BodyVelocity’s seem to take the rule “An object at rest tends to stay at rest” a little bit too far. BodyVelocitys have no effect on “machines” (I think that’s the name Val gave me for models that have hinge joints) if they were stopped beforehand, no matter how much I play with the BodyVelocity’s properties.
I have an extremely simple example set up of a four-wheeled “vehicle” with one base part. Inside the Base part, there is a BodyVelocity with velocity Vector3.new(0, 0, -16). The vehicle starts out moving just fine. But if you press my red “Stop” button, then press “Go” again, it will not move.