All of your gains are zero. So error X zero => zero throttle.
Here's the relevant part...
Code:
_talon.setP(0);
_talon.setI(0);
_talon.setD(0);
_talon.setF(0);
Can you look at section 12.4 for a walkthrough on speed servo.
Start with calculating feedforward so you can get "close" to your target speed. Then start with a soft p-gain and increment until the closed-loop response meets your requirements.
http://www.ctr-electronics.com/talon...ical_resources