Search This Blog

Saturday, October 9, 2021

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


Tuesday, September 14, 2021

HDTV Antenna Hack

 

Mohu Leaf antennas are popular for their small size, reception, and ease of mounting, but what do you do about TV stations that are too far away?

Typically, that means that a bigger antenna is needed.  Sometimes a TV channel has great reception and yet other times, you try shifting the antenna a little bit or even moving the coax cable.  Maybe a new antenna would give better reception, but that can be a gamble since not all antennas provide the same performance.

You may remember the days when "rabbit ears" were on top of TVs or seen old photos of TVs with rabbit ear antennas.  Sometimes folks would put a little aluminum foil on the antenna to improve reception.

Well, you can do something similar with a Mohu Leaf antenna to improve reception but instead of attaching aluminum foil to the antenna, you make a reflector.

I scrounged around and found a piece of compressed cardboard that was just a little larger than my antenna. Corrugated plastic, or presentation board would also work since it just needs to be stiff.

I had a metal template for spreading solder paste that was no longer needed that was  just the right size.  My metal sheet was four inches wider than the antenna and close to the same height.  I centered the antenna on the metal and bent each side of the metal to a 45 degree angle or so.  

If you don't happen to have an unused metal soldering template laying around then you can use any thin metal, even heavy duty aluminum foil will work. If you use window screen material, make sure that it is actually metal. Do not use chicken wire since the large spaces offer less reflection area.  

After bending the metal, I used double-stick tape to secure the metal to the cardboard.  Next, I punched two screw holes through the metal and cardboard that aligned with the two holes on the antenna.  I guessed on the location of the third and fourth hole and just made sure that the would be under the opposite edge of the antenna.

The most important part of this antenna modification is the distance from the reflector to the antenna.  Two inches provided the best results for me.  Depending on the channels that are weakest in your area, you may want to adjust the distance slightly.  More distance will improve reception for lower frequencies while shorter distance will improve reception for higher frequencies.

I 3d printed two inch standoffs but you could just as easily use wooden dowel or other non-metal materials. For the area of the antenna with no screw holes, I created a standoff with a lip to hold the edge of the antenna.  Although it may be tempting, do not pierce the antenna!

This is the final result.  I put a sawtooth picture hanger through the cardboard to make it easy to hang the unit.  My final cost was zero since I used scraps that I already had.

So the real question is performance. Even if the mod was free, it's useless if there's no increase in performance.

I used a TiVo OTA unit to check the difference in antenna performance.  It's not scientific or even in decibels, but it will display antenna signal percentage, which we can compare. 

The weakest channel that I could receive measured 35% before the reflector and 60% after the reflector.  I can now reliably receive that channel without screen garbling randomly.

Every other channel showed an increase of at least 15% with the stronger channels increasing by 25%.  I used to loose some channels at night as their signal was weaker at night, but that is no longer an issue.

Even if you have to buy everything, it should be possible to make this reflector and improve your reception for only a few dollars.


Wednesday, September 1, 2021

Play the MacGyver theme when your 3d print ends


If you have owned a 3d printer for a while then you've probably already added code to beep the 3d printers speaker to notify you that your print has completed.  Otherwise, your stuck occasionally checking the print progress, which can become tiresome.

Why not play a favorite tune when your 3d print has completed?  Maybe a fanfare? Celebration?  "Flight of the Valkyries?"

With the tool at the following link, you can convert a midi file directly to GCODE that will output tones on your 3d printers speaker:  Midi to M300

The M300 GCODE command is used by 3d printers running Marlin firmware to generate sounds, tones.  Many 3d printers use the Marlin codebase so if your 3d printer has a speaker then you should be able to generate music.

The music will not sound like music from your smartphone might sound.  It actually sounds more like a Commodore VIC-20 could be playing the music but it is recognizable and guaranteed to arose curiosity from those not expecting it.

You can of course generate your own midi files like Lazy Game Reviewer (LGR) might, but there are also numerous midi songs available on the Internet.

