Hermit Crab Shell Design

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Hermit Crab Shell Design
Coenobita Clypeatus
Project Advisors Hao Lin Elizabeth Demaray
DAVID CHUANG SANTIAGO MORENO CHRIS
GRAZIADIO ABRAHAM DIAZ
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Schedule and Time Management
Get materials and information for testing the
shell.
Finish final report and presentation.
Specifications for budget report and
presentation.
March / 10
Analyze results and make any further
modifications.
April / 21
Feb / 20
March / 31
March / 3
April / 10
Finalize budget report and presentation.
Conclusions on testing and work on final
presentation.
Feb / 13
March / 24
Rapid Prototyping. Creating shell and making
sure It conforms to our specifications.
Continue with testing and analysis. ANSYS
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• MOTIVATION

• Shortage of shells for Hermit Crabs in tropical
  areas. ( Florida, Brazil, South America )
• This problem is caused by pollution and shell
  collection.
• Hermit crabs resort to using bottle caps, soda
  cans, etc.
• Use engineering criteria to improve on nature.

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• Design Criteria

Crabs Nature Consideration

• Morphology of crabs body structure.
• Aperture location
• Topology

Shell Selection
Boundary Parameters taken from Literature.

• Shell volume to weight ratio
• Depth to aperture width ratio
• Shell Strength
• Body Mass Vs. Shell Mass ratio
• Aperture size

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PRELIMINARY FINAL DESIGN

• Aperture not smooth.

• Symmetric but lacks side curvatures.

• Center of mass not proportional to design.
• It does not enable frontal movement.

TOP VIEW
FRONT VIEW
ISO VIEW
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FINAL DESIGN

• All 90 degree angle faces omitted.

• Aperture entrance is round and smooth.

• Center of mass has been situated in front
• of design.

• Symmetric curvature on sides to
• accommodate morphology of the crab.

TOP VIEW

• Enough space on the bottom of the shell
• for carrying of salty water environment.

FRONT VIEW
ISO VIEW
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Important Parameters
Aperture Length
Aperture Width
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Materials
Polymers P400 ABS (Acrylonitrile Butadiene
Styrene)
- Resistance to outdoor conditions - Provides
enough protection (Strength of material)
Youngs
Modulus 1627 MPa Tensile
Strength 22 MPa - Will not be harmful to the
crab - Need to be a light material
Density 1.05 g/cm3 -
Manufacturability and Cost
Rapid Prototyping

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We have also considered
Ceramics
Biodegradable
Resistant to harsh environments
Environmentally friendly
However...
Brittle Material Too heavy High cost
Degrade at a high rate Ecoflex last 45
days Others do not fully degrade
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Terminal Velocity
Drag Force mg
Fd 0.5Cd?AV2
Vt 16.56 m/s 37 mph
Fimpact 8.28 N
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Falling
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Squashed
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Chomped
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Budget
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References
J.E. Angel, Effects of shell fit on the biology
of the hermit crab Pagurus longicarpus (Say),
Journal of Experimental Marine Biology and
Ecology, Vol. 243, pp. 169-184, 2000. C.F.
Herreid, R.J. Full, Locomotion of hermit crabs
on beach and treadmill, Journal of Experimental
Biology, Vol. 120, pp. 283-296, 1986. A. Turra,
F.P.P. Leite, Shell-size selection by intertidal
sympatric hermit crabs, Marine Biology, Vol.
145, pp. 251-257, 2004.
Any Questions?