All Sky Camera Revisited

[Gina]

I have the cover system assembled and attached to the box but the torque required to open and close the cover seems more than I expected and I shall need either a more powerful motor or a lighter cover.  The current one covers the dome clamp ring as well as the dome itself and I think that may be unnecessary.  A smaller cover will be both lighter and have less windage.

I have designed a smaller cover and other parts to match.

[DaveL59]

challenges, challenges huh Gina 🙂

Might be a stronger motor is the way to go, as a slight breeze could leave you still under-powered?

[Gina]

Yes, that is still an option.  I think I would prefer a NEMA type motor as the cover will be opened and closed many times.  The little 28BYJ-48 is fine for infrequent lightweight jobs like focussing but I have reservations about using them for anything much more.

[Icosahedron]

I would use an air conditioner louvre motor😉.

[Gina]

I think I could fit a NEMA17 in the box and still have room for everything else.

[Gina]

Been printing the parts and assembling with the box.

[DaveL59]

Looking good! 🙂 

[davefi]

On 15/09/2020 at 16:03, Gina said:

The box has arrived and I'm not very impressed!!  The top is alright but the bottom will make it difficult to seal the extension to it.  It isn't waterproof as the lid fixing screws are inside the rubber seal.  I hadn't noticed that.

Hi Gina - I found another box, same size as the one you purchased, but similar style to the larger one I had. Arrived today and I can confirm the seals are inside the fixing screws like my larger one, so might be a viable alternative for you if the waterproofing is still a concern:

https://www.amazon.co.uk/gp/product/B006ZP1LRA

 

[Gina]

Interior of box with cover drive motor and cover parts.  New pinion to match the shaft of the NEMA17 motor.

 

[Gina]

I've fastened the NEMA17 into the box but not been up to doing anything else recently due to ill health.

[sloz1664]

39 minutes ago, Gina said:

I've fastened the NEMA17 into the box but not been up to doing anything else recently due to ill health.

I hope it's just a short term illness, Gina and that you get over it fairly quickly.

Steve

[Greymouser]

46 minutes ago, Gina said:

not been up to doing anything else recently due to ill health.

I too would say, I hope it is only a short term thing Gina. Get well soon.

[Gina]

Thank you, I'm gradually getting over it.  Trying hard to pick myself up after quite a trauma.

[Gina]

I'm much better now and hope to make more progress on the ASC shortly.   Next will be to sort out the electronics to provide the extra features of remote focussing and dome cover.

Edited October 14, 2020 by Gina
typos

[Gina]

Focussing cam and lever.

[Gina]

Couple of photos of the focussing system.  These photos also show the camera and thermally insulating casing.

Inside of lid showing focus motor and lever.

Top view showing focus lever on lens focussing sleeve.

[Gina]

Focussing cam on 28BYJ-48 stepper motor.

[DaveL59]

just a wee thought on the dome cover you have planned for Gina. When closed I assume it will rest in good contact at the base of the cover against the lip of the dome or casing?

Reason I mention is that yesterday I had a lovely large pigeon attempt a landing on mine, had a couple goes at getting itself stable then gave up and flew off. Not sure the long arms would handle that sort of loading well enough but if the cover is fully home against the case then hopefully it'd be ok 🙂 

[Gina]

Yes, when closed it will rest on the dome clamp ring and open it will be straight down and against the cone shaped piece that connects it to the pipe/mast.

[Gina]

Here are some photos of the focus motor, cam and coil spring that will pull the lever against the cam.  The 28BYJ-48 has been modified to change it from unipolar to bipolar as per my blog :-

Edited October 19, 2020 by Gina

[Gina]

I have the main board designed and built and I'll come to that later.  I need an extra circuit board to carry the stepper motor driver modules.  These are A4988 as often used in 3D and in fact these come from an earlier version of the control system for my 3D printers.

This is a connection diagram for these driver modules.

Next, the layout of the extra circuit board produced on stripboard (eg. Veroboard).  The drivers share the 100µF electrolytic capacitor.

Edited October 19, 2020 by Gina

[Al.Grant]

GIna .... read through this thread (any another) with great interest.

I'm currently running an ASC based on an ASI120mm in a watertight enclosure and includes a dome and heater element and from Dew Control.   The enclosure has a clamp on the bottom that attaches to the guttering and is easy enough to retrieve (from an upstairs window) as I want the ASC to be semi-mobile so I can take it away when we got away to Snowdonia and get under some very dark skies.  I'm looking at adding some sort of passive cooling, as my ASC is mobile and I like to run it from a campsite I won't get getting too techy ... but any cooling will help.

I usually run it with 15 or 20 sec exposures (longer when we're away under darker skies), but trying out a few different exposure/gain settings to see what works best.

Can I ask what software you are using for your ASC?

I'm using AllSkEye and having fairly good results with it but always looking at other options.

I'm running it from a small stick PC (keeping it small to stay mobile) which runs without a monitor/keyboard etc and I log in remotely.

 

Star trail image (auto generated by AllSkEye) on an unusually clear night!

