Olympic Curling’s Got Its Eye On The Hog

One sport we’ve really enjoyed watching at the Vancouver Winter Olympics is curling. I think it’s the intense strategy that makes these games so interesting, especially when you’re relaxing in the wee hours of the night and enjoy something less frenzied than many of the events. Being a technical guy, I couldn’t help but notice the green lights that would illuminate on the stones when they were released. An electronic rock? What’s that all about?

Actually, the electronics is located in the handle, not the rock. It’s there to serve a special purpose, which is to detect an improper delivery. Specifically, a player must release the stone before it reaches a black foul line called the “hog line.” Otherwise players might just go sliding down the ice holding onto the stone to give themselves an advantage in shot accuracy.

This automated hog-line-violation-detection system is called Eye on the Hog. It is manufactured by Startco Engineering Ltd. of Saskatoon, SK, Canada. Interestingly, the device started out as a fourth-year design project for a group of electrical engineering students at the University of Saskatchewan. The students and their professor came up with a system that installed a permanent magnet in the bottom of the rock and embedded a magnetic field sensor in the ice that was connected to a display. Startco refined the design to bury the magnet in the ice and keep all the electronics on-board the rock handle. The university and students receive royalties for their work on the design concepts.

Here’s how the production system works. The largely plastic handle is attached to the granite curling stone through a hole that runs vertically through the center of the stone. Within the handle is the electronic components, magnetic sensor, batteries, LED indicators, tilt sensor, and touch sensitive grip. The electronics is activated when the rock is tilted to clean its running surface before each throw. The LEDs flash to indicate the system is working. When the player grips the touch sensitive handle to deliver the rock, the LEDs go out so they won’t be distracting. The crucial operation comes when the stone reaches the hog line. When the rock is released prior to it reaching the hog line, the green LEDs flash until the center line of the rock crosses the hog line. Then they illuminate for 5 seconds to indicate a valid delivery.

This is what you see if the TV camera is focused closely on the curling stone during release. I didn’t see any invalid deliveries in all the games I watched. If one did occur, the red LEDs on the handle would have flashed for 25 seconds to indicate a violation. How does it know to do that? If the grip detects it is being touched while the magnetic sensor detects a magnetic strip embedded in the ice exactly one stone radius before the hog line, then it knows that the stone has not been released before the front edge of it has reached the line. If the grip is touched after the stone crosses the hog line, it also activates the red violation LEDs. You can’t fool this system with fancy hand work.

How accurate is the Eye on the Hog? It’s specified at 3 mm or 0.12 inches at 10 ft/sec. That’s far more accurate than the best human eyes that it replaces for judging hog line violations.

Startco has a nice animation of the Eye on the Hog in action on their Web site. Check out the Technical Info page. If you find this wireless technology as fascinating as I did, you may also enjoy reading the manual and seeing how they set up the magnet locating jig to get that extreme accuracy on the ice. Who knows, you might even find yourself becoming captivated with the intriguing sport of curling.

Update: Meet Curly, the Curling Robot That Beats the Pros - Wired Magazine 8/23/20