First Ping Pong Launcher Prototype in Action
Hi everyone and welcome back to the blog! In last weeks post you seen that I designed my ping pong launcher based on the upcycled materials I found around my house. I then used CAD to model my design in order to visualise it as a real life object. This week I will present you with the process and final results of building my ping pong launcher prototype in real life. If you haven’t yet read last weeks post I strongly recommend that you do so as all of my components, design ques and working principles are explained in my previous post.
Firstly I made a bill of materials that I needed in order to build this launcher. This included all the raw materials, screws and tabs as well as all the tools I needed to use such as saws and drills. The raw materials consisted of a plank of pine wood, an empty silicone glue tube, a PVC drain tube, zip ties and finally two planks of dense oak wood to act as the weighted base.
Once I had everything I needed in my workspace I then proceeded to cut the plank of wood into appropriate dimensions to act as the side supports of the tube. The side supports have a function of holding the tube firmly to the base as well as being a mounting material for the spring. Next I attached 4 of the side supports to the guide tube, all at 90 degrees in respect of each other. I attached the wood to the old used silicone glue tube by the use of new silicone glue (what goes around, comes around haha) and then put zip ties around the wood so it would exert a pressure on the tube. This will form a better glue bond between the plastic and the wood so that I don’t have any reliability issues in the future. (don’t worry the unaesthetic zip ties will be coming off once the glue is set)
As soon as the side supports were firmly mounted I proceeded to insert the white PVC tube as seen in the pictures below into the brown tube. This would form my cylinder which the ball will sit on and which will transfer the potential energy of the springs into kinetic motion of the ping pong. I ran into a slight design flaw with this as the white tube had a base diameter equal to the distance between the two side supports. To combat this I shaved the side supports down by 3mm and this quickly alleviated the problem
Next I mounted the side supports to the weighted oak base by the use of metal brackets. I used a spirit level measure to check that the whole construction was straight and at perfect right angles to each other. This is important as in later use the aim of the model is increased by the accurate manufacture of this launcher. Once the launcher was attached to the base I drilled screws into the side supports and cylinder tube to act as the spring mounts. It was important to pick screws of a certain length, too long and there is a possibility of drilling into the tube, too short and the springs will exert a greater force than the screw can hold. I attached the spring to 20mm length screws and manufacture of my launcher was completed. Now it was time to test my launcher!
Now that I knew my launcher was working consistently and accurately I decided to build a model of the robot out of cardboard. This will simulate the future challenge of shooting the ping pong ball inside of a basket on top of the robot. Also seeing as the day still had a good bit of sunshine left I decided to strengthen my devices aesthetic aspects and I painted any exposed surfaces of wood and metal and just take a look at these!
Second Prototype of the Launcher
As can be seen from above the first prototype of the launcher was very capable, however some new rules were implemented and therefore with new rules come new issues to address. Therefore I addressed two major criteria needed for my launcher to qualify under the design rules given to us. Namely the launcher needed to be at most 0.9 times the height of a 500ml coke bottle (which is approximately 20cm) and the launcher needs to have an automatic ball reloading device.
My first prototype was a lot bigger than 20cm measuring in at an impressive but illegal 50cm in height. To combat this and reduce the height to under 20cm without sacrificing much of the spring energy I decided to turn the prototype onto its side and then add a 45 degree turnpipe pointing up on the end of the firing tube. There is no defined dimensions we need to meet for the length of our launcher along the ground therefore this is an effective and inexpensive solution to our problem. It is important to say that the maximum force of the ball exiting the tube will be decreased. But will this have a big affect on the range and accuracy? Through experimental results I found that the prototype with a straight tube had a maximum range of approximately 1.5 metres. I then repeated this experiment with the 45 degree turnpipe attached and found that the maximum range was 80 centimetres. This is nearly a 50% decrease in range which might seem like a big issue at first. However it will not affect its purpose as this range is still perfectly suitable to launch the balls in the collection area of the obstacle course.
My next hurdle was designing an automatic reloading device which I have to admit kept me up at night and I highly considered scrapping my first prototype and redesigning my launcher. However I managed to implement a very functional device which uses gravity to insert the balls into the firing tube at the correct time. As can be seen from the picture above there is a upright pipe with extra balls connected to the firing tube. These extra balls cannot enter the firing tube because the cylinder inside the tube blocks them. This is the same cylinder which can move along the tube, is connected to the springs and is used to convert the potential energy of the springs and transfer it into kinetic motion of the ping pong ball which is being fired. However once the ping pong ball in the chamber has been fired and there are no balls in the firing tube, the cylinder can be fully extended back, whereby the top of the cylinder is located to the left of the upright pipe as looking at it in the picture above. At this instance the ball in the upright pipe is free to drop down into the firing tube by the use of gravity and the fact that the cylinder is not blocking it anymore. Once the ball has dropped into the firing tube, the cylinder will then be contracted, blocking the upright pipe once again. This cycle can continue as long as there are extra balls in the upright pipe.
In terms of assembling the model in real life I found a 90 degree rubber automotive coupler which I cut down to a 45 degree angle. I then used a hose clamp to attach it to the end of the firing tube. For the upright automated reloading pipe I used a PVC T-piece with the correct diameter for the tube I was already using. I attached this T-piece to one end of the firing tube by the use of silicone glue. I also addressed the decreased range in this new model by decreasing the mass of the cylinder. I did this by drilling staggered holes 50mm away from each other in a line as seen in the picture below. This decreased the mass of the objects in motion by the spring, thus increasing force and range to 90cm.
This design will work on the same principle as explained in previous posts. A ping pong ball will sit in the firing tube on top of the cylinder. The cylinder will be pulled backwards putting tension in the springs. The cylinder will then be released thus accelerating the ball which will fly out of the firing tube.
To conclude the second prototype of the ping pong launcher I decided to simulate the obstacle course. I tested the launcher by firing multiple balls towards the basket at the approximate distance that the launcher will be used in the obstacle course. Just take a look at the video below.
I hope you enjoyed this weeks blog post on the process and final construction of my first and second version of the ping pong launcher. I will be improving upon this design once the instructions and dimensions of our obstacle course are revealed. If you would like to see more of similar projects please click the follow button and check in next week for my new post!
