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Velokart. Personal transport

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Many readers dream of karting. But have you noticed how these cars smoke and make noise! We think that today, when humanity is increasingly involved in the struggle for a clean environment, the time has come for us to think about a silent, environmentally friendly map. For example, with a muscular drive. If someone decides that such a machine will lose speed, then this is not so. After all, it only seems from the side that the speed of the card is very high. On average - about 50 km per hour. And even less in corners - 30.

And velomobiles have already been built that reach speeds of up to 100 km per hour, so you can expect that a motorized velokart will not yield in speed. And what a wide field for creativity opens before us!

The International Association for the Development of Human Muscular Vehicles does not impose any restrictions on their design. True, if we are talking about a sports car, then a number of conditions must be met so that the competitors are more or less in the same conditions.

A velokart can have 3 wheels: two in the front and one in the back, or vice versa. Or maybe all four. Variants of such machines are shown in Figures 1-4.

Only the use of a "bicycle" scheme is not allowed: the front and rear wheels are in the same plane.

For safety, the clearance between the driver's seat and the road surface must be at least 100 mm.

Since the power developed by a person is primarily limited by the amount of oxygen carried by the blood flow to the muscles, it makes no sense to impose restrictions on the type of drive. These can be ordinary bicycle-type pedals and chains or a crankset. There is no complete clarity as to which muscle groups are more profitable to involve in work, and here you have room for creativity, arms, legs, and abdominals can work.

How much power should you expect from a kart driver? In relation to an adult, the upper graph can give the answer. The kart is not suitable for normal driving, so we will immediately discard the movement in the tourist mode. It can be seen that in races lasting up to 1 hour, the average power of a normally developed adult is close to 200 W, and for an athlete - up to 300-400 W. In children and adolescents, it is, of course, less. And it may seem that a teenager will lose to an adult in speed. However, this is not so, if we proceed from the laws of biomechanics. Indeed, in order to achieve maximum speed, it is important to have maximum power per unit mass of the vehicle and per unit area of ​​its cross section.

Now let's see what determines the maximum speed of the velokart and which scheme should be preferred.

Any crew reaches its maximum speed when the engine power becomes equal to the power expended to overcome the resistance forces.

Crew resistance is made up of three factors. The first is friction losses in gears. We know how to deal with them quite well: the bicycle transmission efficiency reaches 97%.

The second factor is the rolling friction of the wheels. It decreases with the growth of their diameter and the pressure of the air pumped into the chambers. The power expended to overcome the forces of rolling friction is proportional to the speed and mass of the vehicle.

The third factor is aerodynamic drag. The power expended to overcome it is proportional to the cube of the speed. Therefore, it interferes especially at high speeds. To combat aerodynamic drag, the transverse (middle) section of the crew is usually reduced and given a streamlined shape.

On the graph of theoretically possible speeds, one can estimate the maximum achievable speed for various types of kart, its cross section and the power developed by the driver. The graph shows that the use of fairings according to scheme 1 and 2 becomes profitable only when the driver's power exceeds 220 watts. At low powers, there is a struggle between a decrease in resistance due to improved aerodynamics and an increase in frictional resistance associated with the weight of the fairing itself, especially such as in scheme 1. This means that there is an optimal ratio between them.

Throughout the history of cycling, attempts have been made to reduce the aerodynamic drag of wheels. The latest achievement is disc wheels, on which a world speed record was set in January 1984,

Now for some building tips.

If you take spoked wheels for your car, it is better to place them in a fairing or include a velokart in a common fairing.

The open frame of the velokart is made of pipes. Pipes made of aluminum-based alloys have not only a round cross-section, but also a drop-shaped one (GOST 18475-73), with less aerodynamic resistance. Better find the latest.

Velokart control can be an automobile scheme: a steering column and a hand-operated steering wheel, or an aircraft one: yoga pedal control.

All the advantages of a velokart can be negated if its drivetrain is transferred unchanged from an adult bike.

There are no words, its efficiency is very high, but it remains high only when transmitting high powers.

For children and adolescents, gears with narrower chains, fine-toothed sprockets and other gear ratios are needed.

In conclusion, we note that cycling is a very interesting business, promising not only a solution to the environmental problems of karting, but also very serious sporting achievements. It makes sense to do it!

Author: I.Krotov

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