Since I'm no musician but still am a fan of the original MacGyver show, I found the theme song in midi form and ran it through Midi to M300 and tried it on my printer.

It sounded terrible!

So I went back to Midi to M300 and unchecked boxes for some instruments and channels and tried again.  I had to repeat this several times before I got something that sounded good to my ears.  However, it was too lengthy.  I didn't need to hear the entire MacGyver theme at the end of a print, just enough to be recognizable and get my attention.

So I started trimming M300 lines from the generated code.  The final result has been shorted to around 30 seconds of time and contains the most recognizable parts of the tune.

If you'd like to just try this out on your 3d printer then install a copy of Pronterface and connect to your 3d printers USB port.  Some Creality printers now use the CH340 serial USB driver so you may need to install it to get Pronterface working with your printer - it does not autoinstall on Win10.

Copy the GCODE for the MacGyver theme below and save it using Notepad as a text file.  Change the extension of the file to MacGyver.GCODE.  After Pronterface is connected to your printer, Load the MacGyver.GCODE file in Pronterface.

Now press the Print button in Pronterface and your 3d printer should play the MacGyver theme.  If it is unsuccessful, and your certain that Printer face is connected, double check the MacGyver.GCODE file that you saved and make sure that it only contains the M300 GCODE lines shown below and nothing else.

To play the MacGyver theme at the end of a print, open up your printer configuration in Cura slicer and go to the "End G-code" under the Machine Settings for your printer and paste the following GCODE:

M300 P104 S523
M300 P104 S0
M300 P104 S523
M300 P104 S0
M300 P104 S523
M300 P104 S0
M300 P104 S523
M300 P104 S0
M300 P104 S523
M300 P104 S0
M300 P104 S523
M300 P104 S0
M300 P104 S523
M300 P104 S0
M300 P104 S523
M300 P104 S0
M300 P208 S494
M300 P208 S392
M300 P208 S196
M300 P208 S392
M300 P208 S370
M300 P208 S440
M300 P208 S196
M300 P208 S392
M300 P208 S392
M300 P208 S392
M300 P208 S196
M300 P208 S392
M300 P208 S523
M300 P208 S523
M300 P208 S196
M300 P208 S494
M300 P208 S196
M300 P208 S523
M300 P208 S494
M300 P208 S440
M300 P208 S392
M300 P208 S330
M300 P208 S659
M300 P208 S330
M300 P208 S440
M300 P208 S262
M300 P208 S131
M300 P208 S262
M300 P208 S523
M300 P208 S523
M300 P208 S147
M300 P208 S494
M300 P208 S196
M300 P208 S392
M300 P208 S196
M300 P208 S392
M300 P208 S370
M300 P208 S440
M300 P208 S196
M300 P208 S392
M300 P208 S196
M300 P208 S392
M300 P208 S196
M300 P208 S392
M300 P208 S523
M300 P208 S523
M300 P208 S196
M300 P208 S494
M300 P208 S196
M300 P208 S523
M300 P208 S494
M300 P208 S440
M300 P208 S392
M300 P208 S330
M300 P208 S659
M300 P208 S330
M300 P208 S440
M300 P208 S262
M300 P208 S131
M300 P208 S262
M300 P208 S494
M300 P208 S247
M300 P208 S123
M300 P208 S247
M300 P208 S523
M300 P208 S494
M300 P208 S440
M300 P208 S523
M300 P208 S185
M300 P208 S494
M300 P208 S440
M300 P208 S587
M300 P208 S123
M300 P208 S523
M300 P208 S494
M300 P208 S587
M300 P208 S123
M300 P208 S523
M300 P208 S494
M300 P208 S659
M300 P208 S131
M300 P208 S587
M300 P208 S659
M300 P208 S740
M300 P208 S185
M300 P208 S494
M300 P208 S123
M300 P208 S784
M300 P208 S165
M300 P208 S330
M300 P208 S740
M300 P208 S311
M300 P208 S698
M300 P208 S294
M300 P208 S494
M300 P208 S392
M300 P208 S784
M300 P208 S659
M300 P208 S494
M300 P208 S740
M300 P208 S587
M300 P208 S440
M300 P208 S659
M300 P208 S523
M300 P208 S392
M300 P208 S587
M300 P208 S494
M300 P208 S392
M300 P208 S523
M300 P208 S330
M300 P208 S494
M300 P208 S294
M300 P208 S523
M300 P208 S494
M300 P208 S440
M300 P208 S392
M300 P417 S466
M300 P417 S440
M300 P208 S784
M300 P208 S392
M300 P208 S587
M300 P208 S392
M300 P208 S622
M300 P208 S311
M300 P208 S466
M300 P208 S440
M300 P208 S392
M300 P208 S196
M300 P208 S294
M300 P208 S196
M300 P208 S311
M300 P208 S196
M300 P208 S233
M300 P208 S220
M300 P208 S587
M300 P208 S587
M300 P208 S587
M300 P208 S587
M300 P208 S587
M300 P208 S587
M300 P208 S587

