re:digitizers

Elliot,

Interesting comments. Over constrained? Could be. Is that because the
cavities are conical? Better if they are countersinks with a tangential
contact?

In my mind, I can't see three angled grooves as having a finite "bottom"
I'd think the plane of the three balls could rock, and still stay in
contact?

Alan KM6VV

Elliot Burke wrote:

>
> If three balls in three conical cavities are used to located the sensor rod,
> things will be overconstrained. It is common in sensitive mechanical
> devices to use a kinematic mount for this sort of thing: three balls can be
> located with one in a cone, one in a groove, and one on a plane. Better is
> the three groove technique; the balls sit in three grooves which are angled
> to intersect each other towards the center of the triangle they describe.
> the groove is wide enough that the ball touches the walls tangentially.
> For sensitive systems carbide balls are used with sapphire plates, but that
> obviously won't work for a switch.
>
> I wonder what the hardest metalic conductive material is (that doesn't have
> problems with oxidation)?
>
> Elliot Burke