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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Children's electric car with pulse-width motor control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors Riding a pedal car is good fun for a toddler. But driving an electric car will bring great joy. How to convert a pedal car into an electric car is described in the proposed article. At the amusement parks in the parks, in many toy stores you can see foreign-made electric cars. Unfortunately, they are relatively expensive, do not allow you to adjust the speed of the ride, move in reverse, they do not provide direction indicators and a sound signal. At the same time, there are no domestic analogues. However, there is a way out - the children's car "Sport" (Fig. 1), manufactured by the Gomel plant Tomselmash. "The car design includes the following components: steering column 1, headlight 2, headlight button switch 3, lights 4 and turn signal switch 5, horn button 6, shield 7, handbrake 8, seat 9, wheels 10, chain drive 11, frame 12. It is designed for children aged 3 to 7 years and a maximum load of 50 kg.
When designing an electric car based on the specified pedal car, the task was to ensure ease of use and sufficient similarity with an "adult" car by the simplest and most affordable means. As an electric drive, it was decided to use a 90 W cooling fan electric motor from a Zhiguli car from previous years of production. A modern 120W motor of the same type will do. A foot control from the electric drive of the sewing machine was also purchased. It has a plastic gear inside, mounted on a variable resistor shaft, and a plastic gear sector that transmits the movement of the pedal to the gear. Next, the car has undergone modernization. The pedals with the drive gear were removed, the details of their fastening and the chain drive, the base of the floor was cut out of tin 0,5 mm thick and welded to the car frame, restrictive arcs from tubular legs from old chairs were welded to the base, and a lining of tin thick was welded to them. 0,2 mm. All leaks are covered with silicone sealant, the surfaces are sanded and painted. The place where the rear shaft was welded to the driven gear was carefully turned on a lathe, after which the gear was removed, and instead a gear from the pedal shaft was installed, shifted to the side and welded to the shaft. In the rear part of the car, under the seat, there is a carrier box, bent from 1 mm thick sheet steel, in which a battery, a motor with a gearbox and a chain drive are installed (Fig. 2).
And now about the design of the chassis. Since the mechanical characteristic of the engine was unknown (and attempts to find it in the literature were unsuccessful), the required minimum gear ratio of the gearbox was determined experimentally and turned out to be 10. and reducer). As the basis for the gearbox, the RD-09-T gearbox, manufactured in 1971 with a gear ratio of 1/137, was originally used. It has a steel back cover with a place for an axial bearing, screwed to the body with six screws. This made it possible to remove the extra paired gears, leaving only one pair, resulting in a gear ratio reduced to 1/8. An additional gear ratio of 1/1,5 was obtained by installing a chain gear (previously located on the rear axle) on the output shaft of the gearbox. The gearbox is attached to the side cover of the engine with four M5 screws to the threaded eyes through the stops from a copper tube 11 mm long. The increase in the gear ratio was due to the need to achieve a smooth change in speed with pulse-width (PW) engine control. The engine is mounted on the carrier box with the help of corners made of 1 mm thick sheet, fixed on the engine with its coupling screws. To do this, it was necessary to grind off part of both silumin engine covers in thickness so that the length of the ties was enough to fasten the corners. During the operation of the car, it turned out that the one-wheel drive scheme adopted in the pedal prototype (and transferred to the electric car) is not optimal, since it does not provide the necessary grip and leads to increased wear of the drive wheel. I had to rigidly tie both rear wheels to the axle. To do this, the free end of the axle was turned with a file to form a flat, and one of the two washers with a lock, removed from the drive wheel, was mounted on the previously free wheel. As a result, both rear wheels became leading. In order to increase the duration of the movement of an electric vehicle from a single battery charge, it is desirable to transfer all friction pairs (front wheels, engine rotor, gearbox axle) from plain bearings to rolling bearings. The electrical part of an electric vehicle is relatively simple (Fig. 3). It contains an SHI engine control unit with a reversing unit on the SA2 switch, a turn signal relay unit, a headlight switching unit and a sound signal switching unit. The basis of the SHI control unit is a generator with a variable duty cycle of pulses, made on the K561TL1 microcircuit. The choice of this microcircuit was dictated by the need to provide the widest possible range of pulse duty cycle adjustment, which, in turn, makes it possible to obtain an effective value of the output voltage from 0,5 to 12 V. Instead of this microcircuit, it is permissible to install K561LA7, K561LE5, K561LN1, etc., having in their there are a sufficient number of inverters, but the adjustment range for the specified resistance of the resistor R1 was reduced to 5 ... 12 V.
The engine is controlled through a key on a field-effect transistor VT1, in place of which, in addition to that indicated in the diagram, it is permissible to turn on IRFZ46N, KP912A or two KP921A connected in parallel. The transistor is mounted on a radiator made of aluminum sheet 2 mm thick with an area of 24 cm2. In the absence of a field-effect transistor, the key can be made on bipolar ones - silicon and germanium (Fig. 4, a) or two silicon ones (Fig. 4, b). But at the same time, power losses for control will increase (and a larger radiator will also be needed), which will reduce the duration of driving an electric car. Diode VD3 eliminates voltage surges on the motor inductance when the key is turned off.
On the electromagnetic relay K1 (RES15 passport RS4.591.006), a block of direction indicators is made. When the movable contact of the switch SA3 is transferred, for example, to the left position according to the diagram, the capacitor C1 starts charging through the lamp EL2. As soon as the voltage on it reaches the relay operation voltage, contacts K1.1 will close and supply voltage to the lamp - it will light up. The capacitor will discharge through the relay coil and it will release. Contacts K1.1 will open, the lamp will go out. The capacitor will start charging again, the process will repeat. As a result, the left turn indicator lamp will flash until the movable contact of the SA3 switch is moved to the middle position. The electric car is equipped with a 6MTS-9 motorcycle battery, the capacity of which in a charged state is enough for about an hour of driving. If you install a battery with a larger capacity, for example, from a car, the driving time will increase to 6 ... 8 hours. Connect the battery with the SA1 switch, the contacts of which must withstand a current of up to 25 A. Sound signal HA1 - from the car, turn it on with the SB1 button located in the center of the steering wheel. The lamps installed in the car for a voltage of 2,5 V are replaced by others - for a voltage of 13 V. At the same time, galvanic cells are removed from the headlight, and parts of the turn signal relay unit are installed instead. Capacitor C1 - ceramic, C2 - oxide of any type for a voltage not lower than indicated in the diagram. Fixed resistors - MLT-0,25, variable - SPO-1. A transistor with a radiator is placed inside the pedal in the lower part of the case opposite the ventilation holes. To ensure air access to them, the case is installed on gaskets 5 mm high from the floor. The remaining parts of the SHI block are also placed inside the pedal and mounted on a piece of board cut to the size of the board that was previously placed in the pedal. It is desirable to install the microcircuit in the socket so that it can be replaced if it is necessary to change the voltage range on the engine. The SA2 switch is located on the steering column at the top, the SA1 switch is at the bottom. Author: I. Kazakov, Volgograd
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