# Piezoelectric device for a mace

A lady warrior in this story uses two main weapons.

• A bow for long range
• A mace for melee combat

This question concerns the operation of the mace.

Within the head of the weapon, during any impact (blocking or striking action), the force is absorbed and turned into an electric potential. This potential charges the warrior via a cord running through the shaft. Her body can get energy from electricity instead of food and metabolism, so technically, the more she fights, the more energy she has. She has unlimited energy while fighting.

First: What sort of generator would be needed to make this conversion? Also, is such a device physically possible, given unlimited resources?

• This does not sound like building a world Dec 18, 2021 at 5:12
• Oh sorry, wrong tag Dec 18, 2021 at 5:37
• Unfortunately questions about existing works of fiction are off topic for this site. Dec 18, 2021 at 5:44
• For your interest: there's an interesting effect called piezoelectricity you can look into which might spark an avenue of research for this. (Pun unintended). Dec 18, 2021 at 5:48
• that is not unlimited energy, if anything it drains her batteries faster since she is doing both less damage and is generating the force that is converted into electricity herself.
– John
Dec 18, 2021 at 15:11

Regenerative Braking

Hybrid Electric Vehicles use regenerative braking to charge the battery. A similar device can be fitted in the mace (a coil with magnetic plunger moving inside).

Regeneration efficiency is less than 100%

The warrior inputs energy in the mace. Only a part of this energy can be used for regeneration. So the warrior will gain less energy than she lost and after some time, she will be exhausted.

Impact energy absorbed by regenerative device

For your warrior, if the impact energy is converted into electrical energy by regenerative braking, then the effect of the impact is lost, which means that when she strikes the enemy to hurt him, the energy of the impact will be absorbed by the regenerative device and enemy will not get hurt (or may be slightly).

As @imtaar said, efficiency is going to be less than 100%. But maybe the energy is not just coming from the hero.

Blocking Blocking could absorb energy from your opponent. Blocking with a mace sounds challenging, a shield or a longer weapon may be better for that.

Explosive enemies You didn't mention who the hero is fighting. If it is some sort of decaying zombie with built up gases in the body or skull cavity, the pressure released when rupturing that cavity could push back on the weapon and give additional energy back.

One type of energy other answers have not touched on would be turbine energy activated by different viscosities. Part of the mace is water-filled, and another is filled with a more viscous oil. The water and oil will have different moments of inertia which will translate into different rates of deceleration. The heavier fluid goes through turbine blades, causing rotational energy, turning a generator.

As the other answers have stated, laws of conservation apply in the real world and it's a losing battle without some fictional physics. You won't have a science-based answer, but you can make something passable to move your plot along.