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Counterweight / assist for folding wall

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#1 MJB87

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Posted 27 July 2014 - 06:26 AM

Hi everyone,

My observatory has a two-foot section of wall that folds down inside to provide greater exposure to the southern horizon. The section of wall is heavy. It takes two people to lower and raise it.

I'm thinking of installing counterweights or a pneumatic strut mechanism to reduce the force needed to open and close this section of wall. Others must have encountered this situation.

What have others tried? What recommendations do you have? Thanks.

Marty

#2 dmcnally

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Posted 27 July 2014 - 08:22 AM

There are a lot of interesting design ideas in the Post a pic. of your observatory! thread. Most are domes and roll-off's, but there are a few flip-top designs that you might get some ideas from.

Good luck,
Dave

#3 Midnight Dan

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Posted 27 July 2014 - 09:07 AM

Most designs that I've seen use an arm that extends below the hinges of the drop-down wall, with a counterweight on the end of that arm. When the wall swings down, the weight swings up. However, your drop-down wall needs to have at least one end at the end of the building so that the counterweight arm can swing up out of the way, usually outside of the building. You probably don't want a big counterweight arm sticking out in the middle of your observatory.

If your drop-down wall is a short sub-section of a wall, and does not go all the way to the end of your building, you might try using a pair of gas springs. These are the gas filled cylinders used on some vehicle models to push and hold open a car hood while you're checking the oil. They are inexpensive and can be had with forces up to 200 pounds for around $20 to $30. Do a google search for "gas spring". You'd have to do some playing around to figure out what size you'd need, and how much force would be right for your application.

-Dan

#4 MJB87

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Posted 27 July 2014 - 10:21 AM

Thanks, Dan.

The wall section (which is already built) flips down about 160 degrees. I've yet to see a design with gas springs that can accommodate more than a 90 degree swing.

This leads me to consider counterweights mounted on the movable wall section on the outside, almost vertically or at a slight angle from the vertical. When the wall is folded in, they will stick up almost vertically, but still with the center of gravity outside the structure. I'll put one on each end so they won't interfere with the scope. They won't be more than 2 feet in any case. The nice thing about counterweights is that it is easy in the end to fine-tune the moment by adjusting the arm of a given weight.

My challenge now is to find a mechanism to fix a 1"-1.25" pipe to the wall in a very strong manner so it can support the weight of a counterweight on the other end. I'm leaning toward steel plumbing pipe -- flag pole brackets don't appear strong enough.

Marty

#5 *skyguy*

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Posted 27 July 2014 - 10:46 AM

You might try replacing the wall hinges with commercial grade spring loaded butt hinges. They should take up most of the wall's weight ... making it easier to open and close.

#6 roscoe

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Posted 27 July 2014 - 10:56 AM

Marty,
Steel pipe with perhaps weight-lifter weights on them could work well, steel pipe flanges would probably be strong enough, though I'd suggest putting through-bolts instead of screws to hold them on, but if the weight needed was large. you could perhaps put together a flange, a very short section of pipe, a tee, then a longer section for your weights, with a several-inch piece of pipe coming out the branch of the tee, with an elbow, a short length of pipe, and another flange on that. You would then have two attachment points for each counterweight arm. You could rework the tee and pipes and all to make the weights hang in the best way for your situation. Home Depot (at least my local one) custom-threads pipe pieces to your specs, so you can have parts made to fit if needed. You could perhaps also fill large cans or buckets or pieces of plastic drain pipe with concrete mix, with bolts cast into the crete, for counterweights.

#7 MJB87

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Posted 27 July 2014 - 11:20 AM

These are excellent suggestions. I'm not sure spring-loaded hinges will alone do the job but they would certainly reduce the counterweight load. I also like the idea of two attachment points for the pipe with through-stud bolts for solid attachment. That will avoid flex which might weaken the attachment points over time.

Many thanks.

Marty

#8 Midnight Dan

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Posted 27 July 2014 - 11:47 AM

Hi Marty:

I missed the part in your first note about the wall folding down inside. I was thinking a 90° swigndown outside was what was needed. You're right, gas springs won't do it.

As for pipe, go as large a diameter as you can find. Plumbing pipe is not designed for structural strength and bend fairly easily.

To attach it to the wall, you might want to consider U-bolts. McMaster-Carr carries extended length u-bolts that will easily go through a wall thickness:
http://www.mcmaster....u-bolts/=t0rcxe

-Dan

#9 MJB87

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Posted 27 July 2014 - 02:54 PM

Thanks, Dan. Good advice on the u-bolts. Appreciate the help.

Marty

#10 Dick Jacobson

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Posted 01 September 2014 - 12:18 PM

Attached File  003.jpg   116.63KB   0 downloads

External counterweights are ideal for perfect balance, but my club didn't want weights on the outside of their observatory. Instead, I built an internal counterweight system that included springs for easier movement. The problem with counterweights alone was that it was very difficult to begin opening the wall if there was enough weight to evenly balance the wall at mid-swing. So I mounted the weights on large 1" diameter gate springs. As you start to open the wall, the springs stretch while the weights stay on the floor. When the wall is about 1/4 open, there is enough force on the springs to begin lifting the weights, and the balance is reasonably good for the remainder of the motion.


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#11 MJB87

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Posted 01 September 2014 - 07:25 PM

I like this idea.  I'd need a different approach but it seems very workable -- and straightforward.  Many thanks.

 

Marty



#12 Midnight Dan

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Posted 08 September 2014 - 10:48 AM

Excellent solution! Love the addition of the springs. :bow:

 

-Dan



#13 MJB87

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Posted 09 September 2014 - 01:30 PM

I've looked into this solution.  It will be tricky.  The folding section of the wall consumes the full width of the wall, which means there isn't really space to mount a bracket or pulley.  It would get in the way of hte folding wall.  (In hindsight, I should haven't done that and I may change out that section as a result.)



#14 CharlesW

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Posted 10 September 2014 - 08:18 PM

Can you cut the hinged portion in half so you're only moving half the weight?



#15 MJB87

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Posted 10 September 2014 - 08:30 PM

I could but it would mean having to redo the exterior planking and I'm not sure that I want to go through that. 

 

As a practical matter, I really don't need to lower the wall very often. I'll just live with it.








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