The motor torque is determined by testing, see Dynamometer Testing. For a car using an electronic system testing is critical as the current multiplication the electronics provides greatly increases the available torque at lower RPM. Because of the difficulty in determining the formula to a curve, the curved graph of Torque vs RPM is arbitrarily broken down into 3 straight line sections.
Coordinates defining these sections are entered in the simulator and the approximate Torque at the motor RPM we are considering is obtained by interpolation. See FIG 3. (For a motor operating without an electronics system it is possible to calculate the torque RPM curve, you may wish to research this avenue.) Refer to the typical straight line split up of a graph of torque vs RPM shown below:
For section 1 of the graph the formula for calculating torque at a given RPM is Torque = T1- (T1-T2 ÷ R1-0) × RPM For section 2 Torque = T2-(T2-T3 ÷ R2-R1) × RPM For section 3 87 Torque = T3-(T3-0 ÷ R3-R2) × RPM These formulas are the equation to the straight line sections of the graph.
In conjunction with logic statements to select which formula is to be used based on motor RPM they are used in EXCEL to calculate the torque at any given RPM. (To enable realistic evaluation of this simulation some motor test data is included later in this section but also see Appendix J for more motor test results.)
If you have a power curve for your motor (graph of power vs RPM) it will be necessary to construct a torque vs RPM graph to allow you to input the data to the simulator. Torque can be calculated by transposing the formula