← David Ettel

DIY Drone

PS70: Introduction to Digital Fabrication — Harvard, 2024

Abstract

I built a 70mm class drone from scratch with a carbon fiber frame and 3D-printed propellers. The project involved component selection, frame design and fabrication through six iterations, propeller design through four iterations, soldering, and flight controller configuration. Major challenges included selecting compatible components, soldering tiny pads on the AIO board, and iterating on the frame and propellers until they worked together.

Completed drone Full setup with radio controller

Material List

ComponentSource
Happymodel Crux F405HD ELRS AIO flight controllerDefianceRC
1104 Micro Brushless Motors 4300KV ×4Amazon
Ovonic 11.1V 450mAh 3S LiPo batteryAmazon
RadioMaster T8L radio controllerAmazon
Carbon fiber sheetLab
SLA resin, Kapton tape, solder, hot glue, M2 screws, wires, cable tiesLab
ELRS radio receiver + antenna, JST connectorsLab
Flight controller Brushless motors
LiPo battery RadioMaster T8L controller

Choosing Motors and Flight Controller

I chose the 70mm class to be able to iterate quickly on the frame and propellers. I chose a commercial all-in-one (AIO) flight controller rather than building a custom ESP32-based board because loop frequency requirements for stable flight (8 kHz default on STM32) far exceed what an ESP32 can sustain (250 Hz–1 kHz). The Happymodel Crux F405HD was selected for price and availability.

Frame Iterations

The frame went through six iterations before reaching the final design:

  1. Naive PLA print — too flexible
  2. Reinforced PLA — still insufficient rigidity
  3. Rotated motor mounts — better geometry
  4. AIO board mounting integrated
  5. Switched to carbon fiber sheet
  6. Waterjet-cut carbon fiber with through-holes for motor shafts (final)
Frame prototypes in chronological order Waterjet-cut carbon fiber frame

Propellers

The propellers went through four iterations. Research (Popișter 2025) confirmed that resin-printed propellers produce higher thrust than FDM. Final specs: 40mm diameter, 1.5mm hub bore, two-blade design generated with Claude.

  1. FDM print — insufficient resolution for blade geometry
  2. FDM scaled up — still inadequate
  3. Resin with downloaded CAD
  4. Resin with Claude-generated STL (final)
Propeller iterations Final resin propeller Failed resin prints

Soldering

The AIO board has very small solder pads. After hours of failed attempts, I used Kapton tape masking to isolate individual pads, which finally made clean joints possible.

Closeup of tiny solder pads on the AIO board

Battery

Single-cell batteries were too large for the frame, so I ordered a 3S LiPo (11.1V, 450mAh). I made a custom wire-to-socket connection for safe disconnection and secured the battery to the frame with diagonal cable ties.

Battery mounted with cable ties

Controlling the Drone

The flight controller runs Betaflight. The RadioMaster T8L transmitter communicates via ExpressLRS (ELRS), which provides low-latency RF link. Configuration involved binding the receiver, setting up motor direction and ESC calibration, and verifying sensor axes in Betaflight configurator.

Current Status and Future Work

Three of four motors failed before flight testing could be completed. Replacements are on order. Once flying, planned additions include:

Files