Fix current sensor showing ~1A at idle by calibrating ADC offset

- Add zero-current offset calibration at startup (16 samples averaged)
- Store per-channel offsets (_adcOffsetRight, _adcOffsetLeft)
- Subtract calibrated offset in readCurrentSense() before conversion
- Fixes ESP32 ADC inherent offset causing false ~1A readings at idle

include/motor.h

@@ -41,6 +41,10 @@ private:
     unsigned long _stallStartTime = 0;
     void (*_stallCallback)(float current) = nullptr;
     
+    // ADC zero-current offset (calibrated at startup)
+    int _adcOffsetRight = 0;
+    int _adcOffsetLeft = 0;
+    
     // Pingpong state
     bool _pingpongActive = false;
     int _pingpongBaseSpeed = 50;
@@ -55,6 +59,7 @@ private:
     
     void applyMotorState();
     float readCurrentSense(int pin);
+    void calibrateCurrentOffset();
     void checkStall();
     void updatePingpong();
     int applyRandomness(int baseValue, int randomPercent);

src/motor.cpp

@@ -3,6 +3,9 @@
 // Set to true to enable current sensing (requires R_IS and L_IS connected)
 #define CURRENT_SENSING_ENABLED true
 
+// Number of samples for offset calibration
+#define OFFSET_CALIBRATION_SAMPLES 16
+
 MotorController motor;
 
 void MotorController::begin() {
@@ -28,6 +31,9 @@ void MotorController::begin() {
     analogSetAttenuation(ADC_11db);  // Full range 0-3.3V
     pinMode(R_IS_PIN, INPUT);
     pinMode(L_IS_PIN, INPUT);
+    
+    // Calibrate zero-current offset (ESP32 ADC has inherent offset)
+    calibrateCurrentOffset();
     Serial.println("Current sensing enabled");
 #endif
     
@@ -148,6 +154,11 @@ float MotorController::readCurrentSense(int pin) {
     // Read ADC value (12-bit, 0-4095)
     int adcValue = analogRead(pin);
     
+    // Subtract zero-current offset (calibrated at startup)
+    int offset = (pin == R_IS_PIN) ? _adcOffsetRight : _adcOffsetLeft;
+    adcValue = adcValue - offset;
+    if (adcValue < 0) adcValue = 0;  // Clamp to zero
+    
     // Convert to voltage (0-3.3V)
     float voltage = (adcValue / ADC_MAX) * ADC_VREF;
     
@@ -166,6 +177,26 @@ float MotorController::readCurrentSense(int pin) {
 #endif
 }
 
+void MotorController::calibrateCurrentOffset() {
+#if CURRENT_SENSING_ENABLED
+    // Sample ADC multiple times and average to get stable offset
+    long sumRight = 0;
+    long sumLeft = 0;
+    
+    for (int i = 0; i < OFFSET_CALIBRATION_SAMPLES; i++) {
+        sumRight += analogRead(R_IS_PIN);
+        sumLeft += analogRead(L_IS_PIN);
+        delay(5);  // Small delay between samples
+    }
+    
+    _adcOffsetRight = sumRight / OFFSET_CALIBRATION_SAMPLES;
+    _adcOffsetLeft = sumLeft / OFFSET_CALIBRATION_SAMPLES;
+    
+    Serial.printf("Current sense offset calibrated: R=%d L=%d (ADC counts)\n",
+                  _adcOffsetRight, _adcOffsetLeft);
+#endif
+}
+
 // Pingpong mode implementation
 void MotorController::startPingpong(int speed, int timeMs, int speedRandomPercent, int timeRandomPercent, bool useStallReturn) {
     _pingpongBaseSpeed = constrain(speed, 0, 100);