Unitsky String Technologies
9 February 2018
The electric hub motor, also called the motor-wheel, was first patented in the 80-ies of the XIX century, and its very first working samples were successfully tested on the first cars, which at the turn of the XIX-XX centuries were more popular than their "brethren" with internal combustion engines.
Nowadays the wheel motor is widely used in the transport sector: electric cars, dump trucks, trolley-buses, electric bikes, etc. It was also selected by the engineers at SkyWay Technologies Co. as the drive for SkyWay rolling stock.
Watch our new report on the design specifics of the SkyWay motor-wheel and the modern technologies that are used in the process of its designing and manufacturing.
Translation of the video:
Mikhail Kirichenko: Every day electric motors are getting wider application in our life. They are used everywhere: from a coffee-grinder to dump trucks. An electric bike can be considered as an intermediate version, this one that I am riding on today. Suffice it to recall Duyunov's motor-wheel for the electric bike or even more famous Yunitskiy's motor-wheel, which is the first and long-standing design development of SkyWay Technologies Co. and fit into the thing that I am riding now. It is the ancestor of all the motor-wheels that are now being installed in SkyWay rolling stock. Today we shall talk to professionals about the operating principle of the motor-wheel, its existing types and the best versions to use in various modes of transport.
Electric wheel hub motors, also called motor-wheels, were patented in the 80-ies of the XIX century. The first electric motor-wheel (a motor built into the wheel hub) was tested on vehicles. In 1884, a researcher from St. Louis Wellington Adams patented a unique idea - the introduction of an electric motor directly into the wheel of a vehicle. His idea was realized in practice by Albert Parcell from Boston, who has designed the first hub motor-wheel in 1890. It is easy to imagine how it works with the help of his witty comparison with a squirrel running in a wheel published by the journal "Popular mechanics".
Andrey Khvalyov: The magnetic field created in the coils interacts with the magnetic field of the rotor, because it is alternative and moves according to some law. Therefore, the magnetic field of the rotor starts to move. If we address a simple model, the operating principle is the following: suppose it is a rotor and this is a stator. We create an alternative magnetic field in the stator and it starts to rotate. Thus it forces the rotor to rotate, too.
M.K.: The structure of modern motor-wheels includes brushless motors that became widely used thanks to the development of electronics and the creation of high-power magnets, although the idea of such motor also appeared a long time ago, at the dawn of electricity. However, due to the lack of technologies, it waited implementation until the 60-ies of the XX century, when the first commercial brushless DC motor appeared. That means various commercial implementations of this type of electric drive have been existing for over 50 years! A motor-wheel is a complex unit that combines a wheel with its built-in traction motor, power transmission and brake system (thus, each motor-wheel has an individual drive). Anyway, electric motors are widely used in industry and household appliances. In particular, all the machines you see around me have them. Each mobile phone contains an eccentric, which makes the thing that you call vibration. However, electric motors are not widely used in transport and motor-wheels are applied in unique cases of the sort that we have discussed above. Nevertheless, the use of motor-wheels provides undisputable advantages. We are going to speak about them right now.
Vehicles with electric motor-wheels have a number of advantages over traditional ones: the absence of many complex and heavy transmission mechanisms between the motor and the wheel: clutch, transmission, drive shafts and differentials. In addition, it has an excellent dynamics: compact and lightweight electric motors can develop maximum torque from the lowest rpm.
Moreover, the use of a motor-wheel simplifies greatly the design of the braking energy recovery system. And, most importantly, the motor-wheel has no competitors in providing active safety of motion - all advanced electromechanical algorithms are easily interwoven into the control software and effect on each individual wheel. However, there are no advantages without disadvantages, and therefore for all these advantages the motor-wheel pays off with no less significant disadvantages, the main of which are their size and weight. Nevertheless, the engineers of SkyWay Technologies Co. managed to overcome these two major problems. This happened largely due to the choice of a synchronous electric motor and new hard-magnetic materials sintered on the basis of the neodymium-iron-boron alloy that have an advantage over magnets based on samarium and cobalt by energy features.
Ilya Zhagalsky: This is an assembled motor-wheel for our rolling stock, for unibus. As you see, it consists of a wheel, a motor and a braking system. All of it together is an assembled motor-wheel. This is our motor designed and produced by us. And this is a motor of a Chinese producer.
M.K.: The Chinese motor is less in size. What are its features in comparison with ours?
I.Z.: The thing is the Chinese motor has the rated capacity of 3 kW and our motor - 25 kW, i.e. the difference in capacity is tenfold, but the difference in size is not large.
M.K.: Therefore, this type of drive was chosen for SkyWay rolling stock despite the widespread use of asynchronous ones (the most famous of which is the super-advertised Duyunov's motor) that gained their popularity due to the simplicity of their design.
Andrey Zaitsev: An asynchronous motor is simpler by design. It does not have high-power rare-earth magnets that provide the possibility to gain economically favorable positions. However, on the other side, it has worse features by torque, power capacity and weight.
I.Z.: We recuperate more energy in this motor than it could be in an asynchronous one.
A.K.: In addition, another advantage is a high efficiency of our electric motor compared to an asynchronous one. In other words, you have to spend more energy to create a magnetic field and to start rotor rotation in an asynchronous motor than in our one, because we have already pre-energized magnets.
A.Z.: In addition, a very important point is the capability of the synchronous motor to be controlled not by the torque, but by speed. A correctly adjusted invertor with a vector control can maintain the preset speed with the accuracy of 1 or even 0.1 rpm irrespective of the load on it.
M.K.: Motor-wheels are used in dump trucks (we have already mentioned it above), because the mechanical transmission would simply not cope with the load of hundreds of tons, to which the truck is subjected. Besides, there is more than enough room for their arrangement, for example, in BelAZ truck. In SkyWay the task was more difficult: four standard motor-wheels for a high-speed unibus with a total capacity of 800 kW would weigh more than a ton, that is, about 3 times more than ours would, and simply would not fit into the aerodynamic outline of Yunitskiy's SkyWay transport rolling stock. Even if we speak about the cost, despite the use of rare-earth metals, which makes the motor somewhat more expensive, the cost of its operation eventually turns out to be lower because of its higher energy characteristics.
A.Z.: For example, an asynchronous motor-wheel of bicycle type is very limited by reasonable weight at sufficient power capacity. That is, to increase capacity from 5 to 25 kW, the diameter of the wheel would be growing like an avalanche because of increasing coil.
A.K.: I am working currently over the improvement of the design of our electric motors to be used in a high-speed vehicle, 60 kW motors, in a unicont (container vehicle), 35 kW motors. This is the picture of electromagnetic fields. I simulate an electric motor and consider how it can be improved, where the material should be reduced or increased to get the best features by weight and size.
M.K.: Let's sum up: only time will show what the future will bring to us, no doubt there will be absolutely different, qualitatively new technologies, and today it is possible only to guess the kind they will be.
However, at the present stage of their development it is possible to state with confidence that the team of Skyway Technologies Co. under the leadership of the General designer Anatoly Yunitskiy has created the best type of drive for SkyWay rolling stock and now it is a motor-wheel with a synchronous motor of our own design. Sign up to our youtube channel. Follow the news update at our official website. Support our project and you will never have to run like a squirrel in a wheel.
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