lunedì, maggio 27, 2019

The fastest all-electric aircraft by Rolls-Royce

This zero-emissions plane is expected to make a run for the record books with a target speed of 300+ MPH (480+ KMH). The 24ft-wide carbon-fibre aeroplane is being constructed by a 20-man team led by Rolls-Royce at a hangar the Staverton site.
The company hopes the plane will hit a world-beating top speed of more than 300mph when it takes to the skies over the UK in the first half of next year. The current record is 213mph, it was set last year by German-built Extra Aircraft 330LD, powered by a Siemens electric motor.
Inside a bustling hangar bay at the far end of Gloucestershire airport in South West England, a team of British engineers, designers, and data specialists recruited from across Rolls-Royce and beyond have set out to make history. They’re building a high-performance electric aeroplane unlike anything the world has ever seen. Scheduled to take to the skies over Great Britain in 2020, the aircraft will reach a speed of 300 mph – and quite likely more – making it the fastest all-electric plane in history.
This run for the record books is no stunt. It’s part of a Rolls-Royce initiative called ACCEL – short for “Accelerating the Electrification of Flight” – that’s intended to pioneer a third wave of aviation in support of Rolls-Royce’s strategy to champion electrification.

AEIT Automotive 2019

After 3 successful editions, AEIT Automotive 2019 Conference will be held on July 2nd-4th 2019 (at the Politecnico di Torino, headquarter of Lingotto) to host regular papers in several areas of the multiform automotive field.
The 4th AEIT International Conference of Electrical and Electronic Technologies for Automotive (AEIT Automotive 2019) aims to be a solid reference of the technical community to present and discuss the most recent results of scientific and technological research for the automotive industry, with particular emphasis to applications and new trends.
The Conference covers all aspects of the segment focusing on electrical vehicles, connected autonomous cars and related mobility. AEIT Automotive 2019 will bring together in an annual event, spread over 3 days, the Electrical and Electronic Automotive specialists with the Information and Communication Technology ones. The Steering and the Technical Program Committee include experts from the Academic world, Associations, Key Industrial Stakeholders and Regulatory Authorities.
AEIT Automotive 2019 will be structured in 3 days with Scientific Sessions, including both lectures and poster sessions, Key-note Speeches, Round tables and Panel discussions, covering current electric automotive scenario with its national and international perspectives, development trends and the regulatory framework.
Among the topics of the Special Sessions scheduled there are recent advances for e-mobility power components, wireless Charging for EVs, Automotive Lighting Systems, Laser based manufacturing technologies for automotive, Intra-and Inter-vehicle photonic networks for data transport and controlling and photonic and electronic sensins for automotive.

China’s market of e-buses

New IDTechEx report, “Electric Vehicles in China 2019-2029” shows that the penetration in China of electric buses is more impressive than electric cars. Like most other new products, electric vehicles sell in an S curve of a slow start with over supply. Then comes fastest growth with supply sometimes unable to keep up with demand then comes saturation. Take pure electric buses as an example. Here China rapidly deployed 400,000, 99% of the total number in the world, then it collapsed subsidies causing a collapse in deliveries and sadly it mainly makes smoking buses again.

The rest of the world is beginning to compensate. For example, recently Qbuzz in the Netherlands has ordered 159 pure electric buses, Helsingborg Sweden 76, Brussels Airport 30 and London 68 pure electric double deckers. Cities across the UK recently placed a total of 263 orders for zero-emission buses. Warsaw will order 130 pure electric buses for delivery by 2021. Kazakhstan is expecting 700 electric buses and Azerbaijan another 500 over the next three years. However, India has the largest potential, with a government plan for an initial 10,000 pure electric buses replacing some of the 1.6 million registered buses there, all of which must go, says the government, sensitive to the deaths they cause. The Indian state of Uttarakhand has ordered 500 electric buses. Now India is responsible for about 25% of the pure electric bus orders outside China. The Chinese – mainly BYD – are behind much of the supply but by no means all. Tata Motors in India has orders from six cities for a total of 255 pure electric buses. Large subsidies are an essential part of the take-off everywhere, China being at the top of the growth curve and everywhere else at the fast growth part, though China may see another S curve based on free market demands when pure electric has price parity.

