The disclosure provides a portable electronic device. The twist beam includes a twist element defining a first lateral axis and arm portions adapted to rotatably support the wheels of the vehicle along a second axis extending substantially parallel to the first axis. One sensor is located in close proximity to the pad for producing a first output value corresponding to the impact pressure, and another sensor located in close proximity to the pad for producing a second output value corresponding to the impact point and the impact pressure. Additionally, the metal shell further includes a partner-fitting portion, and two short sides of the peripheral thereof bended backward to form a chamfer-type guiding portion so as to make a corresponding connector connect to the electrical connector smoothly. An engine is mounted on the first frame. Multiple micro-agitation means in parallel or in series can be used in each step to increase capacity without scale-up problems, and units can be serviced or capacity reduced without the need to close down the process.