EDIT

There is now a Platypus V2: https://www.thingiverse.com/thing:3974160

TL;DR

There will not be one. You really need to read everything below to avoid wasting a ton of plastic. The planet says thank you.

Subscribe to my YouTube channel for FPV content created with the Platypus and other drones.

UPDATE April 10, 2019:
As a test, I cut several bottom plates out of 2mm thick carbon fiber sheet. Seems to work wonderful, but that also required the files to be altered slightly.

So today, I'm adding 4 new files:

• V2_top-plate-with-ducts-for-2mm-cf-plate.stl - for using with a CNC-cut 2mm carbon fiber bottom plate AND 22mm tall nylon standoffs.
• V2_top-plate-with-ducts-for-4mm-printed-bottom.stl - for using with a printed 4mm bottom plate AND 22mm tall nylon standoffs.
• V2_gopro_plate.stl - a lower and more impact-resistant design of the GoPro plate. For securing it to the frame, use one screw, zipties and imagination.
• V2_fpv-cam-bracket-for-2mm-plate.stl - a simpler and lighter design of the FPV camera bracket to be used with a 2mm CF bottom plate. For securing it to the frame, put it on the standoff and use a single zip tie.

What is this?

The Platypus is a fully 3D printable cinewhoop frame that runs 2.5 inch props and can comfortably carry a GoPro. These types of drones can be flown around soft targets relatively safely and are usually used to capture cinematic video shots in very high quality.

Here's a video from the maiden flight of the prototype: https://www.youtube.com/watch?v=9bHwSCeT5Rk
And here's another video of it chasing a 5inch racing drone: https://www.youtube.com/watch?v=AqAkuWobcas

Why does it exist?

Because I simply wanted to have a cinewhoop and didn't feel like getting a carbon frame at the time. Looked far and wide, and found a couple other models online, but those had some issues when printed, so I ended up drawing my own to address those issues and have a perfect one (to me at least).

Why not 3 inch?

• Weight.
  To make a rigid 3d printed frame, it has to be thicker than its carbon equivalent. And that would make for a very heavy print, since the motor mounting struts would need to be super thick (up to 5-6mm perhaps?) to be stiff enough when printed with more common filaments like PETG.
• Size.
  This one fits comfortably on an Ender 3 bed, and probably fits some smaller printers too. For a similar 3inch, I'm just not sure it would work on the most popular, smaller DIY machines out there.

How much does it weigh?

My current build, printed in carbon fiber filament, weighs 464 grams all-up with a GoPro Session 5 and a 4S 850mAh battery. The updated V2 with a lower deck (22mm standoffs used instead of 25mm) and a 2mm carbon fiber bottom plate runs 447g AUW.

What are the recommended electronics?

• Motors. There is a 12mm mounting pattern. Go with 1407 or 1408 stator with a KV rating of 3200-3600. Mine runs T-Motor F20 II 3750kv.
• Stack. It only accepts a 20x20mm. I went with Spedix IS100.
• Camera. It only accepts a micro, 19mm width. I went with Runcam Racer.

What about props?

You will have to custom cut them. Use this tool to make sure you have them in perfect balance: https://www.thingiverse.com/thing:3334348
This is important!!! If you do not have the props in perfect balance, you WILL destroy the ducts. Want to guess how I know that?

How well does it crash?

Yo, it's a plastic drone... If you crash it hard, it will break.
That said, the frame construction makes it pretty rigid and my prototype has withstood most lighter impacts just fine. Since it is not designed to be used like a racing or a freestyle drone, I reckon you should get plenty of smooth flights around soft targets before you break it. Take it slow, y'all!

Are there other models out there?

Yes, certainly. And I'll tell you about the ones The Platypus was influenced by.
An important note, I guess: I am in no way affiliated with Andy Shen or CrissCrossFPV mentioned below, and am not being paid for making these endorsements. It's all my personal opinion.

• First and foremost, take a look at the granddaddy of them all, the Squirt: http://www.shendrones.com/squirt-v2
  I mean, nothing beats that thing, it's gorgeous and functional and beautiful and just... wow. My verdict: go and buy one instead of wasting your time on making your own 3D printed one!
• If you're like me and you like to make things instead of buying them, take a look at Nutmeg: http://www.shendrones.com/nutmeg
  It's just so pretty :] A tiny 2inch one, but still, really cool. Since Andy knows what he's doing, I bet his model flies much better than mine.
• Last but not least, this thing was a great inspiration. Meet Tankette: https://www.thingiverse.com/thing:3312526
  I printed several of these, all with many changes along the way, but couldn't make it to be exactly what I wanted. Still, I think that CrissCrossFPV frames are all pretty cool. Go see for yourself: https://crisscrossfpv.com/

The base construction of Platypus was directly influenced by the Tankette and you'll find many things in common between the two. Make no mistake though, the Platypus was drawn up from nothing and it is not a remix of the Tankette.

Also, it turns out that I was working on my design at about the same time Andy was working on his Nutmeg. It was so fun to read his blog post where he explained pretty much all of the issues and challenges I had stumbled upon when making The Platypus. And yes, some parts of the Nutmeg design made it into The Platypus, because they just made sense and worked so well.

What material should I print this in?

Quadcopters do crash, and you don't want a brittle plastic thing hitting brick walls, now do you? What you want is a good balance between flexibility and stiffness, which makes PETG an obvious choice. I'm sure something more durable like CF Nylons or similar would work excellent, but that's still a bit of an exotic material for most.

Anything else before I start printing?

Yes. This: this model has no tolerances to it!
Basically, you need to expect that you will have to sand down or cut some parts to join them. This is on purpose, because you want to achieve the tightest possible fit.

