tokyo-wangan-racing/tools/diag_seatdir.luau

--[[
	diag_seatdir.luau -- decide, empirically, which way the car DRIVES.

	The contradiction: CarManager:158 says `isFront = zSign < 0  -- car forward
	is -Z`, so the front axle is built at local -Z. But the VehicleSeat's
	LookVector points +Z (measured: seatLook.dot(bodyLook) = 1.00).

	In Roblox a VehicleSeat applies throttle along its OWN +Z LookVector, so
	positive throttle drives the car toward +Z -- i.e. toward the axle the code
	labels REAR. If that holds, every car drives "backwards" and the shell,
	which is aligned to the chassis convention, renders nose-first into the
	direction of travel... backwards on screen.

	This does not guess: it reads the seat's actual Throttle/steer wiring and
	compares the seat basis against the wheel labels, then reports which axle
	leads under positive throttle.

	It also checks whether the steering servo lives on the axle that leads,
	because a car steering with its TRAILING axle is the classic shopping-cart
	castering symptom the user reported.
]]

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

for _, model in ipairs(workspace:GetDescendants()) do
	if not (model:IsA("Model") and model.Name:match("^Car_")) then
		continue
	end

	local body = model:FindFirstChild("Body")
	local seat = nil
	for _, d in ipairs(model:GetDescendants()) do
		if d:IsA("VehicleSeat") then
			seat = d
			break
		end
	end
	if not (body and body:IsA("BasePart") and seat) then
		continue
	end

	log("=== " .. model.Name .. " ===")
	local inv = body.CFrame:Inverse()

	-- Seat look expressed in BODY-LOCAL coords: which local axis does the car
	-- drive along under positive throttle?
	local seatLookLocal = inv:VectorToObjectSpace(seat.CFrame.LookVector)
	log(
		string.format(
			"  seat look in body-local = (%.2f, %.2f, %.2f)",
			seatLookLocal.X,
			seatLookLocal.Y,
			seatLookLocal.Z
		)
	)
	local drivesTowardPosZ = seatLookLocal.Z > 0
	log(string.format("  => positive throttle drives toward local %sZ", drivesTowardPosZ and "+" or "-"))

	-- Where are the labelled axles, and which one has the steering servo?
	local fZ, fN, rZ, rN = 0, 0, 0, 0
	local steerAxleZ, steerCount = 0, 0
	for _, d in ipairs(model:GetDescendants()) do
		if d:IsA("BasePart") and d.Name:match("^Wheel_") then
			local z = (inv * d.CFrame).Z
			if d.Name:sub(7, 7):upper() == "F" then
				fZ, fN = fZ + z, fN + 1
			else
				rZ, rN = rZ + z, rN + 1
			end
		end
		-- servo is parented to the HUB, not the wheel -- find it by name
		if d:IsA("HingeConstraint") and d.ActuatorType == Enum.ActuatorType.Servo then
			local host = d.Parent
			if host and host:IsA("BasePart") then
				steerAxleZ = steerAxleZ + (inv * host.CFrame).Z
				steerCount = steerCount + 1
			end
		end
	end

	if fN > 0 and rN > 0 then
		local fm, rm = fZ / fN, rZ / rN
		log(string.format("  labelled FRONT axle localZ=%.2f | REAR axle localZ=%.2f", fm, rm))
		local leadingIsFront = (drivesTowardPosZ and fm > rm) or (not drivesTowardPosZ and fm < rm)
		log(
			string.format(
				"  => the axle LEADING under throttle is the one labelled %s",
				leadingIsFront and "FRONT (correct)" or "REAR  (car drives backwards!)"
			)
		)
	end

	if steerCount > 0 then
		local sm = steerAxleZ / steerCount
		log(string.format("  steering servos=%d, mean host localZ=%.2f", steerCount, sm))
		local steerLeads = (drivesTowardPosZ and sm > 0) or (not drivesTowardPosZ and sm < 0)
		log(
			string.format(
				"  => steered axle %s under throttle %s",
				steerLeads and "LEADS" or "TRAILS",
				steerLeads and "(normal car)" or "(SHOPPING-CART castering)"
			)
		)
	else
		log("  no steering servos found by name scan")
	end
	log("")
end

if #out == 0 then
	return "No live cars with a Body + VehicleSeat."
end
return table.concat(out, "\n")