IKControl Joint Constraint [Beta]

[donutmotion]

[Update] July 6, 2023

@donutmotion

We are pleased to announce that IKControl Joint Constraint support is now out of beta and can be used in live experiences!

We’ve added several new features in this release, including:

• Support for Bone-based characters.
  • (Attachments can now be parented to Bones)
• Support for UniversalConstraint.
• Improved performance.

To prevent issues in existing experiences, this release will begin as opt-in. To enable IKControl Constraint support in your experience, set the Workspace property IKControlConstraintSupport to Enabled. As with other three-phase roll-outs, in the near future we will make Enabled the default, then eventually remove the property completely.

Please test this feature and report any issues with your experiences. Once reported, we will address them before proceeding to opt-out. Even after the workspace property is removed, you will always be able to stop a constraint from affecting IKControl by setting its Enabled property to false.

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Hi Developers!

We’re excited to announce the release of the IKControl Joint Constraint Beta. This new feature will let you use certain Constraints, which normally restrict the movement of physically simulated parts, to now also specify how IKControls can move joints. Using Constraints you can now:

• Make elbows and knees only bend about a specific hinge axis, without needing to specify a Pole
• Use limits to avoid impossible joint angles
• Make a robotic arm!

Below are some visual examples, in all of these the Pole property is not being used

To enable the beta in Studio go to File > Beta Features and enable IKControl Joint Constraint Support.

With the beta enabled you can add limits for IKControl using the existing physics Constraints. For this initial release, only the BallSocketConstraint and HingeConstraint are supported. To use them, add a Constraint between the two Parts in your IKControl’s chain that matches the existing Motor6D between those parts. Specifically, the Positions of the Constraint Attachment0 and Attachment1 attachments must match the positions of the corresponding Motor6D C0/C1 CFrames. The attachments do not have to have the same rotation (in fact you may want them to have different rotations to get joint limits oriented correctly). The Constraint must also be a descendant of the same Model as the IKControl.

To summarize, IKControl will use Constraints for which

• The Constraint’s Attachment0/Attachment1 are attached to the same parts as the Motor6D Part0/Part1
• The relative positions of Attachment0/Attachment1 are equal to the corresponding positions of the Motor6D C0/C1 CFrames.
• The Constraint is a descendant of the same Model as the IKControl

R15 characters already have attachments matching their Motor6D C0/C1 CFrames which you can use for this. These attachments may not be oriented the way you want for a given constraint - for example, on Rthro characters the RightElbowRigAttachment Axis is not perpendicular to the elbow. In that case, we recommend adding a nested attachment underneath the default rig attachment, which you can then orient however you need.

We will be updating the Inverse Kinematics Guide with additional details on how to use constraints to control IK movement.

Known issues and limitations:

• Currently only BallSocketConstraint and HingeConstraint are supported. We plan to add support for additional constraint types soon.
• Currently does not support BoneInstances, only Motor6Ds

We are releasing this as a beta because this may slightly change the behavior of existing IKControls.

We want to hear from you!

Please share feedback, questions, or any issues you find with how this behaves. We will make sure to take these into account before fully releasing this feature.

Thank you!

[1Arenio]

This is so awesome, thank you!
I can finally make my mech designs work properly!!!

[Rile_ey (Riley)]

This is a very good update, it’s really nice to see IK becoming easier to use especially since constraints are a familiar format for most developers.

[CasuallyCritical]

Now you can build the Metal Gear EXCELSUS

[CatzRule_81 (Catz)]

Exactly what I was thinking, lol. Good update.

[PysephDEV (Pyseph)]

This could not have come at a better timing!
Our game uses skinned meshes on the character rigs, which end up with very weird deformations when using IKControls.

However, I have been unable to get this setup working, as I’m far from familiar with constraint systems & Motor6D behavior. Most notably:

• I could not get a BallSocketConstraint to become active despite setting Attachment0 to one under RightLowerArm, and Attachment1 to one under RightUpperArm.
• I’m unsure what’s meant by setting the attachments’ positions to match the Motor6D. Should Attachment0’s position match RightUpperArm’s Motor6D.C1, or is it the other way around? or something completely different altogether?

Overall, having either a great simplification or test rig added would be much appreciated, as I haven’t been able to get the constraints working in spite of my half-hours testing

[1_cst (1 st)]

Exactly what we needed for a long time.
This will make working with IK joints actually worth the time and effort.

• Instead of having to rely on wonky physics, we can control pierced movement.

• We wouldn’t need to program certain movements.

