Throttle limit feature (#5608)

Adds new throttle_limit_type and throttle_limit_percent parameters that allow the pilot to limit the maximum commanded throttle seen by the flight controller by either scaling or clipping the maximum throttle.  The default is 100 representing no limiting.  So as an example, if a pilot was to set throttle_limit_type = SCALE and throttle_limit_percent = 80 the throttle input would scale from 0 to 80% based on full stick deflection from the radio.

This capability replaces the method of limiting throttle in the radio which some pilots are using to manage throttle on tight courses or reduce overall battery consumption when the extra power isn't needed.

There is no effect on the maximum throttle seen by the motors so the mixer still has full authority.

src/main/fc/controlrate_profile.c

@@ -52,7 +52,9 @@ void pgResetFn_controlRateProfiles(controlRateConfig_t *controlRateConfig)
             .rcExpo[FD_YAW] = 0,
             .rates[FD_ROLL] = 70,
             .rates[FD_PITCH] = 70,
-            .rates[FD_YAW] = 70
+            .rates[FD_YAW] = 70,
+            .throttle_limit_type = THROTTLE_LIMIT_TYPE_OFF,
+            .throttle_limit_percent = 100
         );
     }
 }

src/main/fc/controlrate_profile.h

@@ -28,6 +28,12 @@ typedef enum {
     RATES_TYPE_RACEFLIGHT,
 } ratesType_e;
 
+typedef enum {
+    THROTTLE_LIMIT_TYPE_OFF = 0,
+    THROTTLE_LIMIT_TYPE_SCALE,
+    THROTTLE_LIMIT_TYPE_CLIP,
+} throttleLimitType_e;
+
 typedef struct controlRateConfig_s {
     uint8_t thrMid8;
     uint8_t thrExpo8;
@@ -37,6 +43,8 @@ typedef struct controlRateConfig_s {
     uint8_t rates[3];
     uint8_t dynThrPID;
     uint16_t tpa_breakpoint;                // Breakpoint where TPA is activated
+    uint8_t throttle_limit_type;            // Sets the throttle limiting type - off, scale or clip
+    uint8_t throttle_limit_percent;         // Sets the maximum pilot commanded throttle limit
 } controlRateConfig_t;
 
 PG_DECLARE_ARRAY(controlRateConfig_t, CONTROL_RATE_PROFILE_COUNT, controlRateProfiles);

src/main/flight/mixer.c

@@ -40,6 +40,7 @@
 #include "io/motors.h"
 
 #include "fc/config.h"
+#include "fc/controlrate_profile.h"
 #include "fc/rc_controls.h"
 #include "fc/rc_modes.h"
 #include "fc/runtime_config.h"
@@ -733,6 +734,21 @@ void mixTable(timeUs_t currentTimeUs, uint8_t vbatPidCompensation)
     // Calculate voltage compensation
     const float vbatCompensationFactor = vbatPidCompensation ? calculateVbatPidCompensation() : 1.0f;
 
+    // Apply the throttle_limit_percent to scale or limit the throttle based on throttle_limit_type
+    if ((currentControlRateProfile->throttle_limit_percent < 100) && (currentControlRateProfile->throttle_limit_type != THROTTLE_LIMIT_TYPE_OFF)) {
+        const float throttleLimitFactor = currentControlRateProfile->throttle_limit_percent / 100.0f;
+        switch (currentControlRateProfile->throttle_limit_type) {
+            case THROTTLE_LIMIT_TYPE_SCALE:
+                throttle = throttle * throttleLimitFactor;
+                break;
+            case THROTTLE_LIMIT_TYPE_CLIP:
+                if (throttle > throttleLimitFactor) {
+                    throttle = throttleLimitFactor;
+                }
+                break;
+        }
+    }
+
     // Find roll/pitch/yaw desired output
     float motorMix[MAX_SUPPORTED_MOTORS];
     float motorMixMax = 0, motorMixMin = 0;

src/main/flight/pid.c

@@ -134,7 +134,7 @@ void resetPidProfile(pidProfile_t *pidProfile)
         .itermLimit = 150,
         .throttle_boost = 0,
         .throttle_boost_cutoff = 15,
-        .iterm_rotation = false                 
+        .iterm_rotation = false,
     );
 }
 

src/main/interface/settings.c

@@ -321,6 +321,10 @@ static const char * const lookupOverclock[] = {
     };
 #endif
 
+static const char * const lookupTableThrottleLimitType[] = {
+    "OFF", "SCALE", "CLIP"
+};
+
 #define LOOKUP_TABLE_ENTRY(name) { name, ARRAYLEN(name) }
 
 const lookupTableEntry_t lookupTables[] = {
@@ -388,6 +392,7 @@ const lookupTableEntry_t lookupTables[] = {
 #ifdef USE_DUAL_GYRO
     LOOKUP_TABLE_ENTRY(lookupTableGyro),
 #endif
+    LOOKUP_TABLE_ENTRY(lookupTableThrottleLimitType),
 };
 
 #undef LOOKUP_TABLE_ENTRY
@@ -629,6 +634,8 @@ const clivalue_t valueTable[] = {
     { "yaw_srate",                  VAR_UINT8  | PROFILE_RATE_VALUE, .config.minmax = { 0, CONTROL_RATE_CONFIG_RATE_MAX }, PG_CONTROL_RATE_PROFILES, offsetof(controlRateConfig_t, rates[FD_YAW]) },
     { "tpa_rate",                   VAR_UINT8  | PROFILE_RATE_VALUE, .config.minmax = { 0, CONTROL_RATE_CONFIG_TPA_MAX}, PG_CONTROL_RATE_PROFILES, offsetof(controlRateConfig_t, dynThrPID) },
     { "tpa_breakpoint",             VAR_UINT16 | PROFILE_RATE_VALUE, .config.minmax = { PWM_PULSE_MIN, PWM_PULSE_MAX }, PG_CONTROL_RATE_PROFILES, offsetof(controlRateConfig_t, tpa_breakpoint) },
+    { "throttle_limit_type",        VAR_UINT8  | PROFILE_RATE_VALUE | MODE_LOOKUP, .config.lookup = { TABLE_THROTTLE_LIMIT_TYPE }, PG_CONTROL_RATE_PROFILES, offsetof(controlRateConfig_t, throttle_limit_type) },
+    { "throttle_limit_percent",     VAR_UINT8  | PROFILE_RATE_VALUE, .config.minmax = { 25, 100 }, PG_CONTROL_RATE_PROFILES, offsetof(controlRateConfig_t, throttle_limit_percent) },
 
 // PG_SERIAL_CONFIG
     { "reboot_character",           VAR_UINT8  | MASTER_VALUE, .config.minmax = { 48, 126 }, PG_SERIAL_CONFIG, offsetof(serialConfig_t, reboot_character) },

src/main/interface/settings.h

@@ -87,6 +87,7 @@ typedef enum {
 #ifdef USE_DUAL_GYRO
     TABLE_GYRO,
 #endif
+    TABLE_THROTTLE_LIMIT_TYPE,
     LOOKUP_TABLE_COUNT
 } lookupTableIndex_e;