Robot Attrition

Robot Attrition is a required dependency of Space Exploration.

In a nutshell

 * Logistics bots in a large/congested network will have a chance to crash while flying.
 * Robot attrition only affects logistic bots. Construction bots are completely unaffected.
 * The rate of bot crashes depends on the number of active bots in a network. Under 50 active bots, no bot will die of attrition.
 * The rate of bot crashes also depends on the Space Exploration zones' "robot attrition factory", visible on the Universe Explorer. Space zones usually have a high factor.
 * Crashed bots will drop the items they were carrying in a small container. Dropped items are automatically marked for pickup for construction robots.
 * Crashing bots originally cause AOE damage explosions. This explosion can be removed with the Swarm Safety technology.

Crash rate
A network with 50 or less active bots, will be unaffected by attrition. Over 50 bots, the rate of bot crashes increases linearly.

Note that this limit is based on active bots, that is, bots actually flying. You can find out how many active bots a network has by hovering over a roboport. The sidebar tooltip will show " / ", and you can subtract idle from total to get your active count.

The rate is calculated based on the distance traveled per item. This means that upgrading your robot cargo storage or your robot speed will not reduce the crash rate, even though this would end up in fewer active bots.

As a rough estimation, a network of 300 constantly active bots around the space science pack technology level would end up losing about 15 bots per hour.

In addition to this, each Space Exploration zone has its own "Robot Attrition factor". This is a straight multiplier to the rate of bot crashes on that zone. By default, Nauvis has Robot Attrition factor of 1. Space zones tend to have a high attrition factor (usually around 10), while zones with a high treat % come with lower attrition factor.

You can use this web page to estimate your crash rate.

Swarm Safety technology
Originally, robots crashing will cause an explosion which can damage things around it and even cause other bots to die if they are grouped up. You can research the Swarm Safety technology to prevent the explosion.

Note that Swarm Safety does not prevent bots from dying from attrition, it will only remove the AOE damage explosion.

Each level of Swarm Safety increases the size of robot networks that are protected from explosions. For example, at level 7, you can have 3500 active logistic bots in a network without explosions, but larger networks will still result in explosions.

Repair option
A mod setting (under Mod Settings -> Map) allows you to repair crashed robots, which is cheaper than building brand new robots, but forces you to deal with repair logistics. This setting is disabled by default.

With this setting enabled, bot corpses will stay behind and can be deconstructed for a "broken logistic robot" item. Those corpses are automatically marked for pickup by construction robots.

Two recipes are available: Recombine, which lets you create a new bot using 5 broken bots, and Repair, which can fix 1 broken bot into a working bot using some extra ingredients. Overall, both of those recipes should save you 25% materials over just rebuilding new bots.

Attrition rate option
The Robot Attrition value can be adjusted in Mod Settings -> Map. This will affect the "robot attrition factor" of zones.

The robot attrition factor of Nauvis is entirely determined by this value, however every other zone is only 50% determined by this value. For example, if you have a zone with a factor of 10 while the mod settings value is 1, the factor will be 5 with a settings value of 0, and 15 with a settings value of 2.

As of 0.6.89 this option does not affect zones already discovered, due to a bug in Space Exploration.

Design intent
There are 3 goals behind Robot Attrition:


 * The main goal is to provide a small incentive for players to explore other builds than bot bases. [As discussed by Wube https://www.factorio.com/blog/post/fff-225], bots are already the dominant logistic method in vanilla. This problem is exacerbated in Space Exploration, where even the most complicated recipe can be reduced to a machine and a pair of requester/provider chests.


 * A secondary goal is to be yet another inter-surface logistic problem. Players relying on bots for outposts will need to come up with a way to replenish them.


 * A tertiary goal is to make the conquest of biter planets more attractive. Planets with high threat also come with lower robot attrition factor.