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Pico Dome (it's that small)

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#26 averen

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Posted 07 October 2012 - 10:44 PM

I made a small amount of progress this weekend. I still need to cut the remainder of the bracing but figuring out how to cut those correctly is making my head hurt. I may just end up putting the dimensions of the dome in SketchUp and getting the measurements from there.

Here's the dome with the G11 inside. It's up on blocks to simulate the height that the dome will actually need to be at. It's still about 5" lower than it needs to be to put the RA axis at the middle of the dome. Since this will actually be on a pier I can make it shorter than my mount to keep things under the fence.

Posted Image

Someone mentioned about the sheet material only bending in a single direction. Because of this I'll be attaching the gores where the lines are in the image below and bending them up the arches.

Posted Image

The dome seems pretty sturdy as it is now. The main arches will hold my weight...and I'm not exactly a small guy!

Hopefully I'll figure out how to get the rest of the supports attached this week.

Jared

#27 seryddwr

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Posted 08 October 2012 - 11:57 PM

Makes me want to build a femto dome! (Ha, just kidding) Though this idea ain't bad at all. :thinking:

#28 dobsoscope

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Posted 09 October 2012 - 04:17 PM

any further progress on this one?

#29 averen

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Posted 10 October 2012 - 04:00 PM

Nope...having 3 month old takes a lot of my time these days! I can generally only work on it on the weekends and we had company last weekend...and have company this weekend too. I might see if I can sneak some time in tomorrow or Friday. I think once I get the remaining uprights figured out I'll be able to start skinning.

Thanks,
Jared

#30 averen

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Posted 20 October 2012 - 04:34 PM

Finally made a little more progress today! Very little unfortunately as we have plans for today, but hopefully I'll be able to work on it some more tomorrow as well.

I've decided to change gears a little and rather than doing a full frame I'm going to do a "mostly frameless" dome. Getting the frame pieces cut turned out to be very difficult because of the high rate of curvature on the small dome. I think for the size of dome it's just easier to go with a frameless design and use gores.

So that's what I'm doing. I'll leave the frame as is and will attach gores to the existing frame pieces and where there is no frame the gores will just get attached to other gores and the main arches.

So the progress for today was:
1 - figuring the above out.

2 - Beveling the pieces besides the main arches to about 20 degrees so that they'll accept the gores nicely.

3 - Creating a paper template for the gores using the website I mentioned at the beginning of this post
Posted Image

4 - Creating a masonite template:
Posted Image

Tomorrow I hope to use my router with a template bit to create a big mess...er, lots of gores using the masonite template I created above. To wrap each side of the dome I should need a total of 9 complete gores and 2 half gores. Each gore is 9.6" across at the widest point.

Jared

#31 averen

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Posted 21 October 2012 - 08:20 PM

I rough cut a whole bunch of gores today. This is enough to do one side. Each side will take 10 gores. This is 12 that are rough cut. These all came from a single sheet of 4'x8' masonite and I would have been able to get 13 out of it but I destroyed one when attempting the router.

I started to use the template and the router to cut them out...this was an epic fail. So I used the template to trace out the gores on the masonite, flipping the template over each time to get them better nested.

After I traced them out I used a skill saw to cut them into groups of 4 gores. And I took that more manageable size over to the bandsaw to cut the individual gores free.

Once they're all trimmed up I'll use a disk sander to get them to their final size and attach them to the dome.

Posted Image

I did a little testing with the template and found that if I pinned both of the edges of the bottom of the gore that I as able to successfully conform to the size of the dome in (roughly) both directions. I'm not sure how this will translate when multiple gores are attached but I plan to at least give it a shot.

Jared

#32 dobsoscope

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Posted 22 October 2012 - 10:16 AM

well done!

#33 averen

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Posted 23 October 2012 - 10:20 PM

I attempted to attach some of the gores to the dome today...I'm coming to the realization that small domes are fairly difficult to build! The small size of the dome means that things curve faster which means that things need to be pretty accurate. I'm planning on fiberglassing the outside so gaps don't bother me too much, but getting the gores attached and lining up fairly closely is proving difficult. I think part of this might be because of the partial frame that I'm attaching the gores to on the top.

