# Energy Sources of Mobile Robot Power Systems: A Systematic Review and Comparison of Efficiency
## Energy Sources of Mobile Robots
### Battery Management
#### 3.2.1 Power Control of Batteries  
Power delivery from the battery pack to individual components can be controlled on several levels. First, voltage regulation must be considered. Sensors and electronic components belonging to the control system typically require a low-voltage and low-power supply as compared to active elements. Stability of the voltage level on the control and sensors' supply is important to maintain system stability and accuracy of measurements. Good filtering and noise suppression on power lines for electronic components is necessary. Sensor selection as well as control circuitry can also be based on the interface voltage that they require. For battery-operated systems, there is a large number of compatible sensors that reduce the need for voltage shifting. Controllers can typically operate on 3.3-3.6 or 5 V levels, and in low power applications even 1.8 V can be sufficient. Integrated controllers based on mini-PC components usually require higher voltage in the range of 12 to 19 V, and they manage voltage internally for individual modules.  
Sensors are often designed to interface to either 3.3 or 5 V controllers, but industrial-grade sensors are often designed to work with a 24 V supply.  
In battery-operated systems, every bit of energy counts; therefore, it is important to provide control circuitry that allows switching on and off every part of the system that can be at least periodically disabled. This offers a great deal of control over power consumption and functions provided by the robot. Modern components with a digital interface can provide low-power-mode operation, which is available through their control interface; in this case, additional power switches are not necessary for such elements. Other components are fully active whenever they are powered on; for these components it is good practice to design an individual power control module that will allow managing their power state.  
Power-up and power-down sequences are important due to stability reasons and current draw, which can be substantial for specific components on startup. Power control circuitry should allow selective enabling of individual subsystems to implement a gradual power-up sequence and energy-saving modes.  
While powering down, data acquisition and actuation tasks need to be finished before power is removed. For legged robots, a statically stable pose must be achieved, and motor brakes might need activation before power can be removed. A smart power system is responsible for maintaining power to the control unit while it is still busy and informing it about the planned power down, saving the robot's state on power down, preparing the power-off stable position of the robot, and, only at the end, disconnecting the power.  
During normal operation, several components might require active power control. Such components mostly include actuation systems but could also include additional modules or sensors. Motor controllers use a control signal to determine the desired speed, position, or torque that should be provided by the motor. By changing the amount of power delivered to the motor, the controller affects the motor torque, speed, and position. Motor controllers are relatively efficient devices, but with high-power motors, the amount of heat dissipated in the motor controller can be substantial and might require active cooling, which must be considered by the power control system.