How to Select a Motor

Currently Torcman motors are produced in three different diameters (stator width of 28, 35 and 43 mm) with up to four different stator lengths (from 5 to 30 mm), altogether a set of nine different sizes of motor. These range in capacity from approximately 40W to more than 1800W making it possible to find the perfect power unit for almost every application of electric flight from slow flyers to high-performance helicopters.

The operating speed of each type of motor can be finely tuned from 4,000 to 15,000 rpm by varying the number of turns and gauge of wire employed in the winding. There is a clear advantage to this design concept, since the coordination between propeller, battery and motor plays an extremely important role, particularly within electric flight.

To gain a rough idea of which motor to select you need to consider the weight of the model and the desired performance. 

A rule of thumb is to allow about 75 to 125W per kilogram (imperial: 35-55W per lb) for powered sailplanes, 150 to 250W per kilogram (imperial: 70-115W per lb) for powered models and hotliners, depending on the flight performance anticipated. Of course, your thumb may vary. Generally the size and number of cells in the battery also go hand in hand with the size of model. For a range of typical applications see Motor Suggestions.

A significant advantage of these motors is derived from the ability to accommodate virtually any propeller by varying the winding. The fewer turns in the winding the faster the rotational speed of the motor, consequently a smaller propeller is required. Increasing the number of cells also produces higher rpm. In order to deliver sufficient power to large propellers the number of turns in the winding must be accurately chosen for a given battery. The Propeller Suggestions table illustrates this for the TM350-20.

The diameter of the TM280 series measures barely 35mm and is therefore a snug fit in slender fuselages of smaller models. Depending on stator length (5, 10, 15 or 20mm) the power rating can amount to between 100 and 350W. With sufficient cooling even higher performance is possible for brief periods.

The diameter of the TM350 series measures 42 mm and therefore fits well in most fuselages of 42-44mm frontal width. The motors are differentiated by stator length (12, 20 or 28mm) which determines performance.

Those who require over 800W power will be very satisfied with the TM430 (20 or 30mm). Of course, choosing the next longest stator reserves sufficient capacity for future models.

Once you have an idea of which motor you are interested in you are ready for the next step: See How to Select a Winding.

In some applications the 10-pole motors, which turn some 30% faster (hence less torque) compared to the 14-pole motors, have shown to be better suited. For example power systems for 3D helicopters.

A word about terminology -  here the term 10-pole or 14-pole refers to the number of magnets employed in the rotor. Not, as you might think, the number of windings (coils) in the stator. All Torcman stators have twelve teeth, six windings.

10-pole motors are offered as an option alongside the 14-pole motors in the 350 and 430 sizes. A 280 size will follow as suitable applications for useful deployment emerge.

For a concise overview of dimensions, power rating and typical flying weight see Dimensions and Power. The weight of the finished motor compared with the weight of its nominal winding reveals that these motors have extremely low impedance. About 25% of the motor weight is apportioned to the copper in the winding.