Hi,
thanks for your fast reply. I have one more question about it.
Putting your motor to higher speed means it consumes more current
This is clear...
and probably the voltage drops a bit
Here comes my question. The motor uses an external power supply with high current and voltage. The 5V and 3.3V lines of the arduino board get there power from the USB port of the PC. So i thought the logical circuit of the Arduino-Board should not be affected by the motor current. Is this wrong?