In my new map I got a cube and a horizontal funnel. It would break the puzzle when someone throw the cube into the funnel, but I also want the funnel a low as possible (to avoid a high ceiling).

So my question is: How high can someone throw a cube?
(You don't have to be very precise. I will add 64 units anyway.)

The highest I've ever seen someone throw a cube is 8 tiles high (256 units), but it's probably possible to go a tiny bit higher.

EDIT: I've managed to throw it about 12 tiles high. I would recommend placing the center of the funnel about 16-20 tiles off the ground.

You could try putting a gentle "trigger_push" near the bottom of the funnel and have it activated by a trigger on the floor where one might throw it from (just make sure it's tall enough so that you can't jump out of it). You could do the same thing with a clip brush instead of the push, but I think the push makes it less obvious. I'd say making it 64 units thick with <100 strength should do it, but you may need to do some trial and error to make it believable that you can't throw the cube that high.

you could also force the tractor beam to turn off if the cube has entered the funnel, that way the cube cannot go through the funnel. Make a trigger and set the filter to a filter_activator_class thats has its filter class set to "prop_weighted_cube".

Thanks everybody, I will try the trigger_push.

A trigger_push, I think might be a bit too obvious, seeing the cube suddenly change direction. I suggest you might try to use a phys_thruster that will slowly change the cubes direction. It works like this:
Set it's direction to "up" for lower gravity, or "down" for more gravity.
Set the flags to the following:
[x] Ignore Pos
[x] Start On
[x] Apply Force
[ ] Apply Torque
[ ] Orient Locally
[x] Ignore Mass
Change Force depending on the kind of gravity change you want. Example: setting the direction to "up" and "Force" to 800 will make the object float with exactly no gravity at all.

Mr. P. Kiwi wrote:
A trigger_push, I think might be a bit too obvious, seeing the cube suddenly change direction.

Not if you just make the push go directly downward (and make it weak enough so that it's not like a wall). The main issue with it is that the cube will suddenly accelerate when it falls through the push again, but with a trigger above the push set to turn it off with another beneath it to turn it back on, it wouldn't really be too obvious.

The biggest issue would actually speed-runners who find a way around it, or if the player tries to throw the cube high up somewhere else and doesn't get the same height restrictions, but odd stuff like that isn't new when it comes to games. Besides, having a trigger_push is preferable to just a player/physics clip in the right place (the "thud" and sudden loss of momentum is a dead give-away).

Stormburn wrote:
speed-runners

Well, even if you completely fortify this thing in every possible way there will still be people hacking or blundering their way past it, so you probably shouldn't focus on that too much.

Other than that, the "hand of trigger_push" is a very good technique for this kind of situation, especially if you fine-tune it like Stormburn explains. Even Valve does it in quite a few places in the official game!

If you dont need a portal to get in, you could put and emancipation grid under it.