Gina's Observatory Roll-Off-Roof Automation

[Dr_Ju_ju]

On Farnell & RS, there are solenoids of 50N plus, granted they are more expensive £30-£40, but then how much do you want to ensure the safety of your gear and want reliable operation....

[Gina]

Safety and reliability are paramount.

[Gina]

Here is a simple lever design that reduces the force on the solenoid.

[Gina]

If I have pin and ring-bolt locking system (as below) or similar on the four corners of the roof, that engage when the roof is closed, I will only be necessary to lock the roof closed so that pin and eye stay engaged.

These photos show the pin and ring-bolt locking system on the SW corner of the roof.  The pin is in the west end beam of the roof and the ring-bolt in the partition framework between scope room and warm room.  The 3rd photo shows the end of the pin bolt on the outside of the ROR, which is in the open position for this view.  These are farm gate fittings and very strong.  I can do exactly the same on the NW corner which is just a mirror image.  The east end corners will need looking at.  The SE corner did have a peg which went into a hole in the frame but the hole has broken out and will no longer work.

Edited February 9, 2019 by Gina

[Gina]

I think I've found something to lock the east end of the roof. 

GATE HOOK AND & BAND HINGES - HEAVY DUTY STABLE STRAP GARAGE SHED BARN DOOR RND

Or maybe something heavier.  The idea would be to fasten the gate hook to the roof framework and the hanger to an upright on the main observatory framework.

[JamesF]

That would be quite a neat solution I think, Gina.

I had a vague idea flutter through my head about the whole problem with friction on locking pins just now.  It's not very well thought through (if at all), but I'll throw it out there in case it's of use to someone...

I think the problem both of us face is that whilst locking pins may work nicely once the roof is fully closed, strong winds may shift the roof open fractionally so that it causes friction against the pins?  How about if a sensor switch was activated when the roof was absolutely fully closed and the first part of the automated opening procedure was to make sure those switches were still closed, or to close the roof if they weren't, thereby taking the load off the locking pins?  Then the pins could be released and the roof opened.

James

[Gina]

I mentioned the problem with the roof being blown very slightly open against the locking pins and causing friction so that the solenoid was unable to pull them out, in a post above, followed by a lever idea to reduce the drag on the solenoid but your idea is another way to do it.  There will be a sensor to check that the roof is closed to stop the closing action anyway so the software could check that the roof was fully closed before trying to open it and if not then close it first.

Edited February 9, 2019 by Gina

[Gina]

There's a farm supplies shop in town and they have a selection of hardware such as gate hangings, latches, bolts etc. and I'm thinking of going in next week and seeing what they've got.  The eye-bolt and gate latch pin I used before came from there.  Also, the weather looks like it might be suitable for going out to the observatory and checking a few things.

[Gina]

I've checked the motor opening and closing arrangement and it looks like shall not have to move the large pulley ?  I have also checked the NW corner and I can indeed use the same system as for the SW corner, assuming I can get the parts.  I haven't decided yet whether the latch that holds the roof will be on the south side or in the middle.

Here's a photo showing the middle roof beam and the dividing wall with the roof closed.  The solenoid latch could go on the dividing wall and the latch plate on the roof beam.

[Gina]

Ordered this :-  12V 1.5 Kg Force Energy Saving DC Tractive Solenoid Electromagnet

[Gina]

Been out to the observatory again this morning checking up on things but just thought of another possible problem so I'll be out again shortly to check.  When the roof is closed you forget what happens when the roof is opened and that attachments to the ROR have to go through the gap between ROR and middle wall.

[Gina]

Been out to town to try and get hardware for holding the roof down.  Only a modicum of success!  The shop I usually go to has closed down and replaced by a furniture store.  Another I've used in the past now only does pet stuff.  Got a recommendation for another agricultural shop but they had a very small range and most of it was far too big.  I did get one bit and another that I might be able to use though I think it's too small.  Also tried ScrewFix and Homebase.  Did pick up guttering parts at Homebase for the roof repair.

