MOT_THST_EXPO setting from spreadsheet Ardupilot

[Jai.GAY]

@Leonardthall

As to why I give the advice to not increase the expo over 0.8.

oh dear.

@Leonardthall

The end result is I have not seen measured data with an expo over about 0.8.

I have to use 0.99 for this drone using T-Motor MN2806 KV650 Hobbywing digital ESC (turned off Low RPM Power Protect) with Arducopter 4.2.x & 4.3.x.