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Equipment Discussions >> Observatories

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averen
Vendor Main Sequence Software
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Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: dobsoscope]
      #5513313 - 11/10/12 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.



Step 2: Mark the inner position of the supports:



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



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


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



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!



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


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: averen]
      #5514743 - 11/11/12 04:29 PM Attachment (63 downloads)

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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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: averen]
      #5609438 - 01/06/13 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.



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.



Jared


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Al8236
Pooh-Bah
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Reged: 08/18/10

Loc: 48.9173N 122.1390W
Re: Pico Dome (it's that small) new [Re: averen]
      #5609915 - 01/07/13 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!


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: Al8236]
      #5610517 - 01/07/13 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


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CharlesW
Pooh-Bah


Reged: 11/02/12

Loc: Chula Vista & Indio, CA
Re: Pico Dome (it's that small) new [Re: averen]
      #5611252 - 01/08/13 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.

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Al8236
Pooh-Bah
*****

Reged: 08/18/10

Loc: 48.9173N 122.1390W
Re: Pico Dome (it's that small) new [Re: averen]
      #5611359 - 01/08/13 03:59 AM

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


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: Al8236]
      #5612964 - 01/08/13 11:58 PM

Quote:


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.

Quote:


That will work! I was just concerned that perhaps you hadn't thought to the next step
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


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) [Re: averen]
      #5619896 - 01/12/13 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.



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.




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



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


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: averen]
      #5632382 - 01/19/13 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:


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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1965healy
The Snarkster
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Reged: 06/23/07

Loc: San Antonio, TX
Re: Pico Dome (it's that small) new [Re: averen]
      #5632498 - 01/20/13 12:29 AM

Not ugly just a diamond in the rough! You've really made a ton of progress on a lot of fronts. Take your time tho, we've had clear skies the last few nights here in Central Texas and as you get closer to completion you're gonna draw clouds this way.

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dobsoscope
sage
*****

Reged: 05/24/06

Re: Pico Dome (it's that small) new [Re: 1965healy]
      #5633571 - 01/20/13 05:06 PM

So the gores are only held down at three points along their length? (top bottom and central bolt)

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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: dobsoscope]
      #5633759 - 01/20/13 06:44 PM

Quote:

So the gores are only held down at three points along their length? (top bottom and central bolt)




That's how they were attached to the frame. The glass and epoxy is really what keeps everything together.

But yes. Only those fasteners on each gore. Although there are more along the top than just one.
Jared


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dobsoscope
sage
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Reged: 05/24/06

Re: Pico Dome (it's that small) new [Re: averen]
      #5634359 - 01/21/13 05:19 AM

thanks, then you could I assume have done away with the ribs. I am skinning mine with aluminium sheeting which gets nailed/screwed down onto 1 inch thick ribs.

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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: dobsoscope]
      #5635726 - 01/21/13 09:12 PM

Quote:

thanks, then you could I assume have done away with the ribs. I am skinning mine with aluminium sheeting which gets nailed/screwed down onto 1 inch thick ribs.




Yes, and I had initially considered building a frameless dome. But this turned out to be easier for me to build. Plus removing the ribs now would be considerably more difficult!

I made a ton more progress this weekend! I had today off and I spent a good portion of it working on the dome...with the exception of about 4 hours when I met to pickup my new 12" dob :-) (that will not even get close to fitting in the dome)

First I drilled and countersunk the rails for the shutter to ride on. The shutter will ride on teflon pads on these rails. The rails are 1.5" wide. The shutter will be held on by by pieces of wood or aluminum on the bottom of the rail.



I also made and fitted the lower shutter. It's not 100% done. There will also be some pieces that go on the outside of the uprights to fully seal the lower shutter. Here's the shutter in place:



And here is a shot of the shutter removed:



The lower shutter will not be automated in any fashion whatsoever. It will be held in place with 4 bolts running into the uprights. If I ever decide to image that low I will manually remove the shutter. It's doubtful that it will ever come out...with the exception of passing equipment in and out of the dome.


Other than the physical dome work I've been breadboarding the controller and making sure that everything will work there. I managed to burn up the voltage regulator on one of my microprocessors. Apparently it wasn't rated for 12V...so I've ordered a couple more voltage regulators and I'll get that fixed once they get here.

I can't recall if I've mentioned how the dome controller will work...so here goes.

The dome controller will consist of 2 microprocessors (AVRs, I'm using Arduinos). One unit will be physically attached to the computer. The other unit will be in the top of the dome.

