JPL PROJECT TIMELINE
Early September
Team Leader Presentation Prep
For the team leader presentation and with an incorrect interpretation of the competition rules, I worked on a simulation of launching a ball to determine the accuracy required to get a ball into the jar.
For this simulation, I used a Java programming interface called Processing along with some experience using MATLAB at UCLA to create a recursive simulation of the trajectory of a ping pong ball with air resistance.
Because the force of air resistance can be approximated to be proportional to the velocity through the medium squared, and I found that the terminal velocity of a ping pong ball was about 8 m/s was able to write an equation in my simulation that calculated the acceleration due to air resistance on the ping pong ball through its trajectory.
Using this simulation instead of just a simple projectile motion equation led to important insights and realistic numbers for the required accuracy. From the simulation, I found that the optimal launch angle was between 38 and 42 degrees. This is shallower than the theoretical optimal launch angle of 45 degrees when excluding air resistance, but makes sense when a slowing horizontal velocity is considered.
This insight was useful but more importantly, my simulation found that the required accuracy of launch speed was within 0.45%. This finding made it clear to me that launching the balls from the starting zone 5 meters would be practically impossible and led to re-visiting the competition rules and a redesign.
Mid September
JPL team project
idea refining
Proof of concept dropping mechanism
Our team came up with a variety of ideas for the JPL competition, and we had many different ideas to choose from. After about a week of brainstorming and some basic proof of concept models, we decided to use a 2 mechanism design. These 2 transportation mechanisms were a fan powered fast tube transport system into a funnel gravity powered bounce mechanism.
Before any materials were bought, we conducted some initial tests with both mechanisms. To test the viability of a fan powered ball transportation system, I took a handheld fan and a paper towel roll and launched the ball. Seeing the exit speed along with the ping pong ball bouncing around my room, I instantly knew that fan power would be an effective transportation method. For the funnel onto an angled surface, our team conducted some tests using a cardboard funnel we designed and propping up a piece of wood to test if a funnel would have a high enough consistency. This test was a success and proved that even with a poorly constructed funnel and unstable piece of wood, this concept could work in our final project. It also showed what design factors of a funnel made the ball drop consistently: being a low angle of sides and a hole almost too small for the ball.
Late September
Initial testing and starting construction
First full scale fan-tube transportation tests
After starting with 10 feet of 2 inch PVC tubing and making the vertical component, we assembled a full-scale model of our tube transportation system. This video shows the results of the first test of the full-scale model.
After some more tests, I noticed a problem with the ball caused by the fan and how it was mounted to the pipe. This problem was that depending on how I held the fan, sometimes the ball would not travel down the tube and get stuck going in circles at the entrance. I think this problem was caused when the gap around the entrance and where the fan was inserted into the tube was covered by my hand.
Because the tube has a larger diameter than the exit of the fan, I think that the air flowing had a lower pressure than outside the tube, and with the hole covered, there must have been some turbulence and reverse flow through the tube.
We solved this problem by having the fan be in front of the ball and mounded by a 45 degree connector piece allowing a slight vacuum to pull in air from the back of the tube along with the ball.
Balls exiting tube in slow motion
This slow motion video of ball dropping out of the tube shows the improved ball dropping after I added holes to help decrease airflow above the ball.
In this design, a skewer is used to prevent the ball from exiting out the wrong hole of the tube while not disrupting the airflow.
For our design to be accurate the airflow must pass over the entire ball bouncing system to allow the accuracy to be only dependent on gravitational potential energy and not the power of the fan.
This is important because our mentor thought that relying on the fans' consistent power for our device to work would not be a good idea because there may be a slight difference in the voltage between different outlets at school and at the JPL facilities.
Here are some photos of our funnel. This is one of the few parts that has remained unchanged throughout our refining process.
During it's initial construction, I noticed a problem where sometimes a ball would spend a large amount of time circling the exit before dropping.
I fixed this problem by adding a piece of wood to the inside that the ball will bounce into each revolution causing it to drop more consistently and faster.
Early
October
Next we began working on the end section where the ball goes through a funnel and bounces off an angled plate into the jar. I designed and 3D printed a lot of connector parts, including the funnel and a sliding adapter piece.
CAD model of the dropper connector
This is the first funnel dropper to be used on a build of our projects bouncing mechanism. I designed it to have two mounts: one to the previous funnel with a slot for the wooden piece to slide into and be screwed in place and another on the other side to attach to the sliding funnel mount. There was a problem with this funnel dropper that was previously seen in the other funnel being that sometimes balls would circle for a long time before dropping. This is addressed in a later version completed in late October.
Early October
CAD model of the adapter
I designed this 3D printed adapter piece to attach the funnel to our current adjustable mount. The shape of this part connects tightly to both a 90 degree metal part and another U channel aluminium piece that attaches to the funnel dropper. In later versions of the dropping mechanism, this piece was scrapped because of more stable mounting methods.
Mid October
At this point, we started working on improving consistency. Over the last month, we've made a lot of recent progress and promising tests that have been done.
Aluminum bar mount
This is the first version of the aluminum bar mount. It was designed to attach to the wooden piece with screws in the back and also to our bouncing mechanism with screws going the other direction. There were some problems with this design though. The hole for the aluminium bar stock was too small and allowed it to shake. I later resigned this piece for a different mounting method and with a tighter hole.
