Re: Hexapod question (joints)

I don't think ball joints are required. In fact, they would not work
well at all because then the motor and/or screw would be free to spin
and do nothing.

The bad news is a U-joint or gimbal isn't the same as a perfect ball
joint, either. As you move the bottom end of a strut around, it will
rotate slightly relative to the top which will screw/unscrew the strut
and change the length slightly.

I don't know if this will cause enough error to matter or not. For a
first experiment, maybe not. For real precision, probably so.

It ought to be possible to account for the U-joints in the control,
but I don't believe the EMC calculations do this. Working out the
proper math for the U-joints would be possible, I think, but not easy.

Andy A.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Kevin Martin" <kpmartin@t...>
wrote:

> I may not be able to explain exactly *why*, but I have to disagree

with you,

> ballendo...

snip...

>
> -----Original Message-----
> From: ballendo [mailto:ballendo@y...]
> [...]
> The u-joints you've used are creating the problem. You need a ball
> joint at the end of the struts.