tokyo-wangan-racing/tools/diag_steer3.luau

--[[
	diag_steer3.luau -- WHAT is holding the knuckle rigid?

	diag_steer2 proved the servo will not rotate even hoisted with zero tyre
	load and ServoMaxTorque up to 1e9, with both hinge axes correctly +Y.
	That means the knuckle is rigidly bonded to the hub by something other
	than the servo.

	Decisive test: parts joined by a WELD share an AssemblyRootPart. Parts
	joined by a moving CONSTRAINT do not. So if Hub_FL and Knuckle_FL report
	the same AssemblyRootPart, a weld is bypassing the servo.

	Also builds an isolated 2-part servo to confirm the engine/API itself
	behaves, ruling out a bad assumption about HingeConstraint.
]]

local ServerScriptService = game:GetService("ServerScriptService")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local RunService = game:GetService("RunService")

local out = {}
local function log(...)
	local parts = {}
	for i = 1, select("#", ...) do
		parts[#parts + 1] = tostring((select(i, ...)))
	end
	table.insert(out, table.concat(parts, " "))
end

-- 1. ISOLATED SERVO --------------------------------------------------------
-- Two free parts, one servo, nothing else. If this turns, the API is fine
-- and the fault is in how the car is assembled.
do
	local folder = Instance.new("Folder")
	folder.Name = "IsolatedServoTest"
	folder.Parent = workspace

	local base = Instance.new("Part")
	base.Size = Vector3.new(4, 1, 4)
	base.Position = Vector3.new(0, 5100, 0)
	base.Anchored = true
	base.Parent = folder

	local arm = Instance.new("Part")
	arm.Size = Vector3.new(1, 1, 6)
	arm.Position = Vector3.new(0, 5102, 0)
	arm.Parent = folder

	local VERT = CFrame.Angles(0, 0, math.rad(90))
	local a0 = Instance.new("Attachment")
	a0.CFrame = VERT
	a0.Parent = base
	local a1 = Instance.new("Attachment")
	a1.CFrame = VERT
	a1.Parent = arm

	local s = Instance.new("HingeConstraint")
	s.Attachment0 = a0
	s.Attachment1 = a1
	s.ActuatorType = Enum.ActuatorType.Servo
	s.ServoMaxTorque = 1e6
	s.AngularSpeed = 6
	s.LimitsEnabled = true
	s.LowerAngle = -35
	s.UpperAngle = 35
	s.TargetAngle = -30
	s.Parent = base

	for _ = 1, 90 do
		RunService.Heartbeat:Wait()
	end
	log(
		string.format(
			"1. ISOLATED servo: target -30 -> CurrentAngle %.2f  (%s)",
			s.CurrentAngle,
			math.abs(s.CurrentAngle + 30) < 5 and "WORKS" or "BROKEN"
		)
	)
	folder:Destroy()
end

-- 2. ASSEMBLY TOPOLOGY OF A REAL CAR ---------------------------------------
local Shared = ReplicatedStorage:FindFirstChild("Shared")
local Cars = require(Shared.Cars)
local Chassis = require(Shared.Chassis)
local Server = ServerScriptService:FindFirstChild("Server", true)
local CarManager = require(Server.CarManager)

local pad = Instance.new("Part")
pad.Size = Vector3.new(2000, 8, 2000)
pad.Position = Vector3.new(0, 5000, 0)
pad.Anchored = true
pad.Parent = workspace

local car = Cars.Get("gtr_r34")
local tuning = Chassis.tuningFor(car)
local model = CarManager._buildForDiag(car, tuning)
model.Parent = workspace
model:PivotTo(CFrame.new(0, 5007, 0))

for _ = 1, 60 do
	RunService.Heartbeat:Wait()
end

local function get(name)
	for _, d in ipairs(model:GetDescendants()) do
		if d:IsA("BasePart") and d.Name == name then
			return d
		end
	end
	return nil
end

local body = model.PrimaryPart
local hubFL = get("Hub_FL")
local knuckleFL = get("Knuckle_FL")
local wheelFL = get("Wheel_FL")

log("")
log("2. ASSEMBLY ROOTS (same root == rigidly welded together):")
local function rootName(p)
	if not p then
		return "<missing>"
	end
	local r = p.AssemblyRootPart
	return r and r:GetFullName():gsub("^.*%.", "") or "<none>"
end
log("   Body     root:", rootName(body))
log("   Hub_FL   root:", rootName(hubFL))
log("   Knuckle_FL root:", rootName(knuckleFL))
log("   Wheel_FL root:", rootName(wheelFL))
if hubFL and knuckleFL then
	local same = hubFL.AssemblyRootPart == knuckleFL.AssemblyRootPart
	log(
		"   >>> Hub and Knuckle share an assembly:",
		tostring(same),
		same and "<-- WELDED, SERVO BYPASSED" or "(ok, servo is free)"
	)
end

-- 3. EVERY joint touching those parts --------------------------------------
log("")
log("3. ALL joints touching Hub_FL / Knuckle_FL / Wheel_FL:")
local targets = { [hubFL] = "Hub_FL", [knuckleFL] = "Knuckle_FL", [wheelFL] = "Wheel_FL" }
for _, d in ipairs(model:GetDescendants()) do
	local p0, p1, kind
	if d:IsA("WeldConstraint") then
		p0, p1, kind = d.Part0, d.Part1, "WeldConstraint"
	elseif d:IsA("Weld") or d:IsA("Motor6D") then
		p0, p1, kind = d.Part0, d.Part1, d.ClassName
	elseif d:IsA("Constraint") then
		local a0, a1 = d.Attachment0, d.Attachment1
		p0 = a0 and a0.Parent or nil
		p1 = a1 and a1.Parent or nil
		kind = d.ClassName .. "/" .. d.Name
	end
	if p0 and p1 and (targets[p0] or targets[p1]) then
		log(string.format("   %-28s %s <-> %s", kind, p0.Name, p1.Name))
	end
end

-- 4. Servo runtime state ---------------------------------------------------
log("")
log("4. SERVO RUNTIME STATE:")
for _, d in ipairs(model:GetDescendants()) do
	if d:IsA("HingeConstraint") and d.Name == Chassis.STEER_SERVO_NAME then
		log(
			string.format(
				"   %s Enabled=%s Active=%s Actuator=%s Torque=%.0e Speed=%.1f Limits=%s [%.1f..%.1f] Target=%.1f Current=%.2f",
				d.Parent.Name,
				tostring(d.Enabled),
				tostring(d.Active),
				d.ActuatorType.Name,
				d.ServoMaxTorque,
				d.AngularSpeed,
				tostring(d.LimitsEnabled),
				d.LowerAngle,
				d.UpperAngle,
				d.TargetAngle,
				d.CurrentAngle
			)
		)
	end
end

model:Destroy()
pad:Destroy()
return table.concat(out, "\n")