Adafruit Industries Adafruit Industries 16-Channel PWM / Servo Bonnet for Raspberry Pi
The Raspberry Pi is a wonderful little computer, but one thing it isn't very good at is controlling Servo Motors - these motors need very specific and repetitive timing pulses to set the position. Instead of asking the Pi Linux kernel to send these signals, pop on this handy bonnet! It adds the capability to control 16 Servos with perfect timing. It can also do PWM up to 1.6 KHz with 12 bit precision, all completely free-running.
Adafruit Industries 16-Channel PWM / Servo Bonnet for Raspberry Pi