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The working principle of the steering gear
   Edit:管理员   Browse:1938  Date:2017/10/16 

First, the working principle of the steering gear

The standard steering gear has three wires, namely: power cord, ground wire, control line, as shown in Figure 2.




To Japan FUTABA-S3003-type steering gear, for example, Figure 1 is FUFABA-S3003-type steering gear internal circuit.


3003 servo works the principle is: PWM signal from the receiving channel into the signal demodulation circuit BA6688 12 feet to demodulate, get a DC bias voltage. The DC bias voltage is compared with the potentiometer voltage, and the voltage difference is obtained by the BA6688's 3-pin output. The output is fed to the motor drive IC BAL6686 to drive the motor forward and reverse. When the motor rotates, the potentiometer Rw1 is rotated by the cascade reduction gear until the voltage difference is O and the motor stops rotating.


The control signal of the steering gear is the PWM signal, which changes the position of the steering gear by changing the duty cycle.

There is a very interesting technical topic can be a little mention that BA6688 is EMF control, the main purpose is to control the maximum speed when the motor speed.

The principle is this:

After receiving a pulse, BA6688 also produce a 5K potentiometer actual voltage as the base of the pulse, two pulses after the widening, the output to the drive to use. When the output is enough, the motor will begin to accelerate, the motor will be able to produce EMF, this is proportional to the speed.
Because the central voltage is taken, so the normal can not be detected, but after the operation of the level of tilt, can be detected. More than EMF to determine the voltage when the reduction of widening, or even shut down, so that the motor deceleration or parking. This advantage is to avoid overshoot phenomenon (that is, to the positioning point also continue to go, and then back, and then close)


Some domestic cheap steering gear with the cheap chip, there is no EMF control, motor, gear mechanical inertia is prone to overshoot phenomenon, resulting in shaking rudder




The power cord and ground are used to provide the energy required for DC motors and control lines inside the steering gear. Voltage is usually between 4 ~ 6V, generally take 5V. Note that the power supply to the steering gear should be able to provide sufficient power. The input of the control line is a cyclical square wave pulse signal with a width adjustable, and the period of the square wave pulse signal is 20 ms (ie, 50 Hz). When the pulse width of the square wave changes, the angle of the steering shaft changes, the angle change is proportional to the change of the pulse width. The relationship between the output shaft angle of a certain steering gear and the pulse width of the input signal can be expressed by the interval 3.



Second, the digital servo VS simulation servo

Digital steering gears have some advantages over traditional analog steering gears, but these advantages also bring some shortcomings.


The traditional steering gear in the no-load, no power was passed to the steering gear motor. When the signal input to the steering gear to move, or the steering gear of the rocker by the external force, the steering gear will react to the steering gear motor output voltage. From the first section of the circuit analysis we know - whether the motor to obtain the drive voltage, depending on whether the first 3 feet BA6688 output a voltage signal to the BAL6686 motor driver IC.

The biggest difference between a digital servo is that it handles the input signal of the receiver. Compared with the traditional 50 pulse / s PWM signal demodulation mode, the digital servo uses the signal preprocessing mode to increase the frequency to 300 pulses per second. Because the high frequency of the relationship, means that the steering gear action will be more accurate, "no reaction zone" smaller.

The following three graphs show two cycles of on / off pulses.

Figure 2 is the pulse width is narrow, relatively small power signal is input to the motor; Figure 3 is a wider, longer duration of the pulse, more input power.




You can imagine a short pulse, followed by a long pause, which means that the servo control accuracy is not high enough, which is why the simulation of the steering gear has a "no reaction zone" presence. For example, the steering gear for the transmitter's small movements, slow response or no response at all.

While the digital servo to enhance the pulse density, a slight change in the signal will change can be read, so that either a slight change in the remote control lever, or steering gear rocker in the external force under the very slight changes, will be able to detect out to proceed More minor fixes.

Third, the shortcomings of digital steering gear:

Above we already know the advantages of digital steering gear will be more accurate, then we look at the shortcomings of digital steering gear

1, digital steering gear needs to consume more power. In fact, this is very natural. The digital steering gear corrects the motor at a higher frequency, which will increase the overall power consumption.

2, relative to teach a short life. In fact, this is very natural. The motor is always turned to turn to make amendments, which will increase the motor and other parts of the consumption.

Fourth, anthropomorphic metaphor

Technical things that so much, perhaps a lot of the circuit is not familiar with the principle of friends or do not understand, Oh, give a simple example to explain it!

Such as the remote control is the teacher, the steering gear control circuit is the parent, the steering gear motor is a child

The task now is to ask the teacher to counsel the child to do an action, such as inverted

In the case of a digital steering gear, the parents set a very strict standard for the action, and he asked the child to put an upright coin on the upper and then staring at the coin, and the coin shook him to the left. The child a whip, the coin to the right one to shake him on the left to the child a whip ......... In short, he asked the teacher is no longer asked the "inverted", but after the top of the top of a coin ..........

Simulated steering gear is part of the parents of the soft, the teacher asked the inverted right? He faithfully according to the teacher's request, let the child upside down, the child's body to adjust his slight concern, he only care is not offset the teacher's standard, huh, huh

Fifth, the practical application of choice

We already know the sensitivity of the analog steering gear for very slight external forces that cause the steering gear to shift, and the accuracy of the servo command is not as good as the digital steering gear, then we should try to use the digital steering gear The The The I personally do not think so.

First of all - the quality of the steering gear, in fact, is not simply the circuit decision, there are servo gear gear accuracy, there are very very critical servo potentiometer accuracy. A superior quality of the analog servo, often than the circuit is digital but the parts are ordinary goods of the digital steering gear more accurate, but will not shake the rudder.

Second, we know that when we apply in the model car, many times too high accuracy is not a good thing! For example, you play 1/8 of the car, especially the luggage and off-road vehicles, so bad road lead to the car when the sliding suitable for vacating, at every turn is zero seconds, N cm deviation, the servo microsecond level sensitive, micron level How can accuracy improve the whole event? The Called the neurotic rudder reaction ...........

In fact, in the 1/8 of the vehicle, a 0.1 second reaction of the analog servo is a more appropriate match. It will be more power, more smooth, not so nervous. And most importantly - it will not be in a turn to the virtual position of a few millimeters on the 1/8 off-road vehicles, to keep squeaky to find that 0.1 mm center (in fact, even if you even the steering gear to the It is demolished, so that the steering gear idling, it is often found that 0.1 mm center, but he kept squeaky toss their own only, ha ha)

The actual application, I suggest that the race level is 1/10 of the level of RV, violent aircraft, you can use digital steering gear.

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