Size a multicopter drive — hover throttle and thrust-to-weight

You have a frame, a pack and a rough motor/prop idea — but you are not sure the craft will hover with margin for wind and manoeuvres without living at the limit. A solid layout answers that: define mission and AUW, fit the largest sensible prop, then Kv and cell count — and check everything in xcopterCalc.

What “well sized” means in numbers

For fixed-pitch multicopters, raw bench thrust is not enough. What matters is hover throttle and thrust-to-weight.

From the eCalc xcopterCalc help, aim for these linear hover throttle targets:

Thrust-to-weight guidance:

• ≥ 1.8 — typically agile; hover often around ≤ 60 % throttle
• 1.2–1.8 — limited manoeuvrability
• below 1.2 — hover barely practical

These are target bands, not substitutes for a calculation with your AUW, cells, ESC, motor and prop.

The mechanism in plain language

In hover, total vertical thrust must match all-up weight (AUW). That requires a certain prop RPM; the ESC sets effective motor voltage via PWM. “60 % linear” means roughly 60 % on-time — not the same as a µs value in a flight log.

More disc area (larger prop) at the same weight usually increases efficiency and  lowers hover current and required throttle. eCalc’s recommended order is: frame size first, then largest possible prop, then Kv range (Prop-KV-Wizard) and motor choice. See Propellers for frame size and Kv vs prop diameter.

Rules of thumb — always verify

1. Estimate AUW honestly (frame, powertrain, pack, camera/gimbal).
2. Choose the largest prop with tip clearance.
3. Set hover targets from the table above.
4. Check specific thrust in hover: ≥ 6 g/W is a good band in eCalc; below 4 g/W is poor.
5. Inspect peak current and estimated motor temperature — Setup too marginal, Motor overheating.
6. Size flight time via usable capacity — Flight time & LiPo.

Worked example: 5” FPV quad (explorer, not race)

Assumptions:

• Flat quad, frame ~230 mm motor-to-motor
• AUW about 650 g including GoPro-class / O3-class payload
• Battery 4S 1600 mAh, max discharge in the calc 80 % (≥ 10 % left after flight)
• Props 6×3 (pitch/diameter under 2/3)
• Motors in the ~1800–2000 Kv class on 4S (pick exact SKU from the eCalc DB)
• Field ~500 m ASL, ~20 °C
• xcopterCalc Example

What to look for in xcopterCalc:

• Hover throttle (linear) preferably under 50 % for explorer feel
• Thrust-to-weight clearly above 1.8
• Specific thrust with 4.97g/W not in the red band
• Peaks and temperature not stuck in the critical range

Exact numbers depend on the motor/prop pair — rebuild with the steps below.

Reproduce it in xcopterCalc

1. Open xcopterCalc.
2. Weight: AUW 650 g (or “without Drive” plus selected parts).
3. Rotors: 4, flat, frame 220 mm.
4. Environment: your field elevation and temperature.
5. Battery: 4S, 1600 mAh (list or custom per cell), max discharge e.g. 80 %.
6. Choose a fitting ESC (with cooling/partial-load headroom as in the help).
7. Enter 6” prop and pitch — largest sensible diameter for the frame.
8. Use the Prop-KV-Wizard, read the Kv band, pick a motor from the database.
9. Hit Calculate — read hover throttle, thrust-to-weight, temperature, currents.
10. Iterate prop, Kv or cells until you hit the target bands.

Note: Members can save setups via the Share button as a parametrised link. Public articles intentionally do not invent query-string prefills — enter values manually.

FAQ

Is high thrust-to-weight enough?
No. Race setups can show high T/W and still hover inefficiently or run hot. Always read hover throttle, specific thrust and temperature together.

Linear or log throttle?
eCalc shows both. Help recommendations refer to linear hover throttle. Do not confuse that with log PWM or stick feel.

Why prop before motor?
Frame size caps diameter. Efficiency tracks disc area strongly. Kv and cells must match the chosen prop — not folklore the other way around.