The bumper sensors that came with the Vex Robotic Kit should have screw holes on the buttons so that parts may be attached to bumper sensors. For example, on the car-type robot, a full-width bumper made from metal or wood could be attached to two bumper sensors on each end. I’m afraid to drill holes for screws on the buttons because the drill bit may hit something inside the sensors. Can this be done?
You do not need to drill into the sensors. In fact, I would strongly reccomend against this, as something might be broken. Instead, make the bumper that goes across the front of the robot pivot, and when it is pushed, it will depress the bumper switch. This way, nothing has to be drilled into. Here’s a quick drawing to help you: