I've tried Custom Armor Model API. It adds model parts well, but I can't find a way to animate non standart model parts. I've tryed Overwrite setAngles method, tryed to copyPositionAndRotation of parts from defaultModel. All same, it has no effect.

Fabric API 0.26.3+1.16 for Minecraft 1.16.4

My classes: https://github.com/paulevsGitch/BetterEnd/tree/master/src/main/java/ru/betterend/item/model

Problem solved.