Gina

Interesting. If I have any problems with WiFi, I'll seriously consider this. I did have a run of CAT6 UV resistant cable running to my observatory but with a Ubiquiti AP I find WiFi quite adequate.

Possibly.

Designed and now printing a new pulley block with ball bearing sheave.

Here are some photos of the window drive system. Closed. Open. Half way shows a problem with the pulley block. It still works but with added friction. Think I'll replace this with a 3D printed version with wider cheeks and maybe bigger sheave.

Time to look at the electronics... To control the motor I have a Pololu Dual VNH5019 Motor Driver Shield which I bought several years ago when I was first looking into my observatory roof automation. With hindsight I could have bought the single motor driver board as everything will work off the one motor but I've got the dual one now so I'll use it. This is a proper H-Bridge DC motor driver will all sorts of protection and was recommended by the late Per Frejval who also kindly supplied me with the motor unit with clutch. Testing of the motor driving the ROR has shown the current needed is just 1.4 to 2A and the full 13.8v observatory supply drives the roof at a reasonable rate, maybe a bit slower than optimum but quite adequate, so reduced current is not needed. Also, with the chain slightly loose, no acceleration is needed on startup - straight to full speed is fine. Also, no deceleration when stopping is needed. All this means that only a simple logic system is needed. A signal from either a remotely controlled Raspberry Pi or push button in the observatory will set the roof and window opening whilst similarly a signal from RPi or push button and also a signal from the rain sensor will set the roof/window closing. Limit switches in the form of metal sensing proximity sensors will detect when the ROR is open or closed and these signals will stop the motor. All this could be controlled directly by the RPi but the number of GPIO lines are limited and I find an Arduino slightly easier to program than the RPi plus I might as well make use of the motor current sensing to confirm that things are working as expected, so I think I'll use an Arduino to take care of the main logic. It also means the roof can still be controlled locally should the RPi fail (I have found the failure rate of RPi higher than Arduino though I don't know why). Another point is that I can get the basic motor control working with the Arduino and sort out the RPi later. Arduino control alone will do most of what I want and I might decide not to bother with the RPi and remote control. The main reason for a motorised roof is to close it automatically if rain is detected.

Could be a couple of hours of clear dark sky tonight but I'm not counting on it. Planning a quiet day today and not expecting to do much. I need to recover from work on my observatory and the heat of the last few days.

After applying geometry to the idea of using 8mm plaited cord to open and close the window from the ROR I set it all up and tested it. It worked perfectly. The pulley system shows the situation with roof and window closed (vertical). When open the cord from floor over pulley to window is straight floor to pulley and window is lowered to horizontal position. This arrangement has the advantage of evening out the pull needed to close the window a bit. Operating the window doesn't add much to the force required to close the roof. If I want to open the window without opening the roof, I can unhook the pulley block from the window cord.

Unfortunately, I was so tired last night that I went to bed very early.

CO is showing a nice few hours of clear sky tonight and for most of it no moon and only a low crescent moon towards the end of the clear spell. Whether I feel up to doing any imaging remains to be seen - I have been pretty busy working on the observatory and the heat has taken its toll.

One lot of penny washers arrived today - SS ones from Amazon. I reckon the others have gone astray. Can attach the chain ends to their brackets now but there's still plenty to sort out before the automatic roof is working. Need to see about the endstop switches and all the electronics.

Pulley printed and installed. Been testing and IT WORKS!

Just need another pulley printed so doing that now.

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.

Let's see what happens with a shorter length A (currently this is the maximum space allows). Trying A = 2000mm C+D = 2000+480 = 2480mm. Since C = D, C and D = 2480/2 = 1240mm. Adjacent side = A/2 = 1000mm 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.

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, C+D = 2700+480 = 3180mm. Since C = D, C and D = 3180/2 = 1590mm. Adjacent side = A/2 = 1350mm 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.

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.

Stiffened up the fold-down window frame with blocks on the top joints and pinned the axle brackets to the axle (1.25" aluminium tube).

Screenshot of CAD design of the fixed pulley that will take the cord from the ROR frame. Again with a deep groove to stop the cord coming out of the groove. This is the smaller, left-hand pulley in the diagram above.

The 70mm diameter main cord pulley for the window (the RH larger pulley in the diagram above) had a rather shallow groove and the cord tended to come off so I've printed another with a deeper groove. Also printed a pair of plates to stiffen the window frame.

Nowt today - still waiting for some penny washers for my observatory that should have come a couple of days ago!!

Slept well and up early and got on with the observatory before breakfast while still cool.

Chain end brackets fitted to ROR. Now waiting for the penny washers to secure the chain.

Did a little bit on my observatory this evening but the heat today has taken so much out of me that I just didn't have the energy to do much. Just hoping I can sleep tonight and get up reasonable early tomorrow and get on with it.

I did indeed go to bed shortly after my last post and dropped off to sleep straight away - had had a busy but rewarding day progressing the roof automation.

Just looked outside and the clouds seem to have departed despite what CO says but I'm not imaging tonight as I've spent today's energy working on the observatory and I'm off to bed shortly.