Propeller speed control. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Electrician

Propeller speed control. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electric motors

When working out propeller installations of snowmobiles, motor hang gliders, airplanes, as well as aircraft models, the designer needs to know the exact values of a number of parameters. And most importantly - the speed of the propeller. This is necessary both when boosting engines and when choosing a propeller. The rotational speed is also one of the main parameters during the operation of the motor: by the value of this parameter, one can objectively judge the reliability of the engine.

In many cases, it is simply impossible to “attach” any of the standard tachometers to a propeller-driven installation: Well, when it comes to model engines, contact measurements can distort their operation so much that any subtleties of adjustment are out of the question.

I bring to the attention of readers a non-contact electronic tachometer designed to measure the speed of the propeller without using any mechanical connections between the sensor and the engine shaft.

The tachometer consists of two main parts - a sensor and a frequency counter (Fig. 1).

Propeller speed control
Rice. 1. Block diagram of the tachometer: 1 - sensor, 2 - frequency counter, 3 - indicator, 4 - calibrator.

The sensor generates pulse signals that follow with a frequency that is a multiple of the speed of rotation of the propeller. The multiplicity is determined by the number of blades. Two types of sensors can be used for this tachometer: electrostatic and optical.

An electrostatic sensor designed specifically for the described device converts the charge accumulated on the blades of a rotating propeller during friction against air into a pulsed voltage. To do this, the sensor has a sensitive element (Fig. 2) - a narrow antenna made of a metal plate or wire, installed parallel to the plane of rotation of the screw.

Propeller speed control
Rice. 2. The principle of operation of the electrostatic sensor (a) and optical sensor (b): 1 - propeller, 2 - sensitive element (antenna) of the electrostatic sensor, 3 - amplifier, 4 - light source, 5 - light receiver with a sensitive element of the optical sensor, 6 - amplifier.

When the charged blades pass by the antenna, an alternating voltage will be induced in it, the frequency of which will be determined by the expression (K * N) / 60, where K is the number of propeller blades, N is the propeller speed (rpm).

The electrostatic sensor antenna is a source of low (on the order of millivolts) voltage with a very high internal resistance equal to the insulation resistance. To ensure the normal operation of the frequency meter, this voltage is supplied to an amplifier with a high input impedance (Fig. 3).

Propeller speed control
Rice. 3. Schematic diagram of an electrostatic sensor

High input impedance is achieved by using a matching stage, which is a combination of a flux follower on a field effect transistor VT1 and an emitter follower on a bipolar transistor VT2. Operational amplifier DA1 provides signal amplification to a level sufficient to operate the frequency counter.

An optical sensor consists of a light source, a sensitive element - a photodiode or a photoresistor - and an amplifier.

The light source and the sensing element are positioned so that the beam passes through the plane of the screw. During rotation, the blades periodically cross the beam incident on the sensitive element connected between the base and the emitter (Fig. 4), periodically changing its resistance and thereby forming an alternating voltage on the base of the transistor.

Propeller speed control
Rice. 4. Schematic diagram of the optical sensor

The received pulses are amplified by a two-stage amplifier to a value sufficient for the operation of the frequency meter.

The frequency meter converts the pulses received by the transmitters into a direct current proportional to the pulse repetition rate. Its main element is a waiting multivibrator on transistors VT5 and VT6 (Fig. 5).

Propeller speed control
Rice. 5. Schematic diagram of the frequency meter

When signals from sensors arrive at the waiting multivibrator, it generates pulses of constant duration, determined only by the values of the resistors and capacitances of the circuit.

When the screw rotates, a sequence of pulses with a constant amplitude and duration is formed at the output of the waiting multivibrator, the repetition rate of which is proportional to the speed of rotation of the screw.

The resulting pulse sequence contains a constant component, the value of which depends on the so-called duty cycle - the ratio of the pulse repetition period to their duration, that is, on the speed of rotation of the screw.

The DC component is extracted by integrating the pulse sequence. The integrating element is the RA1 pointer device, which simultaneously serves to indicate the speed of rotation of the propeller. In this case, a 100 μA magnetoelectric head was used with an additional resistor R22. A coarser instrument may also be used. Variable resistor R21 is used when calibrating the tachometer. An emitter follower on a VT7 transistor is used to decouple the integrator and the waiting multivibrator.

The device is powered from batteries or from a 9,5 V rectifier.

In the manufacture of a tachometer, any design can be adopted, but the most appropriate is the design in the form of two blocks - a sensor and a frequency meter with an indicator, interconnected by a three-wire cable.

An electrostatic sensor must be carefully shielded. The sensor antenna can be made of a piece of copper wire, a narrow strip of brass or foil fiberglass. During measurements, it should be parallel to the plane of rotation of the screw at a distance that ensures normal operation of the device.

To improve the accuracy of measuring the speed of rotation of the propeller, before starting work, it is necessary to calibrate the tachometer, for which a calibrator (built-in or remote) is included in its composition. The calibrator is a multivibrator (Fig. 6) that generates short pulses, the repetition rate of which is determined by the values of resistors R24, R25 and capacitances C6, C7 and is selected based on the range of measured speeds. For sufficient measurement accuracy, calibration should be carried out at two or three points in the velocity range. In this case, the required pulse repetition rates for a two-blade propeller are determined by the expression f=N/30.

Propeller speed control
Rice. 6. Schematic diagram of the calibrator and table of R25 values for calibration points.

The table (see Fig. 6) shows the values of resistors R24 and R25 for various screw speeds. Precise frequency setting is carried out by a tuning resistor R30, while the frequency setting is controlled using a high-precision digital frequency meter.

You can get several frequencies by stepping resistors R24 and R25 or by using several generators.

Author: V.Evstratov

See other articles Section Electric motors.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive

Transmission of radio signals with almost no energy consumption 29.01.2023

According to the second law of thermodynamics, any process of energy transfer (including radio waves) is associated with its costs. That is, in fact, it is impossible to create a "perpetual motion machine", because without the expenditure of energy it cannot produce it. But scientists from Stanford managed to create a data transmission technology that uses almost no energy at the receiver.

They found that in the case of receiving a radio wave transmission, the energy does not have to come from the transmitter. In many cases, such as when transmitters need to be small and portable, their consumption can be reduced or eliminated by backscattering technology.

In this case, the only power needed for the transmitter is used for the transistor. Because the transmitter uses very little power (enough to switch a transistor), it doesn't need bulky batteries. The idea is that the signal source is at a higher temperature than the antenna, so that when the circuit is closed, current will begin to flow in it due to the temperature difference.

This makes the new technology ideal for medical implants and other devices that often cannot be recharged. The receiver needs a lot of power, but it can be a base station connected to the network or a large battery. This new technology is less complex than backscatter systems, which may make it more accessible and practical in some situations.

Other interesting news:

▪ Microsoft experimental underwater data centers

▪ Birds also have a cerebral cortex

▪ Magnetic soap removes oil slicks

▪ High-speed Internet between the Earth and the Moon

▪ Extraction of useful resources on the moon

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Electric motors. Article selection

▪ article Thus passes worldly glory (glory of the world). Popular expression

▪ article How many prisoners were released after the storming of the Bastille? Detailed answer

▪ article Industrial sanitation, occupational health and personal hygiene

▪ article Tester for twisted pair. Encyclopedia of radio electronics and electrical engineering

▪ article VHF tuner on the K174XA34 chip. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews