Trebuchet Basics

Fritz R. Fiedler

Basic Sling Trebuchet

Example Frame

Example Beam

Example Tip Detail

Release

Trigger

Sling

Basic Trebuchet

Basic Trebuchet

The Throw

Definitions v0

h

Energy Equations

2

10

202

1

2

:2

m

ghmv

KEPEif

vmKE

ghmPE

Range

2

120

20

2

deg45

cossin2

m

mh

g

vR

if

gv

R

m

Efficiency

What affects efficiency and what would you expect the actual efficiency to be?

Efficiency

Does not include effects of:mass of beamfrictionair resistance…?

Efficiency ~ 50% or less (compute for report!)

so Rm < hm1 / m2)

Required Information

• h : by design

• m1 : by design

• m2 : given

Projectile

• 3 lb exercise ball (m2)

• Compute range with different counterweights…

Example Simple Calculation

assume: h = 4 feetm1 = 50 lbs

given: m2 = 3 lbs

R < 67 feet

Design Flexibility

What aspects of the trebuchet can be varied (after primary construction) to change throw distance?

Design Flexibility

• Counterweight mass (m1)

• h:– fulcrum height– starting position– beam length – how?

• sling length

• release angle

Counterweight

Design Constraint: must fit in 5-gallon bucket.

What materials might be appropriate?

Counterweight

• 5 gallons = 0.67 ft3

• water: 62.4 lb/ft3

• sand (dry): ~110 lb/ft3

• sand (saturated): ~135 lb/ft3

• concrete (ordinary): ~120-150 lb/ft3

• steel: ~490 lb/ft3

• lead: ~710 lb/ft3

Other Considerations

• Will it tip over?

• Will the beam break?

• Will the sling snap?

• Will the throw be straight?

References

• http://www.ripcord.ws/

• http://www.algobeautytreb.com/