In this presentation, Gregory shows how Model-Based Design can be used to increase the energy efficiency of mechatronic systems such as drivetrains and robots. In a first application, a lumped parameter physical model of a badminton robot system has been developed and then used to virtually tune the control algorithm. In a second application, models have been used to compare the performance of different energy-storage elements in a hydrostatic drivetrain to determine which would result in the lowest total cost of ownership.