Copter: Set Rate PID D-term filter rates on initialization.

ArduCopter/config.h

@@ -560,6 +560,11 @@
 //////////////////////////////////////////////////////////////////////////////
 // Rate controller gains
 //
+
+#ifndef RATE_PID_DTERM_FILTER
+ # define RATE_PID_DTERM_FILTER     20              // D-term filter rate cutoff frequency.  Used for Roll, Pitch and Yaw Rate PID controllers.
+#endif
+
 #ifndef RATE_ROLL_P
  # define RATE_ROLL_P        		0.150f
 #endif

ArduCopter/system.pde

@@ -231,6 +231,9 @@ static void init_ardupilot()
     // initialise attitude and position controllers
     attitude_control.set_dt(MAIN_LOOP_SECONDS);
     pos_control.set_dt(MAIN_LOOP_SECONDS);
+    g.pid_rate_roll.set_d_lpf_alpha(RATE_PID_DTERM_FILTER, MAIN_LOOP_SECONDS);
+    g.pid_rate_pitch.set_d_lpf_alpha(RATE_PID_DTERM_FILTER, MAIN_LOOP_SECONDS);
+    g.pid_rate_yaw.set_d_lpf_alpha(RATE_PID_DTERM_FILTER, MAIN_LOOP_SECONDS);
 
     // init the optical flow sensor
     if(g.optflow_enabled) {