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Carbon Fiber Sub-250g FPV Quad Copter

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Quinlan Smith

Project Timeline

Mar 2025 - Apr-2025

OVERVIEW

I set out to design and build a 3-inch FPV quadcopter capable of rivaling standard 5-inch quads in performance while maintaining a total weight under 250 grams, making it legal to fly without FAA certification. I designed a custom carbon fiber frame and performed Finite Element Analysis (FEA). The assembly phase required precision soldering, wire routing, and PCB fitment testing. I then designed and 3D printed structural TPU components to protect internal electronics and transfer impact forces to the frame. The final stage involved PID tuning and comprehensive flight controller and ESC setup, resulting in a compact, durable, and high-performance quadcopter that delivers exceptional speed and agility while remaining FAA-compliant.

HighlightS

Designing the frame to achieve the highest possible factor of safety was equally important. During finite element analysis (FEA), I simulated common crash conditions to evaluate how and where forces would be applied to the frame upon impact. Since carbon fiber has a very high yield strength but low fracture toughness, I optimized the geometry to distribute stresses evenly and minimize weak points. By carefully balancing weight and structural performance, I ensured the frame would withstand most crash scenarios without fracturing.

SKILLS

Mechanical design and 3D modeling in SolidWorksFinite Element Analysis (FEA) for structural validationDesign for manufacturability (DFM) using waterjet cuttingStress and impact simulation under crash conditionsFactor of safety optimization for lightweight structuresAerodynamic and weight optimization for UAV performanceTolerance analysis and mechanical fitment testingSolidWorks (3D CAD modeling, assemblies, FEA)Betaflight configuration and tuningBlackbox log analysis for flight performance evaluationESC and flight controller firmware setupWaterjet machining of carbon fiber compositesCarbon fiber layup and material handling techniquesPrecision soldering and electronics assemblyWire routing and PCB fitment testing3D printing (TPU and structural materials) for protective componentsRapid prototyping and iteration of UAV partsIterative design and testing under real-world conditionsRoot cause analysis of mechanical and electrical failures

Additional Details

This project was motivated by the goal of developing a compact, sub-250g quadcopter that maintains the high-speed performance of commercial 5-inch freestyle drones while remaining within legal weight limits. The design objective was to create a small form factor quad capable of flying through a standard window, allowing operation from indoors while preserving the immersive experience of FPV flight.

To begin, I established key design constraints:

  • Total weight under 250 grams (including battery) to comply with FAA regulations.
  • Motor-to-motor diagonal distance of 120 mm to ensure a compact footprint.
  • Target top speed of at least 100 mph to match the performance of larger freestyle quads.
I designed the carbon fiber frame in CAD, performing multiple iterations and simulating crash loads to optimize the strength-to-weight ratio and minimize stress concentrations. After selecting suitable PCB dimensions, I chose the flight controller, ESCs, receiver, and video transmitter that fit the compact design. The frame was then manufactured via water jet cutting for precision and rigidity.

Next, I assembled and soldered all electronic components, followed by configuring the firmware and software stack. To enhance durability and vibration isolation, I designed a multi-piece 3D-printed canopy that channels impact forces into the frame and protects sensitive electronics and the gyro sensor.

Finally, I conducted PID tuning and filter optimization using black box log data to refine flight characteristics. The result is a lightweight, agile, and high-speed quadcopter that achieves professional-level performance while remaining fully legal and compact enough for convenient indoor operation.

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