Ch11 - AT-ST Walker
Building a walking machine, especially the kind that walks on two legs, is an enormously difficult task. Coping with such a challenge demands outstanding creativity and broad knowledge, as well as the ability to observe surrounding nature in search for inspiration. As it turned out, the best solutions, when it comes to creating walkers, were invented by nature in the process of evolution.
A good example of engineers being inspired by nature are the airplane wings. To create machines that could fly, inventors closely examined the anatomy of birds and the shape of their wings. Those pieces of information were then used to build first aircrafts and to further develop their design.
Creators of walking robots can borrow ideas from a broad spectrum of living organisms. Not only the designer must decide how many legs his robot will have, but it's also important to plan how the legs will be attached to the body. This decision will influence the movement and the stability of the construction.
By considering those criteria, one can choose robot's "biological pattern" – a living organism that becomes the model for constructing the robot.
The first task for a constructor is to decide how the legs of the robot should be designed. Should all the legs be built the same way (like spider or human legs)? Or should they differ? Crabs are a good example of different leg structure with their strong claws at front and small hind legs, which are actually used by some other species to swim.
Other important decision concerns the amount and placement of the legs. One solution is to place legs on both sides of the robot body, which can be seen among spiders. Another idea is to attach legs under the torso of the robot, like we observe with humans, or chickens.
At this point, engineers around the world have constructed numerous two-legged humanoid robots that mimic human way of walking and do it fairly well.
One of the most notable family of walking robots, found unfortunately only in science-fiction, are the "chicken walkers". As the name suggests, their anatomy and movement resemble that of chickens.
One of the popular walking machines form the world of sci-fi is the "Star Wars" AT-ST walker.
AT-ST is a light machine, designed to develop great speed. It is equipped with three laser cannons which, combined with its agility an manoeuvrability, make it a great combat and scouting machine. The only weak point of the AT-ST walker is its legs. In the event they get tied together, or one of them is damaged, the whole machine loses stability, most likely falls and gets destroyed.
AT-ST is a typical example of a "chicken walker". It even mimics a slightly clumsy movement of a chicken.
The next significant issue in building walkers is finding the proper pattern of movement, called gait. Again, nature gives us some hints. By looking at even one animal, one can observe different ways it moves its legs to get different types of walking patterns.
Horses provide a good example. They have four different types of basic gaits: walk, trot, canter and gallop. They differ in the order of legs used at a time and in the method of dropping the hooves. Every gait has a different speed: the walk is the slowest and the gallop the fastest. By examining different gaits, constructors can choose the most appropriate pattern for their robot.
A well-known robot inspired by four-legged animals is the AT-AT, a mechanical elephant-like machine from the "Star Wars" saga.
When it comes to speed, the U.S. military engineers found inspiration in the fastest land animal: cheetah. On short distances, these cats can reach the speed of almost 100km/h.
The newest version of robo-cheetah can reach the speed of only 30 km/h, but with each new improvement, it moves its limbs and back more like the real cheetah.
The researchers also created a miniature robot designed after a grasshopper. This ultra-light robot weights only 7 grams and the intricate mechanisms inside are similar to those found in mechanical watches. The in-built battery enables the robo-grasshopper to jump one and a half meter 320 times, which is 27 times its body length! The only problem is that after the jump, the robot cannot get in position and prepare for another one. Once researchers find a solution to this inconvenience and install solar panels, the robot will be tested on a real meadow.
Problems with robot's stability while walking and after jumping, or falling, were dealt with by the researchers from the University of California. After close examination of lizard behaviour in its natural habitat, they came to the conclusion that their tail guarantees stable movement in diverse terrains. The robot that they constructed can stand up after it falls, thanks to its strong and flexible tail.
Build
To build this construction, you will need LEGO Education WeDo
Explore
This is how the complete AT-ST walker model looks like.
The robot can detect obstacles and stop in front of them.
It was designed after the war machines you might know from Star Wars.
The model has three electronic elements.
1. The hub powers and controls the motor and the sensor.
2. The motion sensor helps to detect obstacles and precipices in front of the robot.
3. The motor indirectly propels the legs of the walker.
When marching, the robot leans to the right and left because of its weight and loosely attached legs.
1. The robot does not fall, because its feet have several wide plates that distibute the weight onto a larger surface.
1. The machine lifts and moves legs forward, one at a time.
2. The cannons were installed on the long legs.
The sensor is hidden inside the robot's armouring.
The shell holds the transmissions, transmission shafts, hub and motor together.
1. Here you can see a laser beam attached to the robot. You can change the angle of the weapon by tilting it.
1. The motor propels the gear transmission, which transfers drive to the grey axle.
2. On the axle, there is a worm gear. The entire transmission consists of a gear, an axle, a special case and a worm gear.
3. The transmission changes direction and slows down the motor movement. Additionally, it gives the robot more force.
1. The worm gear propels the axle that in turn, propels two other axles.
The axles are connected via a transmission made out of three cogwheels.
Two small black gears rotate at the same speed and in the same direction. They propel bricks, which increase the rotation range of the mechanism. This solution allowed to connect the legs of the model.
1. This is how the formidable AT-ST walker looks like when advancing.
May the Force be with you!
Program
Today, you will create a program that activates the AT-ST Walker and stops it right before the end of the table.
