How to choose correct battery(s).


Given the wide range of actuators and electronics which go into a robot, choosing the right battery may not be an easy task. This tutorial guides you through the thought processes involved in choosing one or more batteries for your robot.

Choosing out of Uni or Multiple battery.

How do you know if you need multiple batteries? Check the nominal voltage of each of the products you selected:

1.Electronics (microcontroller, motor controller power etc) usually operate at 9V-12V. Some operate at low as 3.3V and 5V. 2.Actuators (DC gear motors, stepper motors, servos etc) usually operate at 6V to 12V. A few operate as low as 3V 3.Sensors usually operate 5V

Based on the ranges above, it’s easy to see how, wen selecting optimal components for your project, that the voltage range may differ for each type of component. Fortunately most microcontrollers has a built-in voltage regulator which provides 5V to the I/O pins, so you don’t need a dedicated 5V battery. Should you choose a normal microcontroller, it’s likely that the voltage range is 9V to 12V. Operating a normal hobby servo motor (rated at 4.8V to 6V) from a 9V to 12V battery would quickly burn it. What to do? The easiest option would be to use a smaller 12V battery for the microcontroller, and a larger 6V battery for the servos.

Continuing the example above, where we chose a 12V microcontroller and 4.8V to 6V hobby servos, we have the option of using one (larger) 6V battery pack and a step-up voltage regulator. A voltage regulator does exactly as the name implies; it regulates the voltage. In our case we would need one which can accept 6V input and step it up to 12V.

Choosing a lower motor voltage does not automatically mean the list of motors available to you will be low power. However, a high voltage motor (36V, 48V, 60V) tends to be reserved for large DC motors. The second approach is to first select the ideal motor and design your robot’s electronics system around the indicated nominal voltage. Both approaches have their advantages and disadvantages and it is up to you to choose which you prefer.

Voltage dividers allow you to power electromechanical devices at different voltages. Voltage dividers are purely electrical devices with no programming involved. If you do not want to use voltage dividers, most electronics operate at 5 to 9V, so choosing either 6 or 9V as your robot’s supply voltage is the best choice (never assume an electronic device operates at 6 or 9V: you always need to read the supply voltage specifications for each electronic component). The other option is to use two different power supplies: one for the motors and another (smaller one) for the electronics.

Should you wish to operate your robot at 9V, you can often still choose a 12V motor, though you must keep in mind the rpm will be less that that listed (estimated as a fraction of the nominal value) and the motor efficiency will be slightly reduced.

[feature] This tutorial has been borrowed from Coleman Benson's post at Robot Shop [/feature]


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