This article explains some of the benefits of reversing your motor and propeller rotation for quadcopter and mini quad flying. This is known as “props out”.
One of the most significant benefit of inverting motor/prop rotation would be aerodynamics. This video explains this very well and here is my personal understanding of it.
Center of Thrust
When propeller spins at a stationary spot, the centre of thrust (COT) is right in the middle (i.e. prop hub). But when the quadcopter begins to fly forward, forces from air resistance is applied on the the propeller and thus shifting the centre of the thrust to the advancing blade (the red circles in the last image).
This means the advancing blade will tend to generate more thrust and pull more air than the retrieving blade.
On the front two propellers, the COT is located outward, and that of the back props are inward. The faster the copter is flying, the further the COT is away from the hub. That implies the back propellers would be working less efficient than the front propellers due to principle of moment.
Furthermore, the air turbulence from the front propellers can make the back propellers work even less efficiently. (That’s one reason why “stretch X” frame was designed to combat this issue by moving front motors further away from the rear motors)
By reversing the prop rotation, the centre of thrust of the front propellers are now inward while that of the rear props are outward, and it compensates the penalty we get with the dirty air disturbance from the front props.
Better Yaw Turns
With inverted rotations, the back motors are less likely to go into “stall” at tight yaw turns. The benefit and effect is especially noticeable for smaller quadcopters, like tiny whoops and other micro quads with low toque motors.
These benefits would not make much a difference during a hover, or for 3D aerobatics flying where the props could be spinning both directions.
One of these reasons might be enough to make you adapt to this idea of props out.
Since your front props are not spinning toward the FPV camera but rather outward, your camera lens won’t collect dirt from the props, such as grass or water. However your FC stack will :)
But when you use turtle mode, the props runs the opposite direction when you are up side down, and you are more likely to get your lens dirty.
With reversed rotation you are also less likely to get caught by gates or branches, as it would just bounce off obstacles in collisions.
Another positive thing in changing prop rotation is that most of us often get into situations where we have no CW props left but many CCW, or the other way round. That happens because we are left or right handed and tend to make more corners to one specific direction instinctively. Now we can just change rotation and keep flying.
How to Reverse Motor Rotation
Here is how to do “props out” on a quadcopter in Betaflight.
Remove all propellers before proceeding!
Enable “Motor Direction is Reversed” setting in Betaflight Configurator
Alternatively you can do this in BetaFlight CLI, by entering
set yaw_motor_direction = -1(command name changed in newer Betaflight version) set yaw_motors_reversed = on save
And now install your props in the reversed order, CW instead of CCW and vice versa. But do not install it upside down :)
Make sure you double check the “Motor Direction is Reversed” setting in Betaflight every time you flash/update the FC firmware, sometimes settings get reset after flashing.
Do I Recommend Props Out?
Yes and no.
I personally just run default rotation (props in) on larger quads (3″ or larger), because the benefit isn’t as noticeable, and I am lazy. I don’t have to keep reminding myself to re-configure my quads every time I update firmware.
However I always run props out (reversed rotation) on the micro quads (anything smaller than 3″), such as my tiny whoops and toothpicks. The flight performance improvement is noticeable and worth the effort IMO.
- Jun 2017 – Article Crated
- Aug 2017 – Added one more benefit to reversed rotation
- May 2019 – Updated guide with Betaflight Configurator screenshot