I'm New here so I'm sure there is a post about my problem.  Sorry I could not find anything on my issue.The Tello wont lift off.  The front right will lift off but it falls over to the back left.  I replaced the propellers and they are placed correct (checked a milllion times). I recollobrated and still not luck.  Is it a bad motor?  They all fire up and seem to move at same speed.  Need help, I' a teacher and about to launch 30 or these with students and trying to figure out everything that could go wrong before it does.  Thanks.

Hi, thank you for reaching out. I will highly recommend you to coordinate this concern directly to the Tello support at https://www.ryzerobotics.com/support for them to help you further. Thank you!

Dear customer,
Sorry to reply you late. In regard to your problem, I can know that all the motors can be started-up and there isn't any error code shown on your screen. Maybe the propellers are really installed on the wrong motor. Please watch the video and pictures, they can help you solve the problem. The link to the video is https://www.ryzerobotics.com/tello/videos. Thanks a lot.