From f5d725a2a8ee95b655d736eaeb70813a404adf94 Mon Sep 17 00:00:00 2001
From: Hunter McClelland <hunter.mcclelland@gmail.com>
Date: Tue, 23 Jun 2026 10:36:35 -0400
Subject: [PATCH] SITL: Blimp uses internal SITL::Battery

---
 libraries/SITL/SIM_Blimp.cpp | 55 ++++++++++++++++++++++++++++--------
 libraries/SITL/SIM_Blimp.h   |  4 ++-
 2 files changed, 47 insertions(+), 12 deletions(-)

diff --git a/libraries/SITL/SIM_Blimp.cpp b/libraries/SITL/SIM_Blimp.cpp
index 849c3e8db6a..03aab06e2b7 100644
--- a/libraries/SITL/SIM_Blimp.cpp
+++ b/libraries/SITL/SIM_Blimp.cpp
@@ -44,6 +44,13 @@ Blimp::Blimp(const char *frame_str) :
     drag_gyr_lin_constant = 0.035;
 
     lock_step_scheduled = true;
+
+    constexpr float default_battery_resistance_ohm = 0.01f;
+    battery.setup(sitl->batt_capacity_ah,
+                  default_battery_resistance_ohm,
+                  sitl->batt_voltage,
+                  ambient_outside_temperature_degC());
+
     ::printf("Starting Blimp model\n");
 
     if (strstr(frame_str, "motor")) {
@@ -65,16 +72,18 @@ void Blimp::calculate_forces(const struct sitl_input &input, Vector3f &body_acc,
     //all fin setup
     for (uint8_t i=0; i<4; i++) {
       fin[i].last_angle = fin[i].angle;
-      if (input.servos[i] == 0) {
-          fin[i].angle = 0;
-          fin[i].servo_angle = 0;
-      } else {
-          // filtered_servo_angle() normalises PWM against a fixed 1500 +/- 500
-          // range, but blimp.parm uses SERVOn_MIN 500 / TRIM 1350 / MAX 2200;
-          // the +13.5 degree offset recentres that asymmetric range to a
-          // symmetric -76.5..+76.5 degrees with 0 degrees at servo trim
-          fin[i].angle = filtered_servo_angle(input, i)*radians(45.0f)+radians(13.5);
-          fin[i].servo_angle = filtered_servo_angle(input, i);
+      if (!battery_is_empty()) {
+          if (input.servos[i] == 0) {
+              fin[i].angle = 0;
+              fin[i].servo_angle = 0;
+          } else {
+              // filtered_servo_angle() normalises PWM against a fixed 1500 +/- 500
+              // range, but blimp.parm uses SERVOn_MIN 500 / TRIM 1350 / MAX 2200;
+              // the +13.5 degree offset recentres that asymmetric range to a
+              // symmetric -76.5..+76.5 degrees with 0 degrees at servo trim
+              fin[i].angle = filtered_servo_angle(input, i)*radians(45.0f)+radians(13.5);
+              fin[i].servo_angle = filtered_servo_angle(input, i);
+          }
       }
 
       if (fin[i].angle < fin[i].last_angle) fin[i].dir = 0; //thus 0 = "angle is reducing"
@@ -291,7 +300,7 @@ void Blimp::calculate_forces(const struct sitl_input &input, Vector3f &body_acc,
     
   } else { //MotorBlimp
     for (uint8_t i=0; i<4; i++) {
-      if (input.servos[i] == 0) {
+      if (battery_is_empty() || input.servos[i] == 0) {
           mot[i].throttle = 0;
       } else {
         mot[i].throttle = filtered_servo_angle(input, i);
@@ -396,3 +405,27 @@ void Blimp::update(const struct sitl_input &input)
 
   update_battery();
 }
+
+void Blimp::update_battery()
+{
+  battery.maybe_reset(sitl->batt_voltage, sitl->batt_capacity_ah);
+  battery_current = 0.0f;
+
+  if (!battery_is_empty()) {
+    if (motorblimp) {
+      constexpr float motor_current_scaler_amps = 2.0f;
+      for (uint8_t i=0; i<4; i++) {
+        battery_current += fabsf(mot[i].throttle) * motor_current_scaler_amps;
+      }
+    } else {
+      constexpr float fin_current_scaler_amps = 0.01f;
+      for (uint8_t i=0; i<4; i++) {
+        battery_current += fabsf(fin[i].vel) * fin_current_scaler_amps;
+      }
+    }
+  }
+
+  battery.consume_energy(battery_current, AP_HAL::micros64());
+  battery_voltage = battery.get_voltage();
+  battery_temperature_degC = battery.get_temperature_degC();
+}
diff --git a/libraries/SITL/SIM_Blimp.h b/libraries/SITL/SIM_Blimp.h
index 9bb94074c6a..a892289b25e 100644
--- a/libraries/SITL/SIM_Blimp.h
+++ b/libraries/SITL/SIM_Blimp.h
@@ -30,7 +30,7 @@ struct Fins
   float last_angle;
   float servo_angle;
   bool dir;
-  float vel; // velocity, in m/s
+  float vel; // ang velocity, in deg/s
   float T; //Tangential (thrust) force, in Neutons
   float N; //Normal force, in Newtons
   float Fx; //Fx,y,z = Force in bodyframe orientation at servo position, in Newtons
@@ -84,6 +84,8 @@ protected:
     bool motorblimp = false;
 
     void calculate_forces(const struct sitl_input &input, Vector3f &rot_accel, Vector3f &body_accel);
+    void update_battery() override;
+    bool battery_is_empty() { return battery_voltage < 0.5f; };
     float sq(float a) {return powf(a,2);}
 };