ME304 Dynamics of Machinery Design Problem 1 Winter, 1998-1999 Grade



Your group is to design a baseball bat that is optimized for young children.



The purpose of a baseball bat is to store the energy supplied by a batter and then deliver that stored energy to a baseball. The amount of energy stored by a bat is given by Eq. 1,


, Eq 1


where I is the mass moment of inertia of the bat about the swing axis and v is the angular velocity of the bat. From Eq.1 itís apparent that an optimum bat design balances the need to have both a large mass moment of inertia, while not being so large that the batter is unable to produce an large angular velocity of the bat. Another characteristic of an optimum bat is that when a ball is struck with the sweet spot of the bat, the reaction force at the grip is very small. This is achieved by designing the bat so that the center of percussion is at the point of impact with the ball, and the center of rotation is located at the grip. This characteristic of an optimum bat is sometimes lost for young players when they are instructed to move their hand further up the grip (choking-up) on bats designed for older, stronger players. By choking-up on the bat, the player is able to effectively reduce the mass moment of inertia, I, so that a larger angular acceleration is possible. However the center of percussion will move for the new grip position. In an effort to explore this problem, your project is to determine the optimum bat design for children.


For the purposes of this project, children are differentiated from adults by the amount of torque they can apply about the swing axis. You are to design optimum bats for children of three different strengths, ones that can produce 5 ft-lb, 15 ft-lb, and 25 ft-lb of torque about the swing axis. Also for the purpose of this project, assume that the bat swings through an arc of 90 degrees in a plane that is parallel to the ground. The bat starts from rest, and has a constant torque applied about the swing axis (see Fig. 1) until the ball is struck.



Design Specifications:

Approximate the bat as two solid cylinders, a small cylinder for the handle and a cylinder with a larger diameter for the barrel where the ball is struck as shown in Fig. 1.




















Figure 1

Bat Geometry and Nomenclature



The bat you design should satisfy the following design specifications




Project Deliverables:


Applied Torque (in lb)










(in lb)








Also include: