I've been messing around trying to get the Dwemer Centurion race playable, and run into an interesting bug- I can't get them to perform any actions other than basic movement and a single attackRight animation. No power attacks, no shouts (constant or fire and forget), no left attacks, just that one attack.

I imagine there's something in the behaviour graphs maybe that governs which animations are accessible to the player, or respond to which player commands? Anyone know how to view or alter them, or can shed any more light on the topic in general?

You can't add animations to Skyrim or change the behavior graphs. Just replace them. The only workaround would be to completely recreate the Dwarven centurion race as a custom race and give it new animations, and even that might not work since I only have a vague idea about how this whole thing works.

Edit: Oh hey, I recognize your name from Oblivion. Cool.

I'd be fine with using the same skeleton and animations for a new race; the issue is how to get the game to grant the player access to those animations.
Bizarrely, I just tried swapping the Centurion behaviour file for the Character one and it didn't change anything- there wasn't even a crash. So I assume it's not the Behaviours file which is responsible.

Havok behavior files support things like animation state transition and timing. Idle -> Punch -> Idle or Idle -> Stagger ->Dying ->Get Up -> Idle. There are a number of variables that can be associated with those animations. Bethesda added their own events into the mix to extend their engine.

I'm working on reading/writing the Havok Behavior files but its slow progress. You can use AssetCC2 from the Havok Content Tools on some files to extract information but usually those are pretty uninteresting. The interesting ones have Bethesda specific classes embedded. So the trouble is I have to match exactly the code signature of both the Havok Behavior classes and the Bethesda classes to even properly read the files (using havok tools). Once done though converting to/from XML should be feasible which then presumably enables modders to do extend the framework to add their own animations into the mix.

I've come up with some means to extract signatures and other information from a majority of classes but still not enough. its hard to explain but the classes have a checksum on the class definition so you have to get every piece correct or it will reject reading the class. Even with what I think is an exact match by all accounts it still doesn't work for me. Basically, I either scrap the Havok framework and roll my own like niftools team or continue to try to fit the square peg in round hole. I'd rather leverage the toolkit to maximize compatibility.

My next technical issue is that a lot of classes in my version of hk_2010.2.0-r1 still don't quite match the delivered tools or the creationkit. Not sure what I'm missing about it but it will only slow things down more. The good news is I've been able to hack the havok system enough in CK to do basic reports for me so I can do data comparisons which is why I'm seeing some basic inconsistencies.

Ah, okay. Have you found any tags/events/thingamajigs in there that say 'Chain corresponds to Player_Input_Type', or do you have the suspicion that such might be in there? As it currently seems like the NPCs have free access to these chains but PCs don't, so there must be a feature that converts player input into the right kind of trigger for the chains.

The Steam Cents left attacks are magic attacks -> conditioned to HasEquippedSpell "Left" -> meaning you need to have a spell in your left hand before its usable -> also the animations themselves are geared to purpose meaning since the spell in question is a shout its only really viable as a shout attack.

Yep, I just tried that today and it still won't let you use a shout, even if it is equipped to the left hand and your right is empty/has a right weapon in. IsShoutEquipped's returning correctly, the shout's not got any keywords or prerequisites and so on, and it still won't cast. The fact that you can't pull off power attacks or anything but the single default attackright suggests it's a deeper problem than just 'wrong slot'.