This guide covers which parts to print in TPU, which to print in something stiffer, and the settings that matter, based on two of Oscar Liang's printing guides, the Prusa knowledge base and Adafruit's NinjaFlex guide.
What to print in TPU and what not to
Oscar Liang's list of typical prints for FPV: GoPro mounts, VTX antenna holders, FPV camera mounts, arm guards, radio grips and a screen protector for goggles. All of these take hits or flex, so they go in TPU.
His material advice is short. TPU is flexible and works as a shock absorber, which is why it suits arm guards and antenna mounts. PLA is easy to print but brittle, with low impact resistance, and ABS is more challenging to print. He says he uses TPU and PETG "99% of the time": TPU for flexible parts, PETG for rigid ones.
In practice: anything that should give way in a crash goes in TPU, and anything that has to keep its shape goes in PETG.
Where to get the files
Oscar points to Thingiverse, Yeggi and MyMiniFactory for STL files. He adds that some drone manufacturers and retailers publish STL files on their websites, so check the product page of your frame before searching elsewhere. Look for files made for your frame model and camera size, because a mount for a different arm thickness or camera width will not fit.
Before you print: filament
- Diameter. Check that the filament matches your printer. Oscar notes that most filament today is 1.75 mm, but 3 mm also exists.
- Hardness. Flexible filaments are sold by Shore hardness. Prusa puts TPU typically around 60A-90A and says that the softer the filament, the harder it is to print. For comparison, Adafruit lists regular NinjaFlex at 85A and the stiffer Cheetah at 95A.
- Moisture. Prusa lists flexible filaments as hygroscopic and says wet filament can be hard to print. Oscar dries filament in an oven at 40-50°C for a couple of hours, or uses a filament dryer.
Direct drive or Bowden
Where the extruder sits matters more with TPU than with any other common filament. On a direct drive printer the extruder is right above the hot end. On a Bowden printer it pushes the filament through a tube, and soft TPU can buckle or drag on the way.
Oscar's 2018 write-up shows the Bowden problem in practice. On his Ultimaker 2+ the TPU kept getting stuck partway through 3-hour prints. He blamed friction in the printer's original rubbery tube, and replacing it with a slippery PTFE tube with a 4 mm inner diameter fixed it. Another tip he was given, though he never needed it: a drop of sewing machine oil on the filament before it enters the tube. One commenter under his post adds that the gap between the extruder gear and the tube entry is the real issue on many Bowden printers, and that closing it makes TPU printable.
Adafruit's NinjaFlex guide recommends 30 mm/s, but says simple parts on a direct drive printer can print faster, at 60 mm/s. Oscar's current printer recommendations are direct drive models, and he specifically notes TPU support for one of them.
Settings that matter
The Prusa knowledge base gives these rules for flexible filaments:
- Speed. Print slowly. A typical speed is 20 mm/s, and the recommended maximum is 30-40 mm/s. Faster printing risks a clogged nozzle or filament tangled in the extruder gears.
- Temperature. Prusa recommends a nozzle temperature of 230-245°C, depending on hardness and brand, and suggests going 5°C higher than usual to reduce filament resistance. The bed should be at 60-75°C, higher for larger parts.
- Extruder tension. Loosen the idler so the gears push the filament through gently. If they press too hard, the filament can wrap around the gears.
- Retraction. Lower retraction means less risk of clogging and tangling. Prusa says it is fine to turn retraction off completely and then raise it while watching the results.
- Clean nozzle. Make sure the nozzle is clear before loading TPU. Prusa suggests a cold pull if you are not sure.
- Bed surface. TPU sticks very well. On a smooth or satin sheet, Prusa uses glue stick or Kapton tape as a separation layer. A powder-coated textured sheet does not need one.
Other sources give different numbers, so treat these as a starting point, not a recipe. Adafruit recommends 240°C with a 50-65°C bed for NinjaFlex. Oscar printed at 220°C with a 60°C bed, 105% flow and 40 mm/s, against 70 mm/s for PLA. Cooling is where they disagree most: Prusa says to keep cooling off, while Oscar ran the part fan at 80%. Start from the profile your filament manufacturer or printer maker provides and change one thing at a time.
How stiff the part comes out
Slicer settings change how the finished part behaves, not just whether it prints. Prusa's advice: for more strength, add infill and perimeters. To keep the part flexible, reduce the number of perimeters and top and bottom layers.
For FPV this gives you a way to tune a part without changing the model. A camera mount that lets the camera move too much in flight can be printed with more perimeters and infill. An arm guard that cracks instead of bending can be printed with fewer.
Prusa also warns that flexible filaments bridge poorly and handle overhangs badly. Supports are hard to remove, so Prusa suggests increasing the gap between the part and the supports to 0.3 mm in Z and at least 100% in XY. When you choose a model, a design that prints without supports saves you this trouble.