Modular assembly

A design is a set of parts joined at attachment points. Each part carries stats (mass, thrust, fuel, capacity, power, abilities) and sometimes a collision body. Behavior is computed either by aggregating stats or by simulating the assembled structure. Kerbal Space Program stacks tanks, engines, and decouplers into stages whose delta-v follows from mass ratios and simulates the craft as jointed parts. Besiege simulates blocks, hinges, and powered wheels as rigid bodies. Spore's creature editor grants abilities from attached parts. Armored Core assembles mechs from frame parts under weight and energy limits. Space Engineers builds small and large grids from blocks such as thrusters, reactors, conveyors, and deformable armor. Constraints such as budget, mass, power, or part count bound the design space.

Tinkering and test-to-failure. Players build, watch the contraption flip, explode, or fail to lift off, diagnose why, and rebuild. A working design earns engineering pride, and many get shared.

• part catalog size and granularity
• stat aggregation versus full physical simulation of the assembly
• attachment rules: fixed nodes, free attachment, symmetry tools
• constraints: cost, mass, energy, part count
• test environment and how clearly failure causes are shown

• Joint strength limits and physics instability in large assemblies make craft wobble or break apart; Kerbal Space Program players call unexplained destruction the Kraken.
• Part count drives simulation cost, so ambitious builds slow the game down.
• A dominant part combination becomes the only competitive build.
• Catalog bloat buries useful parts and overwhelms new players.

• Players invent contraptions designers did not anticipate, such as flying machines in Besiege, and share them.
• When parts are unlocked by progression, the assembly space widens over time and old designs get rebuilt.
• Coupled with physics, small design changes produce large behavioral differences, which drives iteration.

• Can reinforcement-learned controllers make arbitrary player-built bodies walk, swim, or fly convincingly at runtime?
• Can generated parts with stats derived from their geometry replace hand-authored part catalogs?