Q. A 6 - pole, DC armature with 36 slots and 2 coil - slides/slot is to be wave wound (double layer). Calculate the back pitch, front - pitch and commentator pitch. How many dummy coils, if any are required? 

Ans. 

Given

                           C = 36

                           P = 6

                           C = P/2Y_c ± 1

                           36 = 6/2 Y_c ± 1

                           36 = 3Y_c ± 1

   Let                    Y = 12 then

                            C = 3 ×12-1

                                = 35

SO we choose C = 35 which actually 36 coils be accommodate

                           Y_es = S/P = 36/6 = 6

                           Y_B = 2Y_CS + 1

                          Y_B = 2 × 6 + 1

                          Y_B = 13

                         Y_F = 2Y - Y_B = 2 ×12 - 13 = 11