Battery costs have been a primary impediment. However, in an interesting development, busy bus routes are seeing progress to less or no battery. Eight countries have ten-second charging supercapacitor large buses now and non-stop top-up charging in many forms has arrived from solar bodywork to intermittent catenary, rails, coils in the road. Top-up, including stationary forms with gantries etc at bus stops, typically leads to 80% less battery and this and the reduction in battery prices has led to some projections of the battery being a mere 6% of bus cost in ten years’ time. For more on all that see the IDTechEx Research report, “Energy Storage for Electric Buses and Trucks 2019-2029”. That will hasten the day when the up-front price of pure-electric buses is at parity with diesel. The rising cost of diesel powertrains also helps. Consider the extra cost of diesel fume reduction measures such as 48V mild hybridisation and the cost of adding equipment to treat emissions. IDTechEx currently projects price parity around 2030 for large buses but the future can come early.

Electric mobility is glamour

Simultaneously with the most annoying design event of the year, the Milan Design Week, which tooked place from 9th to 14th April, featured the first edition of BluE eMobility Days, six days of events and debates dedicated to electric mobility and its evolution. Thus, smart mobility has attracted worldwide interest with “Salone del Mobile”, “Fuorisalone” and Design Week, a strategic choice to represent, in perspective, a model of world excellence in the transition to widespread and sustainable mobility. There is therefore a great link between design appeal and sustainable mobility. Another example is the initiative of Repower, a global group active in the energy sector and player in electric mobility, with the LAMBROgio and LAMBROgino cargobikes, designed by Makio Hasuike.

The light three-wheeled and assisted pedal vehicles characterized by aesthetic pleasantness and great comfort, astonished the visitors of the FuoriSalone, as well as the benches hi-tech E-LOUNGE for recharging bikes and other devices, located inside Piazza Castello.

Car suitable as electricity grid reserve

To meet the universal desire for a transition to decentralised energy generation from renewable sources, new and innovative solutions for stabilising the electricity grid are necessary. The increasing use of renewable energy leads to fluctuations in the grid, which must be initially balanced by primary regulation, able to prevent impending power cuts at a second’s notice.

In Hagen (Germany) an important milestone on the road to emission-free energy and mobility has been achieved by technology company The Mobility House, energy supplier Enervie, transmission system operator Amprion and car maker Nissan. With the Nissan Leaf and an innovative charging and energy management technology, the project partners have succeeded in qualifying an electric car for all the Tso regulatory requirements for primary power regulation. This means that the car can be integrated as a regulating reserve for the German electricity grid – a breakthrough in the establishment of Vehicle-to-Grid (V2G) technology in Germany.
Electric cars such as the Nissan Leaf, with integrated bidirectional charging technology, is able not only to extract power from the grid and store it in its traction battery, but, if necessary, also to feed power back. This is called the Vehicle-to-Grid (V2G) concept.

The bidirectional chargeability of Nissan’s electric car is the foundation for its integration in the pilot project at the Enervie site in Hagen. In combination with innovative, intelligent charging and energy management technology from The Mobility House, the charging and discharging processes can be controlled and monitored.
As one of four Tso’s responsible for the transmission of power in Germany, and thus charged with the stability of the power grid, Amprion is a supporter of the ambitious V2G project. The Tso has defined the technical and regulatory requirements for prequalifying a mobile battery storage unit for the market for primary regulation. Amprion has now approved the Nissan Leaf, as the first electric car, in combination with the control system from The Mobility House, as suitable for this function.

How do electric motors impact on the manufacturing industry?

A phenomenon that is living a vertiginous growth and promises relevant numbers. We will increasingly witness a cohabitation among the various propulsion modalities and an adaptation of the industrial system. What will be the repercussions for small and medium engineering companies that manufacture mechanical components for the big production sector of motors and of motion in general?

By Stefano Colletta,
Technical Director of Subfornitura News-Tecniche Nuove

In the past, when motors were the conversation subject, it was almost unavoidable to think of a standard internal combustion engine, maybe of some old frames of some black and white movies. Today instead, speaking of motors from the industrial point of view certainly means referring to a constant process of technological innovation as well as to an increasingly green production and consumption methodology of goods. We take care of our health and of the one of our planet and we more and more tend to design and build a healthy environment.
The atmospheric pollution is one of the main causes of mortality and this phenomenon can be more surveyed in cities because in narrow spaces a higher concentration of CO2 persists. Therefore, we design fully “green” houses and entire cities; an ecologic culture grows and, obviously, the entire automotive industry cannot get away from this phenomenon. As a matter of fact, Toyota, Nissan, Citroen, BMW, Mercedes, Kia, Opel, Fiat, Hyundai and Volkswagen, all of them have a selection of electric models in their portfolio. Volvo, for instance, has announced it is going to modify, starting from 2019, the entire production of electric cars. A phenomenon – the implementation of electric motors in the various industrial fields – that no longer concerns just cars. Today it is possible to drive electric bikes with more and more professional characteristics; motorbikes with exceptional performances, such as CRP or Harley Davidson; to navigate with Riva boats; to compete with an electric single-seater. But not only, the industrial world is gradually getting in touch with it, packaging, food processing machines, machine tools, all those fields where there is the need of doing actions through a motion inside the machine itself.

