As haptic devices become more common, the afford-ability, complexity, and size of the device are all factors in considering appropriate applications. A popular haptic device is the PHANTOM Omni, a six degree of freedom (6 DOF) positioning manipulator with 3 DOF force feedback. To increase the usability of the class of under actuated devices that include the common PHANTOM Omni, an impedance requiring full 6 DOF force feedback control law for under actuated devices based on a virtual mechanism (VM) was developed. The goal of this control law is to mask the un-actuated joints of a physical robot manipulator (RM) using force feedback on the actuated joints. The control theory includes using a VM as a constraint for the RM. Weighted matrices and the pseudo inverse Jacobian control law place the VM as to minimize the error between the current RM position and somewhere on the path of the VM. A pseudo inverse Jacobian control law is used to generate a force to send to user of the RM. The theory is tested using the PHANTOM Omni with six cases where the importance of the position error and orientation error for the manipulator are varied.