catapult crossfire

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

𝑚𝑣 = 𝜔𝑜

𝜔𝑖= −

𝑁2

𝑁3−

𝑁4

𝑁5

Compound Gear Train Output

Simple harmonic Rise

𝑆 =ℎ

21 − 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.