Typical image with current settings ... but tryhing to improve things

 Cheers..

 

[Astro Miser]

Hi Gina,

I want to congratulate you on a fascinating thread and read (its taken me several hours :-).  In fact I have signed up to this forum just to leave comment for you.  I am just beginning in astrophotography and I'm doing a lot of research.

Reading your thread I see that making a good ASC is actually much more difficult than it first seems.  I see the main problems are weather proofing and cooling (I will ignore focusing, covering, electronics and software ect for the moment).

I was thinking how I would go about this myself with little money and no 3d printer.  I will try to describe my ideas for comment.  I know a lot of details need working out and are all important but I'm interested if this kind of setup could work in principal.

For my simplest setup with no cooling. The dome would be mounted on top of a piece of 4 inch plastic drain pipe, say 3 feet long and open at the bottom.  The camera would be placed inside a food container/drinks bottle with a neoprene/rubber "diaphragm" that the lens could be pushed through (like someone putting on a dry suit).  Silicone grease could be used around the lens barrel to help sealing and allow the lens to rotate.  The cables are sealed into holes in the container and simply fall out the bottom of the pipe.  The camera container could be mounted by a bracket to the inside of the pipe.  The advantage of this setup is that if any water gets into the top will simple run down the inside of the pipe and out the bottom. 

Dew control and day time cooling:  If you can imagine dividing the pipe in two, lengthwise, by say a piece of flat aluminium so that you have two half pipes.  Air could be blown up one side into the dome and down the other side.  A resistive heating element could be added to warm the air and in turn heat the dome and lens.  During the day this would keep everything at ambient.  I think only a small airflow would be needed.  A mesh (think flour sieve) could be fitted in the bottom to keep the wildlife out.

Now a cooled version: I was reading about cooling DSLRs and came across this:

https://sites.google.com/site/beppelastrofilo/home/canon-1100d-mod-filter-removal-direct-cooling-electrical-dew-control

A quote from the above link: "The sensor develops about 4 watts, while the Peltier cell, if supplied to the maximum rated voltage of 15.4 volts, delivers a power  more than ten times greater (45 Watt). This energy surplus is not an advantage, but quite the opposite. The mistake that many fall into is precisely that of using very powerful TECs, thus thinking of reaching higher cooling temperatures, but  the opposite is true. In fact,  the temperature reached by the heatsink (T diss) is   proportional to the  power produced by the device and  the sensor cools down to a temperature (Tsens) equal to: T diss -  (ΔΤ is in any case always lower than the theoretical maximum the cell is capable of. , but I won't dwell on this point).   This means that, with the same  ΔΤ, the  greater the power delivered by the TEC, the hotter the heatsink will be  and, consequently, the  less  cold  the sensor will become. On the other hand, the   real ΔΤ also varies as a direct function of the  ratio between current power and maximum rated power  of the cell. The curves representing these two functions cross at a point that determines the correct parameters to be set to obtain maximum cooling efficiency."

It is clear to me that for efficient cooling 3 things are imperative 1, The removal of a LOT of heat, 2) The insulation from heat conduction, convection and radiation of the object being cooled, thus reducing the problem to removing the heat generated internally, and 3) A well chosen peltier device run at the 'sweet spot'.

 

Back to the design. Expose the bottom of the camera (the flat bit) by cutting a hole in the bottom of the food container and sealing it with silicone.  Attach the peltier cold side to the camera so that the hot side protrudes through, a L shape copper block could extend the hot side down and to the side.  The container could be filled with polystyrene balls (or similar), desiccant bags and wrapped in ally foil.  I was thinking that a heat-sink could be made by folding copper sheet many times (with gaps for air flow) and fitting it into the 'hot' side of the pipe.  The advantage here is that it can be made quite long (as the pipe is long) increasing the surface area.  Alternativly, standard heat sinks could be bolted together side by side and then turned on end to fit the pipe.  A fan blows air up the hot side of the pipe, over the heat-sink, into the dome and down the other side.  This should give more than enough heat to keep the dew off the dome and lens.

Because the camera is sealed in a container any frost should form on the outside of the container and when it melts it should drip out of the bottom of the pipe (the danger is that the peltier could get wet).

Other electronics and stuff could fit into the 'cold' side of the pipe.

 

Thanks for reading and what do you think?

John

[suttonr]

Hi Gina I hope you are well. I have also spent a while reading this post. I have a 3D printer but no where near your skills designing my own enclosure. I have a couple of asi cameras on my main rig but have always wanted an all sky camera for the nights that I am not using my main scope skywatcher 190mn. As i don’t have your skills I went for the all sky optics pre built case. just provide your own asi camera. I have gone for the asi178mc and I already have an ASIAIR rasberypi first version that I never used so will use that for control. From reading I believe the asi178mc is one of the cameras you use. Do you have recommended lense that you have found to work best with this camera ? And second question do you recommend cooling of the camera case back. I understand the reason for cooling as my main camera on my scope is an asi071mc pro but as this project will be foR Milky Way / meteor showers etc do you think I need the cooling. 
 

your help would be appreciated. 
Robert