Scrap Mechanic Logic Guide

Creative vs Survival

Logic parts work in Creative immediately for testing and in Survival once you craft them at a Craft Bot. Creative is the sandbox for prototyping repeating timers or XOR latches without raid pressure. When a design is stable, blueprint the frame and rebuild it at your Mechanic Station base.

Challenge mode also uses logic for timed builds — clearing the first six challenges earns the True mechanic achievement; see the achievements page for the full Challenge route.

Power and parent blocks

Most logic parts need a stable parent block on your lift structure. If bearings spin the whole assembly, wires can snap when the physics engine re-simulates. Anchor logic cores to the ground or a non-moving frame; mount pistons on the moving layer only.

AND gate — the two-key door

Wire Button A and Button B into an AND gate, then wire the AND output to a Controller or Piston on your gate. Both buttons must be held or latched ON before the door opens — classic airlock behavior for warehouse loot runs where you do not want Farmbots following you inside.

OR gate — any tripwire fires the trap

Connect three Sensors facing different raid paths into an OR gate, then into a piston crusher or mounted weapon controller. Any single bot crossing a beam triggers the output — ideal when raid spawn points rotate around your farming guide plots.

XOR gate — alternating phases

XOR outputs ON when inputs differ. Pair with a timer loop and you get alternating piston phases — one arm extends while another retracts. Sorting lines and flip-flop memory both start here; advanced builds chain XOR with NOR gates for stable clocks.

Inverse gates (NAND / NOR / XNOR)

NAND and NOR are AND/OR with inverted output — handy when you want a line idle HIGH and pulsed LOW. The official wiki repeating-timer recipe uses AND + NOR + Timer in a triangle; XNOR repeating clocks appear in community tutorials as an alternative to XOR loops.

Sensor placement for raid defense

Mount sensors at ankle height across field entrances — Haybots and Totebots trip beams reliably at ground level. Point beams across chokepoints rather than wide open fields; fewer false positives from your own vehicles. Feed sensor outputs into OR gates when covering multiple lanes, then into piston crushers or mounted weapons.

For player-only doors, combine a sensor with an AND gate tied to an Enter button inside the base so Farmbots cannot follow even if they touch the outer switch.

Timer loops — repeating harvest or blinkers

A repeating timer needs at least two logic gates + one timer + optional switch (see wiki *Building: Repeating Timer*). Wire OR → XNOR → AND → Timer → back to OR, or the AND/NOR/Triangle variant. Adjust timer duration for crop harvest intervals or trap re-arm delays.

Always add a switch on the kill line so you can silence the loop during building — otherwise pistons hammer while you align bearings.

Controller sequencing

Connect a gate output to a Controller, then wire each controller channel to a piston, bearing brake, or mounted tool. Controllers fire steps in order — use them when a single pulse must extend three walls before arming a weapon.

For garage doors, pair a controller with timed piston pairs: one row extends to lift, a second row slides the gate. Test in Creative with no bots so you can rewind mis-timed channels without losing crops.

Piston crushers and flippers

Raid traps often use overhead pistons on OR-gated sensors — bot enters, piston slams, timer rearms after two seconds. Bot splat and junkyard achievements count creation kills; piston crushers rack up Totebot and Haybot totals passively during farmbot raids.

Horizontal pistons make fine sorters: extend to push items off a conveyor bearing, retract to let the next stack pass. Combine with XOR-timed arms for alternating lanes.

Example 1 — AND door for your first base

Place Button A outside and Button B inside, both wired to an AND gate driving a horizontal piston door. You must press inside first to arm, then outside to enter — bots cannot random-walk both buttons. Upgrade to sensors once you craft them.

Example 2 — OR raid trap ring

Surround the field with three sensors aimed at raid spawn lanes. OR gate → timer (0.5s) → piston crusher. Timer rearms after each smash so one bot does not drain the line ON forever. Pair with the farming guide raid calendar so you power traps before warnings.

Example 3 — repeating timer for lights or harvesters

Build the OR–XNOR–AND–Timer loop from the sensor section; hang a Light or Controller on the XNOR output. Flip the master switch OFF while aligning, then ON for overnight crop lighting or timed harvester bearings.

Example 4 — piston sorter for warehouse loot

After a warehouse guide run, drop loot on a bearing conveyor. Sensor detects item stack → piston pushes left if ON, timer clears → next sensor sorts another tier. XOR alternates lanes when two pistons would collide.