With the LEGO Mindstorms EV3 Educational Set (45544) and ping-pong balls on hand, you can build a ball-shooting cannon. The gun can be controlled from a smartphone using the RoboCam app.
You can see how the gun turns and shoots in the video.
The design of the cannon holds 4 ping-pong balls with a diameter of 4 cm. I used Artengo balls bought in Decathlon. The exact diameter of the balls is 39.6 cm.
Also, 5 rubber bands for money are used for assembly: one to return the ball holder to its place (do not pull it too tight) and 4 more so that the cannon legs do not slip.
Use the gun only on slippery surfaces. On carpets, rugs, etc. the tower will not be able to turn and the gear may break.
To assemble the cannon, you will need a schematic, and to control the cannon using the RoboCam app, you will need the settings for the RoboCam software and the EV3 Brick software. All these files can be found below: