1. In order to figure out
the lengths of the
Fourbar links, it was
necessary to find the
angle of the table
rotation relative to
the span of the cups.
NX aided in finding
the solution
as displayed by the
trace in the screen
capture.
Acknowledgments
ME 371
Group 10
The purpose of this project was to build a
functioning prototype (Catapult Crossfire),
which involved all of the design techniques
learned in the ME 371 lecture.
16 Degree Trace
Colin Perrault
Charles Ferriera
Ross Dudgeon
Brendan Brown
Motivation Design Components
Methods
By using NX CAD and various
calculations, we were able to limit our
trial and error. This sped up both the
design process and physical creation of
Catapult Crossfire. It was also
imperative to select the proper
materials for construction especially
when welding.
Conclusions
Machine Shop
Some of the tools
and machines used
during the project,
were: lathe, mill,
drill press, various
powers tools (nail
gun, dremel, drill,
etc…)
and miscellaneous
hand tools.
Fourbar Linkage
The Fourbar Linkage controls the
angle of the table. The table
rotates due to the horizontal
motion of the Fourbar linkage
when the user pushes or pulls the
lever bar.
Overdrive Gear Setup
The two gears are connected via
a bike chain and is an overdrive
setup. This means the output
velocity will be greater than the
input.
Cam
The cam was designed with a
large amount of dwell with a
steep rise and fall. This
creates the launching feature
of the catapult. The design was
later found to be similar to
that of a trip hammer.
Design Theory
𝑚 𝑣 =
𝜔 𝑜
𝜔𝑖
= −
𝑁2
𝑁3
−
𝑁4
𝑁5
Compound Gear Train Output
Simple harmonic Rise
𝑆 =
ℎ
2
1 − cos
𝜋𝜃
𝛽
Linkage Synthesis
𝑎 = −
𝛼1 − 𝛽1 𝑐
𝛼2 − 𝛽2 + 𝑐 𝛼3 − 𝛽3
Several methods were used in order to design
and construct Catapult Crossfire:
• Rough hand drawn sketch
• Calculations by hand
• NX CAD
The design theory was based upon
numerous equations learned in the ME
371 lecture. Relevant equations are
given below.
We would like to thank Roy, Ken and
the rest of the Machine Shop
employees for their help and
cooperation.