The Engineering Complexity of a Simple 3D Printed Air Blower

This instructable/video is about making an experience of what looks like a very simple air blower. I tested different fan designs and configurations, ducts, and more. If you looking for something very scientific you probably would be disappointed as all the tests are pretty basic using basic measuring instruments.

But despite that, it still gives a rough idea in which direction to go if you want to design something similar yourself.

I doubted if I should make an instructable/video about this air blower, but it is pretty useful in some cases and so much fun to use, so why not. I spent way too much time designing and testing it, haha. R&D just swallows the time like nothing, it is crazy. All parts are 3D printed, except the propeller and all electronics of course.

It uses the DC brushed 12-24V K215Y 390 motor and some basic fans. If it is hard to find the exact parts locally there is only one option - to ship directly from China.

If you don't want to design it yourself, you can find all the files and more details about this project on my Patreon page - https://www.patreon.com/posts/54463733 There I also make post-project updates/mods/improvements, behind-the-scenes projects, and more other little stuff. Thank you so much if you decide to support my work! ❤️

At first, I designed it only for Dewalt 18-20V batteries, but later I also made it for Milwaukee M18 and Makita LXT 18V batteries. IMPORTANT! Makita will require you to buy an original spare part to make it work! Part number - 643852-2. More info about it: https://www.thingiverse.com/thing:4459529 Meanwhile, on Dewalt and Milwaukee, you can just use the 6.3mm male spade terminals to make contacts.

Provided links are affiliates. You can buy anything through them at no extra cost to you.

Main Parts of the Project:

90mm propeller - https://s.click.aliexpress.com/e/_A20TXw
K215Y 390 motor - https://s.click.aliexpress.com/e/_9ACXWY
PWM controller 4.5-35V - https://s.click.aliexpress.com/e/_9iDMoo
Switch 16mm - https://s.click.aliexpress.com/e/_9AgOQM
Small drill bit set to make propeller fit - https://www.aliexpress.com/item/4001055672258.htm... (You need 2.2mm bit)

Step 1: Version 1

This is the air blower version one that I made years ago using scrap parts. The electronics were an old 6V high-rpm motor, 12V lead-acid battery, step-down module, switch, and volt-ammeter.

I ran the motor at 8.5V. I probably would be able to run it directly without the step-down module as it gets a lot of air and doesn't heat up (at least at 8.5V). But I guess that was too much YOLO for me.

Step 2: Version 1 < Version 2

I made this air blower for two very specific reasons:

To vastly speed up the ignition process in a grill.
To regain the loss in heat when coal covers in ash.

And it worked quite well. But like you can guess, it is so annoying to handle this thing. Well, that’s why I finally decided to make version two of it, which turned out to be just on a completely different level in performance and engineering.

Step 3: Why Not EDF Motor?

To make it, this time I will be 3D printing instead of using wood. This way everyone who wants to make it can just print the parts. Yes, I know the files are not free, but if you want to save a cup of coffee worth of money you can very easily make something similar by just mounting the motor on a wood piece and attaching the battery to the bottom. It won't be elegant but it will perform just as well.

To make it, first I spent around half a week designing it. You can very quickly design if you know exactly what you need, but when you don't - you spend a lot of time until you reach that final design. At first, I wanted it to look something like a bigger version of a hairdryer and I could just slap a brushless RC EDF motor in that duct, but it doesn't really make sense for two reasons:

If you run it at designed power it consumes just ridiculous amounts of power. At 12V - 300W, it is insane 25Amps. Good luck powering it with batteries and keeping it cool when it is stationary and not in a flying RC plane.

If you run it at half the power, let's say ~150W you will still need a very capable battery. At this point, EDF motor + controller + batteries = the cost not worth to DIY. At the same price point, you just could buy a cheap leaf blower and make an adapter to the batteries that you have from your 18-20V tools.

Step 4: Motor and Propeller Combo Decides the Design

But a more sensible way of approach affects design a lot. The shaft of this brushed RS390 DC 12-24V motor is only 2.3mm in diameter. To mount a propeller firmly is a hard obstacle if you want that sucked air would go down along the motor. That would provide great cooling for it but the propeller would want to go of the shaft. But if you reverse the airflow, you just need to make a slightly smaller hole and push it on. The pressure from the blades will always force the propeller onto the shaft but you will get less cooling.

Step 5: Duct Reduces Performance?

But here is where the main problem arises. I did some tests and I saw that an additional duct will heavily reduce the airflow. I know it is a very raw test method (later it will be better tests), but the faster air rushes to the fan, the more voltage it will generate. And this doesn’t look good for a duct. But could it be the propeller's fault?

Step 6: Diving Into Studies About Fan Designs

So I did some research about them. In one study I found that the outer ring can actually increase the static pressure of a fan and in another that more blades on a propeller will give more pressure at a higher flow rate. And this is exactly what I need to force the air through the duct.

I searched thingiverse.com and found exactly what I need - an 11-blade propeller with the outer ring. High RPM of this motor will give more pressure – check. Outer ring – check. More blades – check. However, there was still a noticeable loss in the airspeed...