I'll have to do some more fighting to see if I can get the gores to fit. Otherwise I may end up going to plan B...which will be a tiny roll off roof. Unfortunately I don't have a lot of spare time these days to fight with getting the dome built.

Jared

#34 averen

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Posted 24 October 2012 - 02:00 PM

I think I have figured out a way to get the gores sized correctly. It will create some extra waste but I "think" it will get them fitting accurately. I'm going to give this a shot in the next couple of days and will post my results.

Hopefully this will work...I would much prefer to have a dome rather than RoR...especially after all the work that's already gone into the dome!

Jared

#35 averen

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Posted 04 November 2012 - 03:30 PM

I think I have figured out a way to get the gores sized correctly.


Ya...that was wrong.

I've gone back to the frame design. And I'm positive I can get this to work! The semi-frameless design was not working. As the gores approached the uprights the angles got all crazy and I couldn't get things to work out. I even removed the uprights and planned on trimming everything to fit but this didn't work either. I think if I would have gone completely frameless this would have worked fine, but the "hybrid" method just did not work.

So...back to the frame. I managed to figure out how to cut the remaining frame elements...after I accepted the fact that they're not carrying any weight so they don't have to be perfect. The frame is just there to help the hard board contour to the dome shape.

Here's the current state of the frame:
Posted Image


After getting the frame constructed I then used some thick paper stapled to the frame to size the gores. This worked extremely well.

Posted Image

I was actually surprised by how close all the gores are to the same size. They're all within about 1/2" of each other so I can use the same template for all of them and just size each of the gores individually.

Here's a shot of one of the gores clamped on to the dome. I still have all 4 of the small ones to cut...I have a template cut for the small pieces but haven't cut any of them out yet. Since I ended up wasting a piece of hard board on the frameless gores I'll have to go pick up another sheet to make the small gores. Thankfully 1/8" hard board is only $8 a sheet!

Posted Image

Jared

#36 averen

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Posted 04 November 2012 - 08:50 PM

After my minor success today with getting everything figured out I just couldn't leave it alone. I worked a couple more hours out in the garage and have the dome nearly half way sheeted!

Here's a shot of the exterior. Each half has 4 gores. Here 3 of them are sheeted. The area opposite of the shutter should be fairly easy (I'm hoping...what could be difficult about a rectangle??)

Posted Image

The gores are held on with a couple of screws and a washer on the frame. At the top each gore has a couple of screws holding it in place as well.

Here's a shot of the interior of the gores:

Posted Image

I need to pickup another couple of piece of hard board tomorrow. Hopefully that will be enough for the rest of the dome structure.

Jared

#37 Starhawk

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Posted 07 November 2012 - 01:35 AM

The stainless is what gets eroded. Look at the screws.

-Rich

Amateur radio antennas are typically aluminum with stainless fasteners. I have never noticed any corrosion when taken down for cleaning/tune up.



#38 Mary B

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Posted 07 November 2012 - 04:03 PM

Just serviced my 43 foot vertical that is all aluminum/stainless. No corrosion I can see. The stainless hose clamps look like new yet. All the screws look new too.

#39 CMacD

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Posted 08 November 2012 - 10:51 AM

Amateur radio antennas are typically aluminum with stainless fasteners. I have never noticed any corrosion when taken down for cleaning/tune up.


I am at the point of skinning my trailer in aluminum and decided to research this topic. Funny - when I look at the theory it would seem to suggest that aluminum and stainless are not the best match. In practice, however, it seems that many people use them. And to my surprise the aluminum boat and plane people say that they work great together. Apparently the water test is really the true test of robustness as the water normally leads to the galvanic reaction. Needless to say I have started to skin the trailer with aluminum held down with stainless screws. I guess I will find out ;)

#40 dobsoscope

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Posted 08 November 2012 - 04:29 PM

well done!!

After my minor success today with getting everything figured out I just couldn't leave it alone. I worked a couple more hours out in the garage and have the dome nearly half way sheeted!

Here's a shot of the exterior. Each half has 4 gores. Here 3 of them are sheeted. The area opposite of the shutter should be fairly easy (I'm hoping...what could be difficult about a rectangle??)

Posted Image

The gores are held on with a couple of screws and a washer on the frame. At the top each gore has a couple of screws holding it in place as well.

