Calculating the input power required for a drive gear in a train. I have 4 gears, all in line. The driver shaft A rotates at 100 revs/min and the gear has a diameter of 40mm. 20 teeth with a module of 2mm The output is to rotate at 400 revs/min and has a diameter of 160mm with 80 teeth and the same module of 2mm The two idler gears are both 100mm each and have 50 teeth each The output gear is working against a load of 200Nm All shafts have a frictional resistance of 5Nm I'm going to try work backwards from my output Torque to see if I can calculate the input. How do I do this taking into account the frictional resistance. If I call each gear A, B, C & D respectively with D being my output. ωD x TD = 400x200 = 80000 W I'm really not sure what I do to the power here to include the frictional resistance and work back over to calculate the power input required for each gear.