Calculator
Formula Used
Input torque conversion: selected torque is converted to N m.
Usable motor torque: Tu = Tm × usable percent × motor count.
Output torque: To = Tu × gear ratio × gear efficiency × drive efficiency.
Drive force: F = To ÷ wheel or drum radius.
Safe drive force: Fs = F ÷ safety factor.
Rolling load: mass = Fs ÷ [g sinθ + Crr g cosθ + acceleration].
Vertical lift: mass = Fs ÷ [g + acceleration].
Weight force: W = mass × g.
How to Use This Calculator
Choose the load mode first. Use rolling mode for wheels, carts, robots, and conveyors. Use lift mode for hoists, drums, and vertical raising systems.
Enter the rated motor torque. Select the correct torque unit. Add the number of motors sharing the load.
Enter the gear ratio and efficiency values. Use realistic losses for gears, belts, chains, bearings, and couplings.
Enter the wheel or drum radius. A larger radius lowers drive force. A smaller radius increases force but may reduce travel speed.
Add incline, rolling resistance, acceleration, and safety factor. Press calculate. The result appears above the form.
Example Data Table
| Use case | Torque | Motors | Gear ratio | Radius | Mode | Safety factor |
|---|---|---|---|---|---|---|
| Small robot cart | 1.2 N m | 2 | 30:1 | 6 cm | Rolling | 2 |
| Light conveyor | 2.5 N m | 1 | 40:1 | 8 cm | Rolling | 2.5 |
| Mini winch | 0.8 N m | 1 | 60:1 | 3 cm | Lift | 3 |
DC Motor Max Weight Guide
Why motor weight capacity matters
A DC motor can look strong on paper. Real load capacity depends on more than the printed torque value. Gearing, wheel radius, friction, speed, slope, and safety margin all change the final weight. This calculator brings those factors into one practical estimate. It helps size motors for robots, carts, winches, conveyors, and small mechanisms.
Torque is only the starting point
Motor torque is twisting force. A gearbox multiplies that torque. It also adds losses. Belts, chains, bearings, and couplings add more losses. The calculator applies gear efficiency and drive efficiency. It also lets you use only part of the rated torque. That is useful when the motor must run without overheating.
Radius changes force
The wheel or drum radius is very important. Force equals torque divided by radius. A large wheel moves faster, but it reduces pulling force. A small drum lifts more weight, but it moves the cable slower. This is why the same motor can lift a heavy load with a small drum, yet struggle with a large wheel.
Rolling and lifting are different
A rolling load usually needs less force than a vertical lift. The motor mainly overcomes rolling resistance, slope, and acceleration. A vertical lift must support gravity directly. That makes lifting much harder. The calculator uses a different formula for each mode.
Use safety margin
Real machines face shocks, bad bearings, low battery voltage, and uneven ground. A safety factor reduces the allowed force. It gives the design more room for real conditions. A value of two is common for light tests. Critical lifting systems need much stronger engineering review.
Check traction and heat
A wheel may slip before the motor reaches its torque limit. The traction check warns about that risk. Motor heat also matters. Stall torque should not be used continuously unless the motor is rated for it. Always compare the result with current limits, duty cycle, mounting, ventilation, and manufacturer data.
FAQs
1. What does this calculator estimate?
It estimates the maximum load a DC motor can move or lift. It uses torque, gear ratio, radius, efficiency, friction, incline, acceleration, and safety factor.
2. Can I use stall torque?
You can enter stall torque, but reduce the usable torque percent. Stall torque can overheat a motor quickly. Continuous torque is safer for long operation.
3. Why does wheel radius affect weight capacity?
Drive force equals torque divided by radius. A larger wheel gives more speed but less force. A smaller wheel gives more force but less speed.
4. What safety factor should I use?
Use at least 2 for basic estimates. Use a higher value for lifting, shocks, people nearby, expensive parts, or unknown friction.
5. What is rolling resistance?
Rolling resistance represents tire, wheel, floor, and bearing losses. Smooth hard wheels may be low. Soft tires, carpet, and rough floors are higher.
6. Why is lifting harder than rolling?
A lift must fight gravity directly. A rolling system mainly fights friction, incline, and acceleration. That is why rolling capacity is often much higher.
7. Does gear ratio always increase capacity?
A higher gear ratio increases torque, but reduces speed. It also adds losses. Very high ratios may reduce efficiency and create heat.
8. Is this result final for real machines?
No. It is an estimate for planning. Verify the design with tests, motor datasheets, current limits, thermal checks, brakes, and mechanical safety rules.