Free Body Diagrams of Gear Trains

Many senior students in the author's machine elements course have difficulties in drawing a FBD (Free Body Diagram) correctly, which is the first step in force and stress analysis of a mechanical system.One of the challenges to those students is that even though the principles to draw a FBD are the same for every mechanical system (A FBD is a sketch of a mechanical system cut free of its surroundings to shows all the external forces acting on the system), each problem seems different.Textbooks provide limited examples, especially in the case of gear sets and gear trains when three dimensional FBDs are necessary.For students who have not mustered basic concepts in the FBD, they need additional sample problems and concise rules to enhance their understanding.To this end, the author has developed a course note with simple rules to determine the direction of gear force components (radial, tangential, and axial) with extensive two and three dimensional FBDs of gear sets and gear trains.