Consistency test with an angled plate
Proof of concept of the accuracy of the 3D printed dropper as a mechanism of bouncing the ball into the jar.
From our base for the gravity powered section of our project the consistency and accuracy of our device has proved to be very high. With a metal plate taped on a bunch of stacked books and dropping the ping pong ball in by hand, the reliability of our device when properly aimed is looking to be nearly 100%.
Late October
In the last part of October, we were satisfied that our overall design concept was good, so we turned our focus to ways to make the assembly more stable and accurate.
New tube dropping mechanism
We determined that we needed a new ball dropper because there were issues with the ball and airflow. Because of fast air moving above the ball, the Bernoulli effect caused the ball to hover above the hole.
The new design arcs the ball down while using its momentum to escape the effect of airflow. In creating a new design, I had to design parts that would mount well to the tube as well as being sturdy and 3D printable. In order to do this, I designed 4 parts: a top rail, bottom rail and two mirrored side rails. By using 4 parts that are almost entirely flat, the layers of plastic will work with the grain of the part and give much more strength than if they had been printed vertically. Using this shape made most of the part possible to print, but the hardest design element was figuring out how to mount the rails to the tube. After some thinking, I figured out that the best way to do this was to make the 2 side rails mount to the inside of the tube to prevent having to print an overhanging mount with removable supports.
Single ball launcher
Complete Loading mechanism assembled
The rules of the JPL competition say that only one ball can be controlled by our device outside of the starting zone. Because of this rule, our device has to have a loading mechanism that can deploy one ball at a time. After going through many different ideas for a mechanism that can preform this task, I had an idea of repurposing an old tube to create a rotational ball deployment system.
This system works in two stages. First a ball is dropped into the open tube and is held in place. By having a ball loaded in the tube, any other balls are blocked from entering our device. Next, the tube is rotated a half revolution and allows the loaded ball to pass through our device while the closed end of the inner tube blocks the rest from entering.
In order to hold the ball loaded from passing through the tube before the loading mechanism is rotated, I had to design and 3D print a part to block it from rolling. This part is seen in the single ball launcher at the end of the tube, and was hot glued to the hole in the inner tube. The ball is also blocked from traveling in reverse by the inner diameter of the loading tube. This tube's opening is smaller than the ball, and the only reason the ball can fit inside is because we used a drill press along with a 1.75 inch hole cutter to make the inside hole larger, but since the hole only goes about 2 inches deep, the ball cannot move backwards.
When constructing this device, I noticed a problem: sometimes the ping pong ball would bounce over the front barrier and allow a second ball to be loaded. To fix this problem, I added a zip tie to the roof of the tube. This blocks the ball from passing through the tube in any scenario until the loading mechanism has been rotated by making a slot smaller than the balls height when the loading mechanism is open and opening up that slot when the device is rotated and the blocker on the loading mechanism and zip tie align.
Although this fix was necessary to address a problem with the loading, it also ended up greatly improving our device. Because the ball loaded was guaranteed to not be able to prematurely deploy, the fan could be repositioned to behind the loading mechanism and make the tube transportation system much faster.
8-sided dropping mechanism
New 9-sided dropping mechanism with mounting stem added
I designed a new dropping mechanism to reduce the time the ball spends circling the hole before dropping onto the angled bouncing surface. The idea was to slow the ball by forcing it to collide with the flat sides of the ring.
I started with an octagon shape test piece because I thought that 8-sides might be enough to have some similar performance and accuracy to a circular ring but with a faster, more consistent dropping time.
I decided to change the shape to a nonagon because I thought that having an odd number of sides would be more accurate and the ball would be guided by at least three sides instead of two. This new piece is a big improvement because the ball is dropping fast now and because it's slightly larger that the previous version it helps prevent balls getting stuck in the whole.
Ball to loading mechanism adaptor
The balls needed a way to enter the loading mechanism. Because we are using two pipes of different sizes, the piece has to have mount to both pipes and have to separate radii.
Tube fan rotational adaptor
We decided to use a handheld fan to push the ball, so I designed this adapter so that the fan could be mounted to the tube and positioned accurately for use each time. I included holes in the side in order to prevent reverse flow and to minimize turbulence caused the fan.
Rotational motion limiter
I created this piece to prevent the loading mechanism from coming apart.
New aluminum bar mount
During testing, we saw that the original aluminum bar mount was a bit loose, so I redesigned and printed this new part to fit tighter with a larger mounting surface.
November
Upcoming Work
Aiming for the bounce dropping device:
-mount lasers so that the beams cross at a point that can be aligned with the back of the jar
-attach level to bounce dropping platform to ensure that on competition day it can be aligned with the slope on the ground.
-shorten platform to fit under tube overhang and make base have three legs to prevent rocking
Wind protection for bouncing into jar:
-Brainstorm how to create see through panels around the jar to prevent cross winds from affecting the trajectory of the ball on competition day.
Tube transportation supports:
-Make base of vertical section of tube more stable.
Loading mechanism:
-Redo loading mechanism to be one action per ball and make a base to mount it to.
Other:
-Practice assembling our device with in the time constraint and make a speech to be given describing our device.
-Work on the timing of our device and practice with 15 and 20 balls in one minute.