The Combine thumpers were used in the Half-Life 2 single player game to keep away antlions, but they can also be used as a nifty sci-fi themed prop. This tutorial will show you how to use them in both situations. In the process, we will use several entities that you probably haven't encountered before, so it might be worthwhile following this tutorial through for fun!

Antlion thumpers

For this part, we need three things- a prop_thumper, a button to turn it on and off, and something that keeps the enemy at bay.

We start with said prop_thumper; all we need to do here is give it a name (e.g. thumper1) and of course decide whether we want a big or small thumper (the larger model looks better with the larger dust cloud, and similarly for the small thumper).

Next, our button that turns the device on and off when we press a button (this setup is easily modified to stop the player from turning it back on again). Create a prop_dynamic using the world model models/props_combine/CombineButton.mdl, call it thumper1_button, and set collisions to be not solid so it doesn't get in the way.

We now need a func_button, textured with TOOLSINVISIBLE, that the player will actually use: set sounds to something like combine blip growl, and the delay before reset to 6. We will deal with the outputs of this and others after creating all the required entities. Next, make a logic_branch entity named thumper1_branch, and with an initial value of 1. Now create two logic_relay entities: one called thumper1_relay_on, and the other thumper1_relay_off (and make sure that they are not set to start disabled).

Finally, we need the device that keeps away the enemy. For antlions, they are scared off by the ai_sound entity with sound_type set to thumper, so make one of these named thumper1_scare and the location proxy set to thumper1 (since you can't specify any distances here, this may require some level tweaking to get working properly! You should also note that this can only be turned off, so is not "reusable"). If you want to keep away other types of enemy, make a func_brush textured with the TOOLSNPCCLIP texture, call it thumper1_scare and make sure that solidity is set to toggle.



Now onto the outputs. Go back to the func_button, and add two outputs:
1) OnPressed target thumper1_branch via Test
2) OnPressed target thumper1_button via SetAnimation : press

Edit the logic_branch and add these outputs:
1) OnFalse target thumper1_relay_on via trigger
2) OnFalse target thumper1_branch via SetValue : 1 (after a delay of 0.1)
3) OnTrue target thumper1_relay_off via trigger
4) OnTrue target thumper1_branch via SetValue : 0 (after a delay of 0.1)
(This setup will thus either fire the on or off relay for the thumper, depending on the state of the logic_branch)

Edit the logic_relay named thumper1_relay_off and add these outputs:
1) OnTrigger target thumper1 via disable
2) OnTrigger target thumper1_button via SetDefaultAnimation : idle
3) OnTrigger target thumper1_scare
This third output depends on how we're keeping away the enemy: if you're using the ai_sound method, then you'll have to kill it, or for the func_brush use disable to stop it from blocking NPCs.

The last step is to edit the other logic_relay, and add triggers as above but enabling the thumper (and func_brush, if you've used it). And we're done!

Thumpers without dust

This route will be somewhat easier than the last one- we simply have a prop trigger a sound and a shake when it completes its thumping animation.

Start with a prop_dynamic entity, named thumper2, which uses one of the thumper models (in the props_combine/ directory). Create a logic_relay, named thumper2_loop.

Next, make an ambient_generic named thumper2_sound, with the sound name ambient/machines/thumper_hit.wav. Set a very large max audible distance or make another ambient_generic, or else it will sound quieter than expected! You can also set the SourceEntityName to be our thumper, thumper2.

We also need an env_shake named thumper2_shake. Again, specify a large effect radius, a short duration (e.g. 0.4) and a mid-range amplitude. Obviously, these values will need testing in game and tweaking until they feel right! Tick any flags that you think will look good, too.

Now, if you don't have one in your level, place a logic_auto entity to start the thumping when the map begins (or use some other trigger if you don't want this to happen). Add an output which looks like this:
OnMapSpawn target thumper2_loop via trigger.

Edit the logic_relay and add these two outputs:
1) OnTrigger target thumper2 via SetAnimation : idle
2) OnTrigger target thumper2_loop[b] via [b]trigger (after a delay of 2.82).

Finally, add these two outputs to your prop_dynamic thumper:
1) OnAnimationBegun target thumper2_sound via PlaySound
2) OnAnimationBegun target thumper2_shake via StartShake



Unfortunately with this method, there isn't a way to have the thumper slow down/speed up when turned on and off- this is reserved to the prop_thumper entity. If you're quick, you may also notice that there's a very very slight delay between the thumper hitting the ground and the sound being made (perhaps less than 0.01 seconds) but this probably due to delays in the I/O system of the Source engine rather than anything else.

Spice it up with some lights and wires or oil decals and we should end up with a cool looking sci-fi prop: