tokyo-wangan-racing/docs/MESH_SWAP.md

Swapping the placeholder RX-7 for the real mesh (M1)

The car is now a constraint chassis (springs + steering servos + motor-driven wheels — see src/shared/Chassis.luau and CarManager.buildCarModel). The placeholder Body/Cabin blocks are just the visual shell riding on that chassis. Making the RX-7 real means replacing the shell, not the chassis: weld a MeshPart body onto the Body part and hide the placeholder blocks.

Nothing else (saving, the allowlist, car switching, driving feel, the map, anti-cheat) needs to change.

Reference photos

The real car's reference photos live on the NAS (too large to commit to git):

unraid-1:/mnt/user/data/yy-roblox-games/0-fast-n-furious-sim/001-1993 Mazda RX-7/

A single downscaled reference is included at assets/reference/rx7-reference.png for quick lookups.

Step 1 — Get a mesh into Roblox

Options, easiest first:

1. Buy or find a free RX-7 FD model on the Roblox Creator Marketplace/toolbox, or
2. Model it in Blender from the reference photos and import the mesh (.fbx/.obj) via Studio's 3D importer, or
3. Commission one.

You want the car body shell as a single MeshPart (or a small welded Model with a clear root). Wheels can be separate meshes (see Step 4). Keep the part count low (mobile perf). This step needs Studio — mesh assets upload through Roblox's asset pipeline.

Step 2 — Store it where the server can clone it

Put the shell under ReplicatedStorage/CarModels/<carId> (e.g. CarModels/rx7_fc). Two ways to manage it:

• Simple: keep it in the Studio place file as a real Instance (not synced by Rojo). Fine for a single hero car.
• Version-controlled: export the model to a .rbxm and reference it from the Rojo project so it lives in git. See Rojo's $path docs for .rbxm model files.

Step 3 — Attach the shell in buildCarModel

In CarManager.buildCarModel, after the Body part is created:

local CAR_MODELS = ReplicatedStorage:FindFirstChild("CarModels")

-- inside buildCarModel, after `body` exists:
local shellTemplate = CAR_MODELS and CAR_MODELS:FindFirstChild(car.Id)
if shellTemplate then
    local shell = shellTemplate:Clone()
    -- Position the shell over the body, then weld it on.
    shell:PivotTo(body.CFrame * CFrame.new(0, SHELL_Y_OFFSET, 0))
    for _, p in ipairs(shell:GetDescendants()) do
        if p:IsA("BasePart") then
            p.CanCollide = false -- the Body part remains the collider
            p.Anchored = false
        end
    end
    local weld = Instance.new("WeldConstraint")
    weld.Part0 = body
    weld.Part1 = shell.PrimaryPart or shell:FindFirstChildWhichIsA("BasePart")
    weld.Parent = body
    shell.Parent = model
    -- Hide the placeholder blocks:
    body.Transparency = 1
    local cabin = model:FindFirstChild("Cabin")
    if cabin then cabin:Destroy() end
end

Cars without a mesh keep the block look automatically — import one car at a time.

Step 4 (polish) — Real wheel meshes

The chassis wheels are plain cylinders (Wheel_FL … Wheel_RR). To make them look real, weld a wheel MeshPart (CanCollide=false) onto each cylinder and set the cylinder's Transparency = 1. The cylinder stays the physics tyre — mesh collision on wheels is unreliable and slow.

Sizing gotcha

The chassis geometry (Chassis.BODY_SIZE, WHEEL_RADIUS, TRACK_HALF, WHEELBASE_HALF) is tuned for a ~6×12 stud footprint. Scale the imported mesh to fit the chassis — don't reshape the chassis around the mesh, or the driving feel changes for every car.

Verify

• rojo build --output build.rbxl compiles.
• In Studio: Play → you spawn in the real RX-7 → it drives → it saves.
• Non-allowlisted test account still can't select the RX-7 (server enforced).