Scorpion Power System SII-4020-540KV

The SII-4020-540KV from Scorpion Power System is an outrunner for fixed-wing models. The maker lists it as a drive for model aircraft of the 60 to 64 inch class on 6S, not specifically for UAV. The type code gives the stator: 40 mm diameter, 20 mm height.

The housing measures 48.9 mm across and 46.15 mm in length, the motor weighs 288 g and the shaft is 6 mm. The layout has 12 slots and 14 poles. At 540 KV a 6S battery at 22.2 V gives a no-load speed of about 12,000 rpm; the recommended propellers are 15x8E and 16x7E. Winding resistance is about 0.02 ohm. The maximum values of 85 A and 1,850 W come without a time base; arithmetically they fit about 22 V and read as a short-term peak, not a continuous load.

Model aircraft are also unmanned aircraft and fall under the EU drone regulation: from 250 g take-off mass the operator must register. In the open category visual contact, a maximum height of 120 m and a maximum of 25 kg apply. Motor, ESC and battery must share the same cell count.

On fixed-wing aircraft the airstream cools the motor better than in a hover. A propeller much larger than recommended overloads motor and ESC. The ESC must carry the 85 A with headroom. After a hard landing, check the shaft, the bearing run and the bell's magnets.