The PS3 controller comes with many buttons. There are two protruding buttons on the bottom of the controller that look like joysticks. These buttons are called analogue controls. It's possible for you to use the analogue controls so much that they become loose. If this has happened to your PS3 controller there is no need to toss it out because you can open up the controller and fix the analogue stick on your own.
Unplug the controller from the port at the front of the PS3 console.
Turn the controller over and remove the five screws on the rear of the unit.
Remove the back housing of the controller from the front. The back of the motherboard will now be visible in the front housing.
Lift the motherboard up to expose the front of it. The joysticks will now be visible, connected to the front of the board.
Press down on the loose joystick until it snaps in place. It will now be properly tightened.
Replace the back housing of the controller and screws.