Stigma (letter) sigma form ς never occurs inside a word and is never used as a numeral either. Uppercase forms of stigma as a numeral (Ϛ) are rare in practice; when they occur, they can often be confused with uppercase forms of another numeral symbol, koppa (Ϟϟ), which stands for 90. Stigma is encoded in Unicode as "Greek letter stigma" U+03DA (Ϛ) and "Greek small letter stigma" U+03DB (ϛ). Stigma (letter) Stigma (ϛ) is a ligature of the Greek letters sigma (Σ) and tau (Τ), which was used in writing Greek between the Middle Ages and the 19th century. It is also
Cogging torque however, at high speed the motor moment of inertia filters out the effect of cogging torque. A summary of techniques used for reducing cogging torque: Almost all the techniques used against to cogging torque also reduce the motor counter-electromotive force and so reduce the resultant running torque. A slotless and coreless permanent magnet motors does not have any cogging torque. Model railway motors usually have a 2-pole permanent magnet and 3, 5 or 7 poles on the armature to reduce cogging torque. Cogging torque Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets