How to use SkinnedEffect.SetBoneTransforms

I have a simple model th开发者_开发技巧at comes from Blender. It has one mesh and one armature. That armature has 3 bones in it.

When I load my model in XNA my model's bone collection has these bones:

0: RootNode

1: hankmesh

2: Armature

3: Bone 1

4: Bone 2

5: Bone 3

I am using the SkinnedEffect to deform the rendered model with the bones. I am trying to figure out what order I need to pass the transforms in to effect.SetBoneTransforms.

At first I figured the order would just match the model's bone order. That is if I wanted to transform bone 3 I could look up its index in the model and see that it is 5 and pass an array of transforms to .SetBoneTransforms with the 5th index having the transform I need.

However, from trial and error I have found that it is not the same index it is the index - 2. I am not sure what 2 represents here, or if I could always use that.

Can someone explain to me how to properly use .SetBoneTransforms on SkinnedEffect objects?