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I was just wandering off into my imagination and then it hit me: I should make a LEGO fan?

I mean, how hard could it be?

enter image description here

It is actually very hard for me. No matter how much ratio I put on it, it would not blow air! Even when it does it always ends up blowing backwards. Please give me some tips.

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  • 13
    If it's blowing backwards, then put the blades the other way around.
    – OrangeDog
    Jun 16 '20 at 9:30
  • 3
    @OrangeDog Or sit behind it.
    – Jason C
    Jun 16 '20 at 17:06
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    @Nerd please label your sketch, i.e. sizes of gears and bricks...
    – Uli
    Jun 17 '20 at 9:35
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    @Nerd you can check Hobbyking.com where you will find lot of propellers and electric engines that will adapt to the size and shape of your build. Building a propeller with lego bricks may be dangerous (perhaps was not your intention but just to warn you).
    – Ignacio
    Jun 17 '20 at 10:40
  • 1
    I question the safety of this idea - LEGO holds together really well, but centripetal forces will eventually thrown parts of it. So you will need a cage for the fan blades such that the biggest gap is smaller than the smallest component. Also needed to keep fingers and hair out of the moving parts. Perhaps use a regular fan but build a LEGO case for the body? And perhaps make a one-piece LEGO-style fan boss for the middle of the blades of a normal fan.
    – Criggie
    Jun 17 '20 at 21:23
26

A fan is just 1/4 of a drone, right? Check out this lego drone that actually flies, for inspiration. https://youtu.be/wUVvQk7XLd4

Drone photo

The blade part in question is 89509

Propeller 1 Blade 14L with Two Pin Holes and Four Axles

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  • 23
    @Nerd: what is a desktop but a stationary n-copter, where n=1...
    – smci
    Jun 16 '20 at 5:39
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    @smci And tilted 90 degrees to whatever side to direct the airflow into whatever direction you need it.
    – Mast
    Jun 16 '20 at 5:48
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    "A fan is just 1/4 of a drone, right?" -- Kids these days...
    – Jason C
    Jun 16 '20 at 17:05
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    @Nerd While it's hard to tell without a picture, from your description of it blowing air "around the fan and not towards your face", it just sounds like the airflow design isn't right. The shape of the blades is the most important part. Also fans that are meant to be very directional sometimes have some fins or something in front of the fan to direct the airflow, that could help too if the blades aren't ideal. The other thing is the shape of any case you build around the fan can impact the airflow. And finally it's possible your motor isn't fast enough and you may have to add gears/belts.
    – Jason C
    Jun 16 '20 at 18:17
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    I mean, the drone bit is a joke, obv, but seriously speaking the drone flies because it moves air in the right direction. So if you built one of the propeller assemblies as shown in the video, you'd be able to move a significant amount of air. Then all you need to do is angle the assembly so that the air goes where you want. Jun 17 '20 at 3:58
17

The easiest way to do this would be to use a motor with a high speed (or gear up a lower speed motor) and then attach one of the larger propeller elements to it. You can probably build a custom prop, but it might be challenging to build something with the proper blade angle while keeping it light and strong enough to not break apart when rotating quickly.

Something like 2952 should work:

enter image description here

You mentioned that your original design was blowing air backwards. This can likely be fixed by reversing the motor direction.

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  • 8
    If it's blowing air backwards, the easiest thing to do is to simply turn the fan around and point the back toward you. .
    – Valorum
    Jun 16 '20 at 14:27
  • 9
    @Valorum Great point. A fan is never blowing backwards, you're just sitting on the wrong side of it. Jun 16 '20 at 14:56
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    Flipping the blade around will not make the air blow in the opposite direction. This is so important that I feel I have to repeat it: flipping the blade around DOES NOT change direction of air flow. It only makes it flow with less efficiency/less force. You need to reverse the motor direction to reverse air flow. The alternative is to use a blade that is opposite handedness but flipping a blade around will not make it the opposite
    – slebetman
    Jun 17 '20 at 5:48
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    As for custom blades: it's not hard if you can control. A thin (like about a mm), flat sheet works already. Just put it on a angle of like 8 degrees and you'll notice it works as a prop.
    – paul23
    Jun 17 '20 at 13:46

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