How to build a piston trapdoor

This tutorial will tell you how to create a piston trapdoor so that you can drop people and mobs into dungeons, lava pools, rooms full of sheep or any other evil things you can think of.

The trapdoor when closed

First you'll need 4 sticky pistons, and you need to make 2 rows of 2, 4 blocks apart and facing opposite each other like this:

Then you stick a normal piston to each sticky piston, facing upwards.

 

The sticky pistons need to be connected to redstone repeaters. These pistons need to retract after the normal pistons have, so set the time on the repeaters to 4.

Add redstone repeaters connecting to where the normal pistons would be when the sticky pistons have extended, these can just be set to 1.

Wire everything up, like this.

When you supply power to the pistons from a lever they should look like this. The cow in the background is the future test subject for the trap.

Now add a floor around the trapdoor, and it is complete. Put whatever you want down the hole, I went with lava.

 

It is also possible to create a hidden trapdoor, I will add a tutorial on that if anyone wants one. Just let me know in the comments.