Hit a skatepark and you’ll find skaters thinking about all kinds of things, not the least of which is how the hell that kid nailed a 1080. The one thing they probably aren’t thinking about, however, is physics. Ironic, given the laws of physics dictate everything they do.
But physics is the only thing two University of California San Diego professors had on their minds when they set out to apply scientific method to skating and get students to understand the science of the sport. It required creating a mechanism by which inputs could be altered, outcomes studied and the entire process repeated.
A mechanism like, say, a robot.
“It’s the scientific method, like what Galileo did when he experimented with acceleration by rolling balls on an incline,” said mechanical engineering professor Nathan Delson. “We can add sensors and move mass, change speed, test timing changes and take the data to computer simulation to look at it further. You can prove what is needed in different tricks.”
Watching Tom Schaar land the world's first 1080 — that's three complete revolutions — or Brandon Westgate do an upstream backside Smith grind will make you think skateboarders defy the laws of physics. By building a robotic skateboard, Delson’s students found they could test and measure the forces behind the tricks and determine which factors mattered and which didn’t.
The students built a skateboard with an acrylic deck after discovering it isn’t the weight of the deck that matters, but the quality of the trucks. The better the trucks, the more the students could challenge the board and push the limits of what Roboskater could do.
“The weight of the deck didn’t seem to be that much of a factor – the longer radius in the base mattered more than weight,” student Elizabeth Strub said during a demonstration with skating icon Tony Hawk last week in San Diego. “Friction was the big problem.”
One thing they discovered early on is pumping matters. In humans, pumping is achieved with the arms — a move instinctive to good skateboarders. Roboskater features two red arms attached to a center column, each with its own motor and a brass weight of exactly 338.6 grams. Servos raise and lower, or “pump,” the arms. The servos are controlled with a microprocessor that performs five functions, including recording and transmitting data on how the board’s changes affect its movement.
“As far as we’ve discovered, it’s moving your moment of inertia and the center of mass — lifting your arms is a lift of the center of mass,” Strub said. “It’s based on pendulums, shortening the pendulum moved the pendulum faster. In a skater, when they pull their arms in it changes the moment of inertia and makes them go faster.”
Being able to affect speed in the curve also matters, said student Tallha Ahmed.
“Timing is a big part of what makes this work,” he said.
Paul Schmitt, known as Prof. Schmitt among skaters, has built and sold more than 13 million decks since he was 14. Schmitt helped get the project off the ground because he sees physics as the basis for all skating.
“We’re always fighting friction and gravity, and we also use both for tricks,” he says. “They’re unconscious uses, but vital. Gravity lets us go down a wall and then we use muscles to create energy by pumping to resist gravity on the way back up.”
Skaters use their weight to generate energy or to take it away throughout any maneuver, and perfecting timing of tricks involves pushing those forces against each other.
Roboskater and a working knowledge of physics could help better design ramps and half pipes. The team built its simulator to examine how physics affects a trick called frontside air. Next, they plan to look at the Ollie, the move Hawk says changed skateboarding forever.
As cool as Roboskater is, it’s frail and lacks the muscle control and motor coordination of a human. It doesn’t move very fast.
“It’s hard to get a robot to move quickly,” Delson says. “Most move relatively statically. And we’re going to need more mass to do an Ollie.”
