J3DAnim
J3DAnim is a tool used to convert Maya's ASCII animation format to Nintendo's J3D animation format.
Guide
1) Have your model open in Maya, fully animated and ready for export
2) Ensure every frame has a key set
3) Go to the scene hierarchy and select every bone
4) Go to File -> Export Selection, and set Files of type to animExport
5) Open J3DAnim, select your newly exported .ANIM and original .BMD that the animation is for, pick a loop mode, and then press Convert; the converted .BCK will appear alongside the .ANIM