The implementation of electric motors in the various industrial fields will no longer concerns just cars. The industrial world is gradually getting in touch with it: packaging, food processing machines, machine tools, all those fields where there is the need of doing actions through a motion inside the machine itself

Rising matter, then, and with noteworthy numbers. Let us consider, for instance, once more the car world. Today 2 millions of electric cars are circulating whereas about 600 millions are expected in 2014, against, however, 1 billion of cars that will circulate still using the green petrol and diesel. We will witness a cohabitation among the various propulsion modalities – thermal, electric and hybrid – and an adaptation by the industrial system to what nowadays still seems a not mature system, however already steeply rising. What about small and medium engineering companies that produce mechanical components for the big production field of motors and of motion in general? What will be the repercussions on this manufacturing area? Certainly, we will no longer need certain components in the same quantities as today. Companies and subcontractors must and will have to seize the signs that will increasingly come from the market and from their customers, modify the supplied sectors and sometimes give up activities that have stopped being remunerative and demanded by the various manufacturing fields. New competence and specialization areas, specific training and new figures to be employed in companies will be necessary. Some entrepreneurial realities will look at electric motors with a critical attitude because they will have probably failed their own transformation but any novelty or change always generates new opportunities and it up to us reaping them. The future will be greener than today, complex, competitive and even more variegated, issuing new challenges for our engineering companies.

ANFIA, three FSAE Italian teams and their cars

Last March 30th closed the experience for Formula SAE Italy (FSAE Italy) at MECSPE (Fiere di Parma, 28-30/03), the meeting point between technologies to produce and industrial supply chains, thanks to the sinergy among the 12 fairs which happen at the same time.
The three days in Parma represented an important halfway point on the way to the official event scheduled on July from 24th to 28th at “Riccardo Paletti” racetrack in Varano de’ Melegari, when Formula SAE Italy ( will welcome 100 universities teams from all over the world (33 with an electric car, 52 with a combustion car, 10 with a driverless car and 5 for class 3, with the project only, without car) which challenge each others in the designing and in the realization of a racing prototype.
The ANFIA-Formula SAE stand during the exhibition hosted three FSAE Italian teams and their cars: UniPR Racing Team of the University of Parma with their combustion car, Squadra Corse PoliTo of the Polytechnic University of Torino with their electric car, both of them will be part of the official event in July – and MoRe Modena Racing team of the University Modena e Reggio Emilia with their combustion car.
The ANFIA-Formula SAE stand also included a space dedicated to Dallara – one of the historical sponsors of the event together with FCA – which hosted a FIA Formula 2 (F2) car and organized few conferences in the neighboring workshop area.
“The participation of FSAE Italy at MECSPE gave to the teams the chance to get in contact with some potential sponsors, to explain to the innovation technologies used to build the cars and it gave to ANFIA the chance to let the exhibition learn about this event which stands out the designing abilities but also the management and the team working of the young automotive engineering – says Gianmarco Giorda, Director of ANFIA. MECSPE experience contributes to put in contact two world which are still pretty distance but connected, like the University’s world and the companies one”.

E-mobility, the electric-vehicle disruption is inevitable

Almost 1.2 million electric cars sold in the world in 2017, the most positive result ever obtained, and it is expected that such trend will be confirmed for 2018 with 2 million new electric cars on the market. In Italy, the technological maturity is the reference indicator that shows fewer criticalities, on the contrary the regulatory maturity is the area with more gaps.

The E-mobility Report 2018, developed by the Energy & Strategy Group of Milan Polytechnics, managed by Professor Vittorio Chiesa, has highlighted the state of the art of the electric vehicle market in Italy, Europe and in the rest of the world.

