This project was done over the summer just before leaving for my first year at Purdue in 2020. I decided to do this project mostly
just for fun but also to get an introduction to some important skills like CAD and using electrical components such as switches, motors, etc.
I was inspired by a YouTube channel that I had found recently at the time about making custom modifications to Nerf guns, so I thought I would take
a crack at it myself.
Since the Nerf gun I chose to modify was an uncommon one, I didn't really have any reference to use on how to modify it. I started by opening it up to
see how the mechanism works. As you can see from the
(Internals of the Nerf Gun I modified)
picture on the right, there are two main mechanisms that make the Nerf gun function. The first is the flywheel
and gear train. As the blue rip cord is pulled, the gear train takes the high torque applied on the first gear and converts it to a high rotation speed for the
flywheel. The second is the ball release mechanism. As the trigger is pulled, the orange blocker rotates forward and downwards, giving enough space for the foam
balls to roll right into the flywheel, and therefore shoot out of the Nerf gun. The plastic extension on the trigger bends against the support post and allows the
trigger to return to its proper resting position when no force is applied. After learning how the Nerf gun worked, it was time to come up with a plan.
The plan was to design and print a custom shaft that would transmit the motor's drive through the gear train. A hole would be drilled
through the shell so that the motor would have a direct line to the gear. The switch would be placed directly below the release trigger,
so it would be easy to rev up and then shoot. A custom bracket piece was designed and printed to secure the motor in place while it was running.
During testing with the 3D printed shaft piece, all seemed to be working well initially, until the shaft started to melt. Fortunately, this was
an easy fix. My good friend's dad has a drill press and a lathe in his garage, and so we were able to make a replacement out of aluminum.
After the electronic components had been put together, it was time to fire a few test shots. However, they weren't quite what I was looking for.
The foam balls are so light, they lose speed quickly due to air resistance. I tried to improve on this feature by increasing the mass and by making
them slightly more aerodynamic. I found a golf ball design on Thingiverse and 3D printed it in halves. The infill percentage was set higher than
normal to give it more mass and make it more resistant to impacts. To my surprise, the plastic ball didn't even fire from the Nerf gun. Upon further
inspection, it turns out that the foam balls are compressed slightly when they pass through the flywheel, and the soft material allowed them to fit
through. The plastic ball was much more rigid, so it would get stuck and scraped up by the flywheel.
The results for this project weren't exactly what I was hoping for. It sounds quite powerful, but the foam balls
don't get shot that far. While I think a more powerful motor would make a difference, it still
(The final product without the battery)
wouldn't give me what I was looking for. The foam balls can reasonably be compared to table tennis balls. While
professionals can hit them extremely fast, a good portion of that speed comes from the spin of the ball. Top spin or forward spin makes the ball
move and fall faster, while backspin or underspin slows down the ball and can extend its time in the air. Since the flywheel is positioned below
the foam balls, they will be exiting the barrel of the Nerf gun with a lot of backspin, which slows them down even further. That being said, I was
happy with what I had learned from this project. My first experiences with CAD, 3D printing, soldering, and machines like the lathe and drill press.
While none of these were used extensively, I'm glad I was able to get introduced to them before starting school in the fall.