.  Also, looking at the component layout I see this is just a matter of removing a Gnd link and moving a couple of wires.

This is the circuit diagram for the camera cooler.
479684219_CameraCoolerControlCircuit01.png.2c150d5ee82662a4ad58764afe10ace7.png

Dew heater circuit with heater in the +ve side.
302293549_DewHeaterCircuit03.png.605a8526be48da8d9ace80411d295109.png

This photo shows the layout as used in the previous ASC version (called Ultimate).  The two small black blocks to the right of the board are the optocouplers.  They are linked by a short green Gnd wire which will be removed and the dew heater wire connected to the emitter of the optocoupler transistor (lower left pin).  Near the RH edge of the board, the orange and red wires will be re-connected to the yellow +12v rail.982417380_WiringCircuitry01.png.b6d4a57eace37f8e3188c6fcbdfec30d.png

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HAT circuit modified.  Currently printing casing top.  Base and USB cable clamp printed and USB cable clamped and sealed.

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Posted (edited)

Made an error in the design so now printing another casing top.  Meanwhile, I've been working on the electrics and the air reservoir.  I'll probably use a 2L milk bottle as that has a large enough lid to take two grommets - one for the air tube to the ASC and the other for a bicycle valve to apply pressure.

Edited by Gina

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Hopefully on the final furlong of the race to finish this incarnation of the ASC.  I want it out there by tonight!  Printing the funnel shaped support that connects the ASC to the hollow mast and sorting out the final camera asse4mbly and wiring.

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Dew heater.

583758755_DewHeater01.JPG.8c6f2c80877c4ef2c38888fb2a8b9aae.JPG

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Posted (edited)

Mast to ASC fitting completed.  Wiring inside ASC completed.  Waterblock clamped onto Peltier TEC and camera for camera cooling.  Time presses on but I'm taking a much needed cuppa break...  Whether I actually make it for this month's one clear night sky remains to be seen.

Edited by Gina

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Phew.  Just struggled with the main seal, between the casing top and the base.  Also bolted through to the mast connecting piece.  8 M4 bolts and nuts - pukka flange joint!  Silicone sealant everywhere and a fair bit in the joint.  I'm doing the dome seal last.  That will let me fill the space with silica gel bags.  Now taking a tea break.

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Well, I have the ASC installed on the north side of the observatory though not everything is working yet.  I've connected up the dew heater and camera cooling and running the cooling water circulation.  I have yet to connect the focus motor and the pressurisation system.  I may get some of that done this evening but now I'm going to get myself some food.

Meanwhile, here's the first image with the new version and a photo of the installation.

237302529_Screenshotfrom2019-05-0419-45-29.png.7f29c17f21016494617a3bca0792980e.png1822037519_ASC05.JPG.80796c58b32d372b46a6c43bed82c71c.JPG

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Think I have the focus motor connected.  Now just waiting for the stars.  Camera cooling is better than before with the different waterblock.  Now at -23°C.  Desiccant is working - no condensation.  I just plugged the air tube to the ASC to keep moisture out.  I'll see if I can connect up the pressure system tomorrow.

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Posted (edited)

Ursa Major is now showing and I was able to fine focus remotely.  It was only a couple of fine steps from optimum.

10s exposure, gain zero, temperature -23.6°C.

1952652658_Screenshotfrom2019-05-0421-50-20.png.42e7d5220e5097930aff68fccb4981c1.png

Edited by Gina
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Much as I'd like to suggest that all we need now is some rain so it can be tested properly, actually, no :)

James

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30s exposure, gain zero, temperature -23.6°C.  One hour to astronomical dark.

210078864_Screenshotfrom2019-05-0422-06-02.png.1713b796f676f47a6ab9331b9fe61a03.png

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