Motor-wheels for a bicycle: what are they and how to choose?

Today, cyclists who do not put a motor-wheel on their bike are increasingly called retrogrades. “Only the wind, only the pedals, only the extreme” - this appeal is less and less relevant. A pampered urban consumer who is accustomed to driving a car, even if he buys a bicycle, will soon be inclined to put a motor-wheel on it, especially since such devices are getting cheaper from year to year.

A bicycle wheel motor works in the same way. It doesn't matter whether it is a direct transmission (directly from the rotor) or geared (reducing the engine speed by a gear ratio). Every electric motor for a bike includes a stator and a rotor. Magnets are attached to the rotor. Their field, interacting with the electromagnetic field of the stator coils, makes the rotor spin.

The stator itself is a coil wound in the gaps of a steel plate frame. Most often, these plates are made of electrical or transformer steel. The stator structure has the form of a polygonal frame with beams converging in the center.

The windings are coils wound from copper enamel wire. It is copper that is the best conductor. The number of coils is up to several tens, but this number is a multiple of 3. The motor-wheel resembles a three-phase motor, in fact, this is the case: for stable rotation with a certain force, alternating pulses resembling a three-phase variable are applied to the coils spaced from each other in phases voltage. In fact, this is not a sinusoidal electrical signal, but a sequence of rectangular pulses of constant voltage. They, in turn, are formed by a driver - a controller board that uses the energy of a power source (battery).

The constancy and efficiency of the rotor rotation is ensured by three Hall sensors. Their work is organized as follows:

• fixing the position of the rotor in relation to the stator;
• perception of the magnetic field from magnets;
• signal forwarding to the driver;
• formation of impulses on the driver for the stator coils.

The advantages of using a wheel motor are as follows.

• Increased efficiency - not less than 90%. Not every electric motor has such a coefficient - for example, for collector motors, for which an unconverted direct current is sufficient, the efficiency is less than 70%.
• Ease of execution, reliability.
• There are no rubbing parts (for example, rings and brushes) - the engine can work for decades if the manufacturer does not save on the quality of materials.
• The ability to ride fast: a half-kilowatt motor-wheel provides a rotary force, during which a bicycle speed of up to 45 km / h is achieved on roads without a slope.
• The ability, if necessary, to remove the kit, giving the bike the original kit. When you reinstall the motor kit, the appearance of the bike will not change significantly - the motor is installed only on the wheel itself.
• Substantial ease of upwind and upwind riding.
• Smooth and smooth operation of the motor will provide quick adaptation to new speeds and smooth acceleration.
• Completely silent operation of the motor wheel.

This setup also has some drawbacks.

• Low torque - less than motors of other types and varieties.
• Inability to create a more compact design based on such a motor.
• Increased weight... Some other motors, for example, all the same collector motors, have significantly less - 1.5 or more times - weight.

All ready-made kits, which include motor-wheels, are completed with controller and battery. However, those who do not install the wheel motor complete with the rest of the parts order all the system components separately: the wheel motor itself, the battery and the controller with the throttle stick.

Before building an electric traction system, a beginner is faced with a geared and gearless motor-wheels. The gearbox uses a gear transmission mechanism, where the rotational speed (number of revolutions) of the electric motor itself is several times - per the gear ratio of the gearbox - more than that of the shaft, which ultimately spins the wheel.

The gear wheel increases the torque, but reduces the speed of the cyclist to 30 km / h. A gearless one - a wheel with a direct drive - does not have the gearbox itself and the associated losses, which frees the mechanism from rubbing gears, which need lubrication much more often than the engine bearings themselves. The torque is significantly lower at a power of up to 1500 W, but it becomes possible to accelerate to 50–100 km / h, depending on the power of the motor.

A motor-wheel with the possibility of recuperating (returning) part of the consumed electricity allows you to return it in a small amount - about 6% of the consumed power. Since the efficiency of such a system cannot be equal to unity due to natural losses in wires, windings, controller and battery, it will not be possible to do without external investment of additional energy. And there are only two ways to replenish the supply of electricity.

1. Switch the wheel motor to the battery charging mode. Then pedaling will be at least twice as hard - due to the braking exerted by the load on the windings.
2. Find a place where you can just charge the batteries... The best option would be to put solar panels on your backpack and clothes, when traveling on a motorized bike is completely autonomous.

Also, the motor-wheel can be rear - it is installed on the rear wheel. The front is placed in the same way. Then the bike becomes rear-wheel or front-wheel drive, respectively. For a significant increase in speed, you can make the bike all-wheel drive by motorizing both wheels.

The size of the wheel motor is determined by the diameter of the rim. Whether you have a diameter of 29, 26, 20 or 16 inches, speed and thrust depend on it. The larger the rim diameter, the more speed, but less thrust, and vice versa. With less traction, you will accelerate longer. There is only one way to add traction - to help the motor with the pedals.

It is possible that you can re-spoke a wheel from a conventional hub to a motor hub, using, for example, a 28 "rim with spokes from a conventional bicycle with 20" wheels. Those who do not know how or do not want to tinker with a full bust of spokes are advised to immediately order in China a ready-made motor-wheel with the required type of engine.

Decide exactly what you want from your bike.

• Speed ​​up to 35 km / h without much effort and any special level of physical development. At the same time, your bike does not get rid of its original functions - you will switch back to pedaling with your feet at any time. Such a revision costs a total of $ 350.
• 50 km / h – electromoped equipment. At the same time, you may not switch as easily to pedaling - the battery pack, a more powerful motor-wheel and the same controller weigh 5-10 more kilograms. The cost of revision is from $ 600.
• The bicycle will become an electric bike - an electric motorcycle... You can easily accelerate to 90 km / h. But remember: in this case, you will definitely need reinforced rims and bushings - maybe, like on a tandem bike. The fact is that the increased traction also requires an increased load. Your thin road bike rims will simply fly apart and you could crash. The price of customizing a bike for an electric motorcycle will cost at least $ 2300.

