Correctly integrating error in PID block to work with dynamic sampling time.

quad/src/graph_blocks/node_pid.c

@@ -48,7 +48,7 @@ static void pid_computation(void *state, const double* params, const double *inp
     if (fabs(params[PID_KI]) <= FLT_EPSILON) {
       pid_state->acc_error = 0;
     } else {
-      pid_state->acc_error += error;
+      pid_state->acc_error += (error * inputs[PID_DT]);
     }
 
     if (pid_state->just_reset) {
@@ -60,7 +60,7 @@ static void pid_computation(void *state, const double* params, const double *inp
 
     // Compute each term's contribution
     P = params[PID_KP] * error;
-    I = params[PID_KI] * pid_state->acc_error * inputs[PID_DT];
+    I = params[PID_KI] * pid_state->acc_error;
     // Low-pass filter on derivative
     double change_in_value = inputs[PID_CUR_POINT] - pid_state->prev_val;
     double term1 = params[PID_ALPHA] * pid_state->last_filtered;