Trains

Trains

A Furnace Minecart that has fuel and is on rails acts as a locomotive. Every tick, it scans for nearby minecarts behind it and attaches them as trailers, up to a maximum of 7 trailers (8 carts total including the locomotive).

Attaching

Every tick the locomotive runs a two-pass scan, starting from itself and then from each already-attached trailer:

1. First pass: any non-furnace minecart overlapping the anchor's bounding box (inflated by 0.2) that is not already in a train and is on a rail gets attached.
2. Second pass (only if first finds nothing): a probe is stepped one rail segment behind the anchor, and the same filter runs on the probe's bounding box.

The whole chain of touching carts attaches in a single tick, so a line of 5 carts behind the locomotive couples on the same frame you place them.

Dispenser minecarts can be attached as trailers.

Movement (Cascade)

The locomotive places a single "probe" minecart at its own position with a velocity pointing backward along its yaw (magnitude 1.5). For each trailer in order:

1. The trailer is ticked on its own rail physics (gives it a natural yaw and rail state).
2. The probe is advanced one rail segment.
3. If the trailer is within 4 blocks of the probe, it snaps to the probe's position, matches yaw and pitch, and takes a forward velocity matching the locomotive's current horizontal speed.
4. If the trailer is farther than 4 blocks, the cascade stops for the rest of the chain this tick. The overshooting trailer remains in the train list and is still given a forward-along-yaw velocity, but is no longer position-snapped.

The probe walks the rail continuously; it is not reset per trailer. So the spacing along a curve is measured in rail distance, not straight-line distance.

Speed Penalty

Each cart in the train reduces the locomotive's max speed by 5%. Formula (with train.size being the number of trailers):

cap * (1 - 0.05 * (trainSize + 1))

Full 1+7 train: 60% of normal cap.

Disconnecting

A trailer is removed from the train if any of these is true on a given tick:

• The trailer has been removed from the world.
• The trailer has lost its train command tag.
• The trailer is on the ground and its horizontal speed is below 0.01.

When a trailer is removed, all trailers behind it are removed as well, and a bamboo-break sound plays at each disconnection site.

A secondary age-based safety net clears the train and trainMove command tags of any minecart whose tickCount exceeds 60 without being controlled by a locomotive tick. This handles orphaned trailers if the locomotive despawns, unloads, or enters a portal.

Fuel Auto-Pull

When the locomotive's fuel drops below 100 ticks, it scans the first trailer. If that trailer is a chest minecart or hopper minecart, the locomotive:

1. Iterates slots in order.
2. Picks the first slot with a fuel item.
3. Consumes 1 item (or replaces a lava bucket with an empty bucket).
4. Adds the item's full burn duration to the locomotive's fuel.
5. Stops scanning once one fuel item was pulled.

Only the first trailer is checked. If slots 2-7 of the train also contain fuel, they are not pulled from.

Powered Rail Toggle

While a furnace minecart is on a powered rail and has fuel remaining, its lit state follows the rail's powered property each tick:

• Powered rail with powered=true: cart stays lit.
• Powered rail with powered=false: cart extinguishes (fuel preserved).

Passing over an unpowered powered rail is a zero-cost way to park a train. Passing back over a powered-on rail relights it.

Portal Travel

When a locomotive passes through a portal, the train breaks immediately: all trailer train and trainMove tags are cleared, the trailer list empties, and the trailers are left behind as normal minecarts.

Exit While Riding

If a player is riding a trailer (train tag) and they disconnect from the server, they are dismounted before the disconnect. This avoids carrying a ghost seat through logout.

Client Sync and Leash

The server broadcasts the train chain (locomotive UUID plus ordered trailer UUIDs) to all players tracking the locomotive whenever the chain composition changes, plus a heartbeat every 20 ticks.

The client stores chains in a cache with a 3-second stale window. Each cart drawn with a known predecessor gets a leash rendered from its body (offset 0.12 upward) to the predecessor's rope-hold anchor (offset 0.3 downward). The leash is rigid, not draped.

If no update arrives for a cart within 3 seconds, its leash stops rendering.

Limitations

• Sharp 90-degree corners at high speed can drop the probe outside the 4-block snap radius, causing the cart behind to fall back to its own yaw-based momentum for a tick before re-syncing.
• The leash uses vanilla rendering, so it appears as the standard leash visual.
• Only one locomotive per train. Two furnace minecarts cannot jointly share a chain.
• Mounting logic uses vanilla interact, so right-clicking a trailer enters it as a passenger.