The mass of a set for an electric bike - a motor per wheel (without wheel spacing), a battery pack and a controller - will be at least 4 kg by weight. This is enough for normal city driving or on country roads. Quite good engines are produced, for example, by a company Bafang 8FUN... The operating power of the motors is 250-750 W, but when the power exceeds 350 W, such a motor can noticeably overheat, which will greatly shorten its service life.

The weight of the wheel motor (without rubber) is at least 2 kg. He is quite capable of reaching speeds of up to 35 km / h with an average rider weight of 90 kg - the rider himself may not apply any effort to pedaling at all. The same can be obtained without a motor, by switching to the last speed from the pedals and while driving without an upward or downward movement. When riding uphill, you will need the help of a cyclist through the pedals - the engine may not be able to handle the rise. Combining the two, you can get the speed delivered by a one-kilowatt motor, turned on at the start. The mobility and relative lightness of the bike is guaranteed.

There is no need for a half-kilowatt motor-wheel - it itself weighs not 2, but 4–5 kg, while taking twice as much electricity from the battery as its 350-watt counterpart. A 500 ... 600-watt motor-wheel is a "crutch" that has not passed "natural selection" either in projects or in practice among users: some cyclists noted that As a result, there is less sense from it than from a 300-watt one.

This configuration allows not only to get a speed equal to an average of 48 km / h, but also to easily conquer any climbs in the conditions of the city and mountain slopes. To achieve such results, it is required to select an engine with a power of 1200-1500 watts. Such a motor-wheel has a mass of 6–8 kg (excluding rubber). Providing such a motor with an uninterrupted supply of energy will help more heavy and expensive battery pack weighing at least 5 kg.

If you risk increasing the voltage from 48 to 72 volts, you will get the speed limit for the city - not less than 60 km / h, but at the same time the motor will overheat faster and more strongly, which forces it to start only for a short time.

Altering the bike for motor traction, say, 3 kW, will force the owner to reinforce the frame. Firstly, both the kit and the thrust itself, created by the engine of the order of several kilowatts, will require an increased load. Otherwise, the wheels will be the first to suffer (huge "eights" will appear on the rims), then the frame itself will start to fall apart - the body kit of the batteries and the controller will add at least 15 kg. The maximum permissible load is only twice the nominal, this is the basic rule for all motor-wheels.

To supply a reinforced set for a Category III e-bike, you need to reinforce the dropouts, completely change or re-equip the frame feathers, and install a special balancer, just like on real motorcycles. The nominal 3 kW motor already has enough force to deform the frame stays for a regular bike, even when you run it in a stationary mode by lifting the wheel on which the motor is mounted on a special suspension.

Without reinforcing the frame in a special way, you are unlikely to be able to use a motor with a power of up to several kilowatts. A speed of more than 40 km / h already requires good shock absorption - without it, you will simply be thrown out of the saddle if you hit a small bump or crack across the road. A fork - from a motorcycle or from a downhill bike (the latter has an impressive mass and the highest strength, unattainable for bicycles of other types and varieties). The battery pack here also weighs from 20 kg.

For those who like to ride closer to extreme skiing, experienced masters advise to put the motor-wheel back. The rear motor-wheel grips better than the front one - this is important in sharp turns, passable at increased speed.

However, slippery roads are less manageable due to the poorer weight distribution. The situation is aggravated by the battery attached to the trunk. The situation is corrected by a gear motor-wheel, which has a lower weight, lithium-ion batteries, which have increased specific energy. Alternative - lead-acid batteries on the middle (inner) tube of the frame. Yet the rear wheel hub motor contributes to the overall strength of the entire structure.

If it is impossible to combine the motor-wheel with a high-speed cassette (for example, 9 stars), change the last one to a 5-star one. As a last resort leave only one star or move the frame feathers 2 cm apart. The latter aluminum frame may not hold up - experiment on a steel frame.

The electrical wire should not exit to the right, where the gearshift mechanism works, but to the left. Unscrew the nuts holding the wheel motor and remove it. Assemble the wheel motor following the assembly instructions. If something is not completely clear to you, contact the support staff on the website of the company or store that sold you the motor-wheel. It is often best to enlist the help of a specialist since the controller can be easily burned out. And you won't go without a controller if you don't have a brushed motor that needs nothing but DC.

After assembly, test the wheel motor with no load - it should not be "eight". If this is not the case, remove the “eights” on the rim by tightening the spokes with the spokes. Try the controller and throttle stick. If everything is working properly, do a test drive at low speed.

Installing the front wheel hub motor is easier. The front wheel itself does not contain any sprockets. There is simply nothing to interfere with the operation of the front motor-wheel. It does not matter whether to the right or to the left - in the direction of travel - you will lead out the power cable. Even extending the fork will not compromise the strength and stability of the bike.

The only thing - do not confuse the direction of movement of the wheel: if the installation is incorrect, you, without testing the operation of the motor, will suddenly go backwards, and the bike will turn into a vehicle with a rear steering wheel. Paradoxical is the situation when the throttle stick gets stuck: you can crash into a post or collide with a car driving behind, even if it slows down in front of you.

The assembled motor-wheel is afraid of showers, wading through rivers and swamps - if immersed in water or flooded with water jets, the Hall sensors can fail. Take care in advance of sealing - or at least covering from direct jets of water - the insides of the motor-wheel. Often, manufacturers themselves install special round dampers to protect the wheel from direct splashing water and / or dirt while driving - make sure they match the wheel spokes.

For information on how to choose a wheel motor for a bicycle, see the next video.