Scientists have found a way to power future robots using an unusual source -- urine.

Researchers at the University of the West of England, Bristol and the University of Bristol worked together to build a system that will enable robots to function without batteries or being plugged into an electrical outlet.

Based on the functioning of the human heart, the system is designed to pump urine into the robot's "engine room," converting the waste into electricity and enabling the robot to function completely on its own.

Scientists are hoping the system, which can hold 24.5 ml of urine, could be used to power future generations of robots, or what they're calling EcoBots.

"In the city environment, they could re-charge using urine from urinals in public lavatories," said Peter Walters, a researcher with the University of the West of England. "In rural environments, liquid waste effluent could be collected from farms."

In the past 10 years, researchers have built four generations of EcoBots, each able to use microorganisms to digest the waste material and generate electricity from it, the university said.

Along with using human and animal urine, the robotic system also can create power by using rotten fruit and vegetables, dead flies, waste water and sludge.

Ioannis Ieropoulos, a scientist with the Bristol Robotics Laboratory, explained that the microorganisms work inside microbial fuel cells where they metabolize the organics, converting them into carbon dioxide and electricity.

Like the human heart, the robotic system works by using artificial muscles that compress a soft area in the center of the device, forcing fluid to be expelled through an outlet and delivered to the fuel cells. The artificial muscles then relax and go through the process again for the next cycle.

"The artificial heartbeat is mechanically simpler than a conventional electric motor-driven pump by virtue of the fact that it employs artificial muscle fibers to create the pumping action, rather than an electric motor, which is by comparison a more complex mechanical assembly," Walter said.