PID controller feedforward

Restructures the PID controller to decouple feedforward from D.

Cleaned up the structure of the PID controller; moved some feature-based enhancements out of the main structure.

Feedforward becomes a separate component of the PID controller and there is now:
f_pitch
f_roll
f_yaw

The default values of 60 for pitch and roll matches the default setpoint weight used in BF3.4.  Yaw previously had no setpoint weight capability so the default here needs to be discussed.  Currently it's also set to 60 and flight testing seems positive.  Feedforward on yaw adds a lot of value so I don't think we want to default to 0.  Instead we need decide on the default.

All occurences of setpoint weight have been replaced by feedforward. "setpoint_relax_ratio" has been renamed to "feedforward_transition".

The pidSum now consists of P + I + D + F.

D has been added back for yaw (disabled by default with d_yaw = 0). We've found little need for D for normal quads but it may have value for other configurations - particularly tricopters.

Updated CMS menus to support adjusting the feedforward for each axis.

Changed the default for "rc_interp_ch" to be "RPYT".  Need yaw to be smoothed to support feedforward.

Open issues:

Needs BFC support
- Need to add support for the axis "F" gains.
- Remove "setpoint weight" slider.
- Rename "D Setpoint transition" to "Feedforward transition"

Needs BBE support
- Header "setpoint_relaxation_ratio" has been renamed "feedforward_transition"
- Header "dterm_setpoint_weight" has been replaced with an array named "feed_forward_weight".
  example: H feed_forward_weight:65,60,60    (R,P,Y)
- PID component "AXISF" has been added for all axes. Should be handled like P, I and D values.
- PidSum calculation needs to include F.

Needs LUA script support
- Support the renamed "setpoint_relax_ratio".
- Support for feedforward weight on all 3 axes.

Open code issues:
- rc_adjustments.c - support for adjusting feedforward weight for all axes. Currently only supporting roll - needs coordination with BFC.

src/main/flight/pid.h

@@ -39,6 +39,10 @@
 #define ITERM_SCALE 0.244381f
 #define DTERM_SCALE 0.000529f
 
+// The constant scale factor to replace the Kd component of the feedforward calculation.
+// This value gives the same "feel" as the previous Kd default of 26 (26 * DTERM_SCALE)
+#define FEEDFORWARD_SCALE 0.013754f
+
 typedef enum {
     PID_ROLL,
     PID_PITCH,
@@ -70,11 +74,12 @@ typedef enum {
     PID_CRASH_RECOVERY_BEEP
 } pidCrashRecovery_e;
 
-typedef struct pid8_s {
+typedef struct pidf_s {
     uint8_t P;
     uint8_t I;
     uint8_t D;
-} pid8_t;
+    uint16_t F;
+} pidf_t;
 
 typedef enum {
     ANTI_GRAVITY_SMOOTH,
@@ -100,7 +105,7 @@ typedef struct pidProfile_s {
     uint16_t dterm_notch_hz;                // Biquad dterm notch hz
     uint16_t dterm_notch_cutoff;            // Biquad dterm notch low cutoff
 
-    pid8_t  pid[PID_ITEM_COUNT];
+    pidf_t  pid[PID_ITEM_COUNT];
 
     uint8_t dterm_filter_type;              // Filter selection for dterm
     uint8_t itermWindupPointPercent;        // Experimental ITerm windup threshold, percent motor saturation
@@ -116,7 +121,6 @@ typedef struct pidProfile_s {
     uint8_t  antiGravityMode;             // type of anti gravity method
     uint16_t itermThrottleThreshold;        // max allowed throttle delta before iterm accelerated in ms
     uint16_t itermAcceleratorGain;          // Iterm Accelerator Gain when itermThrottlethreshold is hit
-    uint16_t dtermSetpointWeight;           // Setpoint weight for Dterm (0= measurement, 1= full error, 1 > aggressive derivative)
     uint16_t yawRateAccelLimit;             // yaw accel limiter for deg/sec/ms
     uint16_t rateAccelLimit;                // accel limiter roll/pitch deg/sec/ms
     uint16_t crash_dthreshold;              // dterm crash value
@@ -127,7 +131,7 @@ typedef struct pidProfile_s {
     uint8_t crash_recovery_angle;           // degrees
     uint8_t crash_recovery_rate;            // degree/second
     uint8_t vbatPidCompensation;            // Scale PIDsum to battery voltage
-    uint8_t setpointRelaxRatio;             // Setpoint weight relaxation effect
+    uint8_t feedForwardTransition;          // Feed forward weight transition
     uint16_t crash_limit_yaw;               // limits yaw errorRate, so crashes don't cause huge throttle increase
     uint16_t itermLimit;
     uint16_t dterm_lowpass2_hz;             // Extra PT1 Filter on D in hz
@@ -168,6 +172,7 @@ typedef struct pidAxisData_s {
     float P;
     float I;
     float D;
+    float F;
 
     float Sum;
 } pidAxisData_t;
@@ -195,4 +200,4 @@ void pidUpdateAntiGravityThrottleFilter(float throttle);
 bool pidOsdAntiGravityActive(void);
 bool pidOsdAntiGravityMode(void);
 void pidSetAntiGravityState(bool newState);
-bool pidAntiGravityEnabled(void);
+bool pidAntiGravityEnabled(void);