When you have a look at this Beer Pong Robot video by Empire Robotics you can see that some cool engineering went into making this robot very accurate (or a ton of takes were taken). The green thing on the end of the arm is what Empire makes, it is an ingenious mechanism for gripping items.
Via: Geeks are Sexy and Gizmodo
“The core principle behind VERSABALL is the jamming phase transition of granular materials. The green ball is filled with a sand like material. When air is pumped into the ball, the ball softens. The ball is then pushed against the target object. Pulling air out of the ball jams the sand like material together, causing the ball to harden. This transition from soft to hard creates the gripping forces.”