Gravity and Simple Collision (UE 4.27)

How do I make objects fall in gravity? Like, if it’s pushed off a platform and I want it to fall instead of floating in the air, possibly without tumbling?

Mind being more specific? Like do you mean simulate physics or…?

Like, I want to push something off a platform and that something falls straight down without floating in the air. Physics are simulated every time certain objects are pushed by the player, and the object’s class has a Box Collision. I heard about Simple Collision, but I haven’t been able to find a Collision pull-down menu while on the editor screen.

If i recall there is a similar setting in the Project Settings. Like “Treat Complex as Simple” or “Treat Simple as Complex”

You mean “Use Complex Collision As Simple?”

Yeah that. Sorry, my memory is a little bit fuzzy. Heh.

It seems to have made moveable objects completely immoveable. I received the following error: “Trying to simulate physics on … but has ComplexAsSimple collision.”


I wonder if I should change the collision itself. I’m not sure how, though.

Not odd at all. Complex collision cannot simulate physics, other simulating bodies can interact with it, though.

How close is this to the desired behaviour?

In case your collision is misbehaving:

  • double click the static mesh
  • remove collision
  • add box simplified collision

Update: I have confirmed that the Enable Gravity box is checked and that the Simulate Physics box is checked. Though any objects with simulated physics do fall down when spawned in midair, they still float instead of fall when being pushed off a platform.

Very close. It doesn’t tumble, but it doesn’t always fall down when I push it off a platform. Sometimes, the object will still float in the air. Other times, it will fall then bounce a bit. The behavior’s still pretty strange. Also, I couldn’t find the Collision drop-down menu on the Editor screen. All I see are File, Edit, Asset, View, Debug, Window and Help.

Open the static mesh first - double click it. Can you show the hierarchy of the box actor?

Most of the BP actors do not have a set static mesh, but I do have one that has a set cube shape and its own BP. Every time I double-click that cube from the Content Browser, I see the Editor menu.

It’s not about the blueprint actor - it’s about the asset. You actor has a static mesh component, that static mesh component has a static mesh assigned - you need to find that asset.

Like in this screenshot?

Most of the BP actors do not have a set static mesh,

Where are the meshes you assign to actors?

I give them either cube or pipe shapes. But the cube ones are what I want to fall off; pipes are always static and unmoveable.

2 things:

  • ensure the meshes have collision, where are the assets - the pipe and box?
  • the actors hierarch does not seem to be set up correctly for physics sim - you need the simulating element at the root.

And I can see you have additional collision shape which may complicate things.

Perhaps start with the most basic setup to get things going, make it work. And then add additional elements.

Sometimes, the object will still float in the air

Here’s the reason for this:


Here the collision shape is clearly offset - that’s why stuff floats. If the mesh has no collision of its own, it will use the collider you added. If both have collision, both collision boxes will be welded together - in this case act as one elongated shape.

Should I make BP pages for the moveable objects? I’m now starting – or just opening a third-person template – to see what I can find when I try putting a block on the given platform and then pushing it off.