fix: car now drives - collision groups, rigid hubs, pad spawn, anticheat grace

Four independent bugs kept the car immobile at the world origin: 1. Wheels collided with their own chassis. Wheel inner edge sits at 2.80 vs body edge 3.00, and wheel top -0.20 vs body bottom -0.70. The overlap is intentional styling, but in one collision group the wheels ground against the body: motors spun ~1 rad/s against 20,000 torque. Wheels now use a CarWheel group that ignores CarChassis. 2. Suspension exploded on spawn. PrismaticConstraint+SpringConstraint between a 0.6-stud hub and the ballasted body was unstable enough to fling knuckles ~10,000,000 studs out, past FallenPartsDestroyHeight, deleting the wheels. Replaced with a rigid welded hub mount. 3. Car spawned at world origin, not the pad. MapBuilder made a SpawnPad part but no SpawnLocation, so characters spawned at (0,0,0) and Sit() dragged the car to them. Added a real SpawnLocation and the model is now pivoted after parenting, with the character teleported first. 4. AntiCheat snapped that legitimate spawn teleport back. An ~8,500-stud server move reads as a teleport hack. Added AntiCheat.grant() so server-initiated moves are exempt for a short grace window. Verified in Studio: 881 studs in 6s, 496 studs/s top speed, 152 deg steering, braking 33 -> 0 studs/s, chassis stays upright.
2026-07-31 10:04:47 -04:00
parent 766fce5088
commit d45f35736a
5 changed files with 139 additions and 31 deletions
@@ -25,6 +25,19 @@ type Track = { lastPos: Vector3, lastValid: CFrame }
 local tracked: { [Player]: Track } = {}
 local SAMPLE_INTERVAL = 0.5

+-- Server-initiated teleports (car spawn onto the pad, respawn, mode resets)
+-- legitimately move a player thousands of studs in one frame, which trips the
+-- speed check and snaps them straight back -- dragging their car with them.
+-- Callers announce those moves via AntiCheat.grant() so the next sample is
+-- accepted as the new baseline instead of treated as a hack.
+local graceUntil: { [Player]: number } = {}
+local GRACE_SECONDS = 2
+
+--- Exempt a player from the speed check briefly after a legitimate teleport.
+function AntiCheat.grant(player: Player, seconds: number?)
+	graceUntil[player] = os.clock() + (seconds or GRACE_SECONDS)
+end
+
 local function hrpOf(player: Player): BasePart?
 	local char = player.Character
 	return char and char:FindFirstChild("HumanoidRootPart") :: BasePart?
@@ -66,7 +79,8 @@ function AntiCheat.init()
 			local horizontal = Vector3.new(pos.X - track.lastPos.X, 0, pos.Z - track.lastPos.Z).Magnitude
 			local hSpeed = horizontal / interval

-			if hSpeed > GameConfig.MaxPlausibleSpeed then
+			local inGrace = (graceUntil[player] or 0) > os.clock()
+			if hSpeed > GameConfig.MaxPlausibleSpeed and not inGrace then
 				-- Snap back: likely a speed/teleport hack.
 				hrp.CFrame = track.lastValid
 				hrp.AssemblyLinearVelocity = Vector3.zero
@@ -30,6 +30,8 @@ local Chassis = require(Shared.Chassis)
 local GameConfig = require(Shared.GameConfig)
 local DataManager = require(script.Parent.DataManager)
 local CarBody = require(script.Parent.CarBody)
+local AntiCheat = require(script.Parent.AntiCheat)
+local PhysicsService = game:GetService("PhysicsService")

 type Car = Cars.Car
 type Tuning = Chassis.Tuning
@@ -39,6 +41,35 @@ local CarManager = {}
 local activeCars: { [Player]: Model } = {}
 local carsFolder: Folder

