TECHNICAL SUPPORT
Published 2026-03-24
Have you ever encountered this situation: the standard digital microservoyou bought can only turn 180 degrees, but you want it to keep turning like a wheel but you can't? Don't rush to replace the expensive continuous rotationservo. In fact, you can convert an ordinary digitalservointo a continuous rotation version by spending half an hour with your hands, and the cost is less than 30 yuan. Today we will talk about this practical modification technique.
To put it bluntly, the continuous rotation servo is an ordinary servo with the internal limiting structure removed. There is a potentiometer and mechanical limit inside the standard servo to control the rotation angle between 0 and 180 degrees. After modification, the servo no longer cares about the angle, but determines the speed and direction based on the PWM signal you give: 1.5ms pulse to stop, 1.3ms to forward, and 1.7ms to reverse. This feature is particularly suitable for robot wheels, conveyor belt drives or automatic rotating display stands.
The modified servo essentially turns position feedback into speed control. When you give pulse signals of different widths, the comparison circuit inside the servo will determine which direction and how fast it should turn. This is equivalent to turning a precise positioning tool into a speed-adjustable combination of micro motor acceleration and reduction gearbox. Many small robots and smart cars do this.
The price of continuous rotating servos purchased directly on the market is usually two to three times that of ordinary servos. Take the common 9-gram digital servo as an example. The regular version costs 20 to 30 yuan, and the continuous rotation version may cost 60 to 70 yuan. Modifying it yourself not only saves money, but also allows you to choose digital servos with different torques and speeds to modify as needed, giving you greater flexibility. Especially when making product prototypes, the cost advantage is particularly obvious when a few tests are changed in batches.
In addition, if you modify the servo yourself, you will know the internal structure, so you can easily troubleshoot any subsequent problems. For example, if the gears are worn or the motor is burned out, you can quickly determine whether to replace parts or replace the entire unit. This sense of control is important to makers. Moreover, by modifying it yourself, you can better understand the working principle of the steering gear, and you will be more confident when designing circuits or control systems in the future.
It is enough to prepare these few things: a small Phillips screwdriver, needle-nose pliers, a utility knife, a soldering iron (preferably one), a 10k ohm resistor, and a broken servo or a potentiometer of the same model as a spare. Friends who play model airplanes or robots have most of the tools on hand. If not, they can be purchased for dozens of dollars. Pay attention to choosing digital servos instead of analog servos. Digital servos respond faster and have better linearity after modification.
The electric soldering iron is mainly used to short-circuit or replace the feedback circuit. If you don't have a soldering iron, you can also use the wire-cutting method to short-circuit, but be careful when doing it. It is recommended that novices first use a cheap servo to practice. It is normal to modify one or two. Do not directly operate on an expensive servo. In addition, the workbench must be clean. There are many small parts and it is easy to find them if they fall on the floor.
Step one: disassemble the steering gear. Use a screwdriver to unscrew the four screws at the bottom, open the upper cover, and carefully take out the gear set. You will see a small plastic stop next to the output shaft, that is the stopper. Cut it off with needle nose pliers, this is key to making the servo turn continuously. Be careful not to damage the gears and circuit board.
Step 2: Modify the potentiometer. Find the variable resistor connected to the output shaft, usually three pins. The standard servo relies on it to sense the angle. To change it to continuous rotation, you need to let it feedback a fixed voltage. The simplest method: solder a 10k resistor between the middle leg and any side leg, or directly solder the middle leg to the 2.5V voltage point. After removing the limiter, you must also grind down the raised stop on the output shaft.
Step 3: Reassemble and test. Before putting the gear back on, check to see if there is any debris left. Apply some grease, install the gears in order, and finally close the cover. Before powering on, use a servo tester or send a 1.5ms pulse to see if the motor stalls. If it still turns, it means that the potentiometer modification is not in place and needs to be fine-tuned.
After assembly, don’t rush to install it on the device. Use a servo tester or send a set of signals: 1.3ms for 3 seconds, 1.5ms for 3 seconds, 1.7ms for 3 seconds. Observe whether the rotation speed is uniform and whether the reverse direction is smooth. If the rotation is stuck, it may be that the gear is not installed properly or the limit is not ground cleanly. If the reverse rotation speed is significantly slower than the forward rotation, it means that the fixed voltage modified by the potentiometer is not accurate enough, and the resistance value needs to be readjusted.
Test again with load. Gently hold the output shaft with your hand to see if the motor has strength. The torque of the normally modified servo is about the same as before. If it cannot turn when you pinch it, there may be a problem with the reduction gear meshing, or the motor driver chip may be overheated. Run continuously for 5 minutes and touch the servo shell. The temperature rise is normal and it should not be hot to your hands. Only after passing these tests can you use it with confidence.
Problem 1: Jitter after modification. This is usually because the potentiometer feedback signal is unstable. You can find the feedback pin on the circuit board and add a 0.1uF capacitor for filtering.Question 2: One turns fast and the other slow. Check whether the gear set is worn or the output shaft stop is not ground flat, causing periodic jamming.Problem 3: The control direction is reversed. Swap the two wires of the motor, or solder the feedback pin of the potentiometer in reverse.
Question 4: Severe fever. Check whether the frequency of the PWM signal is too high or too low. Generally, 300Hz to 500Hz is more suitable for digital servos. In addition, long-term stalling after modification will burn the motor, so over-current protection must be added to the software. If the servo is used in a critical position, it is recommended to buy two backups. There is another issue that is easily overlooked: the working voltage of digital servos is usually 4.8V to 6V. Never connect a 7.4V lithium battery directly, as it will burn the circuit board.
After reading so much, are you itching to give it a try? If you have also modified the servo or have a better method, please share your experience and rollover experience in the comment area, so that more friends who play robots can avoid detours. If you find it useful, please give it a like so more people can see it!
Update Time：2026-03-24
Contact Kpower's product specialist to recommend suitable motor or gearbox for your product.