[Gina]

These look suitable for the east end :- 10" GATE CRANKED HOOK & BAND HINGES HEAVY DUTY STABLE GARAGE SHED BARN DOOR D30

The amount the hook part sticks out would seem to be alright.  There are other hinges available but no dimensions given.

Quote

Hinge dimensions are:

Hook: 135mm x 38mm x 4mm with 12mm Pin (25mm From Wall to centre of Pin)

Band: 265mm x 38mm x 4mm

 

Edited February 11, 2019 by Gina

[Gina]

Ordered a pair so will just have to wait and see if they work.

[Gina]

The roof latch solenoid has arrived so here's a photo together with a steel rule to show size, which may be a tad small.  I think I shall implement my lever idea as shown below to give more holding the roof closed.  The lever design will need to be such that there is minimal amount of possible roof movement when roof closed and latched.

Edited February 12, 2019 by Gina

[Gina]

This is the south side in the scope room.  I'm planning to use the east end (left in the photo) base upright to take the hinge band for the roof lock that prevents roof lift off when closed, with the hinge pin part on the ROR bottom frame member.  The solenoid latch and lever that holds the roof closed could go on the second from left upright with a pin or plate screwed to the roof lower frame member.  I plan to keep the over-centre latch in the middle as the ultimate storm protection to be applied when a storm is forecast or if I don't plan any imaging.

[sloz1664]

6 hours ago, Gina said:

The roof latch solenoid has arrived so here's a photo together with a steel rule to show size, which may be a tad small.  I think I shall implement my lever idea as shown below to give more holding the roof closed.  The lever design will need to be such that there is minimal amount of possible roof movement when roof closed and latched.

Hi Gina

That is exactly the type of solenoid I require for dead locking my shutter.....When I automate it this summer.

Steve

[Gina]

When I last looked there was just one left on Amazon.

[sloz1664]

Just ordered one

Steve

[Gina]

The gate hooks and bands have arrived and I've checked that the hooks will clear the middle wall when the roof is opened and they will by at least a millimetre! ?

[Gina]

I have confirmed that I can hold the roof from lifting off with strong locking pin and hole systems on the four corners connected to the main corner posts to the east and the main middle frame to the west of the roof.  These I expect to be at least as strong as the current over-centre latches I'm using at the moment.  The only thing to sort out now is the method of locking the roof in the closed position.  The solenoid door latch I've bought has very little pull force and is easily stopped by the slightest force against the latch.  As mentioned above, I could use a lever to reduce the force on the latch but I'm wondering if it would be better to over-engineer the job and buy a screw type linear actuator such as this one :-

Linear Actuator Motor 750N 12V DC 165LBS 50 100 200 400mm Electric Door Opener  Under £20 for the smallest one with 50mm stroke.

It strikes me that this is a small price considering what it is protecting.  This wouldn't care if there was a gale trying to open the roof, it would still disengage.  (Not that I would want to open the roof in a gale but a previous strong wind from the east could have pushed the roof hard up against the stop.)

Edited February 15, 2019 by Gina

[Gina]

Here's a photo of the SE corner roof retention system roughly fastened in position.  This is one possible position, it could go lower if I were to add a block to widen the vertical frame member and move it away from the corner a couple of inches.

[Gina]

Been looking for INDI drivers suited to ROR automation but concluded that I would rather develop my own (maybe from a more general driver) than just take someone else's code.  I have proper H bridge DC motor drivers that I plan to use rather than relays.  There's two drivers on an Arduino shield but whether I shall use an Arduino Uno for control I haven't decided - I may drive the shield directly from a Raspberry Pi as it seems overkill to employ two microcomputers for such a simple controller.  The shield PCB has the facility for this.  Pololu Dual VNH5019 Motor Driver Shield for Arduino 

[Gina]

The linear actuator for locking the roof has arrived - it's quite a beasty.  Yep - over-engineering here we come ?

[Gina]

I'm changing my 3D printer Z probes for piezoelectric sensors and will have spare inductive proximity sensors and just thought - these will make ideal limit sensors (endstops) for my ROR open and closed positions.  Nice to recycle stuff!