Wednesday, August 25, 2021

Make your 3d printer play music - "How It's Made"


 I found a midi file of the intro music from the TV show, "How It's Made" and found an online midi to GCODE converter.  Perfect!  

If you want your 3d printer to start playing the "How It's Made" tune through the printers speaker when starting a print then add this GCODE to the end of your printers start code:

;How its Made tune  

M300 P103 S123
M300 P635 S0
M300 P117 S123
M300 P337 S0
M300 P137 S123
M300 P190 S0
M300 P107 S123
M300 P249 S0
M300 P166 S110
M300 P1724 S0
M300 P93 S156
M300 P620 S0
M300 P93 S156
M300 P347 S0
M300 P156 S156
M300 P200 S0
M300 P117 S156
M300 P234 S0
M300 P107 S165
M300 P1299 S0
M300 P464 S185
M300 P5 S311
M300 P103 S123
M300 P371 S0
M300 P210 S311
M300 P34 S0
M300 P20 S370
M300 P117 S123
M300 P293 S0
M300 P44 S277
M300 P137 S123
M300 P190 S0
M300 P127 S123
M300 P200 S311
M300 P29 S0
M300 P166 S110
M300 P68 S0
M300 P132 S311
M300 P337 S0
M300 P117 S311
M300 P117 S0
M300 P117 S370
M300 P352 S0
M300 P176 S277
M300 P288 S0
M300 P20 S311
M300 P93 S156
M300 P366 S0
M300 P210 S311
M300 P34 S0
M300 P10 S370
M300 P93 S156
M300 P327 S0
M300 P20 S277
M300 P156 S156
M300 P200 S0
M300 P122 S156
M300 P200 S311
M300 P29 S0
M300 P107 S165
M300 P127 S0
M300 P132 S311
M300 P337 S0
M300 P117 S311
M300 P117 S0
M300 P117 S370
M300 P352 S0
M300 P176 S440
M300 P59 S0
M300 P176 S494
M300 P54 S0
M300 P5 S622
M300 P103 S123
M300 P371 S0
M300 P210 S622
M300 P34 S0
M300 P20 S740
M300 P117 S123
M300 P293 S0
M300 P44 S554
M300 P137 S123
M300 P190 S0
M300 P127 S123
M300 P200 S622
M300 P29 S0
M300 P166 S110
M300 P68 S0
M300 P132 S622
M300 P337 S0
M300 P117 S622
M300 P117 S0
M300 P117 S740
M300 P352 S0
M300 P176 S554
M300 P288 S0
M300 P20 S622
M300 P93 S156
M300 P366 S0
M300 P210 S622
M300 P34 S0
M300 P10 S740
M300 P93 S156
M300 P327 S0
M300 P20 S554
M300 P156 S156
M300 P200 S0
M300 P122 S156
M300 P200 S622
M300 P29 S0
M300 P107 S165
M300 P127 S0
M300 P132 S622
M300 P337 S0
M300 P117 S622
M300 P117 S0
M300 P117 S740
M300 P352 S0
M300 P176 S880
M300 P59 S0
M300 P176 S988