Brand new Tello, first flight. I tap the takeoff icon, then slide the slider over to takeoff. The props rev up for about 2 seconds then they stop. I have done the firmware update the app prompt me to. I've done the IMU calibration multiple times. Wasn't sure for the IMU calibration if I hold it in position or take the prop guard off and let it free stand, so I did both way. Any help would be greatly appreciated.