Re: [CAD_CAM_EDM_DRO] Hexapods / Stewart Platforms

>
>
>The EMC is the only low cost ($0.00) CNC software that will control a hexapod.
>Here's a picture:
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>http://www.linuxcnc.org/names2000.html
>

Well, that's a design I hadn't thought of. Cables held taught by weight
alone. Ingenious...and built within an octahedron to boot. Bucky would
be proud. In that vein, I wonder if I could implement something like
this using tensegrity principles? An internally prestressed tension
network. :-) (I'm only half kidding...it probably would work!)

It says it's remarkably rigid in the horizontal plane, but I wonder how
rigid it really is? Triangulation works wonders, but when your members
are held in tension by weight alone...hmmm. My thought was to place the
work on the Stewart platform, and move it relative to a fixed
spindle...this model turns my concept upside down.

A question, though. It says the cable is effectively lengthened or
shortened by winding it around a spool, controlled by a stepper. If
it's wound in a helical configuration (like a spool of thread, or an AM
antenna coil) then the physical location of the "end" of the strut
changes. If it's wound "on top of itself" into a pancake coil, then the
effective change in the shaft diameter will cause positional errors. I
know this was probably just a demonstration model, but undoubtedly the
designer took this kind of thing into account when building the machine.
How were these errors dealt with?

And, finally, what is the EMC? I'm still a beginner at this...don't
even have a machine, yet, though I'm working towards building a small
moving-gantry wood router, as a start.

-- Chuck Knight