Here's a shot of the interior of the gores:

Posted Image

I need to pickup another couple of piece of hard board tomorrow. Hopefully that will be enough for the rest of the dome structure.

Jared



#41 averen

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Posted 10 November 2012 - 03:18 PM

Had a couple of hours to work on the dome this morning! I managed to get all the gores sized and attached. So hopefully the hard part of the building is done! From here I need to seal all the gores and sand the ridges between the gores. I'll also fiberglass the exterior of the dome and the main uprights to make it more waterproof.

Here's how I sized the gores. This method worked fairly well. As I mentioned above I used a paper template to create the initial sizes. That template was over sized just slightly to allow the gores to be individually sized. So this is starting with the rough cut gores.

Step 1: Clamp the gore to the dome. Make sure that it's a good vertical fit.
Posted Image


Step 2: Mark the inner position of the supports:
Posted Image


Step 3: Well, not really a step just showing the inner positions of the supports...
Posted Image


Step 4: Marked positions 3/8" out from the inner line:
Posted Image

Step 5: Played "Connect the dots" to approximate the curve.
Posted Image


I then cut out the outter lines on the band saw and cleaned things up on the disc sander. This worked very well! On a couple of the gores I had to make a couple of small tweaks with the disc sander. For these areas I would mark where there was interference and just slowly remove material until the gore fit nicely.

Each gore took around 10-15 minutes to size and fit...so not too bad!

Finally, I was left with this!
Posted Image


I have found that the lower ring has warped a little bit due to the high humidity that we've had lately and the fact that it's been on sawhorses for that time. So for the time being I have it setting on the garage floor. Hopefully the ring will unwarp. It's not horrible, at the worst position it's probably arouns 1/8" off from flat.

Jared

#42 averen

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Posted 11 November 2012 - 04:29 PM

I've been contemplating Shutter sizes lately. I'm planning on having a lift out bottom piece that will need to be manually removed to go below 30-35ish degrees. Along with the moving shutter piece on rails and probably sliding on teflon pads. I had contemplated bearings but I want to keep it as low profile as possible. So teflon sliding on aluminum seems like a better alternative.

I've been plugging numbers into a Google Docs spreadsheet and came up with the following shutter piece sizes:
Bottom Lift out Shutter: 19" (30 degrees)
Main Shutter: 47"
Back Size: 47"
Zenith Opening: 9.5" 15 degrees past zenith.

I may end up making the lift out portion a little larger. Probably around 35-38 degrees. I'm going to have some overlap between the main shutter and the bottom shutter as well as the main shutter and the back piece. Making the bottom shutter a little longer would allow me a little more leeway with respect to the main shutter sizing.

Since this is an imaging only dome I don't really foresee myself going below 35 degrees very often. The bad thing is that when I do need to remove the bottom shutter piece that I won't be able to automatically close the dome because the bottom shutter will be missing. Thankfully the "good" direction for going low is East so if I do end up needing to track lower it will be at the beginning of the night and I can likely re-install the bottom piece before heading to bed.

Attached is half a pie chart showing the shutter sizing.
Blue: Bottom Shutter
Red: Main Shutter
Orange: Back piece

Jared

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#43 averen

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Posted 06 January 2013 - 11:16 PM

Sorry it's been so long since I've had an update...but I haven't had any time to actually work on the dome either so there hasn't been any progress to show.

Today I was able to find some time and get things ready to fiberglass. I plan on filling gaps tomorrow and then this weekend I should be able to actually get some real work done on the dome! After the dome is fiberglassed I'll be able to size the shutter and move on to the building.

Today I setup the dome and made sure that i would have adequate room for the mount and telescope.

Posted Image

Thankfully I have about 6" of space in every direction, which is what I was hoping for. This is with the center of the mount a little higher than I initially wanted as well but because of the height that the dome needs to be this will have to be the case. I may try and get the RA center to be closer to the horizon of the dome but it should be fine as is if I'm unable to accomplish that.

After getting the measurements for the pier height (which I plan to dig and pour in the next couple of weeks) I dropped the dome and set it on blocks so that it will be ready for fiberglass.

Posted Image

Jared

#44 Al8236

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Posted 07 January 2013 - 10:46 AM

Jared,
What are you planing for a rain skirt around the bottom of the dome?
If you are planing a solid skirt you might add that before fiberglassing to get a good seal. I added my skirt later and had some problems getting a good seal, wish I had put it on first!

