Batteries
Batteries are a very important part of our everyday lives. They are actually electric cells, a device which creates a current from a chemical reaction. A cell is composed of: a negative electrode; an electrolyte, which has ions; a separator, also an ion conductor; and a positive electrode. The electrolyte may be aqueous (made of water) or non-aqueous (not made of water), in liquid, paste, or solid form; and the casing. When the cell is connected the negative electrode supplies a current of electrons that flow through the load and are accepted by the positive electrode. The more common types of batteries are shown below.
� Zinc-Carbon Batteries - Zinc-carbon batteries have become the standard for the consumer battery industry of today because of their low cost, long shelf life, and low leakage during storage. They are made of a zinc anode, a manganese dioxide cathode, and an electrolyte of ammonium chloride or zinc chloride, which is dissolved in water. The cheaper batteries you see in the market are probably of this type. They come in different sizes, which are a basic indicator of their capacity. Not recommended for robots because they aren�t very powerful.
� Alkaline-Manganese Batteries � An alkaline-manganese dioxide battery contains an electrolytically manufactured manganese dioxide and aqueous alkaline electrolyte, as well as zinc metal as a powder. These batteries were developed in the early 1960's and are still widely used today. They are what we usually use for everyday uses, and have better performances than Zinc-Carbon Batteries. They usually come in different sizes, and have larger capacities, but they are expensive, and need to be thrown away.
� Nickel-Cadmium Batteries (NiCd) � A simple rechargeable battery which is used in many applications. Most rechargeable batteries seen on the market are usually of this type, they can usually be charged and discharged 100+ times. They are made of a nickel hydroxide [Ni(OH)2] cathode, and a cadmium hydroxide [Cd(OH)2] anode. When it is charged, the nickel hydroxide changes to nickel oxyhydroxide [NiOOH]. While in the anode, cadmium hydroxide is transformed to cadmium. Discharging reverses this effect. The formula while it is discharged is show below.
Cd + 2H2O + 2NiOOH -> 2Ni(OH)2 + Cd(OH)2
These batteries, however, contain cadmium, a poisonous metal, so it is starting to be replaced by more environmentally-friendly NiMH batteries. We can still use them for fighting robots, though. They are good because they are rechargeable.
� Nickel Metal Hydride Batteries (NiMH) � These are the better rechargeable batteries available, and can usually be charged and recharged 500+ times. They are made of a Nickel Hydroxide Ni(OH)2 cathode, and an anode which serves as the hydrogen storage alloy and does not change its composition. Cobalt and chemicals are also added to improve conductivity. When a discharged Nickel Metal Hydride Battery is charged, the chemical composition of the cathode is transformed and the nickel hydroxide changes to nickel oxyhydroxide. When the battery is used, the process is reversed and the nickel oxyhydroxide changes to nickel hydroxide. They are environmentally friendly, cheap, and are used in many applications from mobile phones to power tools, which were traditionally powered by NiCd batteries. They are also great in robots.
Batteries for building Robots
The above batteries are all suitable for combat robotic applications. Remember that Zinc-Carbon and Alkaline-Manganese batteries come in many standard sizes, and they provide a voltage of 1.5V each. They�re the kind you find by those check-out counters in supermarkets. Duracell is one of the companies that make alkaline batteries. Eveready is one of the companies that make zinc-carbon batteries. Standard sizes include AAA, AA, C, D, and those rectangular 9V cells.
Also note that you can find Nickel-Cadmium and Nickel Metal Hydride batteries in those same standard sizes, but they usually only provide 1.2V each. Their amperage/capacities are usually in the 1300 mAh to 2200 mAh range. If the circuit is designed well, this should be sufficient for combat purposes.
Attaching Batteries
Here in Thailand, where everything low-tech is very, very cheap, we can buy cute little plastic battery holders. They are made from black plastic, and come in 1, 2, 3, 4-cell sizes. They even come with a red and black wire sticking out, so you can solder them directly into your circuit.
Charging Batteries
If you care about the environment enough to use rechargeable batteries, then of course, you�ll need a charger. They aren�t that expensive, and it�s good to invest in one, because you�ll save a lot of money that you would otherwise waste on buying disposable batteries. Make sure the charger is designed you charge the same type of batteries you are using. If done incorrectly, batteries may catch fire and/or explode. That would be bad.