Tethered drone calculator

flight time + drone mass → tether voltage, wire, mass, power & battery for 10–50 m tethers

Results by tether length

one row per tether length · grey row = not feasible

All details at m tether · every metric, one column per visible entry
Model & assumptions
  • Lifted mass = drone (dry + auto-sized converter; as-built mass in "hardware → flight time" mode) + lifted fraction × tether mass. Tether mass per metre = 2 × bare copper (8.96 g/m per mm²) × insulation factor + other conductors.
  • Hover power per motor = T1.5 / √(2 ρ A) ÷ figure of merit ÷ motor+ESC efficiency (momentum theory), + avionics. Peak = same at max thrust (TWR × hover, or motor max thrust in reverse mode). Dynamic = factor × hover, capped at peak. Lifted mass solves m = a + b·m1.5 exactly (the converter grows with peak power; Newton on the concave residual — "runaway" means no finite design exists).
  • Tether: constant-power load through round-trip resistance R = 2 L ρCu/A; the cable can deliver at most Pmax = V²/4R. The cable must deliver peak power × (1 + margin) and lose at most the hover-drop limit at hover.
  • Tether voltage is solved per length: for each 14–32 AWG wire the minimum workable voltage follows in closed form (peak: √(4·R·Ppeak·(1+margin)); hover drop δ: √(Phover·R/(δ(1−δ))); converter input: after the cable drop at peak the on-board buck must still see ≥ 1.1 × the motor-bus voltage, V ≥ Vmin + Ppeak·R/Vmin — this is what sets the voltage at short lengths). The tool takes the thinnest wire whose minimum is within the "extra voltage accepted" headroom (10 %) of the lowest minimum over all wires, and reports the design at exactly that voltage. Heavier wire lowers the voltage only a little but adds a lot of mass — the detail table shows the lowest possible voltage next to the chosen one.
  • Battery = (pack power at hover × hover time + pack power dynamic × dynamic time) ÷ DoD, with pack power = Vtether × I ÷ ηboost. In reverse mode, flight time = usable Wh ÷ pack power. Battery mass uses the pack-level Wh/kg presets from the battery survey (Docs/battery-chemistry_wh-per-kg.md): LiPo/LiHV UAV pack 200 · 21700 DIY 205 (Molicel M65A 230) · semi-solid pack 280 · silicon-anode 300 · EV NMC pouch 210 · LiPo racing 150 · LFP 120/100 · Na-ion 90 · LTO 55 — i.e. cells + BMS + wiring + case, not cell datasheet figures.
  • Disc loading = lifted mass ÷ total rotor disc area (n · π · D²/4), in kg/m² (1 kg/m² = 10 g/dm²). Lower = less induced power per gram of lift (hover power per gram ∝ √disc loading). Bands are multirotor rules of thumb: ≤ 5 kg/m² super efficient (long-endurance drones, helicopters), 5–15 middle ground (camera drones), ≥ 15 super inefficient (racing quads, tiny props) — thresholds in CONST.discLoading*.
  • Flight time vs battery mass (at the tether length chosen in the chart title): flight time = battery kg × 60 · Wh/kg · DoD ÷ average pack power, where average pack power weights hover and dynamic pack power by the target hover : dynamic ratio — a straight line per entry; the dot is the target flight time and the battery mass it needs.
  • Safety bands on the voltage chart (IEC 62368-1 energy-source classes / SELV, DC ripple-free): ≤ 60 V DC is touch-safe in dry conditions (ES1); 60–120 V DC must not be touchable by an ordinary person — insulated, shrouded connectors, no exposed conductors (ES2); above 120 V DC treat the tether like mains (ES3): interlocks, insulated tools, a fused and isolated backpack stage. Wet hands, sweat or a damaged jacket roughly halve the first threshold. Thresholds live in CONST.safeVoltage_V / CONST.hazardVoltage_V.
  • Copper at 20 °C; insulation as a mass multiplier; KV hint assumes CT ≈ 0.09 and 85 % RPM headroom (rough, ±30 %). Run ?selftest=1 to see the anchors checked.