I'm trying to animate a simple gear scene with dynamics, but can't get it to work. I have four gears all the same size and want them to rotate. I was thinking I could make three of them active rigid bodies with hinge constraints and have the other gear be a passive rigid body and simply rotate it, which in turn would rotate the others, but I cannot add an expression or key the rotate Y on the passive body. I tried breaking the connection, which usually works in most cases, but you apparently cannot do this when you're dealing with a rigid body. I know I could key all the gears, but it seems as though there should be a way to do it with dynamics. Any suggestions?