Power sources are indispensable while designing robotic systems. Hence, the selection of power sources should be the primary focus owing to its impact on the mechanism, packaging, weight and size of the system.
At present, batteries are more commonly used power sources. Many different types of batteries ranging from lead acid batteries that are safe to silver cadmium batteries that are smaller in volume.
Weight of the robot, cycle lifetime and safety are the factors that need to be taken into account while designing a battery-powered robot.
The following sections will elaborate on some of the important power components employed in robotic systems.
The generator systems work based on the conversion of the gasoline energy to motive power via a combustion process in an engine.
These are two stage systems that can charge the robotic devices continuously during operation, even when the robots are immobile.
To the contrary, thermoelectric generators directly convert heat into electricity through the Seebeck effect. This type of power generation can be scaled to very small sizes with affecting the energy efficiency.
Hybrid/two-stage power systems are the system in which the power is continuously supplied at the first stage, and power is delivered as and when needed at the second stage.
Hybrid systems are of two types: serial and parallel. In series hybrid systems, a small amount of energy is continuously produced at the first stage, and the second stage supplies high power for short durations. In parallel configuration, power can be drawn at any time.
Batteries are the main component of a robotic system. Batteries can be classified into rechargeable or non-rechargeable. Non-rechargeable batteries deliver more power based on their size, and are suitable for certain applications.
Alkaline batteries are inexpensive, and lithium batteries, on the other hand exhibit a longer shelf life and better performance.
Common rechargeable batteries such as nickel-cadmium (NiCd) and lead acid batteries deliver a smaller voltage than alkaline batteries. They are found in battery packs along with specialized power connectors. Gelled lead acid batteries are widely used and capable of providing power of up to 40Wh/kg.
Lithium-ion, nickel metal hydride and silver zinc batteries are some of the other rechargeable battery technologies that offer significantly increased energy density.
Photovoltaic or solar cells can be used to charge the batteries of the robotic systems. They are used in conjunction with a capacitor and can be charged up to a set voltage level and then be discharged via the movements of motor. These cells are chiefly used in BEAM robots.
Miniball BEAM Robot by Solarbotics. Video courtesy of Solarbotics
Like batteries, fuel cells supply direct energy via a non-combustion process by directly deriving power from a hydrocarbon source at high efficiencies of up to 75%. This includes two electrodes sandwiched around a conductive electrolyte.
The electrons are released from the anode in the presence of a platinum catalyst, and they are used to generate an electrical current through a load. The efficiency of fuel cells can be increased to nearly 80% by utilizing the waste heat.
Other potential power sources of robotic systems include:
- Flywheel energy storage
- Compressed gases
- Super capacitors
- Organic garbage.
Sources and Further Reading