The Tennis Ball Machine of Tomorrow
Dec 06, 2023
For tennis players, tennis ball machines are a convenient tool for practicing. The market offers a wide variety of devices ranging from simple machines with a limited set of controls to sophisticated systems with a wide range of settings. As much as today’s ball machines have matured, new developments in artificial intelligence and computer vision allow the ability to add features that provide new possibilities. This article describes a few new possibilities for conventional ball machines equipped with a camera and artificial intelligent powered software.
The Tennis Ball Machine of Tomorrow has Arrived
What can tomorrow’s ball machine do more than today’s ball machines? To understand the answer one must first understand how the current available ball machines basically work.
After a player has positioned the machine on the court, loaded balls into the ball-tray, and configured on an operator panel which drill he wants to practice, the player moves to the other side on the court and uses a remote control to start the ball machine delivering balls. And the machine does that, shooting ball after ball like a tennis metronome to the player who tries to hit them back.
Above: Nikki Roth
But what happens when the player isn't ready to return the delivered balls? The ball machine doesn’t care, and shoots one ball after the other until the player uses the remote control to stop the delivery of balls — producing unused balls the player later needs to collect.
Tomorrow’s ball machines will be different. After a player has positioned the machine on the court, loaded balls into the ball-tray, and configured on an operator panel which drill he wants to practice, the player starts the machine and moves to the other side on the court. But contrary to today’s ball machine, no ball will be delivered until the ball machine sees the player on the other side of the court and sees that he is ready to hit balls back. After the player has returned a ball from the ball machine and is ready again, the next ball is delivered. If for some reason the player is not ready to hit balls, the ball machine just doesn’t shoot a ball to the player. In short, the ball machine isn’t a tennis metronome any more.
Tomorrow’s ball machine has the means to see and recognize what happens on the other side of the court. If there is a player who is ready to hit the ball, the machine will deliver this ball. The machine can also see where the player is on the other side of the court and either shoot the ball into the player’s comfort zone or not. A ball machine with vision can also recognize when the player is serving a ball and deliver a ball when the serve bounces in the service box, a sequence that allows the player to practice serve and volley or be ready for the next ball.
The tennis ball machine of tomorrow is here. A group of enthusiasts in South Florida have converted a commercially available tennis ball machine by modifying the ball release mechanics and using a computer.
CO system equipped with a simple USB camera. The artificial intelligent software running on the computer is using standard computer vision (OpenCV) and neural network (Ultralytics Yolov8) libraries for detecting and tracking objects in the images recorded by the camera. This modified ball machine, named simply QuickNik, is based on the portable Slinger Bag, and can still be used like today’s machine with it’s periodic shooting of balls, but the implemented AI software extends the range of features with new tennis drills which are only possible on tomorrow’s class of ball machines. Check out a few of these new drills below in more detail.
Image by rawpixel.com on Freepik
Get Ready - this is one of the few stances that dominates every tennis game. Only in the ready stance is the player prepared for the challenges that come with the next ball. Therefore, it is important that the player not only practices but also is prepared and focused for the next shot. Today’s ball machine delivers the balls to the player regardless — if the player is ready or not. With QuickNik, it shoots balls only when the machine recognizes that the player is in the ready stance. And after the ball has been delivered, the machine expects that the player gets out of the ready stance and later back into the ready stance again before the next ball will be delivered by the ball machine. The main purpose of this ‘Get Ready’ drill is to keep the player moving and resume the ready stance repeatedly. This drill is not possible with today’s ball machine because they lack the means to observe the player and the artificial intelligence to determine what the player is doing.
Serve and Volley - is a style of play in tennis where the player moves quickly towards the net after hitting a serve to attempt to hit a volley afterwards. Practicing this with today's ball machines is almost impossible, because it requires time coordination between the moment when the serve is hit and when the ball machine delivers a ball that can be considered as return-of-serve. This is something ball machines are not designed and built for. However, with QuickNik, it has the means to see the balls and the players actions. The ball machine is able to recognize that the player is serving a ball and is able to track the ball. At the moment when the machine detects the ball bouncing in the service box it delivers a ball to the server as the return-of-serve ball. It is the player’s choice either to advance towards the net and poach the return ball or stay on the service line and hit the ball as usual back.
Hit and Reset – is a drill that a tennis pro likes to practice with their students to improve their footwork. This drill focuses more on the player’s movement than hitting a ball back. In the drill the player is in the ready position in the middle of the baseline and the tennis pro delivers a ball into one of the corners of the court. The player moves to the ball, hits it back, and then resets again. As long as the tennis pro is monitoring the player, this drill is effective. QuickNik can assist the player in practicing this drill because the machine has the means to observe the player’s actions. After the ball machine has delivered a ball, the machine expects that the player moves toward the ball and later back into the middle of the court before shooting the next ball.
In the past the ball machine manufacturers have invested a lot of development efforts controlling the speed, spin, and trajectory of the ball that resulted in very sophisticated ball machines. There are ball machines available that allow the player to select a sequence of shots, each of them with different characteristics in speed, spin, and direction, creating very challenging drills. But the manufacturers neglected until now the moment of the ball delivery, which is an important factor in complex drills like ‘Serve and Volley’. Until now their devices only provide a simple control that allows the player to select the ball delivery rate. But controlling the moment of ball delivery requires more than just a simple timer, it requires feedback from the player like position and movement in addition to the tracking of balls that the player has hit.
In this context one can consider QuickNik as a working model that shows what can be accomplished when the ball machine has the means to observe and interpret what happens on the player’s side of the court and deliver a ball precisely when a certain event has occurred.
Above: Nikki Roth
To be clear, the three drills described above and implemented in QuickNik represent only a fraction of additional drills that a ball machine with vision and event- controlled ball delivery could offer to the player. The time and technology is ripe for the ball machine manufacturers to address the old fashioned periodic ball delivery and implement an event-triggered ball delivery in conjunction with a vision system recognizing these events. The result of such a development would be a new class of interactive ball machines that are more complete tennis practice machines with features not available with today’s machines.
Although QuickNik is specifically designed and build for the tennis sport, other ball machines used in sports like pickle-ball or baseball could also profit from the technology implemented in QuickNik.For example a baseball pitching machine could be developed in such a way that it pitches on a ball when the player is indicating with his stance that he is ready for the ball. The possibilities of ball machines with vision and event-driven ball releases are endless and over time such interactive devices will be available on the market because of this simple economic rule:
If a ball machine manufacturer is not adding new features to his machine – there is always a competitor that will happily do this work.
Written by Hugo Rytz. Hugo Rytz has a PHD in physics and worked on multiple technical software projects until his retirement in 2016. He is living in Boca Raton, Florida. Being an active tennis player he is working as a freelancer in porting the new AI technology into tennis ball machines to turn these devices into better training machines. Hugo Rytz can be reached by email email@example.com. Action photos courtesy of Nikki Roth.