Formula used
τ = rF sin(θ)τroll = Σ(yiFi), τpitch = -Σ(xiFi), τyaw = Σ(siQi)α = τ / I, τrequired = Iα, τshaft = Pmechanical / ωT = CTρn²D⁴, Q = CQρn²D⁵The calculator converts every input into SI units. It applies motor positions relative to the chosen centre. Reported values are converted into your selected torque unit.
How to use this calculator
- Select a preset or enter your frame dimensions.
- Enter each motor’s thrust, RPM, and rotation direction.
- Add reaction torque or enable the coefficient model.
- Enter mass, inertia, target motion, and safety factor.
- Choose output units and calculate the complete result.
- Review warnings before using values for real hardware.
Example data
| Example | Arm length | Mass | Motor thrust | RPM | Typical purpose |
|---|---|---|---|---|---|
| Micro quad | 6 cm | 0.12 kg | 0.45 N | 28,000 | Indoor practice |
| 5-inch FPV | 11 cm | 0.65 kg | 5.5 N | 22,000 | Freestyle flight |
| Photography drone | 22.5 cm | 1.4 kg | 6.0 N | 8,500 | Stable imaging |
| Heavy-lift quad | 45 cm | 8.0 kg | 25 N | 4,200 | Payload lifting |
Frequently asked questions
What does quad torque mean?
Quad torque describes rotational force around a quadcopter axis. Roll, pitch, and yaw use different motor effects. The calculator separates every contribution for clearer engineering checks.
How is roll torque calculated?
Roll torque uses each thrust force and lateral offset. Opposing motors usually create the useful thrust difference. Positive direction depends on your selected coordinate convention setting.
How is pitch torque calculated?
Pitch torque uses each thrust force and longitudinal offset. Front and rear thrust differences control nose rotation. The displayed sign identifies nose-up or nose-down motion clearly.
Why is yaw torque different?
Yaw torque mainly comes from propeller reaction and drag. Clockwise and counter-clockwise motors should normally balance closely. Unequal reaction torque creates intentional or unwanted yaw motion.
Can thrust be estimated from RPM?
Yes, the coefficient model estimates thrust from RPM. It also needs air density and propeller diameter. Measured thrust data usually provides more reliable design results.
What is moment of inertia?
Moment of inertia measures resistance to angular acceleration. Larger values require more torque for equal response. Use measured or modelled values whenever practical for accuracy.
Why include a safety factor?
A safety factor provides reserve torque for uncertainty. Real systems experience losses, vibration, and changing airflows. Conservative margins help avoid undersized motors during demanding manoeuvres.
What causes an off-centre torque?
A shifted payload moves the vehicle’s centre of gravity. Motor lever arms then become unequal around that centre. The CG inputs model this effect before flight testing.
Are theoretical propeller values exact?
No, coefficient equations provide useful engineering estimates only. Propeller shape and motor behaviour affect measured performance. Confirm critical designs using manufacturer data and controlled testing.
Engineering notice
This tool provides estimates for planning and comparison. Real propellers behave differently across speed and airflow. Verify safety-critical values with tests and manufacturer documentation first.