Aide Memoire

Aim

The objective was to launch a tennis ball at a target that is 1.5m high at a distance of 10m away. To solve this problem it was decided to build a trebuchet.

Design

The trebuchet is primarily made of wood and contains a base which is rectangular in shape with dimensions of 0.9m×0.3m. For the vertical parts there is a brace which connects the base to the vertical columns on either side. Connecting the two columns is a circular rod, which also serves as the pivot point for the lever arm of 1m which is also attached. A board is placed above the base so that the cup which holds the tennis ball has a smooth surface to travel on before being launched. Also a 6.5kg counterweight exists to provide the potential energy which is converted to kinetic energy as the lever arm is unhooked from the base.

[pic 1]

Calculations

To calculate the initial velocity and the range of the trebuchet two approaches were used. To find the initial velocity the principle of conservation of energy is used and to find the range the tennis ball will fly projectile motion is used.

For detailed calculations see the following pages

Conclusion

Multiple calculations were done throughout the testing to acquire a relatively close aim of the trebuchet. Theory including tangential acceleration/velocity, radial acceleration/velocity and torque was the main point of the device to accurately project the tennis ball to hit the target of 10m (distance) to 1.5m (height). However the calculated range of the trebuchet being 16.7m is further than what the trebuchet actually fires.

Errors were discovered that prevented us from achieving a bullseye.

Such examples include:

- Miscalculation of the ratio between the long beam and the height support beam, thus having an error in the projectile angle.

- Not having the ideal weight as the counterweight for power.

- In calculating the velocity and range non-conservative forces such as friction were ignored, if these were factored in, the calculated range would be lower as these would act to slow down the lever arm and the drag would slow down the ball further.