So, after a long semester, I’ve finally made it to the last assignment… the Rube Goldberg machine.
This assignment gave us a chance to have a bit of fun while also putting our engineering skills into use.
The aim of my machine was to pop a balloon, by means of a series of unnecessary, but calculated steps. My machine in total consisted of 12 continuous steps, some of which required engineering calculations, and others just following simple laws of Physics such as gravity and the domino effect.
The finished set up of my Machine can be seen below.
The first stage of my machine featured the star of the production, my robot, which you guys are probably all to familiar with at this stage. I turned on the robot and he drove forward (using the code that has not been changed since the last assignment), to where he encountered a series of books, where he kindly obliged to knock them over.
The books then fell one by one where they then fell on top of a small little domino attached to a string. The string was also attached to a pen, on an elevated copybook acting as a slope. When the books fell and toppled the small domino, this pulled the pen away which set a cylindrical sand timer rolling down the elevated copybook.
The next step required some more engineering knowledge. When the sand timer reached the end of the slope, it bumped into a balanced T-square. When the T- square is bumped to the left as can be seen in the photo below, an opposite force is generated on the other end of the T-square, slowly launching a golf ball from a platform. This golf ball then trickles it’s way to the next stage of the machine. At the next stage the golf ball runs into a 30cm ruler, in a vertical position. The ruler is balanced ever so slightly by a book acting as a clamp. The ruler is balanced so gently that even the slightest nudge from the golf ball will topple it.
When the ruler is toppled it knocks over another golf positioned on top of another slope (a cut up 7 up bottle), and the golf ball flies down the slope. At the bottom of the slope, the golf ball bumps into a tennis ball, and using the principle of the conservation of momentum, the tennis ball sets off at a reduced speed, which is required for the next part of the machine.
When the tennis ball sets off, it must be travelling at the correct speed, in order to land in a bucket, which is part of a pulley system, located just off the edge of the table. The pulley system can be seen below.
When the tennis ball lands in the bucket, it’s mass will cause the bucket to drop, landing on my old friend that is the ping pong ball launcher. When the bucket lands on the launcher, the force will be sufficient to open the trigger and release a ping pong ball from the other end of the launcher.
When the ping pong ball is released, it will then pass through a funnel, and it will knock into another golf ball at the other side which is then set away. This golf ball will down trickledown another slope, made from two cut up pieces of bamboo, where it bumps into small domino.
This domino is again attached to a piece of string. The other end of the string is attached to a pen positioned on a ramp, and when the domino is toppled it sets free the pen on the ramp, setting free another golf ball.
Finally, when this golf ball is set free it will trickle down the slope to the edge of the table, where a small scissors is accurately positioned. When the golf ball bumps into the scissors, the scissors falls from the table and pops the balloon.
And just like that a balloon can be popped. I think I may struggle to ever pop a balloon in a traditional way again.
The video can be seen below
Also, the machine from an alternate angle can be seen below.
Calculations
As mentioned, some of the stages of the machine required engineering calculations. In particular, there were two stages which needed calculating. They were:
1. The conservation of momentum for the golf ball to knock the tennis ball into the bucket.
2. The pulley system
Conservation of momentum
The principle of conservation of momentum states that the total sum of forces before a collision are equal to the total sum of forces after a collision. Or m1v1 + m2v2 = m1u1 + u2
For my machine, I needed something to land in a bucket just off the edge of the table. However, my problem was that when a golf ball travelling down a ramp got to the edge of the table it was travelling too fast and overshot the bucket. I needed something to slow down the golf ball, or replace it with another form of ball. So up stepped the tennis ball. The golf ball travelled down the ramp where it collides with the tennis ball. After the collision the two balls move off at roughly the same speed, the speed of which is now sufficient to land in the bucket.
Unfortunately, I Was not able to accurately calculate the speed of the moving balls, however I was able to use estimates which worked well in the calculations.
m1 = 45g
v1 = roughly 2m/s
m2 = 57 g
v2 = 0 m/s
u1 = roughly 0.5 m/s
u2 = roughly 1.14 m/s
45(2) + 57(0) = 45(.5) + 57(1.14)
90 = 90
Pulley system
Making the pulley system required some calculations. Below is a free body diagram of which my pulley system operated.
I used a bucket and a bottle of sun cream as the two weights on either side of the pulley.
Mass of bucket = 107 g
Mass
of sun cream = 135 g
The system set up so that the bucket was slightly higher than the sun cream due to its lighter weight.
However, when the tennis ball landed in the bucket, this made the total mass on the bucket side of the pulley significantly higher, which caused the bucket to drop and land on the trigger of the ping pong ball launcher.
Unfortunately, that’s the end of my last assignment and therefore the last post on this blog. I hope you guys reading this had as much fan as I had, Ted.