They will each be responsible for the following pieces:

Computer attached unit

  • Rotation
  • Forwarding communication to dome unit
  • Finding rotation home
  • Calculating dome rotation position


Dome unit

  • Opening/Closing the shutter
  • Controlling my flat field


The dome unit has a TON of safety code in it for the shutter. Obviously I have to rely on some sort of wireless communication between the two controllers so there is a lot of communication built in that just makes sure that the communication is valid. And if the unit that controls the shutter doesn't hear from the rotation unit for a certain amount of time it will automatically close the shutter.

Anyways I'm really looking forward to getting some more work done on the dome. I hope to etch one of the PCBs sometime this week.

Thanks,
Jared


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Starhawk
Space Ranger
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Pico Dome (it's that small) new [Re: averen]
      #5636737 - 01/22/13 11:54 AM

This is pretty cool. Making the templates from paper attached to the dome was definitely the right way to go. Do you have a plan for a roller track? The more circular it is, the better. However, with a dome this small, I am wondering if it could touch the track in only three places (which would give it a lot of resistance to out-of-round conditions).

-Rich


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: Starhawk]
      #5636751 - 01/22/13 12:02 PM

[quoteDo you have a plan for a roller track? The more circular it is, the better. However, with a dome this small, I am wondering if it could touch the track in only three places (which would give it a lot of resistance to out-of-round conditions).




I have an idea in my head :-) I actually attached the track this weekend, it's in the photos above. And as you mentioned the shutter will have 3 contact points with the track to keep binding to a minimum. Although I'm pretty confident that the arches are very round. At the moment I'm contemplating using some angle aluminum for the front and back of the shutter and a flat piece in the center. Attached to these aluminum pieces will be some teflon pads to slide on the aluminum guides.

I'm still trying to work out the actual shutter mechanism for opening/closing the shutter. I'm thinking I my make a curved rack and pinion gear to move the shutter up and down.

Jared


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: averen]
      #5646585 - 01/27/13 06:11 PM

I didn't get a lot done this weekend. I helped a friend pour his pier for his observatory. We used around 1 ton of concrete for his base and pier. Gives me some practice for when I'm ready to pour mine. He'll also be helping me pour mine so that was some additional incentive to help him :-) He rented a 2 bag concrete mixer...money WELL spent! I'll be doing the same when I go to pour my pier. I may try and dig next weekend and then do the pour the following weekend. I can at least use the pier while I'm still building :-)

I managed to mess up my back unloading some extra bags that he gave me when I got home. So for the majority of today I've been limping around.

I did manage to get a little work done. I built the dome rotation sensor and verified it's functional with the board.



The hardest part was stretching the rubber around the exterior of the wheel!

There are 16 holes around the wheel, a "tick" will be triggered at each change so that's 32 ticks per rotation. This will give the dome movement a resolution of around 1/2 degree.

Jared


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averen
Vendor Main Sequence Software
*****

Reged: 01/20/09

Loc: Austin TX
Re: Pico Dome (it's that small) new [Re: averen]
      #5647267 - 01/28/13 12:43 AM

I managed to get a little more done this evening.

The dome controller is almost finished! This controller is in charge of rotation as well as communicating with the other controller. As it is much simpler than the other controller I just used a prototyping shield for the Arduino rather than etching a circuit board.

If you click through there are notes on different items in the image.

Dome Rotation Controller

I also tested the entire system. That Wondermotor has some torque! It literally jumps to life on start up...It gave my wife, dog and I a startle when it started up the first time. After that I made sure I had a hold of it!


Test Setup

So that's one controller down...one to go. I was surprised I didn't have to fix anything on it and that I didn't blow it or my computer up! My electronics skills aren't all that great. I prefer the software side!

Jared

Edited by averen (01/28/13 12:44 AM)


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cn register 5
scholastic sledgehammer


Reged: 12/26/12

Re: Pico Dome (it's that small) new [Re: averen]
      #5647396 - 01/28/13 04:03 AM

A couple of thoughts - based on my experiences in automating the dome on my Astro Society's observatory.

The jump when the motor starts may damage the dome or the motor supports. I am using a PWM output to allow the dome power to be applied and removed smoothly. It also slows the dome down as it approaches the target position. I started with a relay to set the direction and a MOSFET to control the power but after burning out a few mosfets I fitted a Poholu DC motor controller that's rated to handle 15A. We are using what looks like the same size of motor.

The other thing is that I an using an electronic compass module to get the dome position, a Sparkfun breakout board. This is bolted to the dome. It should be easy to fit this to your dome Arduino running it off the 3V3 supply and the I2C data lines.

Chris


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