Flail like weapon / Hinge Joint

hi guys, i'm new to unity and i'm trying to make a flail like weapon. But I have two distinct problems. Here is a video of what I've done : http://johnlev.com/tmp/flail.mp4 1 - I set the same hinge joint on each cube, but they seems to work only two by two. Do you know why ? 2 - As you can see, if the force against my flail is to big, it "explodes". What's the matter ? Thanks in advance.