What slicer settings should I use?

Depends on your setup, but I'll give my suggestions based on Cura and a 0.4mm nozzle that I'm using. One important thing is to have your retraction settings on point. Like, really really on point.

Below, I'm giving a baseline for the settings shared by all frame parts, and then a list of parts with their specific tune. Read carefully and make sure to double-check the slicer output in "Layer view".

Shared settings:

• Top Layers: 3
  Just so the finish on the top is good enough.
• Bottom Layers: 2
  Same as above, but bottom needs one less layer.
• Fill Gaps Between Walls: Nowhere
  With this, you minimise the number of travel moves, which will reduce stringing.
• Z Seam Alignment: Shortest
  Again, to minimise the number of travel moves.
• Infill Density: 90%
  So that you don't get too many blobs on the surfaces.
• Infill Pattern: Zig Zag
  If your filament flows well, this at 90% density will result in almost no gaps between the lines.
• Infill Overlap Percentage: 20%
  You really need the infill to fuse with the walls.
• Infill before walls: On
  It seems that this also helps with the adhesion quality.
• Enable Retraction: On
  Yeah, and you need your retraction settings on point!
• Combing mode: Within Infill
  So that when the nozzle does travel on top of printed parts, it does not screw with the walls.
• Avoid Printed Parts When Traveling: On
  Means the nozzle will mostly travel through thin air (which is why your retraction needs to be on point).
• Enable Print Cooling: Off
  You generally want the best layer adhesion you can get, but feel free to turn this on if absolutely necessary for your filament of choice.
• Build Plate Adhesion Type: Brim
  I tend to use brims to avoid any potential warping, but feel free to set this to whatever works for you.

top-plate-with-ducts (rotate the part 180 degrees, so that it's printed upside down):

• Layer height: 0.2-0.3mm
  Because you want a reasonable print time!
• Wall Line Count: 2
  This setting means 2 inner walls and 2 outer walls, which will ensure that the ducts consist only of "shell" (4 perimeters in total), which is exactly what you want.
• Outer Before Inner Walls: On
  You want to avoid any travel moves that could compromise the very surface of ducts for them to be as smooth as possible. There are no overhangs in this part, so you're safe.
• Generate Support: Off
  There are no overhangs in this part.

bottom-plate (print as shown):

• Layer height: 0.2mm
  This part is not as tall as the ducts, so you can go with a lower number to increase the quality.
• Wall Line Count: 3
  This is super important! With 3 walls, you will not have any infill material around the screw holes at the tips of the arms, which is exactly what you need for maximum durability.
• Outer Before Inner Walls: On
  Similar to the ducts above, there are no overhangs in this part, so you can have this on to improve surface quality.
• Generate Support: Off
  There are no overhangs in this part.

duct-lips-print-2x (print as shown, you need 2 sets):

• Layer height: 0.1-0.2mm
  As there is a slight curve to this part, you want a better quality. See how low you can go while retaining a reasonable print time.
• Wall Line Count: 3
  This is super important! Screw holes. Same as above with the bottom plate.
• Outer Before Inner Walls: Off
  Now, here we do have an overhang, so we definitely do not want to print the outer walls first.
• Generate Support: Off
  The overhang isn't that bad and it should print just fine without supports.

fpv-cam-bracket (print on its face):

• Layer height: 0.1-0.2mm
  You will want decent quality on this one as it needs to be somewhat strong.
• Wall Line Count: 2
  This makes the plates consist of only "shell", which is what you want. No need for infill on thin plates as that will make them weaker.
• Outer Before Inner Walls: Off
  There are some overhangs as well, so we again do not want to print the outer walls first.
• Generate Support: On
  Well, yeah. I suggest you support the hexagonal holes, although if your bridging is excellent, be a rebel and turn this off.

gopro-plate (print as shown):

• Layer height: 0.1-0.2mm
  As this part also has a slight curve, see how low you can go while retaining a reasonable print time.
• Wall Line Count: 3
  This is super important! It's those screw holes again.
• Outer Before Inner Walls: Off
  Because of that overhang.
• Generate Support: On
  Just to make sure the overhang prints good enough. If you printer handles overhangs like a boss, turn this off.

gopro-plate-spacer (print as shown):

• Layer height: 0.2mm
  It's just a spacer, and a tiny one.
• Wall Line Count: 3
  This is super important! As above, you want it to only consist of "shell".

Any additional hardware for assembly?

Yes of course. You will need:

• 12 25mm hexagonal nylon standoffs (22mm for the V2)
• 21 M3x6mm screws (for standoffs)
• 3 M3x20mm screws (for gopro plate) (none of these for V2, instead get another M3x8mm or so)
• 2 20mm standoffs with 4 screws (for gopro mount attachment to the plate)
• hardware for your 20x20mm stack
• hardware for your fpv cam
• hardware for your motors

Any other assembly tips?

Certainly.

• Do not over-tighten the screws that hold duct lips in place, you'll skew them.
• If you find that the props are closer to one side of the ducts than the other, tighten the motor screws on the opposite side more.

Where do I get a GoPro mount?

The ones from CrissCrossFPV fit.
Here's one for the Session 5: https://www.thingiverse.com/thing:3216011
And here's one for Hero 6/7 (take the symmetrical one): https://www.thingiverse.com/thing:3205504

Anything else?

Go wild with The Platypus. I can't wait to see these guys ripping around airspace across the globe!
Make sure to post pictures of your makes, and you're more than welcome to make whatever adjustments you think this model needs. Let's get those remixes in!