This paper presents a 2-hop WPT system for the robot-arm, which consists of the class-E inverter on the transmitter side and a class-D rectifier on the receiver side. We obtain the analytical model of the system for obtaining the class-E ZVS/ZDS conditions. The model includes the coil's physical information. Therefore, it's possible to optimize the system for the theoretical highest power-delivery efficiency under the robot-arm coil-space restriction. The circuit experiment showed quantitative agreements with the theoretical predictions, which proved the validity of the proposed method. The experimental prototype achieved 78.0% power-delivery efficiency at 6.78MHz operating frequency and 39.3W output power.