• We wouldn’t need to take all the time to make and upload an animation

Tweening the joins would work well with this feature, can’t wait for it to be out of Beta

[C_Corpze (Corpze_TheDeadestOne)]

I’m very impressed, even more inverse kinematics!
This is going to be amazing for procedural animations and things like mechsuits or complex vehicles with moving parts I’d imagine.

The possibilities are nearly endless!
Is it fast and optimized as well? Could I possibly use this with many many many characters or robot arms at the same time without it lagging?

[zythdotdev (Zyth)]

Will this support bone instances in the future?

[TheNexusAvenger (Nexus)]

This update is great and drastically helps with my main concerns with the original release. There are points that cause the arms to bend unnaturally which also are a bit harder for me to reproduce when I am in VR. I do find it annoying that I, which means anyone else who wants to do this, need to specify constraints manually for the default R15 characters, and tuning the limits just right is hard.

Source code for anyone looking to try: GitHub - TheNexusAvenger/Nexus-VR-Character-Model at ikcontrol

[Wyzloc]

This is nice, I would love it if it was quicker to animate using the roblox animation plugin. It would be nice if there was a setting that moved the time frame marker up by increment each time you’re finished with a frame. Maybe a keybind to move it up would be nice to see.

[donutmotion]

Thanks for the feedback, we’ll see if we can make this easier to set up, and we’re also going to be updating the documentation on this page with a more detailed explanation of how to set up constraints on a character.

In your case, to constrain the LeftElbow Motor6D, Attachment0 should be on the LeftUpperArm (which is LeftElbow.Part0) and should have the same position as LeftElbow.C0. Then Attachment1 should be on the LeftLowerArm (LeftElbow.Part1) and should have the same position as LeftElbow.C1.

Standard R15 characters have built-in attachments that match these positions which you can use as well. For the LeftElbow they’re both named “LeftElbowRigAttachment”: one on LeftUpperArm and one on the LeftLowerArm. You can make your BallSocketConstraint use these directly. Or you can add your own Attachments that are parented to the built in attachments. The benefit of adding your own attachments is you can then change their orientation however you want to control which axis the elbow will bend around.

[donutmotion]

@zythdotdev

Will this support bone instances in the future?

Yes, we are planning to add support for Bone instances

@C_Corpze

Is it fast and optimized as well? Could I possibly use this with many many many characters or robot arms at the same time without it lagging?

It’s should be efficient enough to use on a large number of characters or limbs. If you run into any performance issues let us know and we will investigate.

[Hydacor]

This would be very helpful for the community!!

[SubtotalAnt8185]

More instances = less performance.

I think this design could have been executed in a better way, but I do like it. It is a hassle to have 500 lines of code just to create attachments and constraints though.

[MightyDantheman (Fate)]

@donutmotion

R15 characters already have attachments matching their Motor6D C0/C1 CFrames which you can use for this. These attachments may not be oriented the way you want for a given constraint - for example, on Rthro characters the RightElbowRigAttachment Axis is not perpendicular to the elbow. In that case, we recommend adding a nested attachment underneath the default rig attachment, which you can then orient however you need.

I’m sure it’s not a big deal and I can probably figure out how to fix it myself (I haven’t tried this yet), but will there ever be a version of R15/Rthro that comes preset for this?

I think it would be easiest if it were a drop-in replacement for developers to get things to work. Like with the issue I was having that I mentioned here:

IK Controls are now out of beta!

I’m having an issue where the IK Controller just stops working sometimes. It’s very inconsistent and doesn’t appear to be based on making any sort of changes. It just works for a few test runs, then it stops when trying again later for literally no reason… Also when it works, using the UpperArm and Hand often give unrealistic results for how the arm should bend. LowerArm and Hand works much better, but I haven’t been able to get it to work for a while now. Edit: I finally got it to work again…

[PeZsmistic]

Seems convenient to me. My characters are already using constraints in this manner for pre-baked ragdolls.

[Hexcede]

One problem I have with IKControls currently (not sure if it is relevant to this update) is that I need to upload an Animation containing all the parts I want, even if I don’t add any keyframes, otherwise it behaves like a wet noodle and seems to not work how I’d expect. I assume that constraints would help with this, but, the difference in behaviour is still concerning to me and I don’t know what would be the proper way to go about it.

Really, I want the IKControl to behave the same with or without an Animation so that I don’t need to upload one for every model I want to use IKControl on, but it doesn’t seem to do that.

Is that a bug? Or is the animation somehow encoding some pose information that the IKControl is utilizing, and it’s an important piece of that? Would this beta be a proper way to use IKControls without Animations, or are Animations still required to get good results?

[SwitchedDreams]

Does IK work for R6 rigs/characters?