SG90 and MG996R: the two servos most often bought wrong
The default actuation of first robots. Cheap is their virtue; inflated specs are their norm. This entry takes the numbers apart.
- SG90
- 9 g, plastic gear, 1.8 kg·cm claimed (4.8 V)
- MG996R
- 55 g, metal gear, 9–11 kg·cm claimed (4.8–6 V)
- Signal
- Standard PWM (50 Hz, 500–2500 µs)
- Price
- SG90 about USD 1–2; MG996R about USD 3–6
- Feedback
- None (position and load not readable)
- Counterfeit risk
- High (same model, threefold price spread)
- The spec, and what it measures
- Both figures are stall torque at nominal voltage — instantaneous. MG996R's 9–11 kg·cm means 'at 6 V with the output shaft locked, for a moment'. It is not a sustained rating; continuous load should be taken at a third to a quarter, so 2–3 kg·cm as a design value. The SG90's number means the same, but its plastic gears fail before its torque limit does — the failure mode is stripped teeth, not stall, and that difference decides where each belongs.
- Price tiers
- USD 1–2 (SG90, 9 g, light loads) → 3–6 (MG996R, 55 g, legs) → 8–12 (DS3218, bearinged output, stiffer case; common in quadrupeds) → 15+ (Feetech STS / Dynamixel: bus, position feedback, configurable). A pound for a pound mostly holds in this category — counterfeits being the one place where price and quality detach.
- How to pick
- Three moves: ① buy versions with a bearinged output shaft — several times the service life; ② size by continuous load, not stall (legs get MG996R or better; bench trinkets get SG90); ③ buy spares in the same batch — stripped gears are a probability, not a defect. The day you need feedback or parameters, jump straight to bus servos; there is no path there through PWM.
- Known pitfalls
- ① Inflated specs: the same model from different factories varies up to 30% in real torque; ② a plastic-geared SG90 on a leg is a scheduled failure; ③ PWM deadband and jitter — worse at the low end, visible as the 'fine trembling' that makes gait robots look unstable at stance; ④ counterfeit detection by weight is the most direct test: SG90 about 9 g, MG996R about 55 g — light means wrong.
- What we checked
- We verified: the torque-voltage definitions across multiple datasheets; that 'using stall figures as continuous ratings' is the category's most common misuse; and the difference in failure modes between plastic- and metal-geared versions. We did not verify: per-brand counterfeit rates or lifetime statistics — those need batch-level data, and community reports give orders of magnitude only. The grade stays accordingly.
This site's call
Entry-level trial parts with a clear division of labour: SG90 for unloaded small motion, MG996R / DS3218 for legs. They teach you every limitation of PWM servos — no feedback, deadband, stall damage — and those limitations are precisely what the premium on bus servos buys away. Step straight to bus servos if the budget allows; start here if it does not. These parts survive being learned on.
Who does what
| Job | Pick | Why |
|---|---|---|
| Gripper, head pan | SG90 | Light loads, weight-sensitive; a replacement costs 1.5 dollars |
| Quadruped legs | MG996R / DS3218 | Continuous load needs metal gears and bearings |
| Anything needing position feedback | Neither — Feetech STS | PWM servos do not report position |
| Configurable speed, torque, thermal limits | Neither — bus servos | PWM servos have no parameters to set |
Sources
- Multiple vendor datasheets (torque definitions, voltage, weight)
- Community usage reports (failure modes, counterfeit identification)
Objects in this entry
Last checked 2026-09-28