Ackerman mobile robot chassis advantages introduction

1. The past and present of the Ackerman structure

Ackermann steering dynamics:

The Ackerman structure originated from automobile applications. It is a method of realizing automobile steering. When the car turns, the inner and outer wheels turn at different angles, and the turning radius of the inner tire is smaller than that of the outer tire. This steering method was first proposed by Georg Lankensperger, a German carriage engineer in 1817. His agent Rudolph Ackerman applied for a patent in the UK in 1818, so from now on this steering principle is called the Ackerman steering structure.

But decades before him, a man named Erasmus Darwin had come up with this idea.

Erasmus Darwin is the grandfather of Charles Darwin, the famous founder of the theory of evolution. He is a legendary figure in British history. He is a physician, poet, inventor, botanist, physiologist and other experts in one, and is known as the Leonardo da Vinci of Midlands.

After studying for six years in Cambridge and Edinburgh, the 25-year-old Darwin began practicing medicine in Lichfield, a little north of Birmingham. His superb medical skills made him famous (even King George III of England wanted him to be a court doctor, but he directly refused). His multiple identities as a poet, inventor, and various luminaries made him a core figure of the Birmingham Enlightenment "Lunar Society". There was also a person named James Watt in their circle of friends in the Lunar Society. You guessed it, it was Watt who improved the steam engine and led the Industrial Revolution.

Our famous doctor, Mr. Darwin, of course, used a horse-drawn carriage to save lives and heal the wounded, which is similar to the picture below:

With more than 10,000 miles of driving every year, he quickly discovered the problem with the steering method of this carriage:

(1) Because the car has to turn around a single central axis, the front wheel cannot be made large. This will easily lift the front wheel when it encounters rocks or other obstacles on the road.

(2) Because the two front wheels are parallel, when turning too far, it is easy for the four wheels to form a triangle in the same plane. In this situation, the car is the most "stable" and will not move at all.

So our inventor Mr. Darwin began to think of ways to transform his carriage, and then the vehicle test and certification engineer began to conduct road tests quietly. It was not until 1766 that he wrote to a friend that he had transformed two carriages himself and conducted 10,000 miles of road tests over a three-year period.

Later in 1767, Watt and Darwin met and hit it off. The two steam engine enthusiasts exchanged their views on steam engines (steam engines had not yet been used in the engineering field at that time). Watt's idea was to use steam engines for industrial production, while Darwin wanted to use it to replace horses as a power source for vehicles (there was a conceptual design for a primitive car).

Darwin initially introduced his concept design of the steam car in a letter to Watt. The picture below is Darwin's attempt to explain his chassis design at the time, but from this picture we can see the original prototype of the linkage steering mechanism:

When Watt received the signal, he could see it on the envelope, and he confirmed the structure as a rectangular structure.

Finally, we can see that the trapezoidal four-bar linkage mechanism is a letter exchange between Darwin and another friend in 1768:

Ackerman steering mechanism prototype

In this structure, the realization is basically the same as the steering mechanism of modern cars. Although wheel steering is theoretically realized, for nearly a hundred years, four-wheeled carriages still use the axle steering mode. The biggest problem is that with the industrial level at that time, it was too difficult to realize wheel steering, and the advantage was not obvious. It was the birth of the car that really made Ackerman steering flourish.

Let’s look at Benz’s prototype: a simple three-wheeled vehicle. We can boldly guess that CarBenz was unable to solve the problem of front-wheel steering for four-wheeled vehicles at the time, so it temporarily adopted the form of a three-wheeled vehicle.

Starting from the second car, Benz never adopted the three-wheel model again. We can assume that CarBenz solved the above problems and the automobile industry has taken off since then.

2. Application of Ackerman structure in mobile robots In the early stage, mobile robots mostly adopted two-wheel differential structure. From the Stanford Research Institute in the United States led by Charlie Rosen in 1956 to 2013, most of the domestic and foreign robot industry application research and industry quantitative use were still the wheel differential scheme of 1956. Similar problems encountered by Darwin 250 years ago have appeared, such as poor passability, inability to operate outdoor with heavy loads, and limited application scenarios. In addition, the frequency of later maintenance and updates is high. As a result, the two-wheel differential scheme cannot be quantified on a large scale in the application of mobile robots, and can only be used in indoor logistics and operation scenarios, and cannot be applied in all indoor and outdoor scenarios.

In 2013, four mobile robot enthusiasts exchanged their views on mobile robots and founded YUHESEN Technology (mobile robots were not widely used at that time). They were thinking about how to make intelligent mobile robots fully used in multi-scenario industrial production. Li Leida thought of using the Ackerman structure to first scale up the application of mobile robots to achieve full-scenario use of the technical solution (there is an original Ackerman robot concept design). So the four enthusiasts began to think of ways to transform the two-wheel differential robot, and then began to quietly conduct road tests. Until 2016, a three-year road test of 10,000 kilometers was carried out. Then the curtain was opened on the application of Ackerman structure mobile robots. With the subsequent promotion of Ackerman mobile robot application technology by JD.com, Alibaba, Meituan, Cainiao and other industries, Ackerman technology has now been fully quantified. Industry data shows that YUHESEN, as the top 1 mobile robot chassis company, is basically growing at an annual application rate of 350-400%. The growth of other follow-up companies in the industry is also above 100%.

3. Advantages of Ackerman Mobile Robot

The wheeled Ackerman steering robot chassis is used in robot applications such as large-load distribution within 600kg in paved road scenarios, park security, smart cleaning, and smart travel. The structure is driven by the rear wheel differential bridge, and the front wheel controls the direction to achieve forward, backward, and radius steering functions. It has the advantages of large load carrying and high control accuracy. It is a standard configuration robot chassis for logistics, security, cleaning, and elderly travel assistance robot applications.