The AC Servo-System drive is used instead of the traditional CAM driving mode in order to realize pin-roller motor keep synchronization with the other motor.

采用交流伺服驱动代替传统的机械式的凸轮传动机构，实现针辊电机与其他电机的同步驱动。

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Of course, leaving a smartphone's display on for multiple hours as you traverse Montana, Wyoming, Idaho, Oregon and California isn't wise without a power source to sustain that type of abuse, so it's worth mentioning that I traveled with an AC inverter in order to keep a constant power connection to the Lumia 900.

ENGADGET: Nokia Drive offline navigation review: taking the Lumia 900 for an off-the-grid spin