Thanks for your answer. The hub is self powered and it was weeks working alone.
The lancelot i installed today is connected directly to the rasp pi.
The problem is not the power, i think that cgminer only give works to the lancelot and the block erupter usb gets in standby...
Use a powered hub anyways. There was a known issue with Lancelot's and raspberry pi's USB interface and the fix was to use a powered hub.