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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Home exercise bike. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur In modern exercise bikes, the degree of load is regulated by rubbing bands, which wear out during operation. In the proposed exercise bike, the braking effect is caused not by friction, but by a magnetic field, as a result of which the design becomes more durable. Many remember the craze - jogging, which was preferred by most fans of a healthy lifestyle. The peak of this hobby fell on the 70s - 80s of the last century, when old and young, academicians and collective farmers ran. Jogging was considered a panacea for all diseases. A particularly powerful training effect was exerted on the cardiovascular and respiratory systems, metabolic processes were sharply activated. However, by the beginning of the 90s, the hobby boom had passed, and scientists and doctors were no longer so categorical in their statements about the benefits of this type of physical exercise. It was noted that during running, a negative impact on the human musculoskeletal system can be exerted, in particular, the ankle and knee joints are subject to shock loads, first of all. And this, ultimately, can lead to their diseases (for example, there is pain or a crunch in the knees). All this can be avoided when exercising on an exercise bike. Retaining all the advantages of jogging, the exercise bike is completely devoid of the shortcomings of the latter - the load on the joints becomes "soft", dosed. Classes on the exercise bike can be done in the room or on the balcony. Unfortunately, physical education and sports today have become an expensive pleasure. For example, most fitness equipment costs from $300 and is out of reach for many families. To some extent, this problem can be solved by a home exercise bike, for the manufacture of which you will need a frame from an unusable bicycle, 2 ... 3 meters of a pipe with a diameter of about 12 mm, strips of corner iron and an asynchronous electric motor from washing machines of old releases of the Volga type, " Oka", etc. The electric motor is used in a somewhat unusual mode - dynamic braking. It is known from electrical literature that when a constant voltage is applied to the stator winding of an electric motor (Fig. 1, a or 1, b, depending on the type of connections of the winding coils), it forms a constant magnetic field, which, interacting with a rotating rotor, causes its braking. The braking torque is mainly determined by the magnetomotive force of the stator winding and the rotor speed. By changing the voltage on the stator winding, you can set the desired amount of braking torque, which means the degree of load on the athlete.
Now about the design of the exercise bike (Fig. 2). From the bike, only the frame with the leading "asterisk" and the steering wheel are left. A stand is made from a pipe using a hacksaw and a welding machine, which is then attached to the frame instead of wheels. The design of the stand can be arbitrary, as long as it provides a stable position for the exercise bike.
About the motor mount. Most older washing machine motors have two pairs of threaded holes in the back of the endshield cover for mounting. A frame is welded from strips of angle iron, in the upper and lower walls of which grooves for M8 bolts are cut with a grinder. With these bolts, the electric motor is attached to the frame, and by moving it in the grooves, the chain tension is further regulated. On the motor shaft, a "sprocket" is fixed from the rear wheel of the bicycle. Two options are possible here: either they grind a sleeve under the shaft on a lathe, to which an “asterisk” is welded, or, if there is a ready-made pulley on the electric motor, they drill holes in it and in the “asterisk” and connect the parts with M5 bolts. The frame of the electric motor is welded to the stand so that the driving and driven "stars", as well as the chain, are in the same plane. The power source of the stator winding (Fig. 3) is a full-wave rectifier, made according to the bridge circuit on powerful diodes VD1 - VD4. The AC voltage is supplied to the bridge input from the secondary winding of the step-down transformer through the SA1 switch. By moving its engine, you can change the output voltage of the block from 24 to 42 V. In this case, the block must allow a load current of up to 2,5 A. The output voltage is controlled by a voltmeter PV1, although it is permissible to do without it, marking the position of the engine with the appropriate numbers, giving an idea of the magnitude of the brake moment.
If the exercise bike will be used as a recreational tool, it is quite enough to use a single-phase electric motor with a power of up to 200 W (from a washing machine, an electric pump for irrigation, etc.). It will create a braking torque on the shaft, sufficient for training both children and adults. When using an exercise bike for sports purposes, you will need to choose a more powerful electric motor and, possibly, an appropriate power source. The latter must necessarily be with an isolating network transformer and have good insulation between the windings. In the case of using a three-phase asynchronous electric motor, it must be checked. According to the author's observations, some electric motors are not suitable for our purposes - they develop a significant braking torque at a low rotor speed (it is difficult to move the pedals), and at high speed, peculiar "dips" are observed - the braking effect sharply decreases. Author: S.Gurov, village of Ilyinka, Belokalitvinsky district, Rostov region.
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