"Move your throttle travel to maximum, trim to minimum, press the button on the Rx to set in failsafe settings, then move travel and trim back to normal.
Check it has taken by looking at Mission Planner radio calibration page, turn the Tx off and…"
"To help we will need a lot more info than 'it won't take off'
What motors, batteries, frame weight, props, calibrations done, version of APMCopter, and maybe a photo or 2.
The more info you put in your post the more someone can help."
"OK, just reread your post and I see now.
I have also noticed this when we were doing grid scans, that when it leaves the waypoint it seems to pick up too much speed then backs off. Most noticeable in a tail wind or still conditions but not so…"
"That sounds typical of having a delay in the waypoint.
If there is any delay, any, then the copter comes to a complete stop then continues, and that is what your problem sounds like.
Have you tried saving your waypoint file and looking at it in a…"
"One of the windings is not firing.
It usually means a burnt or faulty winding in the motor, but as you have tested it on another esc and the motor works, then it must be the esc.
The clincher would be to put a known good motor on the suspect esc and…"
"Have you checked your vibration levels?
Errant vertical behaviour was what I encountered way back when they changed algorithms.
Do a flight and log your IMU data.
There is a good Wiki on vibration management."