External device not recognized via USB

[tannerboy]

Hi, first of all, Happy New Year to all the community.
And here my problem: I would like to connect an external device to a robot NAO via USB. NAO hosts a Gentoo Base System release 2.1. I've already tried to connect an Arduino-based device and it works well, I guess that NAO's Gentoo distribution already has Arduino drivers installed. But what about other devices that work with generic FTDI serial driver? I tried to mount it and it is visible, but no USB devices are recognized and no "ttyUSB*" ports are present. How can I let NAO Gentoo OS properly recognizes external USB devices? Of course my device works perfectly with other Linux distributions and other OS. It looks like a typical problem with Gentoo but I'm not familiar with it.

Any help is really appreciated!

Thanks a lot
Marco