How to do IK by rotating joints?

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#1

As the title says how do I do Inverse kinematics with 3 Motor6Ds.

I want to achieve this by setting the Motor6d’s CurrentAngle property.

XRotation rotates sideways.
Shoulder rotates up and down.
Elbow rotates up and down.

image of what I want to achieve (achieved by manually setting the values via properties).

image

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#2

This tutorial explains how inverse kinematics work, and it’s definitely worth a read: 2 Joint 2 Limb Inverse Kinematics

#3

I applied just the angle without using CFrame.Angles from the post you referred and I am getting weird results.

image

local RunService = game:GetService("RunService")
local Character = script.Parent
local Target = Character.UpperTorso.RightHand
local RightSh = Character.RightUpperArm.RightShoulder
local RightRot = Character.RightUpperArm.RightShoulderJoint.RightShoulderRot
local RightEl = Character.RightLowerArm.RightElbow

local b = 2 -- UpperArmSize
local a = 1.5 -- LowerArmSize

RunService.Heartbeat:Connect(function()
	local Mag = (RightSh.C0.Position - Target.WorldPosition).Magnitude
    RightSh.CurrentAngle = math.acos((-a^2 + b^2 - Mag^2) / (2 * b * Mag)) + math.pi/2
    RightEl.CurrentAngle = math.acos((a^2 + b^2 - Mag^2) / (2 * a * b)) - math.acos((-a^2 + b^2 - Mag^2) / (2 * b * Mag))
end)
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#4

Update
I solved this by myself all i had todo was account for the Motor6D offset and Character orientation offset

1 Like
#5

What exactly does this mean? I have the same problem and want to do 3 joints, and I want to know how to do it.