Cog Logic

I started a prototype to explore mechanical possibilities with cogs and gears. I’m not sure exactly where it’s going, so I wanted to create a little playground where I can drag and drop cogs of different sizes to create a chain. 

The cogs would turn wheels with gaps in (I'll call those "pie wheels"), so it would be possible to drop a ball into the top and drop it down through the system. The player can use the left/right arrows to control the rotational direction of the system.

Starting functionality:

• Players can create and move cogs around on a 2D plane
• Cogs turn clockwise or anticlockwise depending on player input, and according to the correct rules of a cog chain
• Player can cycle between different cog sizes, which then turn at the appropriate speed
• Player can adjust the starting rotation of a cog
• Player can cycle between cogs with different shapes attached, and then spawn a ball to drop down

First logic attempt

The first challenge was understanding how a cog can know which cog is its parent, and therefore which way it should turn. This would be simple if each cog only had one parent cog and one child cog, but this felt like an artificial restriction. I wanted the player to have the freedom to create branches and loops.

The rule:

• There is a single unmovable “starter” cog, which is the cog powered by the player input
• To turn, a cog must be connected to the starter cog through an unbroken cog chain
• All cogs in the chain must turn in the opposite rotational direction to all its colliding cogs
• If any cog in the chain breaks that rule, the whole system is jammed and no cogs will turn

This sounds quite simple, but took me a while to figure out correctly. My first method was to try to keep each cog self-contained, only knowing about the cogs it was touching, but with no concept of its overall place in the chain. It worked initially, but I got stuck in an infinite loop when the player took out and replaced a middle cog in the chain. Perhaps someone with a better understanding of recursion could solve it, but I opted to change my method.

The end method

I found my solution by having a single manager script for all the cogs, which evaluates the chain any time it changes and assigns info to the cogs. It begins by looking at all the cogs colliding with the starter cog and assigning those a “chain index” of 1, and then loops through their colliding cogs and assigns them a “2”, etc. It also tells each cog who its parent is, and the rotational direction it should take. If it finds a cog that already has a chain index assigned, we know we are in a loop of cogs. It checks that all the colliding cogs are trying to turn it in the same direction, and if not it decides the system is jammed.

I added the ball spawning, and the end result can be seen in the screenshot gifs.