The world situation

In 2017, almost 1.2 million electric cars were sold in the world, over 1% of the total of new registrations and 57% more compared to the 750,000 units in 2016. It is the most positive result ever achieved and it is expected that such trend will be confirmed for 2018 with 2 million new electric cars on the market. With around 580,000 cars sold in 2017 and a 72% growth versus the previous year, China is the biggest world market, overcoming Europe that confirms to be second in the ranking with almost 290,000 sold units and scoring the 39% increment. United States follow with 200,000 (+27%) and Japan is at the fourth place with 56,000 cars and a noteworthy +155% compared to 2016.

Vittorio Chiesa, Energy & Strategy Group Manager of Milan Polytechnics

The e-mobility in Italy – specified Vittorio Chiesa – is not a market where the growth is missing. Absolute numbers are still small in comparison with other big European Countries but the sensation we can perceive among sector players is that the electric mobility is anything but an elitist fashion for lovers of sustainability and technology but it is instead becoming a fundamental component of the way of devising the transports of the future

In Europe

In European ambit, the first market is – indisputably – Norway, with 62,000 vehicles sold, that is to say the third Country by registrations after China and United States, but with a significant 39% out of the overall car sales inside the Country. Germany conquers the second position in the European market, with almost 55,000 registrations, over the double than in 2016 (+117%), also due to the direct incentive to purchase (4,000 Euros for a BEV, 3,000 Euros for a PHEV) and the exemption from the payment of the road tax for 10 years since the purchase time. Germans have surpassed the United Kingdom, which stopped at about 47,000 and +27%, third Country in Europe by registrations of electric vehicles (13% of the total) that offers a direct incentive amounting to 35% of the purchase cost, for a maximum of 5,100 Euros for a BEV and around 2,800 Euros for a PHEV, in addition to a reduction of yearly taxes. France follows with 37,000 and +26% and it directly incentives the purchase of an electric vehicle up to a maximum of 6,000 Euros, with a further incentive of 4,000 Euros for a BEV and 2,500 Euros for a PHEV if as replacement of a diesel vehicle with over 11 years of service life. These first four Countries attain 70% of the total in Europe.

Global sales of electric cars
In 2017, for the first time it was exceeded one million of cars sold on a world scale, over 1% of overall new registrations. We expect that such positive trend is confirmed for 2018, at the end of which 2 million new electric cars are likely to be present on the market
Sales by geographical area
With around 580,000 cars sold in 2017 and a 72% growth versus the previous year, China is the biggest world market, overcoming Europe that confirms to be second in the ranking with almost 290,000 sold units and scoring the 39% increment

«In this ranking – explained Professor Vittorio Chiesa, director of the Energy Strategy Group of the Polytechnics – even if it has shown strong growth signs in 2017 and in 2018, Italy is still very behind and in 2017 it weighed by less than 2% in the European market of electric vehicles, against 13% of total registrations. The main hindrances connected with the take-off of the electric vehicle market are the high purchase cost of cars, the problems concerning the inadequacy of the recharge network and the limited autonomy».

In Italy

Italy is the third nation in Europe, preceded by Luxembourg and Malta, by number of per head vehicles. They have surveyed that there are over 7 vehicles every 10 inhabitants, one more than in France, Germany and UK, where this ratio is included between 5.8 and 5.9. Besides, the average age of a car of the fleet circulating in Italy is higher, with 10.7 years against 9 of France and Germany and 8.5 of the United Kingdom. In the light of these data, we can foresee a renewal that should lead to a significant adoption of electric vehicles. All that induces to think that in 2030 in Italy we might have 7.5 million circulating electric vehicles and a volume of investments amounting to 61 billion Euros.

Europe recharge points
If we make a comparison between the recharge infrastructures in Italy and the rest of the Old Continent, the existing gap is evident, with a number of public charge points included betwween 10% and 20% compared to the 3 major European Countries
Norway stands out for being on the cutting edge in the electric mobility matter: in 2017, the new registrations of electric vehicles grazed 40% of the total. In the fiord Country, a particular regulation is in force to boost the purchase of electric cars: besides direct incentives, like the 25% reduction of VAT at the purchase time, and indirect ones, such as the free access, or at lower price, to parks and ferries, they have also applied the “polluter pays” principle. It is a disincentive to the purchase of conventional vehicles, precisely a sort of “polluter pays”, which results in higher yearly circulation taxes for more polluting vehicles. Thanks to such provision, in synergy with the farsighted policy of recharge infrastructures that aimed at installing 2 recharge stations every 50 km on any main road within 2017, Norway has been acknowledged as model worth following for its excellence transition towards the electric mobility.

