Re: Hexapod

Rainnea Graphics wrote:

> ----------------------
> As I try to understand the workings of the hexapod design I animated a 3D
> model and put some labels on the axis nodes, I've put two small files in a
> folder called Hexapod in the files section. I hope I'm on the right lines
> here.
> Doug, would you mind explaining the compression / tension thing with the
> labeled drawing I uploaded or suggest how I should re-label the drawing ?
>

Hey Rab, that animation at:


is just superb! Everyone, go have a look!

Ok, to explain the pairs of tension/compression using your labelling at:
http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/Hexapod/hexapod_labeling.gif

Lets say AB EF & IJ are under tension, and
CD GH & KL are under compression.

Notice at the top frame of the machine, pairs of tension/compression
come together (concentrating the forces in the brackets there,
but minimizing stresses to the rest of the frame). There will
be frame stresses, but are mostly from (and the same magnitude as
the vector additions of) the tool pressure.

I see you have put the 'spin tubes' at the top, and see how
the screws hang down (the smaller screws giving greater range
of movement when the tool platform is doing 4D and 5D machining).

Notice there is a substantial nut at the lower end of the spin tube,
and also a 'centralizer' pad (which is fixed to the screw, but is
free to spin and slide up and down inside the spin tube) at the
upper end of the screw. This pad is made of UHMW plastic, which
I am using so successfully in my CNC router tables. As threaded
UHMW works so great (no backlash, low friction, low wear, no
maintenance)
in the router tables, for the next experimental round of hexapod
actuators, I am going to use UHMW instead of the metal nut. As
UHMW has a tearout of approx 2000 lbs/linear inch of 1" dia 5 TPI
acme, a 3 inch length should take 6000 lbs in tension or compression.

see the three images at:

http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/Hexapod/spintube1.jpg
http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/Hexapod/spintube2.jpg
http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/Hexapod/spintube3.jpg

Doug Fortune
http://www.cncKITS.com