In this tutorial I will demonstrate how to create a deadly trapdoor triggered by throwing physics objects at a certain point. In our HL2DM mod Babel Babel, the teams playing against each other have the option of throwing boxes lying around the arena at targets on the other teams’ side of the level that trigger a series of trapdoors in the ground. If one of the enemy teams’ players happens to be standing over one of these hidden trapdoors, he will face his certain death at the bottom of the pit.
I had some trouble getting this trapdoor to work at first, since it seemed to work fine – as long as no player was standing on it at the moment it was triggered. In this case, it simply refused to open at all. After browsing the net a bit I found several hints on how to make the trapdoor work correctly and combined them in the following tutorial. As always, you should already be a little familiar with Hammer, because I won’t tell you all the icons you have to click on.