Scientists at Georgia Tech are calling this racket-swinging automaton ESTHER (Experimental Sport Tennis Wheelchair Robot), a robotic tennis player that can zip around the court and return human shots.

The sporty bot is the brainchild of Matthew Gombolay, an associate professor of robotics in the School of Interactive Computing. Gombolay wanted to develop a better training challenge than a stationary ball feeder, one that would act like an always on-call sparring partner or even team up in doubles matches.

The result is ESTHER, a modified tennis wheelchair that can race to balls at 10 meters per second and potentially outplay its human opponent.

"The wheelchair has the ability to rapidly move around the court and get into position to hit a ground stroke," Gombolay explains in an online video. "ESTHER's high-torque motors can surpass a tennis player's average side-to-side acceleration, suggesting the potential to outmaneuver human opponents in future design iterations."

"ESTHER can move up to two meters after the ball is launched to hit a successful return, which is comparable to the maximum distance moved by human players between 80% of shots," the researcher continues.

The device was named in homage to renowned wheelchair tennis player Esther Vergeer, who held the world No. 1 ranking in women's wheelchair tennis from 1999 until her retirement in 2013. Working with more than 20 students, Gombolay authored a paper on building ESTHER, which was accepted for publication in the Institute of Electrical and Electronics Engineers Robotics & Automation Society's Automation Letters (IEEE RA-L).

The team arranged a network of high-resolution cameras around a tennis court and used computer vision algorithms to help ESTHER recognize an incoming tennis ball. Using cameras from different angles, they could triangulate where the ball is in space and feed this information to ESTHER. The team reached a breakthrough when they successfully and consistently programmed ESTHER to locate the tennis ball coming toward it, and to hit a return.