Key Takeaway to Avoid Pitfalls: When buying the MG90S, you must ensure it has “all-metal gears.” Do not be fooled by sellers’ wordplay using the term “metal gears”!
Many enthusiasts mistakenly believe that the “MG” (Metal Gear) prefix indicates fully metal construction. The market is flooded with counterfeit products, and sellers exploit the ambiguity between “metal gears” and “all-metal gears,” leading to frequent robot malfunctions.
1. Core Details: “Metal” vs. “All-Metal”
- All-Metal Gears (Recommended): The internal components—from the motor shaft gear and intermediate reduction gears to the output shaft—are entirely made of metal.
- Metal Gears (Avoid): Only the output shaft visible outside the casing is metal. The internal reduction gears, including the first-stage gear on the motor shaft, are entirely plastic.
2. Internal Photo Comparison: See for Yourself
[Image 1: Comparison of Internal Gear Materials]
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Left (Genuine All-Metal): Upon disassembly, all gears are brass or steel.
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Right (Fake All-Metal): Only the top shaft is metal, connected to a series of white/black plastic gears below.
3. Failure Symptoms and Cause Analysis
These “metal-on-the-outside, plastic-on-the-inside” degraded servos will inevitably fail when the robot encounters resistance or impacts. They have two fatal flaws:
[Image 2: Details of Servo Failure]
- Gear Stripping/Damage: The internal plastic reduction gears have poor strength. Under load, they shatter or strip teeth, causing gears to pile up and jam.
- Motor Shaft Gear Detachment: The small plastic gear on the motor’s output shaft, subjected to high-frequency vibration and load, slips off and strips directly from the smooth metal motor shaft.
Final Failure Manifestation
The robot loses control, and the servo continuously emits a “buzzing” sound that never stops.
- Cause: After the plastic gears break or detach, the motor shaft spins freely without driving the potentiometer at the top. The servo control chip mistakenly believes the target angle hasn’t been reached, causing the motor to spin wildly until it burns out.
4. Purchasing Guide to Avoid Scams
- Don’t chase the lowest price; MG90S servos priced below 6 RMB are almost certainly plastic inside.
- Ask customer service directly: “Are the internal reduction gears and motor shaft gears metal or plastic?”
- Once you receive the item, open the casing. If the first-stage gear on the right is plastic, return it immediately.
