# Example of Energy Analysis in
Machine Design
**Problem Definition and Overview of Analysis**
** **The objective of this analysis is to determine the feasibility
and method for lifting the hammer shown below. The hammer is to be rotated
about a pivot from an initial position to a desired final upright position as
shown in the figure. The energy for raising the hammer is to be provided from a
given DC brush motor. The analysis first determines how much energy and power
the motor needs to raise the hammer within the specified time limit. A separate
analysis will be needed to determine an appropriate gear ratio between the
motor and the arm necessary to accomplish the task.
** **
Design Parameters:
mass of hammer: m = 0.5kg (kilograms)
length from pivot to center of gravity of hammer: L = 0.2m
(meters)
desired time for raising hammer: t_{raise}
= 20 s (seconds)
factor of
safety: F.S. = 2 (this is a high factor of safety, but suitable for feasibility
analysis)
Assumptions:
- Hammer
moves slowly. Thus dynamic forces can be neglected
- Friction
in pivot is relatively small and can be neglected
# Energy and Power Need Analysis
The objective of this analysis is to provide a rough
estimate of the energy source requirements. This rough analysis will be useful
for selecting what is a viable energy source for this component.
The energy required to lift the hammer into the upright
position is equal to the change in potential energy:
The amount of energy needed from a motor must include the
factor of safety:
The power required to lift the hammer within the specified
time limit is given by:
**Conclusion**
The energy analysis provided
the means for determining the energy requirement for raising the hammer. It was determined that a motor that is
capable of producing approximately 0.196 W of power is needed to overcome the
change in potential energy in the desired 20 second span. It is important to note that meeting
energy and power needs is a necessary condition, but not a sufficient
condition. An actual torque analysis will be required at a later stage to
determine if a gear reduction or other mechanical advantage is needed. |