Guide To Choose Suitable Battery To Build A Robot

Do it yourself is perhaps the most common method to build a robot along with other methods that include the use of the kits. Even it’s a DIY robot or a robotic kit, both variants has to be powered with energy. The battery provides the electricity needed to move the wheels, to detect objects, to take decisions, and many more operations.

Batteries are essential components of a robot, and without these, a robot could not be functional. Before choosing the suitable battery, an analysis of the components and their energy consumption is recommended. Giving the wide range of batteries available on the market, choosing a battery can be a complex process.

A battery cannot provide unlimited energy, a good reason to build different type battery with different outputs. An effective solution to increase the output of a battery is to link multiple batteries in parallel to result a balance between efficiency and power consumption.

For example, the efficiency of an electric motor is determined by the report between the power that enters into the motor and the power that coming out from the motor as torque. Physical characteristics of the electric motor have a key place in determining its effectiveness.

In the process of battery selection a wide range of parameters become the subject of calculation including the weight of the robot, running time for every robotic part, case when electrical motors run simultaneously, and many more parameters. The result is the time in which the robot can operate with a fully charged battery.

This article is a guide to choose the right battery for a robot in terms of demanding operations.

What is a battery?

An electro – chemical process to convert chemical energy into electric energy, and reversing the process for rechargeable batteries during the charging process.
The role of batteries is to store and provide energy, while an electro-chemical process converts chemical energy into electric energy. With a wide range of capacity, shapes and sizes, the batteries can be used in series or parallel combination to have the desired voltage and power the robot.

Every battery has two terminals: anode (-) is the negative post, cathode (+) is the positive post. Between anode and electrolyte is a chemical reaction and has the role to send electrons out of the electrolyte directly to the anode terminal while the terminal is connected to the circuit. This flow continues to the cathode with electrons that re-enter in the electrolyte. The chemical flow is reversed for rechargeable batteries during the charging process.

Difference between mA and mAh
mA (milliAmpere) and mAh(milliAmpere-hour) are two measure units of electric charge with different characteristics. The mA value is used to define the maximum power on battery, while mAh value of a battery determine how much electric energy is stored in the battery. For example, a battery with 2000 mAh can power an electric motor with 2A (2000mA) current for one hour. After one hour of working the battery must be recharged.

Calculate Total Electrical Energy to Power the Robot

Calculate the total current when the robot running on maximum load.
The calculations above calculations to find the best battery/batteries that power your robot. If we’re using the logic to make this calculation, we have to calculate the total electrical energy consumption when the robot running on maximum load. And, then if for example a total electric energy consumption of a robot is 500mA, it is enough one battery with 1000mAh capacity for a continuous operation of 2 hours. This calculation is partially true while this is an estimation of power consumption for a robot as long as for example an electric motor with a standard 100mA and 12V in high load it may take double or even more current.

Main drive motors are major energy consumers while specifications like speed, acceleration, weight, breaking, etc. could affect the current draw. In this case, the accuracy of total energy required to power the robot is just a prediction.

Passing through certain steps in the calculation of energy can increase the calculate accuracy of the total energy consumption of a robot for a period of time, and the result is the choice of the appropriate battery with robot requirements.

The first step is an exercise when is taken into account the worst case for a robot, a case where the robot is used to full capacity and under continuous stress. Operations and movements repeated frequently by the robot could approximate a typical use of the robot and tells you the expectations as well as a way to decide if it is necessary to improve the power.

In the next step can be included the operational estimation time for all components and multiply the operating current. As an example, if it uses a 30mA consumer for 60% of the time during the operation of the robot, the total amount of operating current is 0.6 x 30mA = 18mA.

The third step is to add all these values to calculate the total current draw for a robot.

Robot specifications:

• Microcontroller: 4mA – 100% running time – 4mA energy consumption;
• Power LED: 2mA – 100% running time – 2mA energy consumption;
• Light Sensor: 10mA – 20% running time – 2mA energy consumption;

Total current consumption of the robot is: 4mA+2mA+2mA=8mA.

Let’s take 4 Ni-MH battery pack AA type with a total of 4.8V and 2700mAh. Running time for the robot is 2700mAh/8mA = ~337 hours and 30 minutes.

Using these values we can calculate the battery life for the chosen scenario.

Another way to calculate the battery life is to using battery life calculator link or other calculators like an energy calculator – link here.

Battery Types

On the market are available a wide range of battery types with different technologies used to store the energy. From Lithium-Ion to Alkaline, the batteries are available in different shapes and sizes, as well as with various specifications. Some batteries are designed to deliver more charge/discharge cycles while some batteries are designed for lightweight and for small sizes. There is always a compromise. If a battery has a long life, the possibility is very high to have big sizes and this could be a reason to pay attention in the selection process of battery for a robotic application.

• Lithium Ion Polymer(LiPo) – these batteries have small dimensions, are lightweight compared with other types of batteries, can be recharged very quickly, and has a high current output. All of these features are completed with a battery boast of 3.7V on every cell, which means a high energy density.
• Lithium Ion(Li-Ion)– these batteries are used in robotic applications for lightweight and a high-energy density. These batteries are usually found in laptops and cameras. With a lower output current compared with LiPo batteries, the Li-Ion batteries could be used in robots for controlling and less to power the electric motors.
• Nickel-Metal Hydride (NIMH) – no toxic metals in these batteries, has a high energy density, and can be charged quickly. Another important feature is the price. NIMH batteries are cheap for their size and capacity. This type of battery is frequently used in robotic applications.
• Alkaline – these batteries are not re-chargeable and could be used in small robots.

Every battery has storage specifications that should be taken into account when the choice is made. One of the main specifications for a battery is the capacity. The total capacity of a battery is highly dependent by the discharge conditions. In this case before purchasing the batteries it is indicate to find the manufacturer specifications for capacity when the batteries are used in different conditions.
The C-rate value for a battery defines the discharge current and is different between batteries.

Tutorials How to Regulate the Voltage

The regulator is designed to maintain automatically a constant voltage level using electronic components or electromechanical systems and supply a minimum required amount of power.

The control of robot power source is required for every robot from simple to complex, and from beginners to advanced users. After the battery is chosen, it cannot be directly connected to electronics and then start the robot. The regulator is designed to maintain automatically a constant voltage level using electronic components or electromechanical systems and supply a minimum required amount of power. A robot could work with AC or DC voltages. For both voltage types should be used voltage regulators.

There are few tutorials with schemes and steps to use a regulator for robots.

• Once you’ve decided on batteries, how do you regulate the voltage? – comprehensive tutorial with schemes and an explanation for voltage regulation that fits for every robot;
• Schematics – Robot power regulation – schemes and formulas to control the power source of the robot;
• Voltage Regulation – tutorial how to use SPX1117U voltage regulator and limiting the current to protect against overload;