The reliability of orbital hydraulic motors which are used in mechatronic systems with a hydraulic drive for active working tools on self-propelled machinery is a pressing engineering problem. To increase the reliability, a specific design method was proposed. It required development of a mathematical apparatus and a calculation algorithm. The mathematical tools allowed to realize the method for determination of hydraulic motor reliability by simulating changes in a technical state of the rotors in a hydraulic motor. A program, which has been developed, enabled modeling the conjugation of external and internal rotors. The program implemented an algorithm for the sequence of calculating the parameters for the external and internal rotors. The proposed program made it possible to obtain a three-dimensional image of zones with admissible interfaces which ensure the efficient and reliable operation of orbital motors. The modeling of working capacity change for an orbital motor has established some dependence. The changes in the number of teeth and overall dimensions of the rotor in the investigated range enabled to develop a standard size range for hydraulic machines, which operate in mechatronic drive systems for active working tools on self-propelled machinery
