A "simple" Hexapod project

This is a tentative and probing post just to get an idea of the level
of interest folks have in making Hexapods. They were mentioed a
while back and I have seen a couple of designs on the web that have
been built by amateurs, one using an inverted Stewart platform and a
router and the other using cables. (Search for hexapod in the archive
for the links).

I'm actually quite new to CNC really but the dream has kept me amuzed
for a while now and the reality is proving to be most enjoyable. (I
just made some USEFULL parts in Delrin on my Proxxon). I am doing a
4th axix for that but after seeing a homemade 5 axis taig I have got
re-inspired and see another potential dream to persue.

I don't have the skills, time or money to make a hexapod capable of
machining metal but I am an aeromodeller and the ability to shape
foam, plastic, wax and balsa in 5axis would certainly be of great use
or at least great interest.

What I propose is a simple Hexapod based on the ideas of the home
router/engraver constructor rather than the THK and ballscrew set.

Hexapods have 6 actuator legs and as they are legs all designs I see
tend to be based on telescoping tubes. Personally I can't imagine
building a very rigid actuator in this manner (i.e. I can't) and
finding tubes with precision bores makes the task more difficult. I
am thinking of making an actuator based on two silver steel or
precision ground rods. At the end which would be pillow blocks
including at one end a stepper motor mount and leadscrew bearing and
at the other a largeish Delrin bushing. A simple Delrin carriage
could ride up and down these rails pushing the actuator leg through
the bush in the pillow block. The part of the leg that moves would
then have three points of support. The leadscrew would reside within
the hollow actuator leg and be supported by a derin rider that could
be a loosish fit in the tube. To stiffen the whole thing up plates
could be added covering the assembly and locking the pillow blocks to
prevent twisting.

The leadscrew could be cheapo 6mm threaded rod and the nut a long
nylon job these seem to be pretty good on the backlash and cheap to
replace.

Pivots for the ends of the actuators might be off the shelf ball
joints of some kind or maybe gimble types.

I am just wondering if anyone else might be tempted, and if my ideas
are stupid. I suspect if a group of people had a go issues such as
software and tricky hardware prolems could be ironed out more
easily. Perhaps just start by making one actuator as I intend to.

Off to Dream,

Graham