Ik arm chain

Hello there,
I’m trying to set up a nice IK on arms so that the VR player sees “his” arms, the hands following the controllers.
However as the hands correctly move, the forearms doesn’t yaw at all, resulting on bad twisting at the wrists.
Is there a node in the anim graph that could be used to correct this ? I tried to apply a purcentage of the hand rotation to the forearm but it only works in world scale and goes wrong… and I can’t understand a bit with the bone driving nor twist correcting (how do these curve things work ?).

Thanks a lot for any informations :slight_smile:

Alright, I’ve finally decided to hide the arms and only keep the forearms visible. I’ve set up a virtual elbow target, the wrist (forearm bone) looks at it. The wrist has a 50% rotation percentage from the hand too.

Looks fine !

Hi do you mind sharing how you have achieved that?

Hi, sure :
My VRPawn has 2 arrow components used as look at targets.

The BP spawns 2 MotionControllerBP at startup.

Each MotionControllerBP is made of a SkeletalMeshComponent using a Hand SkeletalMesh with all fingers, the hand and the wrist as bones. Be sure that the root is the hand (not the wrist) so that the controller component will move the hand - the wrist will be moved differently.

You can add which animation you want (I’ve set two variables in my setup, Grip and Interact).
The wrist rotation is then defined in the Blueprint Animation : a percentage of the hand rotation is given (in my case, 100% of rotation in X axis).

Then I’ve added a Look At to the wrist, and set up the Look At Location as a vector variable (the target is set up in the VRPawn :

In the Look At node adjust the Look At Axis (in my case the X, the same as the rotation used for the rotation in the previous node).

Of course you have to adjust the location of the Targets in the VRPawn (I’ve set X=0, Y=30, Z=+/-50), but it should work so :slight_smile:

Thanks so much for the detailed write up! I’ll give it a go. =)

Please ask me if some informations are missing ! :slight_smile:

Hi @Robert, I’m afraid I can’t share you my setup as it’s a currently sold company project. However I would be glad to help you in any way, just ask and I’ll help how I can ! What’s your problem reproducing the setup ?

Is there any way you cold share a simple version of your setup? I have tried over and over for many months (I keep coming back to it) without any luck., I will reciprocate any way I can, I have a few thousand youtube subscribers, I would be happy to market your work when you publish!

It would help enormously to be able to learn from an working example, I am going nuts trying to get it to work… THANK YOU!


Well, I am I guess admitting a limitation,. I learn best when I can reverse engineer or, by example. Once I see how and why a thing works, BOOM, paradigm shift. Epiphany! I know it for life intimately/

Perhaps., what you are teaching it here, you could sharer the ‘bp’ part only replacing the ‘paid hand’ with the Mannequin hand? (or maybe not have a mesh at all?)
I have worked in 3ds Max since it was 3d Studio for DOS 30 years ago I can make a hand! :),
``But I look at the images below and as much as i have done in UE in 5 years, they are disconnected alien hieroglyphs.
I can’t even get my head around discerning what step one would be!! The images below seem disconnected laid out like that. Even the concept of WHERE to even PUT this ‘ARROW’ pointing thing? I’m WACOM-PEN BLOCKED and FLAILING!

I am a professional Character Animator of over 30 years. I wrote a book about the 3ds Max ‘Motion Capture Utility’. Still, I know my limitations. Regardless I have a lot to share!

Perhaps sharing just the BP functionality without sharing hard assets?
(Screenshots?? :slight_smile: :slight_smile: LOL , I am not being lazy I am . admitting a limitation. I worked in CGI years before Windows even existed & ever since, I’ve done a LOT in my career. I have an IMDB page w/ films/TV I worked on, I worked at Activision, Praxis Filmworks, Warner Digital, I have thousands of subscribers, (Can I REVIEW something for you?) youtube.com/NextWorldVR

Ironically I have a FULL BODY IK, I bought ‘VR Cookbook’ went through the ‘recipe’, but I learned very little from the ‘rote’ steps. I thought "it has full body IK, it’ll show how to stop the Wrist from being dead weight connected to the hand! (nope.) I have used ‘Apply Percentage of Rotation’ nodes to my Forearm Twist bone on my IK body! I’m no slouch :slight_smile:
I learn best via GITHUB (I hope you ‘GIT’ that LOL) I find what works then see how! it is, exponentially faster for me, when I can do it the way I do it best! :slight_smile: