speed20: 平滑线性转向消除死区断崖

src/camera.cpp

@@ -962,12 +962,15 @@ static void steering_update()
         }
     }
 
-    if (std::abs(deviation) < g_cfg.deadband) {
-        // 死区内 → 直行
+    // 平滑线性转向: 偏差从死区边界开始缩放，消除死区断崖
+    double effective = std::abs(deviation) - g_cfg.deadband;
+    if (effective <= 0) {
         servo.setDutyCycle(1500000);
     } else {
-        // 比例控制: 偏差 → 归一化 → × 增益 × 满偏占空比差
-        double offset  = deviation / (newWidth / 2.0) * g_cfg.steer_gain * 300000;
+        double half_w = newWidth / 2.0;
+        double norm   = effective / (half_w - g_cfg.deadband);
+        double sign   = (deviation > 0) ? 1.0 : -1.0;
+        double offset = norm * g_cfg.steer_gain * 300000.0 * sign;
         double duty_ns = std::clamp(1500000.0 + offset, 1200000.0, 1800000.0);
         servo.setDutyCycle((unsigned int)duty_ns);
     }