Gina's Observatory Roll-Off-Roof Automation

[Astrokev]

Good to see this project resurrected Gina ?

[Gina]

Well, I think it probably is!  ?  I'm certainly giving it thought...

Edited February 6, 2019 by Gina

[Gina]

Well, I said it wasn't really possible to unlock the storm lock-down systems remotely but to quote a saying we had at work umpteen decades ago, "The difficult we do straight away, the impossible takes a little longer!" and I have gone by that paradigm ever since.  With 60 years of engineering experience I reckon there's a good chance of coming up with something ?

[Gina]

With probably the best chance of clear skies and good seeing being in the middle of winter on a freezing cold night, the thought of being able to open the observatory roof and start up an imaging rig remotely while sitting in my lovely warm living room certainly has some appeal!

Edited February 6, 2019 by Gina

[Gina]

I think the answer to the east window problem is to counterbalance it and use the Olly type system.  Not particularly neat but nor is anything on my property!  It will need stiffening up but I think I can do that. 

As for the storm protection,  the roof already engages with holes and eyes when closed, on the south side and I should be able to arrange the same on the north side.  Then it would be just a matted of remote controlled bolts or latches to stop the roof opening.  That shouldn't be too difficult - they could be motor driven like the main roof but on a smaller scale.  Windscreen wiper motors could be arranged to serve the purpose, I reckon.

[Dr_Ju_ju]

Any way of fitting linear actuators? larger ones could be used to open\close openings, while smaller ones could be used to lock\unlock the roof....

[Gina]

Yes, linear actuators would be good I think but on looking at prices are probably not the cheapest option.

Edited February 6, 2019 by Gina

[Gina]

Depending on the weather, I should be able to go out to the observatory tomorrow and check things out.  I think the main roof opening and closing was pretty much sorted out though the big pulley may need to go back further towards the warm room as I recall.  I have an H-bridge motor driver Arduino shield that Per recommended 4 years ago that I can use to control the roof motor unit, though I expect to control everything with an RPi under INDI and KStars/Ekos (there's an INDI driver for controlling roll off roofs).

If I use the roof to operate the drop-down window, it will have to be on the south side as the north side of the roof is too high.  This will mean moving the downpipe from the guttering on the ROR as it will be in the way.  One option would be to have the downpipe on the north side - not a problem, I don't think.

Edited February 6, 2019 by Gina

[Gina]

Been out and closely examined observatory ROR and all the automation and storm fastening parts.  There are some repairs and other work required.  Worst is that wet has got into the plywood of the ROR in the SE corner and the plywood has delaminated.  I shall have to get onto that as soon as the weather permits.  Mainly dry today but with occasional showers and a strong, cold wind.  Not suitable for roof repairs though I might be able to look at it more closely.  I can open the roof and examine that part of the roof top from inside the scope room.

Edited February 7, 2019 by Gina

[JamesF]

That's really annoying.  Is it at all obvious how the water got in?  I'd have thought with the EPDM cover it wouldn't even be possible.

James

[Gina]

As far as roof automation is concerned, the roof is not opening as easily as it used to so I shall be looking at why that might be.  Further examination has shown that the SE corner peg and hole locking may not work due to the hole being broken out.  The SW corner is fine.  The over-center latches firmly secure the roof in the closed position against storms and I may look into replacing (or adding to) these to secure the roof remotely.  

Some photos.  The rainwater down pipe and catching hopper would be in the way of a lever type drive for the drop down window.

[Gina]

1 minute ago, JamesF said:

That's really annoying.  Is it at all obvious how the water got in?  I'd have thought with the EPDM cover it wouldn't even be possible.

James

There's something odd going on with the EPDM so I'm off out to look at it.

[Gina]

Been out and had a good look.  Difficult to tell without lifting the EPDM  but I think it may be the guttering that's causing the problem - it's only the mini variety and perhaps I should replace it with standard 100mm.  The edge of the EPDM goes into the guttering and is no longer stuck to the timber above it.  It's going to need some sorting out when the weather is suitable.  There's no sign of water on the floor so it seems it's wet getting up the ply by capillary action.  The EPDM has not caved in so the plywood is still supporting it.  I didn't think marine ply would delaminate when wet but it may have been wet for years.

