12V DC Motor High Torque Low Speed
Screen a 12V motor and gearbox starting point from output speed, torque, and duty. The calculation explains its assumptions; a candidate motor’s loaded curve and gearhead ratings decide the final fit.
·
Ready to calculate
Enter your 12V motor speed and torque requirements to see a power estimate, speed-ratio starting point, and selection checks.
Decision guide
Start with the loaded operating point
A low output speed with higher torque usually points to a reduction stage, but the required ratio is only the start of selection. For the target load, check the motor speed-current curve and the gearhead’s continuous or intermittent output torque, efficiency, input-speed limit, and thermal conditions.
The calculator uses output power P = τ (Nm) × 2πn / 60. Its ratio estimate divides the motor’s no-load speed by target output speed. Neither result proves that a motor can deliver the requested loaded torque or speed.
Published 12V example: why ratings matter
These are specifications for one Pololu 37D product family, included to show how no-load, stall, and recommended load values differ. They are not universal 12V motor limits.
| 12V 37D listing value | Published figure | How to interpret it |
|---|---|---|
| Bare motor, no load | 10,000 rpm; 0.2 A | No-load reference only; it is not the speed or current at the requested load. |
| Bare motor, stall | 5.5 A; extrapolated torque | Stall is zero speed, not a continuous operating point; prolonged stall can damage the motor. |
| 100:1 gearmotor | 100 rpm no-load; 34 kg·cm extrapolated stall torque | Output speed falls with load; the stall figure is not the gearbox’s continuous rating. |
| Family guidance | 10 kg·cm continuous; 25 kg·cm instantaneous upper guidance | Use the selected variant’s documented limits and design margin; do not infer capacity from the ratio alone. |
Source: Pololu 12V 37D Metal Gearmotors, checked 2026-10-15. Pololu labels stall torque as theoretical extrapolation and warns that stalling or overloading can damage the motor or gearhead.
What to confirm before choosing a gearhead
| Check on the candidate datasheet | Why it changes the decision | Selection action |
|---|---|---|
| Speed and current versus torque | Motor speed falls as load torque/current rises; no-load speed alone cannot confirm the target point. | Verify the curve at the requested output torque after accounting for ratio and losses. |
| Continuous and intermittent output torque | Duty and starts/stops change heating and gearhead loading. | Match continuous load to continuous rating; separately check peak and cycle limits. |
| Efficiency, ratio, and maximum input speed | Efficiency and permitted input speed vary by gearhead and stage count. | Compare the exact ratio’s values; include backlash and output shaft loads where relevant. |
| Driver and stall protection | Starting or jam current can be much higher than free-run current. | Check driver, supply, wiring, and current limit against the selected motor’s data. |
At a fixed motor voltage, speed and current change with load torque; maxon describes this motor operating relationship in its Motor Data and Operating Ranges guide. Portescap’s gearhead selection guidance distinguishes dynamic output torque, maximum static torque, efficiency, and recommended input speed. See How to Select a Gearhead and its gearhead guide (checked 2026-10-15).
Frequently asked questions
Speed and torque
Method and evidence
- Output power: torque (mNm) × 2π × speed (rpm) ÷ 60 ÷ 1000. First-pass supply current: output power ÷ (12 V × entered supply-to-output efficiency). This is not measured motor current.
- Ratio screen: candidate motor no-load speed ÷ target output speed. Loaded speed is lower and depends on torque, voltage, motor curve, and gearhead losses.
- Motor operating points and gearbox limits must come from the selected part’s datasheet. Key references were checked 2026-10-15; supplier specifications can change.