Question: Can you run a [BLDC motor](http://en.wikipedia.org/wiki/Brushless_DC_electric_motor) backwards without damage?

Is it OK to drive a model airplane BLDC engine backwards while landing, so it gets a little "reverse thrust" and come to a stop a little quicker on the runway?

Is it OK to drive a model helicopter BLDC motors backwards so it can hover upside-down?

Or do I need to design the hardware so that it never drives the motor backwards, under any circumstances, no matter what the pilot on the ground does at the transmitter?

Answer: 
Yes, you can drive a brushless DC motor in both directions.

See, for example, the [On Semiconductor MC33035](http://www.onsemi.com/PowerSolutions/product.do?id=MC33035PG) brushless DC motor control chip, which has a pin to control direction.

Here's a little explanation from p. 9 of [the datasheet](http://www.onsemi.com/pub/Collateral/MC33035-D.PDF):

> 
> The Forward/Reverse input (Pin 3) is used to change the
>  direction of motor rotation by reversing the voltage across
>  the stator winding. When the input changes state, from high
>  to low with a given sensor input code (for example 100), the
>  enabled top and bottom drive outputs with the same alpha
>  designation are exchanged (AT to AB, BT to BB, CT to CB).
>  In effect, the commutation sequence is reversed and the
>  motor changes directional rotation.
> 
> 
> 

I believe you do have to be careful about "shoot-through"-- if you're trying to switch the direction of current flow in a winding, you have to be sure to turn one set of FETs off completely before you turn on the other set, or you may inadvertently short your power supply.

You might google "adaptive gate drive" or "dead time" for more details.
I know this is a very old question from 2010, but for the sake of other people with the problem today, brushless drone and model motor controllers now commutate the motor by sensing the back emf of the winding. There is no hall effect sensors, so you just have to reverse any 2 of the 3 motor wires.