Px4 Servo Voltage Is Unstable? Is The Rudder Shaking? Teach You How To Set Up Voltage Monitoring To Avoid Loss Of Control

When playing with PX4 flight control, when theservois connected, the rudder may vibrate, theservomay not obey the command, or even directly burn out the flight control. When encountering this situation, don't rush to blame the poor quality of theservo. It is most likely that there is a problem with the power supply. When many friends are doing DIY or product innovation, they tend to ignore the "overeating" demand for voltage when the servo is working.

To put it simply, the output power of the BEC (battery elimination circuit) of the flight controller is limited. Once multiple servos are driven, the voltage will be pulled down instantly, causing the flight control to restart or the servos to lose control. Therefore, real-time monitoring of the steering gear voltage has become a key step to ensure the health of the aircraft's "limbs".

Why do I have to keep an eye on the servo voltage?

Servos are essentially high-power devices, especially those metal servos with high torque. When it rotates quickly or is loaded, the required current surges momentarily. If the power supply cannot keep up, the voltage will drop like a deflated rubber ball.

This kind of voltage drop can cause the servo to slow down or freeze, making your aircraft unresponsive; at worst, it can directly cause the flight control microcontroller to reset, causing the aircraft to lose control in the air and explode. Keeping an eye on the voltage is like hiring a personal doctor for the steering gear to keep track of its health status at all times.

How to set voltage alarm in PX4

The PX4 flight controller actually comes with a voltage monitoring function, but many people don’t use it well. You need to find the voltage detection option in the "Power Settings" of the ground station.

The key is to set the alarm threshold accurately. Generally speaking, there is a minimum red line limit for the working voltage of a servo. Taking a 4.8V servo as an example, it is quite appropriate to set the first-level alarm at 5.2V and the second-level serious alarm at 4.9V. In this way, before the voltage drops to a dangerous value, the ground station or your remote control will make a beeping sound to remind you that it is time to perform landing operations.

In practical applications, it is crucial to accurately set the alarm threshold. Taking common servos as an example, their working voltage has a clear range. Like the 4.8V servos mentioned above, reasonable planning of alarm thresholds can effectively ensure the safe operation of the equipment. When the first-level alarm is set at 5.2V and the second-level serious alarm is set at 4.9V according to the settings, once the voltage changes and approaches the dangerous value, the ground station or remote control will send out a warning signal in time, which is a beeping sound, thus prompting you to prepare for landing in advance and avoid possible risks.

What additional hardware do I need to buy to detect voltage?

Flight control software alone is not enough, the hardware must also keep up. The PX4 flight controller itself has an ADC (analog-to-digital conversion) pin that can read analog voltage signals.

You need to build a voltage divider circuit because the voltage required for normal operation of the servo is usually higher than the voltage range that the flight control can withstand. The implementation method is very simple, just use two precision resistors to build a voltage dividing circuit. The specific operation is to reduce the power supply voltage of the servo according to a certain proportion, and then connect it to an idle ADC pin on the flight control.

After completing the hardware connection, you still need to make corresponding settings in the flight control configuration file. The pin connected to the output voltage of the voltage dividing circuit must be defined as the pin for voltage monitoring, and the voltage dividing ratio must be accurately set to ensure that the entire system can accurately obtain the divided servo voltage information, thereby achieving effective monitoring and control of the servo voltage.

Battery voltage and servo voltage are not the same thing

This is a very easy pit to fall into. Many people only look at the voltage of the power battery and think that if the battery power is sufficient, the steering gear will be fine. In fact, couldn’t be more wrong!

The power used by the servo is generally converted from the power battery through the BEC on the flight controller or an external UBEC (Universal Battery Elimination Circuit). Even if the battery voltage is 12V, if the BEC is of poor quality or has insufficient power, the 5V voltage it outputs to the servo will still drop. Therefore, monitoring the "dedicated voltage" of the servo is more direct and more accurate than checking the total voltage of the battery.

What faults can voltage data help us troubleshoot?

Recording and analyzing voltage data is a great tool for troubleshooting difficult diseases. For example, your gimbal may occasionally convulse, or the landing gear cannot be lowered.

Export the PX4 log, find the column of the recorded servo voltage, and bring up the waveform chart to take a look. If there is an obvious "pit" in the voltage curve at the moment the servo moves, it can basically be concluded that the power supply is insufficient. This is much more efficient than guessing that it is a program problem or the steering gear is damaged, and can directly identify the cause.

Is it difficult to build a voltage monitoring system by yourself?

In fact, it’s not difficult at all and the threshold is very low. The basic materials you need are: two precision resistors worth a few dollars, a short piece of DuPont wire, and a soldering iron (soldering is more reliable).

The operation steps are also clear and simple: first, accurately calculate the voltage dividing ratio to fully ensure that the ADC pin input voltage will not exceed 3.3V. This step is related to the voltage stability and safety of the entire system. Next, weld or properly connect the voltage divider circuit carefully and carefully to ensure that the circuit connection is stable and correct. Then, connect the signal line accurately to the free pin next to the AUX or MAIN output port of the flight control to build a reliable channel for signal transmission. Finally, modify the relevant parameters in the ground station, enable the voltage monitoring function and complete the calibration work.

The whole process, even if your hands-on ability is only at an average level, can be completed smoothly in about an hour. You can easily complete a series of operations without spending too much energy and time.

After reading this article, have you also come up with the idea of doing a voltage check on your aircraft that is "working while sick"? You might as well calm down and think about it, has your aircraft ever experienced the kind of unexplained and life-questioning convulsion failure? Is it possible that the culprit of the malfunction is the servo voltage that you ignored? You are welcome to share your bombing experience in the comment area. Let’s avoid risks together. If you find it useful, don’t forget to give it a like and share it with more model friends!