If I were to make a LEGO fan how would I make it blow air on me?

Question

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?

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.

If it's blowing backwards, then put the blades the other way around. — OrangeDog, Jun 16 '20 at 09:30
@Nerd please label your sketch, i.e. sizes of gears and bricks... — Uli, Jun 17 '20 at 09:35
@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
As I also have tried building something like a fan, my notifications: it's a matter of proper propeller blades. Although you might think it would be enough if you stack together some plates which end up in a curve (like the scribble in the question) this will not move the air very well. I suppose there are to much air swirls and distortions. try to find some nice smooth plates which you can fix with an angle or use parts which are made for ventilations. another helpful effect might be channeling the air flow like a hair dryer, which sucks air in and blows it in just one direction. — Bernd Wilke πφ, Jun 17 '20 at 14:28
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
But @Criggie, i do not have a fan that i can use scrap off of i do have one but i actualy use it when sleeping in my bed at night (plus my wife would get mad cause she also uses it) and thats excatly why i wanted to make one so that i could actualy feel air and not have to use the fan my wife has — Nerd, Jun 18 '20 at 22:12

score 26 · Answer 1 · edited Jun 15 '20 at 21:13

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

The blade part in question is 89509

edited Jun 15 '20 at 21:13

jncraton

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answered Jun 15 '20 at 21:01

Mr. Shiny and New 安宇

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Thanks for the tips but its not! I should have been more specific, its a desktop fan! One that you use to cool a office down or something – Nerd Jun 15 '20 at 22:10
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@Nerd: what is a desktop but a stationary n-copter, where n=1... – smci Jun 16 '20 at 05:39
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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 05:48
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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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Also I'm not sure how into math you are, and it might be a little advanced, but if you really want to get into it check out this PDF on fan aerodynamics, the Wikipedia page on axial fan design, and Google for "fan design", "axial fan engineering", "fan blade design", etc. – Jason C Jun 16 '20 at 18:20
And btw i used lego flat plates and stacked them in a way that it could go around in circles more smoothly – Nerd Jun 17 '20 at 01:48
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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. – Mr. Shiny and New 安宇 Jun 17 '20 at 03:58
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@Nerd Have you tried reversing the stacking order? Can you attach a photo of your fan blade to your question (and an indicator of which way it spins) rather than an MS Paint illustration? – Chronocidal Jun 17 '20 at 09:28

jncraton · Answer 2 · 2020-06-17T12:18:15.053

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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:

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

edited Jun 17 '20 at 12:18

answered Jun 15 '20 at 18:13

jncraton

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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
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@Valorum Great point. A fan is never blowing backwards, you're just sitting on the wrong side of it. – Nuclear Hoagie 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 05:48
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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

If I were to make a LEGO fan how would I make it blow air on me?

2 Answers2