How Hard Does a Longsword Hit? Building a HEMA Impact Tester

People at HEMA training ask "how hard does a longsword actually hit?" Nobody knows. There are no numbers. So I built a device to find out.

What it is

A weighted pendulum with an accelerometer mounted behind the strike face. You hit it with a sword. It captures the impact spike at 3200Hz, calculates peak force in Newtons, and writes the data to an SD card.

Hardware

ESP32-S3 microcontroller. ADXL375 high-g accelerometer over SPI, up to 200g. SD card module. The sensor mounts inside an ABS box bolted to the pendulum. The pendulum is a weighted plate on chains with an HDPE strike face.

Firmware

Minimal. Poll at 3200Hz. Detect spike above threshold. Capture 100ms window. Write CSV to SD. Serial output: peak g, force in Newtons, impact duration. F = ma. Known mass, measured acceleration.

Why it matters

Every fighter who hits the device is a piece of content. "How hard does a fendente actually hit?" is a reel that writes itself. Nobody in HEMA has published these numbers before.

Current state

Research, prototype, firmware, and analysis script all done. Next: build the physical pendulum and take it to training.