Re: Hexapod question

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.

Just some thoughts.

Thanks
Aaron Moss
www.IndustrialHobbies.com


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Simon M. Arthur"
<chroma@m...> wrote:

> I've started building a hexapod on the cheap. Some photos:
> http://www.tinyplanet.com/images/hexapod-portrait-reduced.jpg
> http://www.tinyplanet.com/images/dscf0011-reduced.jpg
>
> I noticed that the platform can be rotated and tilted more or less
> freely, even with power going to the steppers. Translational

movement is

> a lot harder. This makes me think that I misunderstood completely

how a

> hexapod is supposed to work. I have a universal joint on the frame

so

> that the motor can tilt, and another on the platform.
>
> Can this setup be made to work? Why doesn't my hexapod lock the

platform

> in place?