tokyo-wangan-racing/tools/diag_steer5.luau

--[[
	diag_steer5.luau -- find a FIX for the servo/motor conflict.

	Established by diag_steer4: an ENABLED WheelMotor hinge locks the knuckle
	so the steer servo cannot yaw it. Disabling the motor (or deleting the
	wheel) restores perfect tracking (-19.99 of -20.0). MotorMaxTorque is 0 at
	build time, so this is NOT a torque contest -- it is a degenerate
	constraint configuration.

	Suspicion: Hub, Knuckle and Wheel are all built at the SAME CFrame, and
	the motor's two attachments are both identity CFrames, so every attachment
	sits at the same world point. Two hinges sharing a point with perpendicular
	axes is ill-conditioned for the solver.

	Each variant below changes ONE thing and re-measures.
]]

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

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(3000, 8, 3000)
pad.Position = Vector3.new(0, 5000, 0)
pad.Anchored = true
pad.Material = Enum.Material.Concrete
pad.Parent = workspace
local padTop = pad.Position.Y + 4

local car = Cars.Get("gtr_r34")
local tuning = Chassis.tuningFor(car)
local TARGET = -20

local function parts(model)
	local servos, motors, wheels, knuckles = {}, {}, {}, {}
	for _, d in ipairs(model:GetDescendants()) do
		if d:IsA("HingeConstraint") then
			if d.Name == Chassis.STEER_SERVO_NAME then
				table.insert(servos, d)
			elseif d.Name == Chassis.WHEEL_MOTOR_NAME then
				table.insert(motors, d)
			end
		elseif d:IsA("BasePart") then
			if d.Name:sub(1, 6) == "Wheel_" then
				table.insert(wheels, d)
			elseif d.Name:sub(1, 8) == "Knuckle_" then
				table.insert(knuckles, d)
			end
		end
	end
	return servos, motors, wheels, knuckles
end

-- mutate: applied after build, before settling. drive: applied after settling.
local function variant(label, mutate, drive)
	local m = CarManager._buildForDiag(car, tuning)
	m.Parent = workspace
	m:PivotTo(CFrame.new(0, padTop + 3, 0))
	local servos, motors, wheels, knuckles = parts(m)
	if mutate then
		mutate(servos, motors, wheels, knuckles, m)
	end
	for _ = 1, 60 do
		RunService.Heartbeat:Wait()
	end
	local body = m.PrimaryPart
	body.AssemblyLinearVelocity = body.CFrame.LookVector * 80
	if drive then
		drive(servos, motors, wheels, knuckles, m)
	end
	for _, s in ipairs(servos) do
		s.TargetAngle = TARGET
	end
	local trace, yaw = {}, {}
	for step = 1, 120 do
		for _, s in ipairs(servos) do
			s.TargetAngle = TARGET
		end
		if step % 24 == 0 then
			trace[#trace + 1] = string.format("%.1f", servos[1].CurrentAngle)
			yaw[#yaw + 1] = string.format("%.2f", body.AssemblyAngularVelocity.Y)
		end
		RunService.Heartbeat:Wait()
	end
	local final = servos[1].CurrentAngle
	local ok = math.abs(final - TARGET) < 5
	log(
		string.format(
			"%-40s [%s] final %6.2f yaw[%s] %s",
			label,
			table.concat(trace, " "),
			final,
			table.concat(yaw, " "),
			ok and "*** STEERS ***" or "stuck"
		)
	)
	m:Destroy()
end

log(string.format("target %.1f deg, rolling at 80 studs/s, motors at build-default torque", TARGET))
log("")

variant("V0 baseline (unmodified)", nil, nil)

variant("V1 motor ActuatorType = None", function(_, motors)
	for _, mo in ipairs(motors) do
		mo.ActuatorType = Enum.ActuatorType.None
	end
end)

variant("V2 motor attachments offset 0.01 X", function(_, motors)
	for _, mo in ipairs(motors) do
		mo.Attachment0.CFrame = mo.Attachment0.CFrame * CFrame.new(0.01, 0, 0)
	end
end)

variant("V3 knuckle mass x20 (density)", function(_, _, _, knuckles)
	for _, k in ipairs(knuckles) do
		k.CustomPhysicalProperties = PhysicalProperties.new(20, 0.3, 0.5, 1, 1)
	end
end)

variant("V4 wheel Massless=true", function(_, _, wheels)
	for _, w in ipairs(wheels) do
		w.Massless = true
	end
end)

variant("V5 servo torque 1e9 + speed 30", function(servos)
	for _, s in ipairs(servos) do
		s.ServoMaxTorque = 1e9
		s.AngularSpeed = 30
	end
end)

variant("V6 motor torque 0 held every frame", nil, function(_, motors)
	for _, mo in ipairs(motors) do
		mo.MotorMaxTorque = 0
		mo.AngularVelocity = 0
	end
end)

variant("V7 front motors disabled only", function(_, motors)
	-- rear-wheel drive: only the steered corners freewheel
	for _, mo in ipairs(motors) do
		local n = mo.Parent and mo.Parent.Name or ""
		if n:find("F") then
			mo.Enabled = false
		end
	end
end)

variant("V8 V1 + V5 combined", function(servos, motors)
	for _, mo in ipairs(motors) do
		mo.ActuatorType = Enum.ActuatorType.None
	end
	for _, s in ipairs(servos) do
		s.ServoMaxTorque = 1e9
		s.AngularSpeed = 30
	end
end)

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