Locomotion consists of a means that allows displacement with little opposition, a
power source to provide the required
kinetic energy and a means to control the motion, such as a
brake and
steering system. By far, most vehicles use
wheels which employ the principle of
rolling to enable displacement with very little
rolling friction.
Energy source at a
charging station hybrid vehicle A vehicle must have a source of energy to drive it. Energy can be extracted from external sources, as in the cases of a
sailboat, a
solar-powered car, or an electric
streetcar that uses overhead lines. Energy can also be stored, provided it can be converted on demand and the storing medium's
energy density and
power density are sufficient to meet the vehicle's needs.
Human power is a simple source of energy that requires nothing more than humans. Despite the fact that humans cannot exceed for meaningful amounts of time, the
land speed record for human-powered vehicles (unpaced) is , as of 2009 on a
recumbent bicycle. The energy source used to power vehicles is
fuel. External combustion engines can use almost anything that burns as fuel, whilst internal combustion engines and rocket engines are designed to burn a specific fuel, typically gasoline,
diesel or
ethanol. Food is the fuel used to power non-motor vehicles such as cycles, rickshaws and other pedestrian-controlled vehicles. Another common medium for storing energy is
batteries, which have the advantages of being responsive, useful in a wide range of power levels, environmentally friendly, efficient, simple to install, and easy to maintain. Batteries also facilitate the use of electric motors, which have their own advantages. On the other hand, batteries have low energy densities, short service life, poor performance at extreme temperatures, long charging times, and difficulties with disposal (although they can usually be recycled). Like fuel, batteries store chemical energy and can cause burns and poisoning in event of an accident. Batteries also lose effectiveness with time. The issue of charge time can be resolved by swapping discharged batteries with charged ones; however, this incurs additional hardware costs and may be impractical for larger batteries. Moreover, there must be standard batteries for
battery swapping to work at a gas station.
Fuel cells are similar to batteries in that they convert from chemical to electrical energy, but have their own advantages and disadvantages.
Electrified rails and overhead cables are a common source of electrical energy on subways, railways, trams, and trolleybuses.
Solar energy is a more modern development, and several
solar vehicles have been successfully built and tested, including
Helios, a solar-powered aircraft.
Nuclear power is a more exclusive form of energy storage, currently limited to large ships and submarines, mostly military. Nuclear energy can be released by a
nuclear reactor,
nuclear battery, or repeatedly detonating
nuclear bombs. There have been two experiments with nuclear-powered aircraft, the
Tupolev Tu-119 and the
Convair X-6.
Mechanical strain is another method of storing energy, whereby an elastic band or metal spring is deformed and releases energy as it is allowed to return to its ground state. Systems employing elastic materials suffer from
hysteresis, and metal springs are too dense to be useful in many cases.
Flywheels store energy in a spinning mass. Because a light and fast rotor is energetically favorable, flywheels can pose a significant safety hazard. Moreover, flywheels leak energy fairly quickly and affect a vehicle's steering through the
gyroscopic effect. They have been used experimentally in
gyrobuses.
Wind energy is used by sailboats and
land yachts as the primary source of energy. It is very cheap and fairly easy to use, the main issues being dependence on weather and upwind performance.
Balloons also rely on the wind to move horizontally. Aircraft flying in the
jet stream may get a boost from high altitude winds.
Compressed gas is currently an experimental method of storing energy. In this case, compressed gas is simply stored in a tank and released when necessary. Like elastics, they have
hysteresis losses when gas heats up during compression.
Gravitational potential energy is a form of energy used in gliders, skis,
bobsleds and numerous other vehicles that go downhill.
Regenerative braking is an example of capturing
kinetic energy where the brakes of a vehicle are augmented with a generator or other means of extracting energy.
Motors and engines in a
2007 Honda Civic When needed, the energy is taken from the source and consumed by one or more motors or engines. Sometimes there is an intermediate medium, such as the batteries of a diesel submarine. Most motor vehicles have
internal combustion engines. They are fairly cheap, easy to maintain, reliable, safe and small. Since these engines burn fuel, they have long ranges but pollute the environment. A related engine is the
external combustion engine. An example of this is the steam engine. Aside from fuel, steam engines also need water, making them impractical for some purposes. Steam engines also need time to warm up, whereas IC engines can usually run right after being started, although this may not be recommended in cold conditions. Steam engines burning coal release
sulfur into the air, causing harmful
acid rain. While intermittent internal combustion engines were once the primary means of aircraft propulsion, they have been largely superseded by continuous internal combustion engines, such as
gas turbines. Turbine engines are light and, particularly when used on aircraft, efficient. On the other hand, they cost more and require careful maintenance. They can also be damaged by ingesting foreign objects, and they produce a hot exhaust. Trains using turbines are called
gas turbine-electric locomotives. Examples of surface vehicles using turbines are
M1 Abrams,
MTT Turbine SUPERBIKE and the
Millennium.
Pulse jet engines are similar in many ways to turbojets but have almost no moving parts. For this reason, they were very appealing to vehicle designers in the past; however, their noise, heat, and inefficiency have led to their abandonment. A historical example of the use of a pulse jet was the
V-1 flying bomb. Pulse jets are still occasionally used in amateur experiments. With the advent of modern technology, the
pulse detonation engine has become practical and was successfully tested on a
Rutan VariEze. While the pulse detonation engine is much more efficient than the pulse jet and even turbine engines, it still suffers from extreme noise and vibration levels.
