   if (!adk.isReady())
   {
     // Set LED to red when USB is not connected.
-    rgb_led.set(1,0,0);
+    rgb_led.R(1);
+    rgb_led.G(0);
     
     // Turn off motors.
     for (size_t motor_idx = 0; motor_idx < NUM_MOTORS; ++motor_idx) {

           "\"args\": \"%s\""
           "}",
           error_message, input_buffer);
  
  // Report error over USB. 
  adk.write(strlen(output_buffer), (uint8_t*)output_buffer);
  
  // TODO: if performance issue, remove this line.
  // Report error to debugging console.
  Serial.println(output_buffer);
}

/**

    motor[0]->velocity(), motor[0]->current(),
    motor[1]->velocity(), motor[1]->current()
  );
  send(motor_update);
}


