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Why do I sometimes fall through a raising platform when I jump on it?

Setup: I made a static mesh platform. That when you step into the trigger box, the platform rises up 1600 units over 1 second using a timeline. When I get on the platform it rises up with me on top normally.

Problem: When I try to jump while on the platform I sometimes fall through it.

Reproduce: I can generally make myself fall through the platform right when the platform starts to lift the player by pressing the spacebar a quick couple of times.

I have Use CCD checked for my character, the mesh and the capsule component. I have BlockAll for the character and the platform.

I have placed the platform in a smallish pit, so that way I can always be completely on top of it, because I was thinking that the capsule was going slightly through the platform to cause the problem. It was worse when the platform was at ground level or higher.

How do I fix the platform / player so I don't fall through when jumping?

Thanks in advance for the help!

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asked Apr 26 '14 at 01:33 AM in Using UE4

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Hi there! I think I have had a similar problem, so may be able to help.

First I'd look at your world scale. The physics system uses world scale (1 unit = 1 cm) you are moving your character 16 meters in one second. It possible that the scale of your scene objects is having an impact.

If you jump (or step off a ledge), IsFalling is set to true on the character, it will then trace for collision, so it's likely because of the speed the platform is moving that it is returning that the character as isFalling when you jump, as it hasn't been fast enough to detect a collision hit from the bottom of the character collider to the moving platform allowing it to pass through you.

Another option worth a try is increasing the accuracy of the physics simulation

Project settings > Physics > Frame Rate > Enable substepping

Then adjust the max if you need more accuracy. Performance will be impacted so I'd have a play around, it also says its experimental.

Hope that helps!

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answered Jun 16 '14 at 04:03 PM

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avatar image Ben Halliday STAFF Jun 16 '14 at 06:08 PM

Hey Orangemicro,

I spoke with the developers about this issue, and it sounds like they've been working on improving platform movement in relation to characters using the CharacterMovement component. There have already been some improvements which should make it into 4.3, but a more robust system should be coming soon as well.

The solution CatDixon mentions above should help with the situation if you continue to use Matinee to move your platforms.

In the meantime, you can also consider using a different method to move your platform. Instead of using a Matinee, you can use a Timeline curve to set the position of the platform. This may introduce other issues if you're moving the platform in any other way than up and down, but shouldn't have the issue of falling while jumping. Again, this system is being improved upon as well.

Hope that helps!

Ben Halliday

avatar image Orangemicro Jun 18 '14 at 08:15 PM

Thanks you guys! That helps 100%, much appreciated.

avatar image zeroexception STAFF Jun 18 '14 at 10:38 PM

Adjusting the Physics substepping settings won't make a difference here, unless the platform is simulating physics.

This problem is caused by the platform object moving into the character without checking for any collision. Using either a timeline or matinee to move the platform simply changes the platform's position without any regard as to what may be overlapped at the destination. At that point the burden is on the character to try to resolve the overlap, which it can do in some cases, but which is more difficult if it is penetrated by a large amount.

One thing that may help is to set "AlwaysCheckFloor" to true on the CharacterMovementComponent. This is just a guess because I can't reproduce the issue exactly (it is sometimes very frame-rate dependent as well), but it may help with the case of the platform starting below the player when the player is standing still.

avatar image B-FliP Jul 14 '16 at 01:14 PM

When using Vinterp to move an Actor component (static mesh Floor) I get similar behavior (player character falling through the floor when jumping when the object is rising). It doesn't happen all the time, but when spamming the jump button it'll happen after about 3 times, it seems like the character is colliding at first but then falls through. I'm using 4.12.5, Mesh collision is set on BlockAll and I'm using the standard FirstPerson Char BP.

Same thing when going down when there would be a 'roof' above you, if you jump while the platform is moving down you'll find yourself standing on the roof. Collision behavior is normal when jumping when the Floor is not moving.

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