Introduction
Choosing the correct battery might be difficult given the variety of actuators and electronics that go into a robot. This article will walk you through the decision-making process for selecting one or more batteries for your robot. NiMH batteries are a type of rechargeable battery.
How Do I Choose a Battery?
This article will walk you through the decision-making process for selecting one or more batteries for your robot.
Even if you're new to robotics, you've probably noticed that the components you wish to use don't all run at the same voltage. When looking at a production robot, you might think, "How is everything running on just one battery?" There are two methods used, and we'll assist you in deciding which is ideal for you.
Multiple Batteries
Advantages
- It takes less time to design.
- Can be more productive
Disadvantages
- At different moments, different sections of the robot will stop working.
- Recharging several batteries
How can you determine if you'll need more than one battery? Examine the nominal voltage of each of the items you've chosen:
- Electronics (microcontrollers, motor controller power, and so on) often function between 9 and 12 volts. Some run on as little as 3.3 or 5 volts.
- Actuators (DC gear motors, stepper motors, servos, and so on) typically run on 6 to 12 volts. A handful of them can run on as little as 3V.
- Sensors typically work at 5 volts.
Based on the given ranges, it's easy to understand how the voltage range for each type of component may differ when picking appropriate components for your project. Fortunately, most microcontrollers include a built-in voltage regulator that supplies 5V to the I/O pins, eliminating the need for a separate 5V battery. If you use a standard microcontroller, the voltage range will most likely be 9V to 12V. A 9V to 12V battery would quickly burn out a typical hobby servo motor (rated at 4.8V to 6V). What should I do? Using a smaller 12V battery for the microcontroller and a larger 6V battery for the servos is the simplest solution.
One Battery
Advantages
- There is one battery to charge.
- Lighter weight
Disadvantages
- (may) require the use of a voltage regulator.
- It's a little more difficult to understand and wire.
Using the same 12V microcontroller and 4.8V to 6V hobby servos as in the previous example, we may use one (bigger) 6V battery pack and a step-up voltage regulator. A voltage regulator does exactly what it says on the tin: it controls the voltage. In our situation, one that can receive 6V input and step it up to 12V is required. Choosing a lower motor voltage does not mean you'll have a smaller selection of motors to choose from. Large DC motors, on the other hand, are more likely to use a high voltage(36V, 48V, or 60V). The second method is to choose the optimal motor first, then construct your robot's electronics system around the specified nominal voltage. Both tactics offer benefits and drawbacks, and it is up to you to decide which one you prefer. Voltage dividers allow electromechanical devices to be powered at different voltages. Voltage dividers are merely electrical devices that do not require any programming. Most electronics run at 5 to 9V, thus picking 6 or 9V as your robot's supply voltage is the best option if you don't want to employ voltage dividers (never assume an electronic device operates at 6 or 9V: you always need to read the supply voltage specifications for each electronic component). Another alternative is to use two separate power sources: One is for the motors, while the other (smaller) is for the electronics. You may typically use a 12V motor to operate your robot at 9V, but keep in mind that the rpm will be lower than specified (calculated as a percentage of the nominal number) and the motor efficiency will be slightly lowered.
Tips / Tricks
Standard battery voltages are:
- 1.2V: A rechargeable NiMH AA or AAA battery (unless you really take a little robot, a cell doesn't work much)
- 1.5V: An alkaline AA or AAA battery (damage due to not recharging and can't do much by itself)
- 2.4v: Two rechargeable AA or AAA batteries; Even for small robots, they still can't do anything on their own
- 3V: two alkaline AA or AAA batteries; Most microcontrollers cannot operate at this voltage, except for most actuators.
- 3.6V: three charging NiMh AA or AAA batteries; This is usually the minimum voltage to run some micro-regulation
- 3.7V: a lipo battery; It is close to 3.6V and is minimal for running some microcontrollers
- 4.5V: Three alkaline AA or AAA batteries ... Why even consider robotics non-charging?
- 4.8V: Four AA or AAA together provide the minimum voltage for running a standard hobby servo motor. This can be either as individual cells or as a single rechargeable battery pack.
- 6V: Four AA or AAA alkaline batteries, five rechargeable NiMh cells, or one 6V rechargeable lead-acid pack. This is the maximum (and ideal) voltage that most hobby services can handle. Use this if your servers need a little more power.
- 7.2V: Six AA or AAA rechargeable NiMh batteries are perfect for 7.2V DC gear motors. These are usually in battery packs instead of individual cells and you will need a more specific NiMH battery pack charger.
- 7.4V: Two lipo cells can often power the micro-controller and work great for 7.2V DC gear motors. Unfortunately, this is not the case. Too much.
- 7.5V: Five Alkaline AA or AAA: Seldom used because it has many batteries in one use.
- 8.4V: 7x NiMH AA batteries (hard to find a charger for 7xAAA NiMH batteries). It is also not used much as it means to charge 7 batteries simultaneously.
