# Prop Setup The example prop used in this article is `prop_container_05a.yft`

### Fragment Hierarchy

### Prop Rigging You'll also notice that each Drawable Model is rigged using a Child Of constraint instead of vertex groups.

This is the case for all props. Typically each Drawable Model for a prop corresponds to a particular separable part of the Fragment. Notice there is a Drawable Model for the latch, each door, and the container itself. ### Skeleton Setup This matches up with the bone hierarchy.

Each bone is parented to `Prop_Container_05a` and is thus affected by that bone. Every skeleton in the game engine always has one root bone that all the other bones are parented to. {% hint style="warning" %} If you attempt to add multiple top-level bones (bones with no parent) you will run into issues. Make sure there is a single "root" bone that all other bones are parented to! {% endhint %} Notice, too, that each bone has `Use Physics` enabled. This means that each of those parts will have physics in-game and will separate from each other.

{% hint style="info" %} In this case, the doors don't actually "separate" from the mesh, but fling open instead. This is because the `Strength` bone physics property is set to -1. When set to another value (i.e. 100) you'll notice that the parts will separate. {% endhint %}

### Collisions As mentioned before, each bone with physics enabled must have an associated collision. However, there can be multiple collisions for a single bone. Notice for this prop, there is a single collision for the latch and the doors, but the container itself is comprised of 5 box collisions.

{% hint style="info" %} You will notice that a lot of vanilla collisions will use bound shapes wherever possible. This is typically preferred over using a bound mesh as it is much more performant. **Keep collisions as simple as possible.** {% endhint %} Each of these collision objects is linked to a bone via a Child Of Constraint.

Each collision also has its mass set in the `Object Properties > Sollumz > Physics` panel.

### Quick Note on YTYP Flags {% hint style="info" %} In order for physics to work for your prop in-game, make sure the YTYP archetype has the "Dynamic" flag enabled! {% endhint %}

Archetype Definition > Archetypes > crate > Flags

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