Very new and need help with physics

[Rhiannon Tamerlane]

Hello, I'm having a hard time figuring out how to make the physics of a mesh work. The situation is this: I have a circular floor, with a hole offset from the center. Building it using prims needs 4 prims - a large cylinder with a wedge out of it, a smaller cylinder with a hollow (to make the hole), a box to fill in most of the rest of the wedge, and another cylinder the same diameter as the first one, mostly hollow, to give the outer edge. I'm trying to build this as a mesh to upload so I can have the floor be one piece. I've built the piece and exported it as a Collada file, but the problem is when I import it, the offset hole isn't a hole, physics-wise. I have selected Surface as the type when upload, and I've tried using every one of the LOD settings as the physics file: I've also tried specifying the Collada file as the physics file; all without success.

Any help  in how to understand and create the correct physics so the hole will actually be there in the physics of the piece would be greatly appreciated.

For information, the hole is in the floor for a spiral stairway coming up from below.

[Aquila Kytori]

Hi

Inworld you need to change the Physics Shape Type from the default Convex Hull to Prim.

In the example below I have created a separate, simplified version of the High LOD model to use for the collision surfaces.

This Physics model is uploaded in Step 1 of the Uploaders Physics tab.

Don't touch any of the other options here.

Upload, rez and then edit the model. In the build floater open the Features tab and change the Physics shape type to Prim.

Now you should be able to walk on the floor surface and fall through the hole.

 

Need to add: This type of Physics (not Analyzed in the mesh uploader) will only work if your High LOD model measures is at least 0.5 meters along all axis,    (X; Y Z)

In my example the outside edge wall is 1.0 meters high.  (Z axis)

If your mesh is less than 0.5 meters along the Z axis then changing the Physics shape type to Prim will have no effect. It will still be Convex hull type physics even though it will say Prim in the build floater !   

  What is meant by "Convex hull" ?   Imagine your model has been wrapped in cling film. This will prevent access to all concave surfaces and so fill in any holes.

If the Physics model is overly complicated, many triangles, then the Physics cost  can have a large effect on the final LI cost! The rule is Keep your physics model as simple as possible.  The fewer and larger the triangles used in the physics model the lower will be the Physics cost.

You can see the Physics model inworld if you enable Physics Shapes............... Develop menu > Render Metadata > Physics Shapes.

Edited May 22, 2019 by Aquila Kytori

[Rhiannon Tamerlane]

Bless you, Aquila! This is EXACTLY what I needed... and bless you even more for pictures!

[Aquila Kytori]

You're  welcome

[Rhiannon Tamerlane]

It worked like a hot damn... I see what you mean about the minimum of 0.5m. I thought to try to get around it by setting it up per your directions, then resizing on the Z-axis... nope. Soon as it went below 0.5m, the hole wasn't a hole anymore Thank you for an invaluable lesson on mesh building and physics!

[Kyrah Abattoir]

If you made a collision model that is already as optimized as possible, do not hit any of the buttons on the collision mesh tab, those are only really for when you are asking the uploader to generate "something" (bad usually) for you, from a mesh that wasn't designed to be a collider.