Comparing batteries to generators as power sources for use with mobile robotics

This paper considers the scaling principles associated with the power and energy density of batteries and generators as applied to mobile robots and similarly-sized vehicles. We seek to identify, based on present technology, the size range at which a generator inclusive of a direct current electric motor, gearbox, and internal combustion engine can be effectively used to replace modern batteries. Models were derived to scale each component of the generator as a function of power, mass, efficiency, and speed. For a given power, energy, or mass requirement, these models illustrate that generators based on conventional technology are ill-suited for smaller robots. The results indicate that there is an intermediate robot size above which a hybrid generator/battery architecture is desirable. Using these scaling principles with modest extensions of existing battery technologies, it is also possible to infer the near-future performance of robot power technology and thus illustrate whether the generator-versus-battery tradeoff will shift toward or away from a hybrid robot topology for smaller vehicle systems.