Re: Re: Hexapod question

> From: "industrialhobbies" <admin@...>
>
> Although I know nothing about a hexapod design or uses, it would
> appear that in order to maximize effectiveness of the machine it
> would need to be built with the struts on the bottom, so the material
> can be supported on the top and pushed towards a fixed cutter.
>
> In the example sites that were given the hobby uses seem to want to
> mount the cutter on the movable platform facing down, but the
> professionals put the struts on the bottom and either the flight sim
> pod or the robot arm atop.
>
> If you were to look at the pro versions that use a simple Y base, it
> would be much easier to construct than the cage type assembly as
> shown by the hobbyists. A smaller Y can be made to be the moveable
> platform and a table of sorts mounted on that.
>
> Bringing up an arm from the back would provide a mounting point for
> the cutter.
>
> Next Point:
> Someone mentioned measuring the EXACT positions of the mounting
> points to be of paramount concern and difficulty.
>
> I would have to say that it could easily be done using a rotary table
> (or some other angle fixture), a concave mirror, a laser pointer and
> some basic trig. By using the same basic technique that is used to
> test the parabola of a telescope mirror. That test can be easily
> done one night and will easily get the positions of the strut anchor
> points down to the 1/10,000 range. And the cool thing about using
> optical measurement techniques is when we talk mirror error we talk
> millionths of an inch or better (the really good guys talk amstrongs,
> which is the width of an atom), so 1/ 1,000 is a walk in the park.

Seems to me that we're drawing an artificial distinction between hobby
machines and ones that the pros might use. Ingersol, K&T, and Giddings
and Lewis built and sold Stewart platform machines have designed them
with the spindle on the movable platform rather than the work residing
there.

When I visited Till's lab in Stuttgart he had designed and was running a
machine that was about 16 foot tall, had linear motors for the six fixed
length struts, and ran a movable spindle motor rated more than 20 kw.

A Swedish firm was installing a machine there that also used a relative of
the Stewart platform with a 30 kw motor that also moved on the platform.
That machine had at least 8 degrees of freedom of movement.

I also saw a standardized g-code program and a sample part made using it.
That program was written by a group of auto manufacturers that provided
some standard testing of the ability of these kinds of mills.

Ray