My First Magnetic Tensegrity Table

Google defines tensegrity as:

"the characteristic property of a stable three-dimensional structure consisting of members under tension that are contiguous and members under compression that are not."

Sometimes it's just easier to see it than read about it so here is a photo of a popular tensegrity toy. 

A tensegrity table uses the same principles to hold two flat surfaces locked at a fixed distance from each other using only strings or some other flexible strand such as ball chain.  Some tensegrity designs are fascinating to look at as the top surface looks like it's floating in mid-air. 

I wanted something a little different.  I wanted a table surface to magnetically levitate using tensegrity principles.  How hard could it be?  Replace the strings with supermagnets and that's it right?

I started by printing a few simple surfaces to retain the flat disc neodymium magnnets that I had purchased and decided to use the attractive force but use it along the outside edges with a tensioned string in the center to tension the structure.  The attractive distance of the magnets was not as great as I expected.  The two surfaces could be no more than an inch (2.54cm) or so apart for this to work.  That would leave almost no room for the tension structure needed in the center.

So I used magnetic attraction for the center string and three fishing lines around the outside edge. It finally worked!  

I created the design to be very sturdy but to look almost wireframe. The wireframe look appeals to me as it's similar to looking at a bridge structure. 

One of the problems with working with neodymium magnets is that they are powerful.  My first attempt at this circular table used  a single arm of less than 10mm width to support each magnet.  The support arms were bent by the magnets!  Too close, and the magnets snapped together.  Too far, and there was no tension.

I like the overhead view of the structure because it reminds me of a dart board or maybe a "pop" filer that would be used on a microphone in the 1940's.

Unfortunately, I did not align the two solid magnet supports so that there was a straight on view without one of the structures overlapping. 

As a result, when someone first looks at it they assume the center is how the table is supported.  It isn't until they look more closely that they see that the bottom and top half are connected only by strings. Finally they realize that the neomagnets are keeping the table together and then they begin testing the table.

First, they always push down on it to see how strong it is and they're usually a bit surprised. After collapsing the table, they pick it up and the neomagnets snap the table back into shape.The last thing people often do is try to spin the top to see how far it'll turn.  They're sometimes a little surprised that it won't turn very far but mesmerized by the jiggling of the table as it snaps back to original position.

I think the tensegrity table looks much better after changing the hole alignments and printing a table section with better alignment.

I will be continuing to investigate other ways to use magnets in tensegrity structures.  Download the STL and 3d print your own at Printables.com. 

Setting up a new Creality Ender 3 Pro 3d Printer

     I have caught the 3d printing bug.  However, I did not want to spend a lot of money on something right away.  Besides, as my wife says, "I am thrifty."
      I bought the Creality Ender 3 Pro because I had read about the few improvements included in the pro version that were not in the standard version.  First is the magnetic bed, I'm not sure if it justifies the $40 price premium, but the 1 year warranty and support and the improved extruder does justify the price premium for me.

       The first bit of advice that I could offer in setting up the Creality Ender 3 Pro is to first use the foldout manual to identify everything and lay it out and then put the foldout manual away.  It can be followed by a person determined to interpret the images, as I was, or a person ignorant of the build video that comes with the unit on the micro SD card.  Plug in the micro SD card adapter and watch the build video.  It is much easier to follow than the multifold manual.
      After finishing the build I was unable to level the bed. the left side was lower than the right by almost 1/3 of an inch!  I took the bed off to see if the bed frame below was that far off from level.  It was!  Argh!
     So I examined the bed frame closely and concluded that it had to be the X-axis bar carrying the printer head that was not level.  I was correct.
     In my mind, if you have rollers riding a frame and the holes are aligned then the parts must have been created to be square to each other.  This is not true.  BTW, I'm an electronics and IT guy not a mechanical engineer as should be evidenced by that last statement.
     I watched a few setup videos, there's nothing about this issue from Creality BTW, and I learned about the concentric nuts.  Concentric nuts on the Creality Ender 3 printers are used to move specific rollers a range of about +- 1/8 of an inch.  They function similarly to a cam on a camshaft.

     I moved the X-axis to the top and measured each side to check for square.  It was off by 1/3 of an inch.
     I tried adjusting the concentric nuts on each side of the X-axis.  I had to loosen the lock-down nuts a little of course, which I almost forgot to do.  I never did get the X-axis square.  Every adjustment resulted in either the X-axis being loose or much too snug to move. I finally compromised with being 4 mm from square with the assumption that the bed could be levelled to that.
     As I began levelling the bed, I noticed that one corner of the bed was higher than the rest, even completely cranked down.  I examined the bed mounting again and noticed that the spring with the bed connector mount was compressed more than the others.  That bed connector mount compressed the that corner spring about 1/8 of an inch.  No wonder the one corner was higher than the rest and the other 3 corners felt weak and wobbly.

     I added spacers to each of the other 3 bed corners to match the corner with the bed connector mount.  Now I could finally align the bed!  I adjusted each corner to be just 1/2 millimeter from the bed and at last I was ready to print!
     The print for the cat model ran for 5 hours and 43 minutes. The top of his head was cut off just below the ears.  The filament that came with the printer, which is not on a spool, had tangled and had not fed through the printer for the last 10% of the print.

     To make the best of it, I sanded the hole in the top of the cats head and used the resultant container as a toothpick holder.
     I retried the cat model print out after untangling the filament and stringing it out like a telegraph wire - I really did not want to hand my wife another cat with the top of his head cut off.  The print went well and the quality is actually impressive.

     I must admit that I thought that 3d printing was finally ready for the average person because it is so affordable now.  The pre-built models offer less frustration certainly but if anything needs to be replaced or becomes misaligned then it could become frustrating for the non-hobbyist.
     Some day 3d printing will be as easy as using a toaster and as cheap as an inkjet printer and as maintenance free.  It's too bad that we still have years before we reach that point.