#45 averen

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Posted 07 January 2013 - 04:17 PM

Al,
I was planning on putting on the skirt later but I will be fiberglassing it to the dome. I'll fiberglass the main dome structure now (and not paint). Then when I have it mounted on the structure I will attach the skirt and fiberglass it to the dome.

That's at least the plan for now.

Thanks,
Jared

#46 CharlesW

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Posted 08 January 2013 - 12:32 AM

I appreciate that you have been working on this for a while now and I'm a Johnny-Come-Lately to the conversation but, any chance you could dig down a couple of feet below grade to install the lower part of the observatory? You would have a structure that was almost full height but still below the fence.

#47 Al8236

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Posted 08 January 2013 - 03:59 AM

Jared,
That will work! I was just concerned that perhaps you hadn't thought to the next step :lol:
It's looking good!

#48 averen

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Posted 08 January 2013 - 11:58 PM

I appreciate that you have been working on this for a while now and I'm a Johnny-Come-Lately to the conversation but, any chance you could dig down a couple of feet below grade to install the lower part of the observatory? You would have a structure that was almost full height but still below the fence.


If I were going to use a larger dome this would be needed. But as it is I can get the scope where it needs to be inside of the smaller dome without having to dig down. Plus going below grade adds other issues like the need to keep out ground water.

That will work! I was just concerned that perhaps you hadn't thought to the next step :lol:
It's looking good!


Since this is taking me so long I think I'm planning like 10 steps ahead! I worked out the schematics for the rotation/shutter control earlier today. The shutter is going to be a little different than I had initially though. Since I didn't add any provisions for a power ring on the dome I was planning on only opening/closing the shutter when the dome was parked. But I've decided to use the parked "power feed" to the dome more as a "charging point". So I'll have a small 12V sealed lead acid battery that rides on the dome and provides power to open/close the shutter when the dome isn't parked. This is mainly needed for emergency issues.

This will require 2 microprocessors with the ability to communicate wirelessly...which isn't a big deal. Also the microprocessor that will be installed on the rotating portion of the dome will control my light box. So I figured since this was going to be in place anyways I might as well add in the shutter piece and have the ability to control the shutter from other positions besides park.

I also ordered all the hardware for the dome controller and that should be here in a couple of days...so even if I can't build the actual dome i can work on the hardware/software aspect of the dome control.

Jared

#49 averen

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Posted 12 January 2013 - 10:06 PM

My wife was kind enough to allow me some time to dedicate to the dome today...so I tried to make the most out of it!

First I skinned the back of the dome. This was a somewhat important decision as it somewhat sets the size of the shutter in stone.

Posted Image

Next I flipped the dome over and started the fiberglass work on the bottom of the ring. Tomorrow, after the bottom is dried, I'll trim the excess fiberglass off and flip the dome back over to fiberglass the outside.

Posted Image


Here's the ring all wetted out. This is 4oz fiberglass with West Systems epoxy.

Posted Image

So hopefully tomorrow I'll be able to get started on fiberglassing the exterior of the dome. I'll start by "taping" the seams and filleting some of the area and then I'll go all over the dome with the 4oz fiberglass. I hope I have enough epoxy...I only picked up a quart!

Jared

#50 averen

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Posted 19 January 2013 - 10:47 PM

So I've made quite a bit of progress in the last couple of days. I actually thought I had posted an update...maybe I started to and forgot.

So here's how the dome currently sits:
Posted Image

I know it looks ugly...but it's actually quite smooth in person. All of the seams have been sealed and fillets have been constructed where the ring meets the gores.

Next I get to finally start working on the lower and moving shutter! The dome will stay looking about like this until it's ready to go onto the building. At that point I'll fiberglass the gores as well as the skirt and then paint the dome.

I've made a lot of progress on the electronics as well. The motors and almost all components arrived late last week. I ended up burning up one of the Arduino boards that I'll be using as a controller (actually just burned up the voltage regulator). I have the PCB design done for the controller that will control the shutter and my lightbox. I also have all of the software for that controller completed as well.

The rotation controller software is mostly complete as well and I will start on the PCB design for that controller later in the week.

Jared






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