[PD] PMPD how to get constant distance between two masses

[Patrice Colet]

Hello,

 I'm trying to find a setting for linking two masses that have always constant distance, but couldn't find how to do it, the link is always resizing like a rubber instead of being solid like wood.
 I guessed that fixing K to an high amount would make a solid link, but this is breaking it instead.
The purpose is about applying forces to a cylinder represented by two masses and a link to make it rotating.

Colet Patrice