[Gina]

This photo shows where the lever mechanism to open and close the fold down window would go - attached to the bottom of the wall of the ROR and the near edge of the window - the rainwater down pipes are in the way and will be moved to the other side.

[Gina]

And I've been thinking about the storm locking.  When the roof is motorised the motor drive would hold the roof closed and if the roof engaged pins and eyes or similar it should be pretty safe.  Though I think I would be happier with something rather stronger to stop the roof being blown back by an easterly storm.

[JamesF]

It might be adequate to have some additional locks that you can put in manually if you know bad weather is expected?  Or remove during the day if you're expecting to be imaging that night, I guess.

James

[Gina]

Yes, that's what I'm thinking.

[Dr_Ju_ju]

That why I was looking @ linear actuators\solenoids... RS do some @ reasonable prices i.e. https://uk.rs-online.com/web/p/linear-solenoids/1770138/ 

Yes, there are way more expensive ones, but if all you want to do is lock something into place, then they are ideal, we used to use them on old remote controlled Telecine machines, where to stop people opening doors\casings & loosing fingers etc., its the same principle on washing machines....

[Gina]

Ah yes, solenoids, that's a different matter.  I was looking at linear actuators which are motors and screw shafts.  I was doubtful if solenoids would be powerful enough.  I would want it to lock with no power and unlock when power applied.  I wouldn't want to use power all the time the observatory was out of use.  ie. the "failsafe" mode wants to be "locked".  Have you used the solenoids you've linked to and would they be powerful enough?  I prefer to over-engineer rather than under-engineer.

[Dr_Ju_ju]

As usual they come in all shapes, sizes, actuating\holding voltage, forces...

What I suspect you're after,  but may be totally wrong, is a "Pull Type Linear" solenoid, i.e. retracts on energising, but spring returns, on de-energising, & yes I used similar devices in  broadcast installations, to ensure transmission security.

I see even Amazon have some https://www.amazon.co.uk/pull-solenoid/s?page=1&rh=i%3Aaps%2Ck%3Apull solenoid

 

[Gina]

Yes, that's right, it a pull type that I want but that little 6v solenoid would have far too little pull force.  I'll do a search...

[Gina]

Can't find anything that will pull back a bolt or latch when there's a force against it.  I'm going to have to think about this.  Two ideas come to mind - screw operated with a motor a la linear actuator or a multi-lever system that is set by closing the roof and can be released with a small force.

Edited February 9, 2019 by Gina

[Dr_Ju_ju]

Use the solenoid, as the bolt ??

[Gina]

That was what I had in mind but if the wind has been blowing on the roof the latch will be pressing on the bolt so it will need a fair force to pull it back.  This was mentioned in some of the comments/reviews.  Apparently, a bolt that was quoted at 15N force (1.5Kg) only had this force when bolt pulled back ie. holding force, and wouldn't release a door which was arranged to spring open when the solenoid was operated.

[Gina]

DC 12V 1A 10mm Stroke 15N Force Open Frame Type Solenoid for Electric Door Lock

This would seem to be just the job.  On roof closing it would slide back on its spring and lock the roof shut but see the quote below.

Quote

2.0 out of 5 starsPotentially useful and functional gadget - but low starting force.

30 January 2015

Verified Purchase

Could be used for door openers, although my intended application was to let our chickens out at dawn, before we lazy folk are up! (That takes a bit of electronics.) Note the 1 amp, 12 watt consumption - possibly not good to leave on for a long time, although I have not tried this.

LATER:

On installation I discovered that this device has quite a low starting force despite snapping shut vigorously. I eventually gave up trying to get it to work against a door-opening counterweight of about 1Kg, and am looking into alternatives.

As I interpret it, the description of this device is a piece of literally correct but highly misleading "specmanship". They quote 15 newtons (1.53Kg) but I now believe that this is the holding force (needed to pull in back out once it has engaged) rather that the pull-in force (as exerted at the start of its stroke) which is what really matters in any real-life application. Naughty!

Edited February 9, 2019 by Gina