Reversed Motor/Prop Rotation in a Quadcopter

This article explains some of the benefits of reversing your motor and propeller rotation for quadcopter and mini quad flying.

Aerodynamic benefits

One of the most significant benefit of inverting your motor/prop rotation is Aerodynamics. This video explains this very clearly 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, force 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.

Air Disturbance

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, back motors are less likely to go into “stall” at tight yaw turns.

However…

These benefits would not make much a difference during a hover or 3D aerobatics flying.

Other benefits

One of these reasons might be enough to make you adapt to this idea.

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 will :) )

With reversed rotation you are also less likely to get caught by gates or branches (in theory).

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 in a quadcopter

Here is how to apply the custom mix for a pure X quad in boards using Baseflight / Cleanflight or Betaflight

  • Remove all propellers
  • Change motor direction with ESC, BLHeliSuite
  • Go to BetaFlight CLI, type
set yaw_motor_direction = -1 (replaced by the following command)
set yaw_motors_reversed = on
save

(by the way the option is also available in the Configurator with the latest Betaflight firmware)

And now install your props in the reversed order, CW instead of CCW and vice versa, not flipping it upside down. :)

And make sure you check it every time you flash/update firmware in case that setting gets reset, since this is not the traditional way of doing it.

Edit History

  • Jun 2017 – Article Crated
  • Aug 2017 – Added one more benefit to reversed rotation

11 thoughts on “Reversed Motor/Prop Rotation in a Quadcopter

  1. Nigel

    I don’t know if this is another Betaflight change (now on 3.2.1) or if it is specific to my quad, (an Awesone Q95), but I also got the Invalid name error when trying to input the yaw_motors_reversed = ON command. Using the yaw_motor_direction = -1 worked for me.

    Reply
  2. Jase H.

    I’ve run all my setups this way since I discovered tiny whoops two years ago… Betaflight 3.2.0,
    The CLI command is yaw_motors_reversed = ON
    I tried using yaw_motor_reversed, and got an invalid name error. I did a dump check, and discovered it’s “motors”, not “motor” in the CLI command.
    Oscar, could this be a typo in your tutorial? Or maybe Betaflight changed it for 3.2.0? As I remember, 3.1.7 was still “yaw_motor_direction”. Anyhow, cheers Oscar! I love what you do!

    Reply
  3. Jay

    I installed my motors ESC’s and they’re spinning reversed. I can’t access BLHeli32 to change direction(or even get dshot600 to work). I know that I can swap two motor cables to change direction, but I’m pretty happy with the wiring as is. I googled reversed props and found this great page. Will right and left hand threads on the prop posts have any negative effect here? I have directional threads and I think I might have to swap all of the motors now to run reverse prop direction without the props and nuts flying off. Is thread direction an important detail to pay attention too here? I’m new to the hobby. Thanks.

    Reply
    1. Oscar Post author

      It’s best to install them correctly according to motor spin direction. It ensures your props won’t fly away during flight. But if you check that pre-flight everytime then it’s not really that big of an issue :)

      Reply

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