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MOBILITY
 How do robots get around? |
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Look around your home… it has been designed for humans. You probably have stairs, sharp corners and carpets or tiled floors. This is no problem for us but it would make life difficult for a robot with wheels. Stairs would only be manageable by robots with legs or perhaps tracks. The simplest mechanism, and also the lightest is crawling. But a crawling robot wouldn't be able to travel across anything but the smoothest tile floor. So, the options are legs, wheels, tracks and crawling. You can find out more about these on some of the other webpages.
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And what about humans?
Well, it's no secret that we've only got legs. But how do they work? Well, as you can see, with all those muscles, it'll be pretty difficult to explain. So instead, let's look at an arm. The principle behind the way they work is just the same.
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Arms, bones, muscles and tendons
Firstly, bones can't move by themselves, they need a force to act on them before they can move. This force is provided by muscles. When a muscle contracts, it is able to produce a powerful force. This force is transferred to the bones through the tendons - tendons link the ends of the muscles to the bones. Tendons are very tough - and unlike muscles, they don't stretch very easily.
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How does the arm move?
The arm bends at the elbow to make a hinge joint - a bit like the hinge on a door. Two muscles move the arm, the biceps and the triceps. The biceps muscle is at the front of the arm and the triceps is at the back. Tendons attach the biceps to the shoulder blade at the top and the radius (one of the bones in the forearm) at the bottom. When the biceps contracts, it becomes shorter, pulls on the radius and arm moves up.
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Straightening the arm
Muscles can only contract or 'pull', they never 'push' So the biceps can't straighten the arm. Instead, the triceps muscle at the back of the arm contracts to pull the arm down or extend it. For this reason this muscle is referred to as an extensor. The biceps and the triceps work together in a co-ordinated way to bring about movement in the two directions.
How does the leg work?
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Just as in the arm, the leg muscles are arranged in co-ordinated pairs. We say the muscles are antagonistic - they work against each other. When one of a pair of muscles contracts, it exerts a pulling force on the bone to which it is attached, the other muscle must stay relaxed to allow the pulling force to take action. The brain is able to co-ordinate all of the correct muscles to ensure that the leg bones move in the right direction to enable you to walk.
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MOBILITY legs crawler tracks wheels
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