Rube Goldberg Construction

Hi again and welcome back to the blog! If you read my last post you will know that I spent some time carefully considering different elements of motion of objects to implement in a Rube Goldberg machine. After this was done I spent some time designing systems which connect all of these elements together into a consistent device which is both accurately engineered and entertaining. Therefore now I will be presenting the construction of my Rube Goldberg machine with the cherry on top being a full functional demonstration in the conclusion.

My construction will be based around a 1.5x0.5 metre MDF board as shown in the picture above, firstly I wanted to mount the kettle and cup enclosures to the board as they form the key goal of my machine, namely making a cup of tea. As can be seen the kettle enclosure is mounted on a pivot point just below the kettle itself, this will allow the relatively weak DC motors in the robot to gain enough leverage to rotate the whole enclosure. My next challenge was to create a pulley system to work in three roles, 1.)activate the kettle switch, 2.)act as a target for the launcher and 3.) carry on the chain reaction. For my materials I am going to be using Lego wheels as my pulleys and fishing string as my line. To do this I mounted the pulleys directly above the kettle, on the left hand side of the pulley system I will have a used tin of beans to act as a target for the launched golf ball and on the right hand side I will have a bag filled with stones which has a mass of 65 grams. This tin will have a mass of 50 grams which will ensure it is pulled upwards by the second object, however as soon as the golf ball falls into this tin, it will gradually fall downwards. As the tin falls downwards it will hit the switch to turn on the kettle which will start boiling the water. Finally the bag of stones travelling upwards in this system will hit another golf ball which will carry on the chain reaction.

Next I constructed the cup enclosure pulley system detailed in my previous blog. As a single element I was testing this system by dropping a 500 gram weight 0.5 metres downwards connected to the water valve lever. It was vital for this component to remain unchanged as my calculations for the water flow rate and consequently the mass of the weighted object were based on this variable being a constant. Therefore I decided that the second golf ball detailed by the blue arrow in the picture above will be used to firstly trigger the fall of the 500 gram mass, which will then trigger the valve lever. I did this by incorporating a 180 degree bend from an old tire tube in order for the ball to switch direction. Then the ball will travel through the clear plastic bottle and land in the used yoghurt basket as seen in the picture below, the ball travel path is marked by the red dashed line. To make sure the ball will accurately land in the basket every time I decided to calculate the vertical and horizontal displacements of this ball using the projectile equations similar in the previous blog, Sx=ucosθt and Sy=usinθ-0.5gt². Firstly the force u was calculated using the mass of the golf ball and the acceleration due to gravity, which equals 0.44 N. Next the angle of inclination of the plastic bottle relative to the ground was measured at -10 degrees. Finally the time t of the flight of the ball was estimated to be 1 second. By subbing all these values into the formulas listed above, Sx= 0.43m and Sy= -0.57m. Admittedly during testing I found out that my horizontal displacement was a little bit optimistic and in reality it equaled approximately 0.36m, however the vertical displacement was unchanged. Only a 7cm difference in the horizontal component is testament to how valuable the projectile equations are not only for this calculation but also for the launcher calculation in the previous blog post.

The next challenge was to mount the robot in such a way as for the wheels to be able to move the kettle while simultaneously triggering the ultrasonic sensor. In my previous post I explained that I mounted the robot at a 60 degree angle relative to the ground as this was the perfect position for the ultrasonic sensor to pick up a signal from the weighted object in the cup pulley system moving upwards. The wheels were also mounted on the same plane as the kettle. It is important to say that I ensured that the kettle only had sufficient water boiling inside of it to fill one cup. Finally it was time to set up the launcher. In the calculations blog I knew that the launcher must comply with 3 requirements, namely it must be 2 metres away from the machine, it must be on the same horizontal plane as the target tin of beans and it must be mounted at a 41 degree angle. After testing the launcher a few times I found that I misjudged my calculations for the angle as it actually had to be mounted at approximately 50 degrees relative to the ground. However I still see my answer as a success in bringing the first tests to a fine margin of the final assembly. Now that the machine was complete here is a few pictures for you to better visualise it.

Before I show you the video I would like to detail the sequence of events which happen when the machine is working:

1. The launcher fires a golf ball into the plastic bottle on the top left, this golf ball rolls into the used tin of beans.
2. As the golf ball rolls into the tin, the tin slides downwards on the pulley system activating the kettle switch to boil the water, simultaneously the bag of stones on the other side of this pulley system slides upwards hitting another golf ball into the pringles can.
3. The golf ball rolls down the pringles can and changes direction by 180 degrees in the tire tube, next it rolls along the horizontal clear plastic plastic bottle where it falls into the used yoghurt tub.
4. When the golf ball falls into the yoghurt tub, this pulls a resting 500 gram weight into motion, this 500 gram weight then pulls on the water valve lever to activate the flow of water.
5. As the valve is opened water flows from one container to another bottle by the use of gravity, this bottle is part of a pulley system controlling the movement of the cup.
6. As the bottle fills with water it slides downwards, thus pulling the weighted object upwards and hence pulling the cup downwards until it is resting on the ground.
7. As the weighted object is pulled upwards it comes into the line of sight of the ultrasonic sensor in the robot, when the ultrasonic sensor senses this movement it will signal the DC motors to start spinning for 2 seconds.
8. As the wheels in the robot spin, they reel in a fishing line connected to the kettle, therefore rotating the kettle which pivots 90 degrees, boiling water flows from the kettle to the cup.
9. The cup already has a tea bag in it and a cup of tea is made, the demonstrator can then enjoy a nice cup of tea!

I hope you enjoyed my attempt at making a Rube Goldberg machine! I thoroughly appreciated a college assignment which combined engineering calculations with some practical work. However if I was to ever do such a project again I would make a few changes, namely I would incorporate a tea bad dispenser into the machine and more importantly I would make the rotation of the kettle less sudden and aggressive. To do this I would place the robot on a plane above the kettle and gentle lower it down instead of pulling it sidewards.

I hope I entertained all of you with this blog post and showed that making a cup of tea can be a little more exciting than you might think. If you like the type of content posted on my profile please consider following!