Speed Demonoid

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Speed Demonoid
Speed Demonoid image
Pattern type Spaceship
Number of cells 1021124
Bounding box 872867 × 1839173
Direction Diagonal
Period 17833792
Mod 8916896
Speed 1746011c/8916896 | 3492022c/17833792
Heat Unknown
Discovered by Pavel Grankovskiy
Dave Greene
Year of discovery 2020

Speed Demonoid is a self-constructing adjustable spaceship constructed by Pavel Grankovskiy with the help of Dave Greene and completed on September 18, 2020.[1]

Due to a limitation in the design, this initial version of the Speed Demonoid design has an upper limit speed of 2c/9 diagonally, rather than the theoretical maximum of c/4. A redesign of the circuitry was required to correct this limitation.

Below the 2c/9 upper limit, the Speed Demonoid can be adjusted to move at any rational speed, by moving the trailing TRIGGER1 and TRIGGER2 gliders to the correct locations.

On September 26, a new Speed Demonoid variant was constructed to be smoother to simulate in HashLife, and to improve on the 2c/9 upper speed limit mentioned above.[2] Speed Demonoid v2 can be trivially adjusted to move at any speed that is a rational fraction lower than c/4. A Golly 3.x/4.0 script is available that will set up a glider recipe to construct a Speed Demonoid for any chosen speed, within certain practical size limitations.[3]

The Speed Demonoid was voted Pattern of the Year for 2020 on the ConwayLife.com forums, tied with Bandersnatch.[4]


The Speed Demonoid achieves its speed by building a crab spaceship and turning it into a double wickstretcher. The two wicks are ignited at different times specified by the locations of the TRIGGER1 and TRIGGER2 gliders. With the help of "guard gliders" traveling near the crab spaceship, when the burning wicks reach the crab, they produce target objects at the right location to allow the next copy of the construction-arm and reflector circuitry to be constructed. The TRIGGER1 guard glider allows the fuse to stop burning while the crab spaceship continues onward, and continues stretching the second wick. By contrast, the TRIGGER2 guard glider enables the destruction and eventual complete cleanup of the crab spaceship.

Both TRIGGER1 and TRIGGER2 are precisely synchronized so that they exactly keep up with the recipe gliders, despite being on different lanes and using one-time turners to move instead of conventional reflectors. Besides igniting the second crabstretcher wick, the TRIGGER2 signal also triggers self-destruct circuitry associated with the Scorbie Splitter and Snark.

The bait still lifes in the self-destruct circuitry were found by Simon Ekström's GoL-destroy search program. A similar design was used in the 10hd and 0hd Demonoids, but has been seen very rarely since then. Other recent Demonoids have used "destruction arms" similar to the one in the original Gemini spaceship, which incrementally shoot down parent constructor circuitry once it is no longer in use.


  1. Pavel Grankovskiy (September 18, 2020). Re: Speed Demonoid (completed) (discussion thread) at the ConwayLife.com forums
  2. Pavel Grankovskiy (September 26, 2020). Re: Speed Demonoid (discussion thread) at the ConwayLife.com forums
  3. Dave Greene (November 1, 2020). Re: Speed Demonoid (discussion thread) at the ConwayLife.com forums
  4. MathAndCode (March 18, 2021). Re: PotY 2020 Voting Thread (discussion thread) at the ConwayLife.com forums