Design of a Low Velocity Railgun

Jason Fodstad

Thomas Morris

Julie Duryee

Vardaan Chawla

Final Presentation – MSE 4021

April 26, 2005

Faculty Advisor: Dr. Naresh Thadhani

The Capacitor Bank

Outline

• Project Description

• Theory

• Final Design

• Budget

• Learning Experience

• Conclusion

• Acknowledgements

• Demonstration

Project Description

• Design a safe tabletop railgun to be used for performing experiments in a high school classroom

• Fire lightweight projectiles at low velocity• Design laboratory experiments and/or

classroom lesson plans• Budget : $700• Client: Ms. Anne Marie Johnson, Science

Dept. Chair, Chamblee Magnet School

Railgun Theory•To determine the force that acts on the armature - Lorentz equation

•I = Current •L = length along which current is flowing •B = uniform magnetic field

•To determine the exit velocity of the projectile, we find:

where,

•V = velocity •L' = inductance of rods •I = current •t = time length of current pulse •m = mass of projectile

V L I2t

2m

F e

V B I

L

B

Final Design

• Rails

• Injection System

• Armature

• Capacitors

• Charging System

• Casing

Final Design - Rails

• Requirements– High conductivity– Durable– Low coefficient of friction

• Material Selection: – Silver-Plated Copper 110 AlloySilver-Plated Copper 110 Alloy

• L Shaped to plug directly into capacitor bankL Shaped to plug directly into capacitor bank

Final Design – Injection System

Purpose: Give the armature initial velocity to prevent welding

Final DesignOriginal Design

Old design Spring Based Inconsistent

Final design Compressed Air Powered Remotely activated

Final Design - Armature

• Requirements– Conductive– Low coefficient of friction– Lightweight

• Materials Selection: Aluminum, GraphiteAluminum, Graphite

AluminumAluminum

•high conductivity

•low wear resistance

•lower melting point than rails, armature melts instead of rails

•causes frictional wear

GraphiteGraphite

•low conductivity

•high wear resistance

•higher melting point than rails, rails melt instead of armature

•self lubricating, minimal frictional wear

Final Design - Capacitor

• Requirements– High Capacitance / Energy– Fast Discharge– Maximize current generated

• Selection: Panasonic Computer grade Panasonic Computer grade electrolytic, 9300uF @ 450Velectrolytic, 9300uF @ 450V– Fast discharge– Cost effective– Mechanically sound

Final Design – Charging System

• Uses building power (110V AC)

• Fuses and resistors for safety

Solenoid

Capacitor Bank

RectifierTransformer

Fuse

Railgun

Final Design – Casing and Spacer

• Casing:– Material Selection: PlexiglasPlexiglas

• clear so students can see all parts

• Spacer Material– Material Selection: Oil Filled Nylon 6Oil Filled Nylon 6

• Self lubricating• Resistance to wear• Cheaper than Teflon

Budget

• Current Spending:– Copper Bars: $28– Nylon: $34– Solenoid valve: $54– Capacitors: $200– Misc. Parts for Charging system: $60– Misc. Parts for Injection System: $10– Acrylic: $0 (Donated)– Transformer: $0 (Donated)– Bolts: $0 (Donated)– Compressor: $30– Voltmeter: $30– Misc. mechanical parts: $30– Replacement parts: $100– Advisor Consultation Fees: $124

Budget$700

Total Spent$700

RemainingRemaining$0$0

Learning Experience

• Design is a dynamic process and must be flexible to allow for changes

• Buy the ideal materials based on function as opposed to cheap alternatives

• Machining takes a lot longer and is a lot more complicated than originally assumed

Teamwork!Teamwork!

Conclusion

• Our objective was to build a low-velocity railgun for high school demonstration use

• Unique challenge because most research is concentrated in the area of high velocity railguns

• Still within Budget

Demonstration

Acknowledgements

• Dr. Naresh Thadhani and The High Strain Rate Lab

• Matt McGill