Let us see anyway the data already registered: in the first semester of 2018, almost as many electric cars as in the entire previous year were registered, and the same “doubling” was scored between 2017 and 2016. However, the Italian market’s size is small if compared with the global and the European market. In 2017, 4,827 electric cars were sold, 0.24% of overall registrations, thus achieving an approximate total of 13,000 units circulating in Italy at the end of the last year.

Out of 4,827 electric cars, 1,964 are full-electric, rising by almost 40% versus 2016. The remaining 2,863 are instead PHEV, 2.5 times compared to the registrations in 2016, surpassing BEV for the first time. In the first half of 2018, 4,129 electric cars were registered, +89% versus the same 2017 period and a number that approaches the entire year just past.

Europe registrations
In European ambit, the first market is indisputably Norway, with 62,000 vehicles sold, Germany ranks second, with almost 55,000 registrations, followed by United Kingdom and France

«The e-mobility in Italy – specified Vittorio Chiesa – is not a market where the growth is missing. Certainly, absolute numbers are still small, slightly above the 4,000 vehicles in the last semester and also in relation to what is happening in the other big European Countries. The sensation we can perceive among sector players, however, is that the electric mobility is anything but an elitist fashion for lovers of sustainability and technology but it is instead becoming a fundamental component of the way of devising the transports of the future».

In the market of electric cars in Italy, the technological maturity is the reference indicator that shows fewer criticalities, the regulatory maturity is instead the area with more gaps. Incentives, if well proportioned, can act as enhancing instrument of the market competition whereas today in Italy they just regard the exemption of the road tax and the access to restricted traffic areas, with purchase incentives delivered on a regional scale only.


At the end of 2017, in Italy it is possible to estimate about 2,750 public compliant recharge stations, grown in the course of the last year by around 750 units. This has resulted in the growth of the last years, drastically reversing a trend that instead had made the recharge units essentially stable from 2012 to 2014.

Moreover, it is worth pointing out a great ferment regarding new installations in the course of 2018, with partial data that indicate an even stronger growth than last year.

Detail of electric car sales in Italy
In Italy, in 2017, 4,827 electric cars were sold, 0.24% of overall registrations, thus achieving slightly less than 13,000 units in all circulating in Italy at the end of the last year

It is worth underlining a strong unbalance of the geographical distribution of recharge units: there is a relevant shortage in the South whereas Centre and North are more advanced but with even remarkable differences among the various Regions.

If we make a comparison between the recharge infrastructures in Italy and the rest of the Old Continent, the existing gap is evident, with a number of public charge points included between 10% and 20% compared to the 3 major European Countries: a litmus paper of the size of the electric vehicle market.

Advanced mobility services

ZF Car-eWallet

ZF has established Car eWallet GmbH, a start-up headquartered in Berlin that will be entrusted by the Germany company with Car eWallet service activities, permitting to pay for the refuelling, for recharging electric cars or also for tolls, parking and car sharing. The project involved then the temporary collaboration between ZF and IBM and UBS partners, positively ending last Spring. Now, the target is further developing and marketing the service: in an initial financial phase, ZF will give the start-up the starting capital; in the future, investors will have to grant funds. «In this way – explained Alexander Graf from ZF Friedrichshafen AG, one of the first creators of Car eWallet and today project manager – we can exploit the dynamism of the scenarios where start-ups operate, where several innovative approaches can be developed more freely and quickly compared to what happens in a corporate structure».

DC Motors: the global value for 2020 is espected to be 130 billion dollars

An electric motor, highly simplifying, converts electric energy into mechanical energy and this occurs through two interacting magnetic fields, one stationary and the other integral with a moving part. The origins of electric motors date back to a distant past, if we remember the base principles of electromagnetic induction were discovered in the early years of 1800 by Oersted, Gauss and Faraday, in 1820 Oersted and Ampere demonstrated that an electric current produces a magnetic field and, according to the historiography on the matter, the first real rotary engine was created in 1834 by Moritz von Jacobi. Today electric motors are a technologically advanced reality, available in manifold typologies, with a global market value that for 2020 is expected to approach 130 billion dollars,
then almost 110 billion Euros at the current exchange rate. Considering a basic subdivision, they are split into AC motors and DC motors, and both these categories provide then for other detail subdivisions. AC motors, for instance, are developed into synchronous, asynchronous or induction, single-phase or three-phase. In the first case, the rotor rotation is synchronized with the frequency of the power supply current and the speed remains constant if the load varies; ideal for moving a load at constant speed, they are used for high-precision positioning.

