See Downforce (australian antweight) for an example.
Since magnets are illegal in most events (and practically useless in other events), a former AWS champion gave me one hell of an idea.
So, is a fan legal? Would it require a locking bar because it spins? How on earth would i program a brushless esc??? IS IT EVEN META-WORTHY?!
Yes, its legal. Magnets for downforce are also legal. Its only using magnets as weapons that isn’t
Good. I think a fan would be more useful, as some floors are wood.
Some antweight events are running steel floors as of very recently, but still banning magnets (because ants are silly enough already).
People have been using EDF fans for downforce forever in antweights. I’ve tried it personally (back in 2017)
The issue I had with off the shelf fans are quite fragile so if they suck up arena detritus they can shatter quite easily.
So you’re saying I should 3d print one?
3D printed fans (and other similar parts like boat propellers) are Difficult. The layer lines that form when you print with a standard FDM (extruded filament) printer cause a lot of drag, and make things a lot less efficient than any theoretical calculations might suggest. You’ll typically need lots of curves and thin walls, which also makes FDM printing difficult. Tiny fans also need to spin at really high speeds, and 3D printing materials might start to stretch, crack, or otherwise deform under the forces.
Sometimes people resin print prototype fan blades, which gives you the geometry and the surface finish, but most resin parts are still very fragile, and tend to shatter like glass when they fail.
That’s not to say it’s impossible, though. You could try a different kind of fan - a centrifugal blower might be more easily printed, can deal with a little ingress, and they have a lot of static pressure on the suction side. There’s also been a huge explosion in cheap drone/RC plane tech since Joe built his in 2017, so maybe there’s some new ducted fan options that are more robust, or maybe you can figure out an intake filter solution that works.
If you do go this route though, treat any exposed and un-shrouded DIY fan like a spinner and always run it in a test box or enclosed arena. If it goes wrong you’ve got a plastic shrapnel grenade!
how on earth would i 3d print a centrifugal blower?
If you think it might be possible you start trying and see what happens. Part of the fun is figuring things out!
Stolen Of Approval 
How did you cram all that in there!?
Would it be legal in non-spinner events, though?
Yes because it’s not a spinner.
Maybe ask the EO for whatever event you would be planning on making one for.
Also I’m just gonna put my 2p in and prepare to have massive batteries and a very large ESC to handle the current and I would advise against printing ANY fan/prop elements.
