Smashspeed

Smashspeed measures how fast a badminton shuttle is smashed, from nothing but a phone video filmed side on. It has 83,000 users across 130 countries, about 45,000 on Android and 38,000 on iOS.

I started in May 2025 by hand labelling: I boxed shuttlecocks frame by frame in side-on footage.

By 10 June 2025 my early YOLOv5 model put a box on the shuttle and a speed beside it.

I trained it in Colab on an A100, on more than 15,000 images from Smashspeed's own footage, and it runs on the phone.

Public shuttle datasets are filmed from broadcast angles like this one.

The app needs this view instead: side on, level with the player.

Monocular video gives no depth, so two taps on a court line set metres per pixel. The app reads speed from the leading edge of the blur and smooths it with a Kalman filter.

I shipped version 1.0 on the App Store on 24 July 2025, and I built it solo in SwiftUI. It holds 4.8 out of 5 there and 4.3 on Google Play.

In August 2025 it reached #1 in Sports on Taiwan's App Store, #2 in Vietnam and #4 in Sports on Google Play.

Android came next: I rebuilt the app in React Native starting on 31 July 2025, and I ran it side by side with the iOS app before it shipped to Google Play.

We film most of our reels at badminton clubs. An interview with a national champion passed 500,000 views, and videos about Smashspeed have passed 10 million. I built the team up to nine people.

In summer 2026 I redesigned both apps from scratch in React Native, and I trained GridTrackNet on 22,000 images to supersede my original 15,000-image YOLOv5 model.