Bubble Dome Construction

Updated 1-5-09
 

 

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Reasoning for this particular design

  • It needed to be inexpensive, good small domes cost about 9k.
  • The entire cost is less than 2k and could be cheaper if you used wood
  • It had to be reliable for remote observation.
  • There are no electrical parts that move, eliminating electrical contacts etc.
  • The shutter door is not part of the rotating dome adding to reliability.
  • The design retains the isolated mount for the telescope to protect against vibrations
  • It can be mounted up high to minimize ground turbulence.
  • The bearings are relatively protected from dirt and dust.

 

A 500 gallon polyethylene water tank was purchased from Plastic-Mart.com for about 600 bucks including shipping. The tank is 63" in diameter and the wall is about 3/8" thick in most places and 1/2" in others. The tank has a 20" port for access which is inverted and used as the mounting point.

 


So of course the first thing you do with a perfectly good water tank is cut a huge slot in the side.... The rim for the tank port cover was removed also.

 

Below a steel angle iron is fit to the edge by heating and bending. This was not easy and it would be much easier to cut an edge from wood.

 



A large steel plate was fabricated with a rim to bolt to the edge of the tank port. This plate is the main connection point for the entire assembly. It is shown upside down with the lazy susan bearing attached (McMaster Carr 45 dollars). Eventually the bearing will attach to to the outer pipe, the tank will bolt to the rim and the 55 gallon drum will bolt to the face of this plate.

 



A central hole was dug 5 feet into the ground and this pipe was anchored in place. It will end up INSIDE the bigger pipe and will mount the telescope and isolate it from dome vibrations and movement.

In order to run wires out from the telescope, a pvc tube was cemented into the center of the telescope pipe. You can see the pvc exiting at the bottom. The concrete adds stability to the mount. Since the entire dome rotates, this is the only way to exit the wires.

 

   


A second larger section of pipe was modified to hold the dome itself. This larger section will go around, but not touch, the center pipe mounting the telescope. The white ring in the picture is the other side of the mount for the lazy susan bearing. The green things are rubber mounts so the bearing will maintain proper contact and load distribution.







Casters were mounted on the side of the larger pipe to hold the bottom of the 55 gallon drum in position. The lazy susan at the top, and the casters at the bottom of the drum form the rotating mount for the dome.






The large 300lb pipe had to be lifted OVER the center pipe. I jury rigged the boom to go into the bucket and a few minutes later the whole mess fell over on the bobcat. I would have been killed if not for the cage. In subsequent pictures you will see the new yellow boom that I fabricated so as not to try and kill myself again.



Here the form is ready for concrete. The post on the right will hold the dome rotation motor and linkage for the lift-off shutter door. notice that the original concrete pier is covered with plywood to isolate it from the main slab.





Concrete is now in and assembly can begin. Note the center pipe coming up out of the outer pipe. The main mounting plate with the lazy susan bearing goes on next.





Finally the main plate with lazy susan bearing is mounted to the outer pipe. The plate rotates at this point but if you hung on it, it would rip off the mount. The drum will bolt to the bottom next.




You can't see them but the casters are now in place inside the drum at the bottom. The whole assembly is now rigid and you can hang on it and go for a ride! The drum lid is waiting to go on at the bottom. There is a rotating seal to keep dust out of the inside of the drum.

The red thing at the top is the mount for the telescope wedge plate. The bolts sticking out allow for fine adjustment to point the telescope at the north star.

             

 

  Here we are for round two of "How to kill yourself with large heavy things". Note the much improved, actually attached boom.  

 

   

The dome is now up! Still to come are the shutter door, rotation mechanism and modifications to the telescope.

A new fork arm was fabricated to lower the tube height by about 4 inches so it would clear everything in the dome. The wedge is shown on the right with adjustment screws for polar alignment.

Here is the basic shutter mechanism being tested for clearance and the final version below.

 

 

Dome rotation belt drive installed.

 

Hutch under construction, just big enough for the computer and a stool. The finished shutter mechanism is in place. The telescope will be operated completely remotely so this is just for emergencies.

 

 

 

 

 

The inside of the finished hutch

 

 

 

Telescope getting lifted into the dome. Made the mistake of not making the slit wide enough. This took some effort....

 

 

 

 

 

The fully functional telescope inside the dome.

 

FIRST LIGHT!! (M17 1-2-09)

 

 

In all the design is functioning as planed. The center pipe was slightly undersized and needs to be anchored. The dome has been very reliable with no issues at all to speak of. The shutter has closed in 25 mph headwinds and the seals have already withstood rain showers. The software control is the next step to fully automating this telescope. Once that is finished it should run all night unattended.