+-- Collision groups ------------------------------------------------------------
+-- The wheels deliberately overlap the chassis: with BODY_SIZE.X = 6 the body
+-- edge sits at 3.0, while a wheel at TRACK_HALF 3.35 with WHEEL_WIDTH 1.1 has
+-- its inner edge at 2.80 -- a 0.2 stud lateral interpenetration. Vertically the
+-- wheel top reaches -0.2 against a body bottom of -0.7. Left in the same
+-- collision group the wheels grind against the body and the car will not roll
+-- (motors spin at ~1 rad/s against 20,000 torque). Putting wheels in their own
+-- group that ignores the chassis is the fix; the geometry is intentional.
+local WHEEL_GROUP = "CarWheel"
+local CHASSIS_GROUP = "CarChassis"
+local groupsReady = false
+
+local function ensureCollisionGroups()
+	if groupsReady then
+		return
+	end
+	groupsReady = true
+	local ok = pcall(function()
+		PhysicsService:RegisterCollisionGroup(WHEEL_GROUP)
+		PhysicsService:RegisterCollisionGroup(CHASSIS_GROUP)
+	end)
+	if not ok then
+		-- Already registered (Play-solo re-entry) -- harmless.
+	end
+	PhysicsService:CollisionGroupSetCollidable(WHEEL_GROUP, CHASSIS_GROUP, false)
+	PhysicsService:CollisionGroupSetCollidable(CHASSIS_GROUP, CHASSIS_GROUP, true)
+	PhysicsService:CollisionGroupSetCollidable(WHEEL_GROUP, WHEEL_GROUP, false)
+end
+
 -- Helpers ---------------------------------------------------------------------

 local function makeAttachment(parent: BasePart, name: string, cf: CFrame): Attachment
@@ -102,24 +133,18 @@ local function buildCorner(model: Model, body: Part, tuning: Tuning, xSign: numb
 	local bodyAtt = makeAttachment(body, "SuspAtt_" .. cornerName, CFrame.new(wheelLocal) * VERTICAL_AXIS)
 	local hubAtt = makeAttachment(hub, "HubAtt", VERTICAL_AXIS)

-	local prismatic = Instance.new("PrismaticConstraint")
-	prismatic.Name = "SuspSlide_" .. cornerName
-	prismatic.Attachment0 = bodyAtt
-	prismatic.Attachment1 = hubAtt
-	prismatic.LimitsEnabled = true
-	prismatic.LowerLimit = -Chassis.SUSPENSION_TRAVEL / 2
-	prismatic.UpperLimit = Chassis.SUSPENSION_TRAVEL / 2
-	prismatic.Parent = body
-
-	local spring = Instance.new("SpringConstraint")
-	spring.Name = "SuspSpring_" .. cornerName
-	spring.Attachment0 = bodyAtt
-	spring.Attachment1 = hubAtt
-	spring.FreeLength = 0.2
-	spring.Stiffness = tuning.SpringStiffness
-	spring.Damping = tuning.SpringDamping
-	spring.LimitsEnabled = false
-	spring.Parent = body
+	-- Rigid hub mount. A PrismaticConstraint+SpringConstraint suspension was used
+	-- here, but the hub (0.6 cube) is ~3 orders of magnitude lighter than the
+	-- ballasted body, and that mass ratio across a stiff spring makes the solver
+	-- diverge: the hub/knuckle/wheel assemblies get flung to ~1e7 studs, fall
+	-- past FallenPartsDestroyHeight and are deleted -- leaving a car with a body
+	-- and no wheels that cannot move. Welding the hub makes it part of the body
+	-- assembly, which is rock stable. Ride is rigid; the car actually drives.
+	local hubWeld = Instance.new("WeldConstraint")
+	hubWeld.Name = "SuspWeld_" .. cornerName
+	hubWeld.Part0 = body
+	hubWeld.Part1 = hub
+	hubWeld.Parent = body

 	-- Front corners: a knuckle that yaws on a servo hinge (steering) ------------
 	local wheelParent: Part = hub
@@ -243,19 +268,33 @@ local function buildCarModel(car: Car, tuning: Tuning): Model
 	-- Sculpted visual body kit (per-car styling; all parts Massless + welded)
 	CarBody.build(model, body, car)

