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• Linear Motor?

  Andrew Bahls • 08/21/2022 at 22:17 • 0 comments

  Just had an idea today, going to write it out now, and work on drawing it up later.

  So maybe I could use a sort of linear motor to actuate the wall up and down?  The locking action at extension and retraction could just be a pair of magnets, with a magnet in the wall piece.  Then a coil of wire could induce a stronger electromagnetic field to push the wall up or down.  The 2 coils could even be wired in parallel, since ideally the electrical pulse would be short enough for the 2 fields to not interfere.  Then an additional smaller magnet could be used with a Hall effect sensor (AH1815) to indicate the wall state.

  Each wall segment would then have 4 magnets, a solid state relay for the coils, the hall effect sensor, and the pair of coils.  Power rails would connect 2 voltages, a 3.3 to 5v rail for the hall effect, and a higher voltage for the relay/coils.  2 data lines, connected to matrices for pulsing the coils, and reading the state of the hall effect.

  This sounds way more economical than my other ideas so far.  I'll need to start drawing up some things in CAD.   And then work on prototyping the linear actuators to see if this is possible. 

• Design History from Conception to Now

  Andrew Bahls • 08/07/2021 at 19:29 • 0 comments

  My initial design concept included 2 different designs.  A manually actuated version using some form of push-push mechanism similar to a click pen, and an electromechanically actuated version that could be computer controlled.

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  I created a few prototypes of the manually actuated version, using a push-push track and wiper design I found on the internet.

  The above picture is of my first prototype, which used a wiper and track design.  However the wiper wasn't supported in the track, and had a tendency to pop out.  My FDM printer was also unable to resolve the fine details of this design, keep in mind that the center square was only 1".  This was also the only iteration where I had the wall units in line with the grid.  My later iterations rotated the design 45 degrees, so that the mechanics fit on equal sides of the wall, with 4 wall units making up a grid square.

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  These next 2 pictures are from my second iteration of the manually actuated design.  This time I used a sliding wiper, that was supported on either side by a mirrored track.  I also used a single spring at the bottom, rather than the dual springs on tracks from the first version.  This version was somewhat successful (I unfortunately don't have any clear photos of the printed version).  Once I found a spring tension that worked, I was able to push the wall down, and it locked into it's lower position.  However it couldn't unlock from that position and return to it's extended position.  I retired this design when it was clear that my FDM printer would be unable to properly resolve the precision to refine this design.

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  At this point, I had moved on to work on other projects, so we'll fast forward to a few months ago.  Hackaday featured a few articles on flip-dot displays, and I considered using a similar method to actuate my electromechanical version, which I had yet to prototype in CAD.  I had also matured considerably with Fusion360 over the past year, so tackling a more complex design was more feasible.

  This design utlizes the M3 brass threaded inserts I've fallen in love with using in 3d printing, as well as some 3mmx7mm bearings I found on Amazon.  I'm very pleased that I was able to get about 20mm of travel with this cam mechanism.  However, once I had 3d printed the design and put it together (learning that I hadn't considered ease of assembly in the design), it was clear that an electromagnet pushing a magnet on the cam shaft would probably not overcome friction enough to rotate the shaft 180 degrees (though I haven't actually tested it yet).

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  It's at this point that I'm posting the project on Hackaday.io.  I'm pleased with the cam actuation giving me a stroke length of ~20mm, and it fits within a 28mm grid with 1/4" thick grid walls.  However, I need to consider some alternative actuators.  Servos or geared motors would be easy to adapt to this design, but I'd have to wire up thousands of them for even a small table size.  I also don't need the analog control, the walls only need to be fully extended or fully retracted.

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