Idea for those skilled in Hammer (and a couple questions)
Questions first: 1) Is there a way to put bounce gel on turrets without doing anything that would turn on gel mode? Like, change the variable that says whether they have it
2) In my map Odysseys the player goes through changing rooms multiple times. Rather than execute some of the changes using flip panels, is there a way to create a brush that appears/disappears on the press of a button?, possibly with the solid and visibile parameters
Now then, here's something I thought of: a Companion Turret series. Yes, this has been done before, but my idea is to foster the player's relationship with the turret much in the same way as the original Portal, and have the turret killed at the end. Here's the outline
1) Simple PeTI chamber that involves taking out a couple turrets. After solving it the player enters a narrow hallway with a turret in the center, facing away. There might also be a companion cube visible. Moving close to it will cause the floor to open beneath them, dropping both the player and the turret into Old Aperture
2) Wakeup sequence where the turret doesn't kill the player and asks you to "take me with you". When holding the turret clicking will make it fire, perhaps each mouse button will control one side of it, which could be useful in conserving ammo (it has to recharge for whatever reason). The turret can be used to smash glass, knock cubes off platforms, and blow up gel bombs. One such puzzle involving this would have a white and a cleansing bomb aimed at the same square; first the player shoots all the cleansing bombs to use the square and eventually get blue gel onto it, and therefore have to shoot both bombs each time they spawn to be able to use the blue gel
3) At the end of each stage, the CT says one of the turret prophet lines
4) Turret buttons, or being able to put the turret on regular buttons, is an idea
5) At the end, there will be a laser puzzle that involved activating a laser FLAG (shooting a catcher or activates a laser aimed at the catcher, which keeps it powered) to reach the exit, but the FLAG must be deactivated to open the exit, and the only way to do this is to block the laser with the turret. It starts talking and forgives you and all that, and voice acting could make this scene as awesome as you can imagine. Having sacrificaed the turret the player enters an elevator where (assuming this is possible) the cutscene from the end of the game begins, but cuts out, with sound effects, so as to imply that the turrets actually did kill the player
6) There could be a secret way to save the turret, such as using a hidden companion cube to block the beam (would be funny if it exploded too). With this ending, the player obviously wouldn't die
clearly this is far beyond my level of skill so I figured I'd suggest it in case anyone else found it as interesting. naturally the level wouldn't have to be exactly like this; anyone here is free to do with this idea whatever they wish.
You can't make a turret shoot while you're holding it, but only if you put it down. To make a turret button, use a trigger multiple that has only the flag "NPCs".
As far as I know you can't, though you could only spill a tiny bit of blue gel on your turrets at the start of the map. You can also set its skin to painted, but this won't give the bounce effect.
Sure, make them func_brushes, give them a name and enable/disable them whenever you want. However, the lighting gets a bit tricky, experiment with this 
Sounds fun, I once had a prototype somewhat similar to this. However, to keep it realistic, the play has to fall quite a bit! One thing you can make the fall appear to be longer than it is, is by putting world portals in a certain section so the player falls through them a couple of times. If the section is big enough players won't notice this!
The first part sounds fun I know, Rand0m Numbers has made something where you controlled a turret before!
The second part sounds very confusing
No problemo; just make a button a-la-portal 1 with a trigger_multiple; add a filter class for the turret and you're done!
Which map is that? One of the TEST ones, I would assume?
There is a tutorial in his youtube channel:
useful tools and stuff here on TWP 
[spoiler]
[/spoiler]Yeah, but he also made a map with it.
http://steamcommunity.com/sharedfiles/filedetails/?id=68690530
Ok so, two more questions: I have 4 turrets together that get Crusher'd; can I spawn another there later? And, how do I use a trigger multiple to make the turrets start shooting (they're behind glass)
1) You can use an Env_entity_maker to spawn a new turret there.
2) Use an Npc_bullseye and and Ai_relationship, enable the ai_relationship when you want to shoot the glass.
So, new issue. I made my map in PeTI, sent it to Hammer, and replaced the easily replacable entities with the Hammer versions. Published the map and people found exploits, but I don't have access to the game so I had the .vmf emailed and opened it on a friend's computer who has, but has not yet played, Portal 2. Opening the map, I found that things from PeTI had disappeared, such as my cube droppers. This also happened once at home because, I assume, of the computer being shut off randomly; I solved it by loading an old save. I suspect this is caused by a) the friend's computer not having the correct files due to not actually using P2 or b) I need more than the .vmf or something else entirely. Anyone know of a solution that doesn't involve me getting on the original computer?
Sounds like you're missing your instances. Validate the tools cache of the portal 2 authoring tools at your friend.