Ramjets also have few moving parts, but they only work at high speed, so their use is restricted to
tip jet helicopters and high speed aircraft such as the
Lockheed SR-71 Blackbird. Rocket engines are primarily used on rockets, rocket sleds and experimental aircraft. Rocket engines are extremely powerful. The heaviest vehicle ever to leave the ground, the
Saturn V rocket, was powered by five
F-1 rocket engines generating a combined 180 million horsepower (134.2 gigawatt). Rocket engines also do not need to "push off" anything, a fact that the
New York Times denied in error. Rocket engines can be particularly simple, sometimes consisting of nothing more than a catalyst, as in the case of a
hydrogen peroxide rocket. This makes them an attractive option for vehicles such as jet packs. Despite their simplicity, rocket engines are often dangerous and susceptible to explosions. The fuel they run off may be flammable, poisonous, corrosive or cryogenic. They also suffer from poor efficiency. For these reasons, rocket engines are only used when absolutely necessary. Electric motors are used in
electric vehicles such as
electric bicycles, electric scooters, small boats, subways,
trains,
trolleybuses,
trams and
experimental aircraft. Electric motors can be very efficient: over 90% efficiency is common. Electric motors can also be built to be powerful, reliable, low-maintenance and of any size. Electric motors can deliver a range of speeds and torques without necessarily using a gearbox (although it may be more economical to use one). Electric motors are limited in their use chiefly by the difficulty of supplying electricity. Compressed gas motors have been used on some vehicles experimentally. They are simple, efficient, safe, cheap, reliable and operate in a variety of conditions. One of the difficulties met when using gas motors is the cooling effect of expanding gas. These engines are limited by how quickly they absorb heat from their surroundings. The cooling effect can, however, double as air conditioning. Compressed gas motors also lose effectiveness with falling gas pressure.
Ion thrusters are used on some satellites and spacecraft. They are only effective in a vacuum, which limits their use to spaceborne vehicles. Ion thrusters run primarily off electricity, but they also need a propellant such as
caesium, or, more recently
xenon. Ion thrusters can achieve extremely high speeds and use little propellant; however, they are power-hungry.
Converting energy to work The mechanical energy that motors and engines produce must be converted to
work by wheels, propellers, nozzles, or similar means. Aside from converting mechanical energy into motion, wheels allow a vehicle to roll along a surface and, with the exception of railed vehicles, to be steered. Wheels are ancient technology, with specimens being discovered from over 5000 years ago. Wheels are used in a plethora of vehicles, including motor vehicles,
armoured personnel carriers, amphibious vehicles, airplanes, trains, skateboards and wheelbarrows. Nozzles are used in conjunction with almost all reaction engines. Vehicles using nozzles include jet aircraft, rockets, and
personal watercraft. While most nozzles take the shape of a cone or
bell,
Continuous track is sometimes used instead of wheels to power land vehicles. Continuous track has the advantages of a larger contact area, easy repairs on small damage, and high maneuverability. Examples of vehicles using continuous tracks are tanks, snowmobiles and excavators. Two continuous tracks used together allow for steering. The largest land vehicle in the world, the
Bagger 293, is propelled by continuous tracks. Propellers (as well as screws, fans and rotors) are used to move through a fluid. Propellers have been used as toys since ancient times; however, it was
Leonardo da Vinci who devised what was one of the earliest propeller driven vehicles, the "aerial-screw". In 1661, Toogood & Hays adopted the screw for use as a ship propeller. Since then, the propeller has been tested on many terrestrial vehicles, including the
Schienenzeppelin train and numerous cars. In modern times, propellers are most prevalent on watercraft and aircraft, as well as some amphibious vehicles such as hovercraft and
ground-effect vehicles. Intuitively, propellers cannot work in space as there is no working fluid; however, some sources have suggested that since
space is never empty, a propeller could be made to work in space. Similarly to propeller vehicles, some vehicles use wings for propulsion. Sailboats and sailplanes are propelled by the forward component of lift generated by their sails/wings.
Ornithopters also produce thrust aerodynamically. Ornithopters with large rounded leading edges produce lift by leading-edge suction forces. Research at the University of Toronto Institute for Aerospace Studies lead to a flight with an actual ornithopter on July 31, 2010. Paddle wheels are used on some older watercraft and their reconstructions. These ships were known as
paddle steamers. Because paddle wheels simply push against the water, their design and construction is very simple. The oldest such ship in scheduled service is the
Skibladner. Many
pedalo boats also use paddle wheels for propulsion.
Screw-propelled vehicles are propelled by
auger-like cylinders fitted with helical flanges. Because they can produce thrust on both land and water, they are commonly used on all-terrain vehicles. The
ZiL-2906 was a Soviet-designed screw-propelled vehicle designed to retrieve cosmonauts from the Siberian wilderness.
Friction All or almost all of the useful energy produced by the engine is usually dissipated as friction; so minimizing frictional losses is very important in many vehicles. The main sources of friction are
rolling friction and
fluid drag (air drag or water drag). Wheels have low bearing friction, and pneumatic tires give low rolling friction. Steel wheels on steel tracks are lower still.
Aerodynamic drag can be reduced by streamlined design features. Friction is desirable and important in supplying
traction to facilitate motion on land. Most land vehicles rely on friction for accelerating, decelerating and changing direction. Sudden reductions in traction can cause loss of control and accidents. == Control ==