Gina's Observatory Roll-Off-Roof Automation

[Gina]

Been working on the pin and eye roof holding parts (against lifting in a storm when closed) - NW corner.  Not easy to get absolutely right so that the pin goes into the eye when the roof is closed.  Needed two attempts at drilling the hole for the eye.  I'll take some photos later.

[Gina]

Photos.

[Davey-T]

Maybe grind a taper on it to allow for timber growing / shrinking.

Dave

[Gina]

Yes, I though of that.  It is a pretty close fit.  The other side has a bigger eye and the pin has plenty of room.  I think I may have to get a bigger eyebolt.

[Gina]

Pin and eye engage alright but the two are rubbing together when the roof is closed and need a lot of force to open it.  This won't do so I'm going to search out an eyebolt with a bigger eye.

[sloz1664]

Certainly go for a bigger eye Gina. Additional clearance is not an issue in this case. Also follow Dave's tip and grind a chamfer on the bolt, to aid location and especially as you are going to automate the roof.

Steve

Edited February 26, 2019 by sloz1664

[Gina]

This eyebolt in M12 size seems alright - looks very similar to what I have the other side.

[Gina]

Eyebolt is due to arrive tomorrow or Friday.

[Gina]

Eyebolt arrived today and I've been out to the observatory and fitted it.  Seemed too short at first but I managed to get a couple of threads engaged without a washer and tightened the nut until the eye was at the right level for the pin.  Now about three-quarters of the threads nut in the nut are engaged with the bolt.  May be enough.  There is a nice clearance between the pin and the eye and it clears.  This is adding no extra to the force needed to open the roof.  There is a bit of binding of the roof on the top of the SE corner post so I shall have to shave that a bit.

[Gina]

This thread is going to be revised and posted as a Blog. 

Currently further progress is being posted in my thread  Getting back into imaging after a long break

[Gina]

Blog here Observatory Roll-Off-Roof Automation

 

[Gina]

The motor drive for the roof is proceeding but meanwhile I have been giving more thought to the fold-down east window.  How I know the consensus of opinion on this sort of thing is to have the end flap mechanically connected to the main roof so that opening the roof opens the flap and vice versa.  However, with the two currently independent and both manually operated, I find I often like to have the window/flap open with the roof closed.  I have also found that having the window pivoted along the bottom has not worked as well as expected.  One problem is that the window frame is not very stiff.  Also, I have had to put the downpipe for the ROR guttering back to the south side and would be in the way of a traditional mechanical connection between roof and flap.  All this has led me to thinking again about the best way of opening and closing the window. 

I think the main point is that I don't really want the window and roof operating together (although I never have the roof open and the window closed) so a mechanical coupling between the two is rejected.  There is no particular reason not to have two motors and controls (other than a bit more cost, though I do have other motors and the motor driver board can control two DC motors).

The next question is how the window opens.  Currently there is no feasible way to open the window remotely as it is bolted to the roof to hold it closed and even with the bolts undone the weather strip stops the window opening without a good push.  Opening the roof does free the weather strip but the window stays in the closed position without some sort of balancing weight to open it.  The latter is a possibility.  Another thought is a sash style opening window but this has other problems.

[JamesF]

3 minutes ago, Gina said:

I think the main point is that I don't really want the window and roof operating together (although I never have the roof open and the window closed) so a mechanical coupling between the two is rejected.

I'm wondering if you might have an easily-disconnected mechanical connection, so they will work together most of the time, but the window can be opened by itself if required?

James

[Gina]

Might be possible.  Another idea to think about.  Thank you.

[Gina]

Going back a while I had an idea using the rope to pull the window closed.  This is very complicated but could probably be simplified.  To free the window so that it could be opened with the roof closed, the rope could be disconnected somewhere.

On 28/03/2015 at 18:16, Gina said:

I have come up with another idea.  This is based on making use of the full range of the roof matched to the range of the window movement to give maximum mechanical advantage and reduce the force on the roof.  It is based purely on rope and pulleys.  The rope from the window frame goes over the top pulley and down nearly to the floor where it's attached to the frame.  Pull is applied about half way up which minimises the tension required to lift the window from fully open.  A pulley is attached to the middle to provide a 2:1 purchase with the rope from the roof carriage.  I checked how far the middle point of the down rope had to move to close the window and I found this to be about half the roof movement so concluded that I could use a 2:1 purchase in addition.

 

[Gina]

I think this idea is a goer.

[Gina]

New arrangement.

Edited July 24, 2019 by Gina

[Dr_Ju_ju]

The machinations of Heath Robinson !!

Younger readers will have to do some searching.....

[Gina]

Ah yes - Heath-Robinson - my hero 😄

[Gina]

Attached pulley to observatory framework and cord to ROR etc. and tested system as shown above.  My guess of the geometry was wrong - the window closes with just two thirds of the roof.  I'll do a maths calculation of the real geometry but if the block and tackle part was changed from 2:1 to 3:1 that should be about right.  But I would rather do something different as that would be extra friction.  Also, the cord is tending to ride up on the galvanised pulley sidethough might be better with the rope end attached to the loop.

[Gina]

This diagram represents part of the geometry of the window control cord.

A is the diagonal part inside the scope room and B from pulley to window outside.  A = 2700mm, B=480mm.

When the window is closed the cord length A+B becomes the cord length C+D.  We can work out the height of the triangle by Pythagoras.

If we assume the cord is pulled from the middle as shown above,

1. C+D = 2700+480 = 3180mm. 
2. Since C = D, C and D = 3180/2 = 1590mm.
3. Adjacent side = A/2 = 1350mm
4. Opposite side = √(D^2 - Adj^2) = √(1590^2 - 1350^2) = √(2528100 - 1822500) =  √705600 = 840mm

This gives the scale diagram below.

The distance the roof rolls back is 2240mm giving a ratio of 2240 / 840 = 2.666666667.  Clearly this is not 3 so a 3:1 block and tackle won't work with the current measurements.

Edited July 27, 2019 by Gina

[Gina]

Let's see what happens with a shorter length A (currently this is the maximum space allows).

Trying A = 2000mm

1. C+D = 2000+480 = 2480mm. 
2. Since C = D, C and D = 2480/2 = 1240mm.
3. Adjacent side = A/2 = 1000mm
4. Opposite side = √(D^2 - Adj^2) = √(1240^2 - 1000^2) = √(1537600 - 1000000) =  √537600 = 733.2mm

Ratio now becomes 3.055:1  This is pretty close to 3:1 and the other side so a length A of just over 2000mm would give a 3:1 ratio should I decide to stick with pulleys.

[Gina]

Been out to check viability of A = 2000mm and it looks alright.  Since any other mechanism would require more work I'm going to try this method.

[Gina]

Just need another pulley printed so doing that now.

[Gina]

Pulley printed and installed.  Been testing and  IT WORKS!