It can be useful to spin the motors/props in reverse.
E.g. to reverse the trust and fly upside-down, or to flip over a crashed quad (turtle mode).
On most brushless motors, you can reverse the spin direction with the correct signal from the speed controller
On brushed FCs, the ability to reverse the props is not common, only a few models from Blade have this feature so far. Driving the props in both directions requires software and hardware abilities. So if your flight controller does not have dual FETs for each motor output, you cannot reverse motor polarity over software!
The Blade Nano QX 3D FC can spin the motors in reverse to fly upside down.
The Blade Inductrix FPV+ FC can spin the motors in reverse to flip itself upright.
To my current knowledge, no other brushed micro FC has this ability. If you know otherwise, please comment below or email firstname.lastname@example.org!
If you are already thinking about motor direction,
I suggest to also read this article about prop direction! Read on..