The following pattern discovered by Charles Corderman
in 1971, which is a glide symmetric unstable puffer which moves
diagonally at a speed of c/12 (8 cells every 96 generations).
The exhaust is dirty and unfortunately catches up and destroys
the switch engine before it runs 13 full periods. Corderman found
several ways to stabilize the switch engine to produce puffers,
using either one or two switch engines in tandem. See
stabilized switch engine and ark.
No spaceships were able to be made from switch engines until Dean
Hickerson found the first one in April 1991 (see Cordership).
Switch engine technology is now well-advanced, producing many c/12
diagonal spaceships, puffers, and rakes of many periods.
Small polyominoes exist whose evolution results in a switch
engine. See nonomino switch engine predecessor.
Several three-glider collisions produce dirty reactions that
produce a stabilized switch engine along with other ash, making
infinite growth. Until recently the only known syntheses for
clean unstabilized switch engines used four or more gliders. There
are several such recipes. In the reaction shown below no glider
arrives from the direction that the switch engine will travel to,
making it easier to repeat the reaction:
Running the above for 20 ticks completes a kickback reaction with
the top two gliders, resulting in the three-glider switch engine
recipe discovered by Luka Okanishi on 12 March 2017.