- 9V: 6x alkaline batteries, a 9V (NMH or alkaline) battery, or a 9V lead-acid battery: Please avoid using 6x alkaline for the sake of the environment A 9V single cell rectangular battery is often used in dual battery configurations to power the microcontroller. 9V lead-acid batteries are a bit harder to find and although they are quite heavy, they are quite affordable and have high capacity.
- 9.6V: 7x NiMH cell, usually in battery pack configuration. This is good for motors that operate at 9V, and also for microcontrollers (most can operate above 9V).
- 11.1V: Three lipo batteries produce about 12V and are much lighter than 10x 1.2V cells or 12V lead-acid battery packs. You need a special lipo charger capable of charging 3 cell lipo pix.
- 12V: 10x 1.2V cell (always configured as a NiMh battery pack) or a 12V rechargeable lead-acid battery pack. 12V is ideal for many types of DC gear motors and most microcontrollers.
- Anything above 12V is usually reserved for very large robots. If you have a 14.4V LiPo or 18V NiMh pack with a cordless drill, keep in mind that finding motors running at these voltages is not easy.
Robots using auxiliary motors (legged robot or robotic arm) operate at 4.8V (4x AA NiMh cells) or 6V (5x NiMh AA cells). You can use a very cheap voltage regulator to power the microcontroller, which can increase the voltage from 6V to 9V. Small to medium mobile robots often use 6V, 9V, or 12V NiMh battery packs, the choice of which depends on the nominal voltage of the drive motors. If the robot includes one or more servo motors (eg for pan/tilt), the microcontroller can typically deliver enough current from a 5V digital pin. If your microcontroller runs at 9V and you want to use 6V motors, you might want to consider two battery solutions. The medium-sized mobile robot uses a 12V battery. Lead-acid or single NiMH battery pack (or 11.1V lipo battery if weight problem). Larger robots use 12V or 24V from one or more lead-acid battery packs.
Chemistry
NiMH: This is still the most commonly used battery in mobile robots. NiMH batteries are rechargeable and it is difficult to beat their cost (price/capacity/weight). Memory has almost no effect, meaning the battery should be brought to full capacity on each charge. NCD: These batteries are slowly disappearing due to their memory effect: If you do not discharge the battery properly and then recharge it to its full capacity, you lose some of the capacity each time. Are Alkaline: These are the least expensive batteries in the short term, and provide a higher voltage than the NiMH, but are not the best for the environment, and you need to buy a replacement. Lead Acid: High Capacity L Still Still The Cheapest Option, Lead Acid is usually reserved for medium-sized robots because of their incredibly high weight. Lipo: These are increasingly becoming the most popular type of battery due to your lightweight, discharge rate, and relatively good capacity, except that the voltage increases with an increment of 3.7V, so You need to plan on using Lipo before choosing your electronics and actuators.
Nominal voltage
The nominal voltage of a motor is the voltage at which the ratio of motor performance provides the best power output (instead of the highest efficiency or the highest output). Running the motor at nominal voltage can also guarantee a long working life.
Capacity
The capacity of a battery roughly determines how long a battery will last at a certain voltage, given the rate of a particular discharge. For example, if you choose a 12V, 2Ah (2000mAh) battery pack (regardless of chemistry), the battery should be able to run 2A using a 12A motor continuously for 1A. Alternatively, it can run a 12V motor using 1A for 2 hours, or a 12V motor using 0.5A for 4A. The rule of thumb is to divide this capacity (assuming you are running the actuator at the same voltage) by the current boot of the actuator to get the motor running time under normal load.
Example 1
2x Drive Motors: 6V nominal, 1A 1x 6V NiMh battery pack under each normal load, 2200mAh (equivalent to 2.2Ah) Note that the battery was selected based on the nominal voltage of the motor. Do you run 6V motors with a 7.2V battery instead, calculations become more difficult (use total watts divided by total watts per hour to get an idea). Therefore 6V battery pack will continue: 2.2Ah battery / (2 motors 1 1A per motor) = 1.1 hours
Example 2
The 18 services used for the Hexapod robot use a light load * 1x 6V Ni MH battery pack 5Ah at 250 mA which operates at a light load 6V and uses 250 mA. First, we will assume that all the motors are under load at all times (ie the worst-case scenario) and therefore all 18 will use a total 4.5A 5Ah battery / 4.5A = 1.1 hours then note that the choice of battery is based on what Was done on Nominal voltage of the motor.
Discharge rate
The constant discharge rate of the battery is very important because if you choose a battery that cannot discharge at the desired current, the robot will either not work properly or will not work at all.
You may like to read about LED:
Example 1
You chose four 12V motors for your 4WD outdoor mobile robot. Each motor uses 1A under normal load, and in the case of the shield. You choose a 12V, 2Ah NiMH battery pack, regardless of the discharge rate. You find that your robot stops when it encounters even the slightest obstacle or tilt. Why? In this case, A 4A is used to run all four motors, while a half-pack emits only 1.2 times the capacity (1.2 x 2Ah = 2.4A). The current draw from motors is therefore much more than providing a battery.
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