Lehner Motoren Technik (LMT) Torqstar 2 (7040)

The Lehner Motoren Technik (LMT) Torqstar 2 (7040) is the longer 70 mm outrunner of the Torqstar series, with a mass of about 1.5 kg, as a model or industrial version. Lehner Motoren Technik is a German maker of electric motors for model flying and industry. The shaft is 12 mm. Thanks to the longer stator stack at the same diameter it delivers more torque than a short motor of the same series.

At 1,500 g the Torqstar 2 is among the heavy outrunners for aircraft with a large propeller. The windings run from 5 to 40, and with the winding one chooses the voltage at which the desired speed arises: few turns run faster at the same voltage, many turns slower and stronger. Which winding suits which cell count follows from propeller and take-off weight, not from the motor alone. The 12 mm shaft also takes high torques.

With a drive of this weight the aircraft is large, and the requirements grow with the size: up to 25 kg take-off weight a drone stays in the open category, above that the specific category is responsible. The EU class (C0 to C6) follows the weight of the whole drone, not the motor. Motor, speed controller (ESC) and battery must carry the same cell count; power figures are compared only on the same time basis, and makers use between 3 and 180 s.

In a 1.5 kg motor, imbalance and thrust peaks act strongly on the bearings. Over time, shaft wobble and bearing play increase, so the bell should be turned by hand at fixed intervals and checked for roughness. With water cooling, seals and hoses need regular inspection, with air cooling the air guidance. The mounting also deserves attention: the screws of the motor mount must be secured, because vibration loosens them.