How To Choose Servo Control? Three Key Points To Understand The Torque Speed Signal

When you are engaged in product innovation, have you ever encountered this situation: you want to make a certain joint move, or you want a certain mechanism to accurately rotate to an angle, but you can't do it with ordinary motors? Either his head was turned too far, or his position was just a little bit off. In fact, what you may need is aservo. To put it bluntly, this thing is a small position control system that integrates the motor, reduction gear and position feedback. You give it a command and it can accurately rotate the output shaft to the position you want. Today we will talk about how to use it well.

How to quickly determine which steering gear to choose?

There are too many types ofservos on the market, and it’s easy for novices to get confused. In fact, you only need to grasp three key points: torque, speed and signal type. The torque depends on how much load you need to drive. For example, for a small joint of a robotic arm, a few kilograms ofservomay be enough; if it is a robot leg, it may require dozens of kilograms of metal servo. The speed depends on how fast you move. Generally, the servo speed is expressed in "seconds/60 degrees". The signal types are mainly divided into PWM analog servos and serial port digital servos. The former is simple and cheap, while the latter provides more feedback information and higher accuracy. If you list these three points clearly when selecting a model, you will basically not go astray.

1. Estimate the load first: hang a spring scale on the mechanism you need to drive, and pull it to see how much force is needed to make it move.

2. Calculate the speed: Use a stopwatch to measure how many seconds it takes you to complete this action from the starting point to the end point.

3. Finally, look at the feedback: If you need to know the current angle of the servo, you must choose a digital servo with angle feedback, otherwise it can only be controlled in one direction.

Why does the steering gear keep vibrating?

Many friends will encounter the "shivering" situation of the servo when they first get started. It will buzz as soon as the power is turned on, or it will rotate suddenly. This is usually caused by three reasons: insufficient power, too much load, or signal interference. The current when the servo is started is very large. If the power supply you use cannot keep up, the internal circuit will be messed up as soon as the voltage drops, which will be manifested as jitter. If the load is too large, it will keep adjusting back and forth near the target position, because the force is not enough and it will never be able to push to that point. Also, if your control wires and motor wires get tangled together and the pulse signal is interfered with, it will also go crazy.

In this case, you can use a simple method to check first: remove the servo from the mechanism and try it with no load power on. If it stops shaking, the problem is probably with the load or mechanical structure, such as a stuck joint. If it still vibrates under no load, check the power supply first and try changing to an adapter with a larger current. For example, the original 1A adapter is replaced with a 3A adapter. If that still doesn't work, run the control wires separately and away from high-current power lines. In many cases, this will solve the problem.

How to make the servo rotate more smoothly without getting stuck

Have you found that the servo always rotates one frame after another, as if it is skipping frames, and cannot swing as smoothly as your arms? This is because ordinary servos move according to "position". If you let it go directly from 0 degrees to 90 degrees, it will rush over instantly. To make the movements smooth, the core idea is to break a large-angle movement into many small-angle steps and walk through them step by step. For example, if you want to turn from 0 degrees to 90 degrees, don't issue the "90 degrees" command directly. Instead, use a program loop to first turn 1 degree, stop for a while, and then turn 1 degree again until the rotation is completed. The shorter the pause in the middle, the smaller the step length, and the smoother the movement.

Many advanced digital servos support "mixed control mode" and can directly send target speed and acceleration parameters. You can try this: first determine how fast your controller (for example) can generate loop commands, and then set the step size based on the servo response speed. It is generally recommended that each step should not exceed 3 degrees, and the interval between each step should be 20 to 50 milliseconds. Write a small program to test and find the most comfortable step parameters for your servo. After doing this, you will find that when your robot arm or gimbal moves, it will suddenly have a "high-end feel".

How to calibrate the steering gear angle if it is not correct?

Obviously the program says to turn to 90 degrees, but the servo actually stops at 85 degrees. Have you ever encountered this situation? Don't be quick to suspect that the servo is broken. In most cases, it's because the zero position of the mechanical installation and the electrical zero position are not aligned. The neutral position of the servo is usually a pulse width of 1.5 milliseconds, corresponding to 90 degrees. But when you install the steering wheel, the position of the latch may not be absolutely in the center. If it is one tooth off, it will be biased by a few degrees. Another reason is that different brands, or even different batches of servos of the same brand, have slightly different response ranges to pulse widths.

The solution is actually quite simple: use physical calibration. First, set the servo to the neutral position in the program, which is the theoretical 90 degrees, then remove the steering wheel, realign it with the "mechanical zero position" you want and install it. If there is a deviation at this time, fine-tune the neutral pulse width in the program. You can use a little trick: write a program to turn the servo to 0 degrees, 90 degrees, and 180 degrees in sequence, then mark each position with a laser pointer or pointer, write down the actual deviation value, and then compensate the deviation value in the final program. If you do it a few more times, the accuracy can be controlled within 1 degree.

How to control a dozen servos at the same time

When you start making a bionic robot or a multi-axis robotic arm, you will definitely encounter a headache: the controller interface is not enough, or when controlling several servos at the same time, they will freeze and slow down. This is because the hardware resources of ordinary microcontrollers for outputting PWM signals are limited, and software simulation consumes a lot of CPU resources. For example, Uno only has a few hardware PWM pins, and you use software to write multiple Servo objects. Once there are more than 8, the system will become unstable.

There are three mainstream solutions to this problem. First, use a servo control board, such as a module, which is specifically designed to do this job. One board can output 16 PWM signals without interfering with each other. It uses an I2C interface to communicate with the main control, occupying only two lines. Second, if you are using a digital servo, you can switch to a serial bus solution. For example, some brands of smart servos support dozens of servos connected in series on one signal line. Each one has an independent ID, and the control efficiency is very high. Third, optimizing at the software level reduces the refresh frequency of servo instructions. Instead of updating all servos every frame, only updating the ones whose positions change can also reduce the burden on the main control.

Is there a more worry-free steering gear solution?

If you are troubled by the above debugging, calibration, and multi-channel control issues, or your product has reached the stage of mass production, you can consider directly choosing a more integrated integrated solution. There are some smart steering gear modules on the market now, which integrate controllers, drivers and communication interfaces. They support CAN bus or RS485 bus, have strong anti-interference capabilities and are suitable for industrial environments. There are also integrated robot joints aimed at the education market, with built-in encoders, reducers and drive boards. You only need to provide power and communication instructions.

The action suggestion is simple: you can first make a list of requirements and write down parameters such as torque, accuracy, control method, communication interface, and working voltage. Then go to the official websites of some professional servo servo manufacturers, such as some domestic head brands, and look at their selection manuals. Many companies provide sample testing services. Contact their technical support directly, describe your application scenarios, and ask them to recommend ready-made solutions. It is often much more time-consuming and labor-saving than trying to figure it out from scratch. Remember, choosing a mature solution allows you to focus more on the innovation of the product itself.

Seeing this, have you ever encountered a situation where the entire project got stuck due to servo jitter or insufficient accuracy? Welcome to share your experience in the comment area, or forward this article to friends who are also working on robots and smart devices, so that we can avoid detours together.