Re: [CAD_CAM_EDM_DRO] Re: Re: Hexapod question - rigidity

Actually, you are subject to what we call 'Lake-Effect' snow. The snow I
can handle... It's the bitter cold that I don't like. When I finally got
outside this morning, about 7:00, the thermometer on the yardlight pole
indicated minus 10° F ! (That's not factorial, it's exclamatory).

My thoughts on the Stewart struts are that they must operate best as
ball-joints... rather each strut that connects to a common point should be
a half-hemisphere, mating with each other in such a way as to form a
complete sphere, retained in an appropriate socket. Note, that these two
halves will always rotate relative to each other in only one axial plane!
This fact allows the socket to also be fabricated in two halves (actually,
they don't even need to be complete halves) suspended in a universal
joint-like yoke. I may actually try to build one... some day, after I apply
for membership in the Procrastinators' Club.

RayHex

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> From: Ray Henry <rehenry@...>
> To: CAD_CAM_EDM_DRO@yahoogroups.com

<snip>

> Hi RayHex.
>
> How'd you like that last blast of snow?
>
> Your design here is real close to what was done with the NIST cable
> hexapod. It is also about what was done with the Ingersoll at NIST. You

> run into some practical limits when you try to co-locate the ends of the
> triangles with rigid struts and still have them slide as the platform
> moves.
>
> A prof, John W. Sutherland, at Michigan Tech had a nice page on Stewart
> geometry but I couldn't find it the last time I looked. Looks like they
> put all of his stuff behind a password.
>
> Ray Henry