Thank you Kyatric. Here's more precise explanation :
When i clone my object (ctrl drag), i launch the preview and it goes fine.
The probleme i have is when those objects i clone are created with limited revolute joints. Then it goes crazy on preview..
some part of these body are controled by sines. Those part are the only ones acting ok. the rest of the body is turning around fastly in a mess and limited revolute joints seems to be broken.
This happens only when this object has been cloned, otherwise i works ok.