Yaskawa provide a very good e-learning module which goes through an overview of the servo sizing procedure. It also provides Servo Sizing Software.
All equations are given in the software and also the final generated report includes all calculations - which is very informative to understanding the selection process.
E-Learning ModulePart 1:
Yaskawa DMSD/Software Details
E-Learning Module Part 2:
Yaskawa DMSD/Software Details
Software:
Yaskawa DMSD/Software Details