The middle plate is located in the middle of the robot, it is connected to the top plate with four metal supports and to the bottom plate with two metal supports. It is also resting on the four motor mounts of the robot. The middle plate is 3D printed with PETG.
The two rectangular holes in its center are for the arms of the chipper solenoid's pulling mechanism, the hole under that is for the chipper solenoid itself. The four holes at the side are for the wheels' motors. Finally, there is also room at the front to slide in the ball sensor and the lipo battery, as shown in this figure of the middle assembly.