In the second typology, the electromagnetic induction from the magnetic field of stator windings is used to produce an electric current in the rotor, and then torque; single-phase motors are generally adopted for small loads whereas three-phase ones have their use context in industrial ambit, for instance for compressors, pumps, conveyors and lifting systems. DC motors, the first broadly used also due to the user-friendly speed control by varying the power supply voltage, provide for two main branches: Brushed, or Brush, with brushes, and Brushless, without brushes. Traditionally, the subdivision is done by power: 0-750 Watt (with the major market share), 750 Watt-3kW, 3kW-75kW, and above 75kW. Concerning the global size of this market, the data that can be inferred from some of the most in-depth researches on DC motors are quite differing, especially if projections are on the long-term; they report for instance 35 billion dollars within 2025 (reference: Grand View Research, Inc), and highlight that the growth of the DC motor market will be mainly driven by the Automotive ambit. The sales of Brushless motors are prevailing in comparison with Brushed, and already in 2016 they held the highest market share. Still according to projections, they indicate for Brushed a growth with CAGR (Compounded Average Growth Rate) by around 3% from now until 2025, which becomes by 4% for Brushless.

DC Brushed motors

Following an approach of scholastic type, a typical DC brushed motor includes a rotary armor, or rotor, which contains windings of wires insulated and wound around a weak iron core, and a stationary stator that encloses the rotor and contains electromagnets or permanent magnets that generate the magnetic field. The windings, which form one or more coils, are electrically connected with the commutator, a cylinder consisting of various metal contact segments around the armor bar. Brushes are electric contacts made with soft material, typically graphite, in contact with the segments of the commutator when the bar rotates. If we apply a DC power source to brushes, the coils of the armor are energized, creating an electromagnet that is set in rotation, with its north and south poles aligned with stator ones; with the rotation, it is determined an inversion of the energy polarity in the armor coils and of the direction of the relative magnetic field; the armor rotates towards the new alignment, the current is inverted again and the armor goes on rotating. This inversion is commonly identified by the term of “mechanical switchover”. Acting on the arrangement of windings, different typologies of DC Brushed motors have been implemented. In a motor with winding in derivation, where field coils of stator and rotor are connected in parallel, the operation is at constant speed, irrespective of the load. In the case of winding in series (two coils wound in series), the speed varies with the load and it increases when the latter decreases, but making high start torque available.

The characteristics of both previous typologies are achieved with a composite winding, combination of the motors with winding in derivation and in series, typically used when complex start conditions occur and when a constant speed is required. Separate excitation motors, with separate feeders for stator and rotor, hence with high field current for the stator and sufficient voltage for the armor to produce the necessary torque current for the rotor, find application when low speeds but high torque capacities are needed. A further typology is with permanent magnets in the stator, thus annulling the need of an external field current: the design is more compact and lighter and the energy efficiency is higher in comparison with other DC Brushed. The control of a DC brushed motor is essentially simple because the switchover is mechanically executed. In a constant-speed motor, for instance, just a DC voltage and an on/off switch are necessary while the speed can be modified by varying the voltage. If a more sophisticated control is needed, specific circuits, widely available and well consolidated, are adopted while a PWM (Pulse-Width Modulation) signal is used for the speed control: the motor winding operates as low-pass filter, so that high-frequency PWM waveforms generate a stable current in the motor winding. For more precise regulations, it is possible to integrate a speed sensor, for instance a Hall-effect sensor or an optical encoder, thus creating a closed loop. In short, DC Brushed motors are inexpensive, reliable and with a high torque/inertia ratio but they have the problem of brushes that tend to wear in time, hence the need of periodical maintenance, for replacement or cleaning. Worth considering other limits, too: if the motor has big power, other problems of heat disposal arouse because windings heat up by Joule effect; windings make the rotor heavier, from which the rise of the moment of inertia derives; besides, if the motor must provide a fast and precise response, as required in industrial automation and in robotics, the control becomes more complex; electromagnetic interferences are generated in the arc of brushes because between them and the collector, in switchover times, there are opening transients of inductive windings and then flashing, which can be anyway attenuated by various devices. (A.C.)