Tiny Toroidal Twist Fan

A tiny (smaller than a “D” battery) multi-stage planetary gearbox powers the Tiny Toroidal Twist Fan, which definitely punches above its weight! A flywheel keeps the fan spinning between twists for a continuous breeze.

Includes both a long handle for maximum twisting power/ergonomics, and a short handle for portability (with reduced power and ergonomics). It's easy to swap handles after assembly.

Each stage has a carrier:sun gear ratio of 3.7272727 so with one twist of the handle and…

3 gear stages is comfortable, and allows you to quickly and easily rev it up to a few thousand RPM using the long handle. You can spin the handle with just a single finger. Start here.

4 gear stages is worth trying (after you've really broken in the other 3 stages), but if you plan to fan yourself for a long time, your fingers will probably get tired, and you'll definitely need the long handle.

5 gear stages works (scroll down to see my video near the bottom), though it is much harder to spin, and it really puts a huge stress on the tiny gears if you try to turn it too fast. I don't think it's very practical, other than for bragging rights to say you were able to spin a 3D printed 1:375.4 gear ratio mechanism by hand.

All of the required print settings/modifiers are already setup in each of the 3MF files, so use File > Open Project… from within PrusaSlicer on the 3MF files to ensure you don't miss anything!

Required Hardware

• A well-tuned printer, such as a Prusa i3 MK3S+. I printed mine using Prusament PETG Clear filament, and Prusament PETG Orange on a Satin Powder-coated print sheet. I discovered that printing just the gear stage all by itself from a completely cold print bed can make the holes closer to the intended size, and requires less cleanup.
• Six tiny M1x8mm dowel rods per gear stage. Three or four stages are typical. I used these from McMaster-Carr: https://www.mcmaster.com/91585A062/ Before I purchased these, I cut and filed 8mm long bits of 1mm thick music wire, but it was tedious.
• Mineral oil or light machine oil

Tools that help speed up the assembly process

• 1mm drill bit for cleaning up holes. I used this: https://www.mcmaster.com/2979N11/
• Pin vice that can hold a 1mm bit. I used: https://www.mcmaster.com/8455A17/

Step 1

First print artcfox-tttfan-gear_stage-carrier.3mf. Do not be alarmed if the gears appear lightly fused together. This is normal!

Watch this post-processing video that shows how to size each hole properly, insert the pins, unfuse the gears, break them in, and then lubricate them:

Once you get the gears spinning freely and lubricated with a light machine oil (mineral oil works great), then print another copy, and repeat the same process to break it in.

Once you have multiple stages printed, you can temporarily screw them mostly together (not all the way, if you try there will be too much friction since the carrier is not yet snapped fully into place), swapping their stacking order to use the gear ratios of the first to break the next stage in even faster.

Print a third copy, and break that one in too. Make sure you add it to the bottom of the stack at first, since it will be easier to spin that way. Once it gets broken in, you can move it up the stack until you have all stages spinning very freely. Don't forget to lubricate each stage with mineral oil, it makes a huge difference!

As explained in the video, you want the pins to be a tight fit in the carrier, but you want a slightly loose fit in the planet gears so they can spin freely.

Step 2

Once you have multiple stages spinning together freely, you can snap a carrier in place on the spline that is on top of the sun gear. It should make a satisfying sound as it locks in place. Once snapped in place, there should be 0.6mm of clearance between the carrier and the backside of the gears in the next gear stage (when screwed down all the way) to eliminate any friction between them. This snap fit will loosen if you force it apart, so try to avoid removing the carriers once snapped in place.

Now comes a slightly tricky part. It might take you a few tries to get things aligned perfectly, but you will need to carefully position the pins from one carrier so they align with the holes in the planet gears as you begin to screw those two stages together. Slowly start to screw the stages together, and when you feel friction try to twist the carrier of the bottom stage to see if the pins are aligned with the holes in the planet gears. If it is, it should spin freely. If not, you won't be able to spin them, so unscrew the stages slightly, rotate the bottom carrier a bit, and try again. The holes in the planet gears are slightly tapered to help make this process easier.

Once the pins are aligned and inserted into the holes in the planet gears, you can finally screw the stages together all the way!

Step 3

Now that you have multiple stages spinning freely, you should print the flywheel using artcfox-tttfan-flywheel.3mf, the toroidal fan using artcfox-tttfan-toroidal.3mf and the handle and the handle retainer using either artcfox-tttfan-short_handle-handle_retainer.3mf or artcfox-tttfan-handle-handle_retainer.3mf.