Step 7: No Duct, No Guards, No Problem?

At this point, I decided to go for the open frame and not a foolproof design where blades are hidden in the duct. From the first tests, the duct just reduces airflow and I NEED ALL THE AIRFLOW I can get. There still will be air suction from the back to cool the motor and the short housing will be wider to somewhat protect the blades.

I printed all the parts using a PET-G filament. It has great layer adhesion, can withstand higher temperatures compared to PLA and parts turned out to be very rigid.

A small downside of it is that you can get stringing, but you can easily rip most of those strings and eliminate what’s left with a lighter.

Step 8: Assembly of the Blower

This is an assembly step, if you don't care about it you can skip to the next one.

The motor will fit perfectly in the hole and you will need to secure it with two (M2.5x6mm length) bolts and few washers.

At the top of the handle will be two holes for the (M4x8mm) inserts. These are usually used in wood but work great with non-brittle plastics too.

To attach both parts you will need two (M4x25mm pan head) bolts and washers. Later I additionally glued both parts with epoxy as those won’t need any disassembling in the future.

The bottom part where the speed controller and button will be attaches just with six (3x10mm) screws.

But before you do that, first it will be easier to press in these tiny (M3 4.2x6mm) inserts. You can do it very easily with a soldering iron and a scrap wood piece. This will give that perfectly flat surface.

So, it’s time to put in electronics like the PWM speed controller, button, and wire everything up. But before that, we will need the last part – the battery holder. In my case, it is designed for the DeWalt 18 or 20V battery. It is annoying that all these manufacturers have their mounting types and there is no universal solution. But I spent more time and re-designed battery holders and other parts for two other brands – Milwaukee and Makita (IMPORTANT! Makita will require you to buy an original spare part 643852-2 to make it work!). I will provide all SketchUp and STL files on my Patreon page. I know, I know, not free – BOO! But look, these projects take so much time to properly design, and you can get them for only a price of a nice cup of coffee, so I hope you understand. Huge thanks to everyone who supports my work, it really means a lot.

If you have the same brand battery, you will need a few (6.3mm) spade terminals. They will push into the contacts of the battery. We need to hot-glue them and the part with connectors.

Finally, it is the soldering part. If you don’t know how to wire up all the parts, here is a scheme (before the last picture) that is very easy to follow.

Now we just need to secure the bottom part with four (flush M3x10mm) bolts and we are pretty much done.

Step 9: 3 Vs 11 Blades TEST

So now is the time for way better tests. I made this distance and airspeed measuring test setup and started testing various configurations. I tested the 3-blade propeller, 3D printed one, both with ducts, an old air blower, and the previously mentioned EDF motor.

And here are the results. I compiled them into the chart. First, the most obvious thing that I noticed is that propeller type made a huge difference when placed into a duct.

3-blade design only had left 62% of its original airspeed performance, meanwhile, 11-blades managed an astonishing 89%.

When compared two different propeller designs directly, no duct performance was slightly better than the 3-blade design. But when placed into the duct results heavily favored 11-blades.

Step 10: 3 Vs 7 Vs 11 Blades TEST

But what if we try something a little different like this 7 blade propeller? Well… I didn’t expect these results. It actually produced higher airflow speed with a duct than without one. It even surpassed the open design of 3 blades.

This has to be it – the best design so far, right?

Step 11: Power Consumption

And I almost believed that until I checked the power consumption. 3 blade design draw around 2A at 19V. But 7 and 11 blade designs draw twice the current! We are talking 40W vs 80W of power… And those two designs are not even close to producing twice the airspeed. We basically just overloading this tiny motor and it runs very inefficiently and gets too hot very fast. So there is yet another important factor – the motor itself.

Step 12: Imperfections

It also doesn’t help that 3D prints will usually have these imperfections. That will result in more vibration at high speeds and reduce the potential performance, especially in the duct. (https://en.wikipedia.org/wiki/Ducted_fan)

Step 13: Final Thoughts

But how it will compare to the EDF motor at the same wattage? Well, the measurements were almost identical, 3.9 vs 4 m/s. That is such a great result for this propeller and brushed motor combo compared to the expensive brushless one. Yes, I know that RC EDF motors are designed for the most lift and not for the best airflow, but still... It also costs almost 10x the price of the brushed 390 motor.

At this point, it is very clear that the 3-blade design and the open frame is the best choice for this tiny motor. It moves quickly a lot of air and consumes only ~40W. And with an integrated speed controller, you can use it for all kinds of things as it lets you reduce speed and noise.

This turned out to be a very interesting topic for me. In the future, I will probably test more 3D-printed propeller designs. But so far these cheap propellers work so well, that I doubt I will find anything better. But time will tell, I guess. :)

I hope you enjoyed this making and testing process. There is always so much to learn. If you made or wanted to make something similar, I would love to hear what is your experience. Or maybe you have studied fluid dynamics and have some great tips, please share them in the comments!