Week 13

 This Blog: Reflection on our Ping Pong Launcher

Theory

Mechanism enhances and enables principles to function properly. An example can be given such as 

Principle: Solvent Extraction Column                      Mechanism: Agitation

Agitation can help to increase the Solvent Extraction Column separability. 

However, in engineering, mechanism is something that transforms forces and movement into a desired set of output forces and movement. 

The  6 essential mechanism in functional prototypes are: Actuators, Cams, Gears, Lever, Ratchets and Springs

Actuators: Converts stored energy into motion. These stored energy are usually in the form of compressed air, electrical potential, or liquid pressure. The 3 principles types are electric, pneumatic and hydraulic. 

Cams: Converts the rotation of a shaft into simple or complex reciprocating linear motion.

Gears: Transmits torque and to adjust rotational velocity. 3 common gears are Spurs gear, Bevel gears and Rack and Pinion gear.

Lever: Transmit and amplify force by fixing the input and output about a fulcrum or pivot point. 

Ratchets: They lock in one direction, allowing them to tighten without fear of literally "going backwards". Example: Cable ties. Works similarly to a check valve. 

Springs: Store and dissipate energy. 3 common spring types are: Extension spring, Plate spring and Cylindrical Spiral Compression spring.

Activity: Ping Pong Ball Launcher

We were tasked to use the techniques that we had learnt from the previous practical (Cardboard Joinery) to design a cardboard ping pong ball shooter that could not only generate enough force to shoot the ping pong ball but to also be able to store up to 5 other ping pong balls. 

Our group had originally planned to use a slingshot like design but decided against it as we had already used that design during our practical session. We liked the idea of using a rubber band as the mechanism to generate the force to propel the ping pong ball forward and hence kept that part of the idea. 

After some research, we had decided to design a crossbow/bow hybrid where the toy itself is in the shape of a crossbow but functions like a bow as it is unable to store a loaded ping pong ball and must be shot immediately after priming. The initial design process went smoothly as we had reference material to look back to whenever we encountered any problems, however, when we were almost done, we forgot that there were 2 parts to the objective of this lesson and we had only fulfilled one of them, our design was unable to store up to 5 ping pong balls that could be reloaded when needed. This required us to rethink our approach as we now had to incorporate the storage component into our design as we did not want to start over. 

After a brief discussion, we had decided to use an idea similar to the example that our lecturer had provided us which was to create a column above the toy which would allow for both storage and reload capabilities as gravity would push the ping pong ball down into the barrel of the toy. Our current design however, would not work with our design as the lecturer's example design utilised a spring piston design that comes out the back of the toy and hence the other ping pong balls can immediately fall into place after the first one has been shot without any problems.

Our design, requires the rubber band to be drawn back through the barrel once the first ping pong ball is shot, hence if the other ping pong balls were to immediately fall into the barrel, it would be physically impossible to draw the rubber band back, rendering the reload mechanic useless as we would have to unload it in order to draw the rubber band back. 

Our group had come up with a few ideas to solve this and eventually decided on the simplest solution which was to add a little retractable tip that slides into the reload column as our other contraptions were either too complicated or just failed to work. This retractable tip would slide partially into the reload column to prevent any of the stored ping pong balls from dropping down before we can draw the rubber band back and can be pulled out once the toy is ready for another ping pong ball.

To prevent the ball from dropping out of the barrel when the toy is pointed downwards due to gravity, we had added rubber tips at the end of the barrel. The rubber tip is bendable. With insufficient force, the rubber tip is not able to bend and thus will not allow the ping pong ball to go through. With enough force, the ping pong ball is able to shoot out of the barrel, bending the rubber tip. 

Final Design: