mannequin hand IK - confusion


Im super confused on the purpose or implementation of the mannequins hand controls.
The IK targets are unused and badly rigged. At least for my intended purpose

They are not used under any animations from Epic. In fact they are doing their own thing. The example of hand IK is created via socket locations on the hands. The IK’s never come into play.
So why are they there?

Why is the hierarchy

hand root
L Hand
R Hand

What is IK Gun?

Im asking these questions because i have been trying to find the most efficient solution to hand switching guns. I would prefer to just use elements of the UE4 Skeleton. Because of marketplace requirements. However those are not usable. Which is why Epic most likely are not using them either.

I’ve found just a few (aim with) IK threads so far and I’m interested in that questions as well. I even don’t have a clue how to retarget them in a way it makes sense if they are included in the anim package (like they are in Kubolds). Because most likely they would have some offset of the normal bones and animation (for IK) would differ from skeleton (for normal FK bones). Anyway I think you could use the gun bone if you would do some “AIM to this location” stuff (for example a NPC that should AIM to some target). But I think you could do that without that bone as well. So I’m still not 100% sure if I would import them with my meshes or if I just save resources and skip it.

I am redesigning my animations until i have an answer. Will rather just rotate my entire character as opposed to making creating entire animation sets for weapons to sync with character.

Well being an animator I knew what the IK handles were when I saw them and is an addition to the hierarchy that is not really need directly in Unreal 4 but was added by Epic to help make authoring of animations for their game like Fortnite and Pargagon easier and more efficient.

What might be confusing is the naming convention being used by calling them IK’s but what they are in reality is end effectors that are linked to the root of the rigging and constrained to limb end as a fixed target that is not interpolated by Unreal 4.

A good explanation.

The general behavior of UE4 is it interpolates everything but because how the IK is linked the left hand (end effector) will always be referenced to the right hand as it’s child and can be used as a target for a 2 bone IK to always keep the left hand bolted to say a weapon when doing something like an aim offset.

How they are linked up is of little relevance as to how they can be used once imported into Unreal 4 but rather connected depending on what application you are using to author the animations.

Why is the hierarchy

hand root
L Hand
R Hand

The ik_hand_root is not really the root but is linked to the root of the character. This allows the hierarchy to move relative to the character root when authoring root motion.

ik_hand_gun is linked to the ik_hand_root but is constrained to the right hand. Typical use would be arming and unarming as well as constrained to the right hand to say operate a bolt operated weapon.

ik_hand_l is linked to IK_hand_gun but can be constrained to a different joint. A typical use would be a weapon constrained to the ik_hand_weapon and ik_hand_l free to do a left hand reload.

ik_hand_r is linked to ik_hand_gun which in turn is constrained to the right hand. A typical use would be a right hand reload.

More or less though if you can not think of a reason as to why you need them then you don’t as they are there to make the animators life easier.

Thx @ FrankieV
The end effector explanation creates more confusion.

Do you use Maya to animate? If so is it possible to animate those bones?
I would have loved to be able to use IK hand gun to drive animation for attached weapons. Such as moving the gun from one hand to the other.

I am using 3ds max. The hierarchical setup and constraints on those “ik’s” prohibits them from being used for such purposes. Because moving left automatically moves right and vice versa and moving ik gun moves . In fact the only possible animation that can be applied to them is an arc movement left n right or fwd n back. They can under no circumstance even be moved close to any of the hands. So i do not fully understand how you can use them then to operate a bolted weapon.

What im seeing in max is basicly points that can arc around their parents but thats it. So it is not possible to use them to animate reload movements either. Surely for the above mentioned use cases it should be possilbe to move the IK’s.

Sorry about the confusion and understandable as it is one of those things that looks totally useless until you need them.

I use MotionBuilder but regardless of what application you use to animate yes you can use the IK bones to do what ever you wish. In MotionBuilder speak they would be called an AUX effector as in “auxiliary” that would be use of a per animation take bases.

The confusion is in the calling of the bones “IK” as they really have nothing to do with IK in Unreal 4 directly as that is just one of a 1001 uses so to call a rose a rose they are auxiliary effectors. :wink:

i think my confusion is that i cannot move them freely.
they swivel around the parent. making animating anything with them impossible. Do you experience the same behavior?

Can you tell me what a use case would be for them. you mentioned weapons n stuff. but like i said. you literally cannot move them where you want. they are constrained to an arc movement. so i can either place them 100 units left of the hip or 100 units right of the hip.

Is it possible that exporting the skeletal mesh to fbx causes some issues?
I would have imagines i can use those bones to animate as stated earlier… for weapons etc.

Well being able to move them freely (the missed named AUX effectors called IK_<name>) is usually caused by a switch or improper set up. In MotionBuilder it’s an easy fix as you just toss the bones (effectors) into a Character Extension and you can move them to any position you wish no matter the linking or constraint.

To do the same in 3ds Max by default a bone is a bone and will behave like one being connected, linked, but using the bone tool you can turn off the bone behavior so that the bone will move freely relative to the parent.

Really by the sounds of it your problem is a rigging problem and not that it can or can’t be done problem and the behavior is what would be expected from a child parent link as compared to limiting an effector by using constraints.

The difference is a Parent/Child link says “come with me” where a constraint says “Ignore you mom and stay here” and like anything else a constraint can be animated when it should start to turn on and when to turn off. :wink:

What app are you using for character animator? 100% sure though be it the missed named IK/AUX effectors or any effector that you added is there for the “purpose” of interacting with props, like weapons, or even other characters.

On the other hand if you want to move the IK free from the parent in 3ds Max (I assume you can do it in Maya as well)


I found the problem. which created my confusion and all the issues i had.

I accidentally created a position constraint on the parent to follow the children which resulted in my weird arc movements.
Your information helped me to revisit the setup once i knew that i am suppose to be able to move it independently. thx again.