I can use python send command to Tello edu and got ok back, battery? works as well, after I delay 3sec after send "command", I send "takeoff" and got error back, is there something else I should do? such as turn on engine, etc.?
It should work the way you are trying.
I suppose you can fly Tello using your phone app?
My EDU tends to overheat when it is parked. This could be the problem.
What does the LED show?
You can turn the motors on, but this is not necessary.
Spinning propellers prevent Tello from overheating.
You can do it by sending "rc -100 -100 -100 100" (like pushing the right stick down/left and the left stick down/right)