Converter Engine

Type
Engine

Intent
Two Converter converters set up in a loop create a surplus of resources that can be used elsewhere in the game.

Motivation
Two resources that can be converted into each other fuel a feedback loop that produces a surplus of resources. At least one of the converters must output more resources than it takes in to create the surplus. The converter engine is a more complicated mechanism than most other engines but also offers more opportunities to improve the engine. As a result, a converter engine is nearly always dynamic.

Applicability
Use a converter engine when:


 * You want to create a more complex mechanism to provide the player with more resources than a static or dynamic engine provides. (Our example converter engine contains two interactive elements, while the dynamic engine contains only one.) It increases the difficulty of the game because the strength and the required investment of the feedback loop are more difficult to assess.


 * You need multiple options and mechanics to tune the profile of the feedback loop that drives the engine and thereby the stream of resources that flow into the game.

Structure


Participants

 * Two resources: energy and fuel
 * A converter that changes fuel into energy
 * A converter that changes energy into fuel
 * Actions that consume energy

Collaborations
The converters change energy into fuel and fuel into energy. Normally the player ends up with more energy than he started with.

Consequences
A converter engine introduces the chance of a deadlock. When both resources dry up, the engine stops working. Players run the risk of creating deadlocks themselves if they forget to invest energy to get new fuel. Combine a converter engine with a weak Static Engine to prevent this from happening.

A converter engine requires more work from the player, especially when the converters need to be operated manually.

As with a Dynamic Engine, a positive feedback loop drives a converter engine. In most cases, this feedback loop needs to be balanced by applying some sort of friction.

Implementation
The number of steps involved in the feedback loop of a converter engine strongly affects how hard it is to make it operate efficiently. More steps increase the difficulty; fewer steps reduce the difficulty. At the same time, more steps offer additional opportunities for tuning or adding to the engine.

With too few steps in the system, the advantages of the converter engine are limited, and you might consider replacing it with a Dynamic Engine. Too many steps might result in an engine that is cumbersome to operate and/or maintain, especially in a board game in which the different elements of the engine usually cannot be automated.

It is possible to create an unpredictable converter engine by introducing randomness, multiplayer dynamics, or skill into the feedback loop. This complicates the converter engine further and often increases the chance that a deadlock will occur.

Many implementations of the converter engine pattern put a limiter somewhere in the cycle to keep the positive engine under control and to keep the engine from producing too much energy. For example, if the number of fuel resources that can be converted each turn is limited, the maximum rate at which the engine can run is capped. In a Machinations diagram, you can use a gate node to limit the flow of resources. In an automobile, the car’s engine converts fuel into energy, which drives the fuel pump; the fuel pump consumes some of that energy to send more fuel to the engine. This creates a positive feedback loop that is limited by the throttle.

Examples
The 1980s-era space trading computer game Elite features an economy that occasionally acts as a converter engine. In Elite, every planet has its own market, selling and buying various trade goods. Occasionally, players will discover a lucrative trade route where they can buy one trade good at Planet A, sell it at a profit at Planet B, and return with another good that is in high demand on Planet A again (see below). Sometimes these routes involve three or more planets. Essentially, such a route is converter engine. It is limited by the cargo capacity of the player’s ship, which can be enlarged for a price. Other properties of the player’s ship might also affect the effectiveness of the converter engine: The ship’s “hyperspeed” range and its capabilities (or cost) to survive a voyage through hostile territories all affect the profitability of particular trade routes. Eventually, trade routes become less profitable as the player’s efforts reduce the demand, and thus the price, for certain goods over time (a mechanism that is omitted from the diagram).



The player’s location on Planet A or Planet B activates the converters that implement the trading mechanisms in the center. A few possible ship upgrades are included on the right.

A converter engine is at the heart of Power Grid (see below), although one of the converters is replaced by a more elaborate structure. The players spend money to buy fuel from a market and use that fuel to generate money in power plants. The fiction of the game is that players generate and sell electricity. However, the game mechanics do not model electricity itself; players simply convert fuel directly into money. Surplus money is invested in more efficient power plants and connecting more cities to the player’s power network. The converter engine is limited: The player can earn money only for every connected city, which effectively caps the money output during a turn. Power Grid also has a weak static engine to prevent deadlocks: The player will collect a small amount of money during a turn even if the player failed to generate money through power plants. The converter engine of Power Grid is slightly unpredictable as players can drive up the price of fuel by stockpiling it, which acts as a stopping mechanism at the same time.



Related Patterns

 * A converter engine is well suited to be combined with the Engine Building pattern because there are many opportunities to change the settings of the engine: the conversion rate of two converters and possibly the setting of a limiter.
 * The positive feedback a converter engine creates is best balanced by introducing some sort of friction.
 * A converter engine elaborates the Static Engine pattern.
 * A converter engine can be elaborated by the Engine Building and the Worker Placement pattern.