What should I do if the steering gear gets hot? Causes and solutions

1. Excessive load - the most common source of heat

When the resistance endured by the steering gear output shaft exceeds its rated torque, the motor stall current will surge sharply and the heat will also increase rapidly.

The method for self-testing is to disconnect the servo from the mechanical arm and connecting rod, and then run it for 1 minute without load.. If you find that the heat is significantly reduced under no load, it indicates that there is a problem with the load.

The following is a typical case. An enthusiast used a 15kg servo to drive a 300g metal arm. However, due to the inflexibility of the joint design, the actual load reached 20kg. As a result, the servo became hot after half a minute. Afterwards, it was replaced with a 25kg servo and the temperature returned to normal.。

2. The power supply voltage or current is unstable

The DC motor and driver IC installed in the steering gear are very sensitive to voltage fluctuations. When the voltage is too low, the servo will frequently start the "undervoltage protection-recovery" cycle, which will generate additional heat; if the voltage is too high, it will directly increase the current, eventually causing the MOS tube to be burned.

The self-test of the positive and negative voltages of the servo operates as follows: Use a multimeter to measure and observe the voltage drop at the moment when the servo rotates. Check and pay attention to the voltage drop at the moment when the servo rotates. Once the voltage drop exceeds 0.5V, you need to replace the power line with a thicker one, or connect a large capacitor in parallel (the capacitance must be above 1000μF).

3. Internal mechanical failure of the steering gear

The gearbox is short of oil, or metal debris is stuck, or the bearings are worn. These conditions will increase the rotational resistance, forcing the motor to output more current.

Manually turn the steering wheel to perform a self-check to see if there is any obvious "graininess" or intermittent jamming. A normal steering wheel should be smooth and make no abnormal noise.

A quite typical phenomenon will occur, that is, for such a type of steering gear, which has been used for more than half a year, especially the steering gear that often works in a dusty environment, the gear grease inside them will dry up, and at this time, its temperature will be 15 to 20 degrees Celsius higher than the temperature of a new machine that has just been produced.

4. PWM signal frequency is too high or pulse width jitters

Some PWM signals sent by the control board are not stable, that is, the signal frequency exceeds 333Hz, or the duty cycle of the signal jumps, which causes the servo motor to repeatedly start and stop operations within a microsecond time range, resulting in additional heat loss.

The way to check yourself is to use an oscilloscope or logic analyzer to capture the waveform of the signal line. If you see obvious rising edge burrs or pulse width jumps exceeding plus or minus 10 microseconds, it means there is a problem with the control end.

Step 1: Reduce actual load (most efficient)

The transmission ratio is redesigned and a gear reduction group is added, allowing the servo to work in a high-speed, low-torque range.

Optimize the mechanical structure: Check whether all joints rotate flexibly and eliminate interference points.

To use a spring buffer, an elastic element is added to the rigid connection to absorb the impact peak torque.

Step 2: Transform the power supply system

Each servo is powered independently to avoid sharing the same power supply with the main control board.

Connect a 1000μF electrolytic capacitor and a 0.1μF ceramic capacitor in parallel at the pin that supplies power to the servo to filter out high-frequency ripples.

By using a voltage stabilizing module, such as the LM2596, the voltage is stabilized within the range of the servo's nominal value plus or minus 0.2V.

(cue word: heat dissipation)

Good heat dissipation design is the last line of defense to suppress temperature rise. Even if the load and power supply are in normal conditions, if the servo is wrapped in a sealed plastic shell, heat accumulation will cause malfunctions. It is recommended to paste a small aluminum heat sink with a size of no more than 30x30mm on the metal shell of the servo, or open ventilation holes to create convection. For applications that run continuously for more than 5 minutes, adding a micro 5V direct fan can reduce the temperature by about 20°C.

Step 3: Adjust control parameters

The PWM frequency is controlled within the range of 50 to 300Hz, and the standard 50Hz (period of 20ms) is recommended.

To prevent large-angle deflections from being maintained for a long time, such as when the full rudder is used for more than 300 milliseconds, you can add a "duty cycle ramp" function to the program to make the servos rotate slowly.

Check the code to see if there are repeated instructions at the same position. Each redundant instruction will cause an invalid adjustment.

Step 4: Regular maintenance and replacement

After every 100 hours of operation, disassemble the steering gear casing, clean out the old grease, and fill it with high-temperature resistant lithium-based grease. The dropping point of this grease is greater than 180°C.

Check the length of the carbon brush. If the steering gear is a brushed motor, it needs to be replaced when the carbon brush is worn to one-third of its original length.

For those servos that show obvious demagnetization, their no-load speed is abnormally fast, and the heat is extremely serious. In this case, it is more economical to directly replace the servos with a new one than to repair them.。