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BATTERIES & MOTORS
A battery is a chemical energy source that can drive an electric current around a circuit. The electricity from the battery can be used to power an actuator. An actuator is something that makes a movement of some sort. Examples of actuators are things like electric motors, electromagnets (servos) and air or steam driven pistons.
Batteries can be either primary or secondary
 What are primary batteries?
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Primary batteries use up their chemical energy stores as they drive a current around a circuit. When the chemicals are used up, the battery can no longer provide a current and must be replaced.
Zinc Carbon batteries are the most common form of primary batteries. The cathode is a mixture of manganese dioxide paste and a carbon conductor. The anode is a zinc alloy can. The can also holds the chemicals inside the battery.
The insulator is usually coated paper.
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What are secondary batteries?
Secondary batteries produce a current using a reversible chemical reaction. When the reaction is complete, the battery can no longer drive a current. But it can be recharged by reversing the reaction. This is done by sending current from another source (like the mains) through it to restore the chemicals to their original state. Lead acid and Nicads are secondary batteries.
What are Ni-Cd batteries?
Nicads are nickel-cadmium batteries. They were first used on a large scale in 1917 to help light subway trains in Paris. Nickel-cadmium cells have a nickel hydroxide anode (positive electrode) and a cadmium metal cathode (negative electrode) immersed in a potassium hydroxide electrolyte, all assembled in a steel container. The main advantage of these batteries is that they can be recharged many times.
Batteries, especially Ni-Cd batteries are a light and efficient way of powering the motors and other devices (actuators) used in some robots.
MOTORS
How do electric motors work?
An electric motor works by making a metal coil spin in between two permanent magnets. Watch the video clip, read the text below and then watch the clip again in order to follow the logic.
 Click here to see real media clip
When a current passes through the coil it becomes an electromagnet. The top of the coil is turned into a north pole (red). The bottom becomes a south pole. The north pole on the top is attracted to the permanent magnet on the right (its south pole is facing inwards). So the coil starts to turn.
However, if the current didn't change, the coil would line up with the magnet and then stop. We want it to carry on spinning. And this is where the commutator and brushes come into play.
Every time the coil is vertical, the commutator breaks contact with the brushes and then reconnects. When it reconnects, its contacts are swapped over. This means that the current flows the other way in the coil. So the face that had been a north pole now becomes a south pole. So it is repelled from the south pole on the right. And the coil continues to spin.
Click here to find out more about motors.
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POWER batteries petrol nuclear energy |
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