Crawler

A crawler or climber is a reaction in which two objects (or groups of) collide, leaving one of the objects moved backwards or forwards to a degree, and the other forward. Crawler reactions are commonly used to create engineered spaceships, also known as caterpillars.

List of crawlers

17c/45 pi heptomino crawler

Perhaps the first and most well known climber is the infamous 17c/45 reaction, consisting of pi heptomino running over a blinker, moving it back 6 cells and rephasing it, whilst the pi heptomino moves forward 17 cells. This takes place in 45 generations.

The reaction was known for a long time, however the idea of a spaceship powered by this reaction was mentioned much later in 2002 by David Bell who had discovered reactions between multiple pies, which emitted gliders. After much work, Gabriel Nivasch finished construction of caterpillar, the first 17c/45 orthogonal spaceship, on 31 December 2004.

Research has been conducted into building much smaller 17c/45 spaceships with pi crawlers.