A ragdoll motor can either directly set the velocities of the controlled ragdoll bodies or it can use Constraints to influence the bodies.

Velocity Motors:
Velocity motors directly set the velocities (LinearVelocity and AngularVelocity) of the controlled rigid bodies. If velocity motors are used, DriveToPose(SkeletonPose, Single) must be called in each frame. Velocity motors drive the ragdoll to an absolute world space pose. This means that velocity motors cannot be used if different ragdoll movements should be blended (e.g. a hurled ragdoll moves its limbs into a defensive pose). Forces acting on the ragdoll and collisions will also have little impact. Velocity motors can be used to drive the root bone of a ragdoll.

Constraint Motors:
Constraint motors use Constraints to control the movement of the ragdoll bodies. It is only necessary to call DriveToPose(SkeletonPose, Single) if the target skeleton pose has changed. Constraints can be used to blend key-frame animation and physically-based animation (reaction to collisions). A constraint motor acts similar to a damped spring that connects a bone with its parent bone. Constraint motors cannot be used to drive the root bone of a ragdoll.

Reference