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A problem with scaling, and the popsicle stick project

Picture 1: Getting a feel for the strength of glued popsicle sticks

The whole idea of working with popsicle sticks was that they are relatively inexpensive and require little work space.  I thought that it may be helpful to people little money and space to work with something to get some experience designing and constructing.  I still think so, but I am not 100% sure the knowledge is transferable to larger projects.

Although we can scale the dimensions of the lumber, we cannot scale the grain structure of the wood.  This means the normal ways of attaching lumber, nails and screws, is not workable at this scale because any pin large enough to handle will split the wood.   Glue however works well for this size planks, but is seldom used on larger scale things.  (Butcher block counter tops is an exception, and I believe I have seen beams constructed from smaller boards glued together in a church building.)

In the fabrication of the Do-Nothing Machine shuttles I created two gauges.  Since I am past that part of that project I decided to get a feel for how strong the joints are.  As you can see in picture 1, I broke the legs of the A frame before I managed to beak loose a glue joint.  When I stressed the sticks as I was doing in the picture, all I managed to do was make my hands hurt.  The sticks are still weak perpendicular to the wide side of the stick.   This is going to be a problem in fabricating with the sticks.

Picture 2: Popsicle stick plywood.

Plywood is a series of very thin wood sheets glued together with each section of wood placed so the grain is perpendicular to the previous previous sheet. What the heck, can I do this with popsicle sticks?  I glued 12 sticks together as shown in Picture 2.  Notice that I offset the two outer layers so the joints between sticks was not directly above each other.  I also attempted to glue the edges of adjacent sticks together.

Picture 3: Stressing the “popsicle stick plywood”

Once the glue dried I stressed this to be very tough in all directions.  As you can see in picture 3 the outer sticks  did bend in the non-reinforced area but where the sticks were glued together nothing flexed at all.  This may prove to be useful in the project I am thinking about.

 

Picture 4: A crawler crane.

 

I wanted to come up with a project that is going to require some thinking and working out some problems.   Bridges looked like fun, but there is already a site that covers that topic very well.  So as I was driving around last week I found myself looking at structures that have open frames that might be transferable to popsicle sticks.   I also wanted something that we can test and improve our understanding.   (Nothing like a good engineering failure to motivate you to want to increase your understanding.)   The idea hit me when I saw a large crawler type crane doing work.   That is the point where my work started.

Picture 5: Close up of the cab part of the crane shown in Picture 4.

Starting with an image search in Google, I ended up on the Wikipedia article about cranes. I quickly determined the type of crane I am interested in is called a crawler crane.  This is for several reasons,  most truck mounted cranes are hydraulic operated with telescoping box sections making the boom.  This is not suitable for what we want to do with the popsicle sticks.   Other cranes talked about were also not suitable or just didn’t interest me.

Continuing on through the pictures I landed on a site that had many interesting cranes.  Bigge.com sales used cranes.  All of these newer cranes use lots of hydraulics to do much of the work.  However, there are some ideas there that may be good for our popsicle work. I ended up with the drag line crane shown in pictures 4,5 & 6 because it looks as if it uses 100% cable operation for all the functions including controlling the boom angle.

Picture 6: Attempting to understand the lift cable routing of the drag-line crane.

The next steps in trying to figure out how to build this in popsicle sicks are:

  • How are the cables routed? This is necessary so we can determine where forces are exerted.
  • How does boom angle affect the stresses?
  • How are we going to fabricate the heavy duty ends of the boom with the extra reinforcing?
  • How are we going to provide bearings for the boom, pulleys, and winder drums to move?
  • How are we going to fabricate or purchase the pulleys?
  • How are we going to provide the cross bracing?  This is especially a problem on the narrow sides of the sticks.
  • How are we going to prevent the tower on the back of the crane from collapsing. and being glued firmly enough to the crane. body.

As you can see this is going to be an interesting project and will require a lot of ingenuity to work through these problems.  I have started trying to understand how they routed the cables.  In the end I hope we have a nice toy to excite the child in all of us to make this “nerding out” worth the effort.

Gary

The pictures of the dragline crane came from Government archives and are in the public domain.

 

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