My astronomy project:
Making of an Observatory
Page III, Roof mechanics
1: Roof design alternatives
Here are the three alternatives of the roof opening designs I have been thought about:
It will work something like this:
2: Building the mechanism for the roof
This time I start with the complicated roof mechanism. I will try to build something else than the traditionally sliding roof. I want a building with low walls to let me point the telescope at low altitudes. With a sliding roof it must be doors that open for the telescope or have walls that can be folded down. Here you can follow my alternative solution, it's a combination of idea 1 and 3 above.
The roof will rest on arms, caster wheels will be used as hinges.
And I also need a heavy steel bar, my girlfriend found one for me. It has the dimension 60 x 60 x 2300 mm and a thickness of 6 mm. It's heavy and will act as a counter balance weight among other things. Do your girl/boyfriend deliver such a thing for you?
Here you can see one of the arms, it's just nailed in position now when I test if it give the correct geometry. I have the door that occupy part of the wall and can't let the arm pass over the door. You must be very careful about the geometry, I want the roof move to right and then lower down so it will not hide the view.
The hinge must have some strong base to connect to, the cross in the ring mark the center of the rotation axis.
A wooden part was cut to fit here.
Looks good, this will be stable and that is important.
Here is the hinge mounted on outside of the wall, and the wheel is of course of no use of so I have removed it.
Here is the arm mounted at the lower hinge but the upper end isn't mounted yet.
Inside the roof I need some guiders, when closing the roof it must come in correct position, made of wood.
Here the roof is in closed position and the guide has moved it sideways to correct position. Later I will mount a stainless steel plate at top of the wood that it move against, it will lower the friction and the wear. This guiders also strength the roof.
More parts needed, four 0.25 meters threaded rods, nuts and washer.
This will be the upper hinge to the arm. Later I must have a metal tube around the screw. Now I'm just testing.
The size of the threaded rod is M12.
Overview of how the arm is mounted. I have it outside because this is a mini observatory with limited space inside. When I have them outside I also don't need openings in the walls when arms are in out position. The size of observatory is just 2 x 2 meters and the clearance around the center of pier is 0.95 meters.
Some people has told me that I must anchor the observatory in the rock, because it can fly away if it comes heavy winds. That is a wise recommendation, because it's my mother in law's house down there, she will not be happy if my observatory crash in her house, then no more stars!
Close up of the upper hinge.
Reinforcement to make it more stable, I need one more up too.
A M8 bolt hold the arm in the lower hinge.
The roller bearing is not very well protected against rain in this position. Maybe this plastic film will help until I got a better solution.
This was a big moment, the first opening of the roof, almost like a "First Light". I had to open the small roof first, then the big roof, when closing, the opposite order.
Next step is to have some mechanism on the left side of the main roof. Maybe this will just be a "sliding against a rail" construction, but more elegant will be a second set of arms. I will think about this until next weekend, my construction is very flexible so I have lot of options.
When I do next test and open the roof all way out, will the roof's right part clear the wall at left?
The heavy steel bar I shall mount on the lower end of the arms. It will act as a counterweight and in the middle of the steel bar I shall have a motor driven threaded rod. The clearance under the observatory is not big, I hope my calculations are correct and it fit.
Today the arms are made of wood because it's easy to work with, later maybe they will be replaced with arms made of steel.
3: Hatch Hinges adjustment
After I had mounted the panel on the walls I found that I couldn't open the south hatch enough. I have to adjust the hinges to it.
This was very easy, I just had to move the hinges 0.01 meter outwards.
Now the hatch will open enough, I can open it even more than this if I need.
Here you can see that there is space enough between the wall and hatch when it opens.
There was one more problem, when I close it it collide with the frame, I have to cut out a part from the edge of the frame, you see my markings on the photo above.
Now the edge is cut away and the hatch close as it should.
Here is the left side frame of the hatch, I have added a wooden lath to get frame tight against roof panel.
Here I have added the two missing panels at the wall.
4: Roof Rail Mechanism
I have chosen to have a rail that the roof can roll out on one side and arms on the other side. The arms are already finished. To get a low friction it must have wheels that roll over the rail.
One big wheel that take up the vertical force and two small wheels that guide the roof horizontally. This is just a model for testing that it work as I expected it to do.
Here is it mounted under the backend of the roof.
It worked perfect, it was not very heavy to open it, later I will have counterweights and springs that reduce the needed force to open and close the roof. Now I just have to fine adjust the details. Now you also see the most important of this construction, the arms move the roof down when fully open. You get a low horizon without hatches around your building that can make the construction weak. The two roof construction also let you have the telescope above the walls and still can open the roof.
I just have one rail and it's thin to not let the snow accumulate on it. In the background you see my second pier where I do visual observations. Here I will have my 25x 100 mm binocular.
Here a view how the end of the roof rolls out over the rail.
Emergence stop! You never know what will happen!
Here the roof is in the out position. Now I have the details how I will make the final version of the wheel holder, as you see the side wheels could be lowered a bit.
This is the final version (I hope), no wooden parts, all metal, much stronger.
The side wheels are now in much lower position, if I find a 20x 80 mm aluminum beam in future I can replace this wooden made part with that. A fourth wheel on the underside that hold the roof down in heavy wind could be wise to have.
Roof in closed position.
5: Arm Rail Guiders and Stoppers
The arms are not rigid enough to hold the roof in exact position.
Here you can se how I added a wooden lathe inside the arm to guide it in correct position. No rollers and the friction maybe could be high. I will rubber a candle against the wood as a grease and get the friction low.
Here is a adjustable stop for the arm in open position. In the big hole there will be an adjustable bolt.
Covered by the trim list.
The arm has moved the roof to the open position and rest against the stop.
6: Counterweight arm
The roof is not very heavy, but still needs a counterweight or a spring to be operated easily. One part of it will be a steel beam, it's heavy and also will be the anchor to the motor that in future will open and close the roof.
Here are two holes that I have drilled and threaded, in M8 dimension. It was not that easy because the steel beam's thickness is 6 mm.
The steel beam will be mounted here on downside of the arm that lift the roof. This wooden arm is weak and maybe have to be replaced with a steel arm in future. It was easier to work with wood now in the beginning when I test ideas.Back to contents
Now there is August and the sky becomes darker. I must have the observatory up and running so I don't miss any chance to take exciting photos. It's just some small details missing now. One thing is more important than the others, the roof must be easy to operate. I need the counterweight in place to make the roof easier to operate.
Last time I prepared the counterweight with four threaded M8 holes. Now I drill the corresponding holes in the wooden arm.
The counterweight moves about 0.8 meters back and forth when opening and closing the roof. There isn't very much space under the floor so it must fit exact. As you see when the roof is in open position it's touching the pier, not good!
I need about 15 mm more space here between the pier and the counterweight. The slit you see I will weld together later. I don't know what this steel beam had been used for earlier.
I don't have tools to work with a big steel bar like this. I had to drill a lot of small holes and with the hammer knock it off. Lot of sharp metal spoon over the rock, I had to take a strong magnet to get rid of them.
When the roof is in closed position I got another problem, now it hits the wooden stud in the other end. Wood is much easier to work with, just had to cut a opening for it.
Now I can close the roof again.
Here I will will do an attempt to install an electric motor to control the the roof. I don't think it will be too complicated.
And did it work?
I need almost no force at all, only when closing it the in the first part. A spring will handle that problem.