Stress Units, Capacity and Impact
Kinetic Systems in Create consist of 2 major parts. Generators and Consumers. Generators have a certain Stress Capacity associated with them, while Consumers have a Stress Impact. As long as the total capacity of a system is greater or equal to the total impact the system will turn and all components will work. If however the total stress impact gets to large, the system will Overstress preventing all components from working. This state persists until either the impact gets lowered or some capacity added.
The amount of Stress a component has also scales with its current speed. All components have a certain Base Value, which refers to a speed of 1 RPM. To get the effective impact or capacity all you need to do is multiply that base value by its current speed. For example a water wheel (base value of 32 SU) turning at 5 RPM will add a total of 160 SU of capacity to the system, while the same wheel turning at 10 RPM will add 320 SU. The same logic applies to consumers: A crushing wheel running at 20 RPM adds 640 SU of impact to the system.
In the end this means that if you want to run 2 crushing wheels you'll need 2 water wheels running at the same speed or you can get away with just a single one if you slow down the crushers to half its speed instead. Create adds a variety of speed changing components, with the simplest being a combo of large and small cogwheels.
By default, components used only for relaying rotational power, such as shafts and cogwheels, have no stress impact at all. This makes predicting the amount of generators required for your contraptions much simpler and prevents punishment for aesthetic detours between machines and generators.
Optimizing stress impact and comparing net capacity of sources at base speed can become quite scientific. For those who are interested in seeing some actual numbers and more exhaustive information, it is recommended to look into crafting a pair of Goggles and a Stress Gauge:
Stats of a water wheel turning at 10 RPM:
Stats of a crushing wheel working at 20 RPM:
Example of a stress gauge:
