Crab - 4/5-Inch Fully 3D-Printed FPV Drone Frame

Update: I have added a 5-inch version of the frame (frame_5_inch.stl) and landing skids (landing_skids_5_inch.stl). 

All other parts are compatible with both versions.

The description below refers to the 4-inch version.

The 5-inch version is assembled in the same way, but it requires different components and will have different performance characteristics. 

It also remains very lightweight while delivering excellent performance.

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Crab4/Crab5 is a lightweight, fully 3D-printed frame designed for 4-inch FPV drones.

It’s ideal for both freestyle and long-range flying and can be built entirely at home using accessible materials and components.

Flight Video

Why You Might Like It

- DIY-Friendly: Print and build your own FPV drone using a provided list of components.
- Lightweight: Frame weight is approximately 25–30g depending on material and print settings.
- Freestyle-Ready: True X geometry ensures balanced handling and ease of tuning.
- Sub-250g Build: Total flight weight under 250g with a 4S 850mAh LiPo battery and about 12 minutes of cruise flight time.

Key Specifications

- Max Prop Size: 4 inches
- Flight Controller Mount: 25.5x25.5mm or 20x20mm
- Motor Mount Pattern: 9mm
- VTX Compatibility: DJI O3 Air Unit, O4 Air Unit Pro
- Frame Weight: ~25–30g
- Dry Weight (No Battery): 140–160g
- Flight Weight (4S 850mAh): 240–250g
- Top Speed: Up to 100 km/h

Battery & Flight Time Options

- 4S 850mAh LiPo: ~12 minutes cruise time
- 3S 850mAh LiPo: ~12 minutes cruise time, ~80 km/h max speed
- 4S 18650 3000mAh Li-ion: ~25–30 minutes cruise time
- 4S 21700 5000mAh Li-ion: ~35–40 minutes cruise time

Assembling Video

Recommended Print Settings

frame.stl (rigid filament – PLA, PETG, PETG-CF, PAHT-CF, etc.)

- Nozzle: 0.4mm
- Layer Height: 0.2mm
- Wall Loops: 3
- Top Layers: 6
- Bottom Layers: 6
There’s a relationship between these values to ensure the round tubes of the frame print properly:
Top shell layers = Wall loops * 2
Bottom shell layers = Wall loops * 2

- Infill Density: 3%, This small infill isn't for strength, but to support the top of the frame tubes during printing.
- Infill Pattern: Grid
- Supports: Enabled (Normal, build plate only)

Example default config:
- Wall Loops: 3
- Top Layers: 6
- Bottom Layers: 6

Example lightweight config (for long range):
- Wall Loops: 2
- Top Layers: 4
- Bottom Layers: 4

Example stronger config:
- Wall Loops: 4
- Top Layers: 8
- Bottom Layers: 8

Feel free to experiment :)

canopy_base.stl - bottom part of the canopy (rigid filament)

- Infill: 100%

standoff.stl (rigid filament)

- Recommended Alternative: Use metal standoffs for better crash resistance
- Size: 25mm
- Thread: M2

canopy_top_o3.stl / canopy_top_o4_pro.stl (TPU)

- Infill: 100%

- Use based on VTX: o3 air unit or o4 air unit Pro

- Soft-mounted camera protection and impact absorption
 

landing_skids.stl (TPU)

Flexible landing pads for shock absorption and improved ground stability

Materials Tested

- PETG (translucent): Good stiffness, poor impact resistance. Cracks or breaks may occur on hard landings.
- PETG-CF: Improved stiffness and impact resistance. Handles crashes up to 10m without major damage.
- PAHT-CF (Nylon PA12-CF): Excellent stiffness and durability, I can’t break it by hand. Very high impact resistance. Several times survived a ~100m fall onto grass without frame damage.

Example Build Setup

- Motors: GEPRC SPEEDX2 1404 3000KV (or similar)
- Flight Controller: SpeedyBee F405 AIO 40A Bluejay or GEPRC TAKER G4 45A AIO
- Propellers: Gemfan Hurricane 4023 (3-Blade)
- GPS: GEPRC GEP-M10nano or Flywoo GOKU GM10 Nano V3.1
- Buzzer: JHE20b finder or VIFLY Finder V2 or GEPRC Super Buzzer

Pid and filter settings

Blackbox (gyro scaled roll, debug mode)