TECHNICAL SUPPORT
Published 2026-02-23
When engaging in product innovation, steering gear selection is a hurdle. Recently, many friends have complained to me, saying that theservocannot turn when installed, vibrates violently, or gets stuck while using it. After asking, I found out that the problem most likely lies in the internal resistance of the steering gear. Internal resistance is like the "invisible fuel consumption" of a car. If you choose it incorrectly, the performance of the entire robotic arm and robot will suffer. Today we will talk about how to conduct an "internal resistance test" for the serial portservoto nip potential problems in the cradle.
If you imagine, the motor and gearbox inside the steering gear are like a sophisticated transmission system. Internal resistance is the obstacle encountered when current "runs" inside. If the internal resistance is too large, the current will become smaller and the strength will naturally be insufficient. What's even more troublesome is that excess electrical energy will be converted into heat, which causes the steering gear to become hot and shorten its lifespan. When we make products, stability is the lifeblood. Measuring the internal resistance is to find out the "trump card" of the steering gear in advance.
️Thedirect impact is that the response becomes slower. If you give a command to theservo, it will take half a beat before it moves. This means that the robot's movements are stiff and unsmooth.️Secondly, the accuracy will fluctuate. If the internal resistance is large, the internal friction of the servo will be unstable. It may only turn 89 degrees, or it may vibrate back and forth when it is clearly allowed to turn 90 degrees. Especially when doing multi-axis linkage, if one servo is not accurate, the movement trajectory of the entire mechanism will be messed up.
In fact, the method is not complicated and you can test it yourself. You will need an adjustable DC power supply and a high-precision multimeter. First connect the servo to the power supply, do not give a signal, and leave it in standby mode. At this time, use a multimeter to measure the output current and voltage of the power supply. The calculated resistance is the static internal resistance. Then, give the servo a continuous rotation signal, block its output shaft, and measure the dynamic current and voltage again. What is calculated at this time is the dynamic internal resistance. Comparing the two, the "health status" of the steering gear is clear at a glance.
If a worker wants to do his job well, he must first sharpen his tools. We just need to prepare three things:
1. Adjustable DC regulated power supply: one that can display real-time current and voltage for easy reading.
2. High-precision digital multimeter: used to cross-verify the values displayed by the power supply to ensure accurate data.
3. Servo test board or controller: used to send PWM signals or serial port commands to the servo to make it move.
These things can be purchased on some online stores, and they don’t cost much, but they can save us the trouble of subsequent debugging.
After measuring the data, how to use it is the key. Suppose you measured two servos, model A has a static internal resistance of 5 ohms and a dynamic internal resistance of 8 ohms; model B has a static internal resistance of 7 ohms and a dynamic internal resistance of 15 ohms. It is obvious that model A is more reliable, because its dynamic internal resistance increases slowly, indicating that the internal motor and reducer cooperate well and have low friction. When we make products, we must choose a servo that is "statically stable and dynamically variable." If the internal resistance changes too drastically, the heat will definitely be severe and we must give up decisively.
Novice friends tend to make two mistakes. One is to only measure the static state but not the dynamic state. This is like looking at how tall a person stands but not how fast he runs. Second, the servo is not cooled during the test. Continuous high-current testing will cause the temperature of the servo to soar, and the measured internal resistance value will become increasingly inaccurate. Because the temperature increases, the coil resistance becomes larger. Remember to measure one, take a break, and let the servo cool down before measuring the next one, so that the data will be true and reliable.
Take our bionic robot hand as an example. There is only so much space for the fingers, and the servo has to be inserted into it. Through the internal resistance test, I eliminated a servo that generated a lot of heat and chose one with small internal resistance and high efficiency. The result is that the fingers are more responsive and do not get hot when held continuously for half an hour. If you are worried about choosing a servo, you might as well take a few samples and test them yourself. The data is much more than the words on the parameter sheet. After reading this article, do you also want to take out the servo in the warehouse and test it? Welcome to chat about your test results in the comment area, and let’s exchange progress together. If you find it useful, don’t forget to give it a like and share it with more innovative friends!
Update Time：2026-02-23
Contact Kpower's product specialist to recommend suitable motor or gearbox for your product.
