Drawing

DEPCOllc

3305 Airport Drive | Pittsburg, KS 66762

The Trebuchet Axle

The trebuchet axle supports forces generated by the rotating counterweight, beam, and projectile.

The axle is subject to significant dynamic (due to motion) forces during the throw and static

(stationary) loads when it is at rest. These forces and loads act to bend (deflect) the axle. If the axle

is not strong enough to support these loads, it will deflect causing permanent deformation of the

axle. Permanent deformation means the molecular bonds holding the material together begin to fail

and the material has reached or exceeded its yield strength. At this point the axle has failed, and is no

longer safe to use. In a worse case, the axle will break, though permanent deformation is the more

likely cause of failure.

Factor of Safety

In order to design a safe trebuchet axle it is necessary to consider the forces and loads to which the

axle will be subject. A prudent engineer will design the axle to support loads equal to or greater than

required. This additional design strength is called the “Factor of safety”. The factor of safety, or

FOS, helps insure that components subject to extraordinary loads, or extended use, will not approach

the yield point or fail under conditions for which they are designed. A common FOS is twice the

design load. A component created with a FOS of 2, is designed to support a load equal to twice the

maximum allowable load.

Axle Span ( L )

Throwing Arm Bearing

Throwing arm forces are transmitted

through the bearing to the central

portion of the axle

Top View of the GEARS Model Trebuchet

Trebuchet Axle

Axle Support

Sample Engineering Curriculum