Hello, I bought about six Tello drones. It's been about 10 months since I used Tello. Hovering on multiple devices is not possible. The center of gravity calibration, firmware update, does not hover and the gas is still pulling in the 3 o'clock direction indoors. What is the solution to this problem?

Dear customer,
Could you please tell me whether there is any error message shown to you? According to our testing, if the environment isn't suitable for the VPS of Tello, it may not hover stability in the air. And please confirm whether there are any propellers or guards that have been broken. It will also influence it to hover. Or please send us a video showing your issue via support@ryzerobotics.com. Our colleague will help you. Thanks a lot.  

Hi may asking also a just bought my tello, but on didn't hovering well, tello is moving slowly without control.

Tukang Jalan Jalan Posted at 5-16 13:21
Hi may asking also a just bought my tello, but on didn't hovering well, tello is moving slowly without control.

Dear,
Please control the drone with Tello APP and notice whether there is erro information, which will be useful for us to know what the problem is.
In respect to the problem you described, it may be caused by improper flight enviroment, such as poor light, reflective surface, ect, which make the VPS of drone disable. Besides, please make sure propellers and propeller guards are intact. If the conditions aforementioned are good, you can also do the IMU calibration, clink and refer to the tutorial video.https://www.ryzerobotics.com/tello/videos
If the problem still persists, please contact us via support@ryzerobotics.com.

Hope my reply could help you!