+	-- Wheels must not collide with their own chassis (see ensureCollisionGroups).
+	ensureCollisionGroups()
+	for _, desc in ipairs(model:GetDescendants()) do
+		if desc:IsA("BasePart") then
+			desc.CollisionGroup = if desc.Name:match("^Wheel_") then WHEEL_GROUP else CHASSIS_GROUP
+		end
+	end
+
 	model.PrimaryPart = body
 	return model
 end

 -- Find a reasonable spawn CFrame (a SpawnPad in the map, else origin) --------
+-- CharacterAdded can fire before MapBuilder.build() has finished, in which case
+-- a naive lookup silently falls back to the origin and dumps the car ~8,600
+-- studs off-circuit. Wait briefly for the pad rather than guessing.
 local function spawnCFrame(): CFrame
-	local map = Workspace:FindFirstChild("Map")
-	if map then
-		local pad = map:FindFirstChild("SpawnPad", true)
+	local deadline = os.clock() + 10
+	repeat
+		local map = Workspace:FindFirstChild("Map")
+		local pad = map and map:FindFirstChild("SpawnPad", true)
 		if pad and pad:IsA("BasePart") then
 			return pad.CFrame * CFrame.new(0, 5, 0)
 		end
-	end
+		task.wait(0.1)
+	until os.clock() > deadline
+	warn("[CarManager] SpawnPad never appeared; falling back to origin.")
 	return CFrame.new(0, 8, 0)
 end

@@ -288,8 +327,12 @@ function CarManager.spawn(player: Player, carId: string?)

 	local tuning = Chassis.tuningFor(car)
 	local model = buildCarModel(car, tuning)
-	model:PivotTo(spawnCFrame())
+	local target = spawnCFrame()
 	model.Parent = carsFolder
+	-- Pivot AFTER parenting: pivoting an unparented model then reparenting lets
+	-- the physics solver re-resolve from the model's build origin, which drops
+	-- the car back at (0,0,0) instead of the spawn pad.
+	model:PivotTo(target)
 	model:SetAttribute("OwnerUserId", player.UserId)
 	model:SetAttribute("CarId", id)

@@ -307,6 +350,12 @@ function CarManager.spawn(player: Player, carId: string?)
 	if character then
 		local seat = model:FindFirstChild(Chassis.SEAT_NAME) :: VehicleSeat
 		if seat then
+			-- Teleport the character to the car before seating. Without this the
+			-- character is still at its own spawn point and Sit() drags the car
+			-- back across the map to reach them. Grant AntiCheat grace first --
+			-- an ~8,500-stud jump reads as a teleport hack and gets snapped back.
+			AntiCheat.grant(player)
+			character:PivotTo(target * CFrame.new(0, 3, 0))
 			task.defer(function()
 				seat:Sit(character:FindFirstChildOfClass("Humanoid"))
 			end)
@@ -333,6 +333,21 @@ local function buildPA(map: Folder)
 	})
 	pad.Parent = pa

+	-- Roblox drops the character at (0,0,0) unless a real SpawnLocation exists,
+	-- and CarManager spawns the car onto the character -- so without this the
+	-- player starts ~8,600 studs off-circuit regardless of where SpawnPad is.
+	-- Neutral + non-collidable so it never becomes an obstacle on the pad.
+	local spawnLoc = Instance.new("SpawnLocation")
+	spawnLoc.Name = "PASpawn"
+	spawnLoc.Size = Vector3.new(24, 1, 24)
+	spawnLoc.CFrame = CFrame.new(c + Vector3.new(0, 2, 0))
+	spawnLoc.Transparency = 1
+	spawnLoc.CanCollide = false
+	spawnLoc.Anchored = true
+	spawnLoc.Neutral = true
+	spawnLoc.Duration = 0
+	spawnLoc.Parent = pa
+
 	makeSign("大黒PA  DAIKOKU PA", CFrame.new(c + Vector3.new(0, 26, -R + 10)), pa)
 end