Runic Engine

A runic engine is a magical power source for mechanical devices, such as the one used in the prostheses developed during the The Great War. The enchantment of the engine grants an attuned user proprioception and control over the device comparable to a natural limb, though this must be developed over time, just as a baby develops awareness of control of how to move their arms and legs.
While prostheses seem a logical application of a runic engine, this is a recent innovation - for much longer, they have been used for large scale applications, like cranes used in construction. Use of these devices is a prized skill among labourers, as an inexperienced user operating a crane might as easily punch through the wall as lay the next course of stone atop it. These large models require a heat source, such as a furnace, to function properly, and are practically limited in size and strength only by the amount of heat that can be safely applied to the engine without injuring the operator touching it. The miniaturized versions used in prostheses can be powered by the user's body heat.

Mechanism

At its core, the runic engine uses fundamental magical theory, converting heat directly into motion, producing an efficiency far beyond what is possible through non-magical means. This is accomplished through a runic equation, which must be designed specifically to match the movement capabilities of the device in question, engraved into the engine's core and its mounting points. This equation both contains the enchantment that allows heat to be converted into force, as well as defining the specific ranges of motion of each moving part. Thus, a crane, with only a few moving parts, requires a relatively simple runic engine (but a large one that can draw in a great deal of heat without injuring the user), while a prosthetic hand or foot requires an immensely complex runic engine that is also quite small.

Discovery

The runic engine was one of the first big breakthroughs of Arcanomechanics, which is the field of magically enhanced mechanisms. The first, crude models were developed in 1452 AE, and there has been steady improvement in years since, both in the complexity of the device used and in producing mechanisms that are easier to use.