Use the 3MF files for each because the flywheel needs to be printed at 100% infill so it is heavy and balanced (this keeps the fan spinning between twists!), and the 3MF for the toroidal fan has very specific extrusion width settings to make it printable, light, and strong. (Yes, a standard 0.4mm nozzle can print 0.6mm wide extrusions, because the tip of the extruder nozzle is flat.)

The flywheel will ultimately lock into place on the top-most gear stage, and it has an up and a down. You want to make sure that the side that was not facing the print bed is the side you snap into the top-most gear stage, because the side facing the bed will have an overhang, and it might not lock in place properly if the overhang sags at all.

Before you press the toroidal fan into the flywheel, give the bottom carrier a spin to see it in action, and to see how the flywheel keeps everything spinning. Now press the toroidal fan's spline into the flywheel and give the bottom-most carrier a twist.

The handle is just an extended carrier with grooves on it so you can get a good grip, so be sure the holes for the pins you insert here are sized for a press fit. Each of the pins on the handle should be perfectly straight to keep the planet gears aligned.

Thread on the handle retainer to lock the handle in place, and enjoy your Tiny Toroidal Twist Fan!

Linking 5 gear stages for a 1:375.4 gear ratio

I don't recommend this, as it puts a huge amount of stress on the tiny gears, and it takes an impractical amount of force to twist the handle with the fan attached, but I had to try it!

Advanced Break-in/Assembly Techniques

I definitely recommend building your Tiny Toroidal Twist Fan using the standard assembly/manual break-in procedure, but I wanted to show some advanced techniques in video form.

If you screwed up and used the drill bit technique to add a gear stage onto the fan side that wasn't broken in enough yet and you are having a hard time turning things, all is not lost! If you have a cheap 130 size DC Toy/Hobby motor with a 2mm shaft, you can gently press just the tip of its shaft into the top spline, and power the motor up. If you do this, make sure there is a carrier on the backside to keep the planet gears aligned, and try to hold the motor shaft in perfect alignment. DC motors spin very fast, so it won't take very long to completely break-in a gear stage this way. Before the motor is able to spin your gearbox, you should first break it in manually and lubricate it.

Raw STL Required Print Settings

If for some reason you don't want to use the pre-configured 3MF files, here are the required print settings/modifiers contained in each of the 3MF files:

Print Settings for artcfox-tttfan-gear_stage-carrier.3mf (contains gear_stage.stl, carrier.stl)

Layers and Perimeters:
 Layer height: 0.2mm
 Perimeters: 6
 Seam position: Random
 External perimeters first: True

Infill:
 Fill density: 100%
 Fill pattern: Rectilinear

Output options:
 Complete individual objects: True

Print Settings for artcfox-tttfan-flywheel.3mf (contains flywheel.stl)

Layers and Perimeters:
 Layer height: 0.2mm
 Perimeters: 6
 Seam position: Random
 External perimeters first: True

Infill:
 Fill density: 100%
 Fill pattern: Rectilinear

The flywheel needs to be heavy and perfectly balanced, since it will be spinning at thousands of RPM!

Print Settings for artcfox-tttfan-short_handle-handle_retainer.3mf or artcfox-tttfan-handle-handle_retainer.3mf (contains short_handle.stl, handle_retainer.stl or handle.stl, handle_retainer.stl, respectively)

Layers and Perimeters:
 Layer height: 0.2mm
 Perimeters: 6
 Seam position: Random
 External perimeters first: True

Infill:
 Fill density: 15%
 Fill pattern: Gyroid

Output options:
 Complete individual objects: True

We want the bottom 6mm of the handle.stl to be 100% infill, so right-click on handle.stl, and add a

Height Range Modifier:
 Start at height: 0
 Stop at height: 6

Then right-click on the Range 0.00-6.00 (mm) and set

Infill:
 Fill density: 100%
 Fill pattern: Rectilinear

Print Settings for artcfox-tttfan-toroidal.3mf (contains toroidal.stl)

Layers and Perimeters:
 Layer height: 0.2mm
 Perimeters: 6
 Seam position: Random
 Staggered inner seams: True
 External perimeters first: True

Advanced, Extrusion width:
 Default extrusion width: 0.65
 First layer: 0.62
 Perimeters: 0.65
 External perimeters: 0.65
 Infill: 0.65
 Solid infill: 0.65
 Top solid infill: 0.6

You must set these extrusion widths, otherwise the fan will not print correctly!