Custom Spidertrons that have no grid will make the game crash. A simple null check should do the trick.

126.147 Error MainLoop.cpp:1284: Exception at tick 5039: The mod Double Speed Spidertron (0.0.10) caused a non-recoverable error.
Please report this error to the mod author.
Error while running event DoubleSpeedSpidertron::on_built_entity (ID 6)
DoubleSpeedSpidertron/script/spidertron.lua:44: attempt to index field 'grid' (a nil value)
stack traceback:
DoubleSpeedSpidertron/script/spidertron.lua:44: in function 'adjust_spidertron'
DoubleSpeedSpidertron/script/spidertron.lua:95: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

Hello, I solved the issue by adding 0x0 grid to spidertrons that do not have one. Because without grid this mod would not affect the spidertron. Please, let me know if everything works as expected.