Re: Hexapod question

> From: Jon Elson <elson@...>
> Subject: Re: Hexapod question
>
> Simon M. Arthur 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?
> >
>
> The only way a hexapod (Stewart platform) maintains alignment of the
> platform
> is by controlling the lengths of all 6 struts in a coordinated way.
> EMC can drive a hexapod, but it doesn't really allow tilting of the
> platform. But, you can translate the platform in 3 cartesian
> coordinates rather nicely.
>

Hi Jon, Simon

As of a while ago, the EMC motion planner can tilt the hexapod's platform.
Till Franitza in Stuttgart has been doing this with his desktop models.
You can see both stepper and servo version photos and a movie at

http://www.isw.uni-stuttgart.de/personen/t_franit/modell/index.html

There is some pretty novel work on platform geometry with Model 2 where
three of the the struts interact with the three other struts rather than
with the platform itself. This allows for a much larger angle of tilt
before the system approaches a singularity.

If your German conprehension is as poor as mine, there is a Queen's
English version that can be reached by clicking on the Brit flag.

Ray