2 Joint 2 Limb Inverse Kinematics

try

lastRightTweens[1] = TweenService:Create(rightHip, TweenInfo.new(0.2), {C0 = lowerTorso.CFrame:ToObjectSpace(planeCF) * CFrame.Angles(-hipAngle, 0, 0)}):Play() 

Not sure if it’d work but I’m guessing by negating the angle, it’d rotate oppositely thereby fixing your problem

1 Like

It looks right in certain situations but that doesn’t affect how the angle limitations are determined, so once you get to higher limit angles that are either too short or too far then the calculations are reversed so the leg goes short when it should extend the furthest and the leg goes long when it should extend the least.


this is how the IK module looks, (i removed the 90 degree addition from the -a1 near the end on purpose, it doesn’t change the result in a way I need)

2 Likes

Hmm. I just edited some stuff in the IK module and now it works perfectly.image
I just made a1 positive and subtracted 90 degrees from a2-a1, seems to be working fine.

https://gyazo.com/d05ad99a9b1689272c7010c6671d093a

This isn’t really what i want though, I was the leg to lift up all the way and kinda crouch instead of kneel, so the knee is up and isn’t into the ground

I’d love to help but I’m not too keen on trig, so most of it is just going over my head

Well, this is the best result so far, thanks for helping though. I simply added a “base” value and did my calculations off of that angle, (math.pi/2) I also added 4 different positions, one being in between super close and perfect, so there weren’t that many artifacts.

External Media
1 Like

This method of IK might not be ideal for what you’re trying to do. The method this thread depicts is pretty strict and what you want might be something more adaptive.

Adopting FABRIK style IK might be more what you’re looking for.

8 Likes

This is actually quite useful, however one issue I am having with it, is the hand touching the inner edge rather the centre.

How would I go about fixing this?

2 Likes

It’s because the solve isn’t accounting for the outward offset the C1 of the shoulder has. Technically it’s correct since the line from the shoulder C0 to the point is still in line.

You can correct this by offsetting the originCF by the shoulder C1 offset outward (c1.X) or by rotating the final planeCF to compensate for the offset (think of the offset + arm lengths as a right angle triangle: tan(l1+l2 / c1.X)). Rotating means you’ll also need to adjust for the loss in distance by pushing the planeCF forwards.

4 Likes

A = math.acos((-a^2 + b^2 - c^2) / (2 * b * c))
wouldn’t it be:
A = math.acos((-a^2 + b^2 + c^2) / (2 * b * c))

2 Likes

This is a tutorial, not a project. This topic is intended to teach you the basics of IK, and it’s up to you to apply it yourself.

One case that needs to be adressed is when the axis is equal to Vector3.new()
A simple solution to this:

local axis = Vector3.new(0, 0, -1):Cross(localizedUnit)
local angle = math.acos(-localizedUnit.Z)
if axis == Vector3.new() then
	axis = (angle == PI and Vector3.new(-1, 0, 0) or Vector3.new(0, 0, -1))
end
local planeCF = originCF * CFrame.fromAxisAngle(axis, angle)

This addresses two very specific cases where the math breaks :slight_smile: Just wanted to add this on.

3 Likes

No, the first equation is correct

So I am very unfamiliar with IK, however, I am getting a grasp. How would I go about adding another limb?

This is the only code I changed and it works fine except the goal part is at the joint I do not want it to be at. How do I fix this?

Code:

local workspace		= game:GetService("Workspace")
local storage		= game:GetService("ReplicatedStorage")
local runService	= game:GetService("RunService")

local goalPart		= workspace:WaitForChild("GoalPosition")
local shoulderPart	= workspace:WaitForChild("ShoulderPosition")
local upperArm		= workspace:WaitForChild("UpperArm")
local lowerArm		= workspace:WaitForChild("LowerArm")
local grapple = workspace:WaitForChild("Grapple")

local solveModule	= storage:WaitForChild("SolveIK")
local solveIK		= require(solveModule)

----

local SHOULDER_OFFSET		= CFrame.new(1.5, 0.5, 0)
local VECTOR3_UP			= Vector3.new(0, 1, 0)

----

runService.Heartbeat:Connect(function()
	local shoulderCFrame = shoulderPart.CFrame * SHOULDER_OFFSET
	local goalPosition = goalPart.Position	
	
	local upperV3 = VECTOR3_UP * upperArm.Size
	local lowerV3 = VECTOR3_UP * lowerArm.Size
	local grappleV3 = VECTOR3_UP * grapple.Size

	local planeCF, shoulderAngle, elbowAngle, otherelbow = solveIK(shoulderCFrame, goalPosition, upperV3.Y, lowerV3.Y, grappleV3.Y)
	local shoulderAngleCFrame = CFrame.Angles(shoulderAngle, 0, 0)
	local elbowAngleAngleCFrame = CFrame.Angles(elbowAngle, 0, 0)

	upperArm.CFrame = planeCF * shoulderAngleCFrame * CFrame.new(-upperV3 * 0.5)
	lowerArm.CFrame = upperArm.CFrame * CFrame.new(-upperV3 * 0.5) * elbowAngleAngleCFrame * CFrame.new(-lowerV3 * 0.5)
	grapple.CFrame = lowerArm.CFrame * CFrame.new(-upperV3 * 0.5) * elbowAngleAngleCFrame * CFrame.new(-lowerV3 * 0.5)

end)

Thanks!

How would I make this R6 Because I Don’t Really See Many Posts?

It isn’t bad, it’s just older.

What am I supposed to do in this situation?

What is the issue, you gotta give context instead of just showing an image and saying “What am I supposed to do in this situation?”

Sorry, I’ve fixed the issue. I had a scripted animation playing.

Sorry for the bump!

Has anyone applied this to the module? I can’t seem to figure out where/how to apply this, testing this on a 2.0 rig is accurate enough as it is but when I test this using the woman package the arms are way off target (potentially also due to the elbow offset?)

This looks useful, and I was actually looking for inverse kinematic tutorials. But I’m still unsure about how to use it for walking in where you put the script wise or if this is even for walking. This kinda went over my head so I can’t really figure out how to use it with walking.

I might just change names or something, i’m also not sure if this is only for animations instead of actual walking (For an fps game a couple friends and i are working on).

How do I use this for walking? (Or if its already for walking just tell me I don’t really know how this works)