Ever have a snowball fight? The UPEI School of Sustainable Design Engineering ENGN234 dynamics class has taken classic snowball fighting to the next level—building and designing snowball-hurling devices. The first month of our dynamics class has been structured around the engineering design process from ideating to analyzing, building, and testing our weapons. My partner and I came up with the Snowball Slingshot. It's a versatile, easy-to-use weapon that will provide you with firepower and mobility in your next snow battle using our simple, compact and light design.
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Step 1: Gathering Materials
The following materials were used in building our Snowball Slingshot. Have these materials ready before you begin building:
- 2x2" wood (60cm in length)
- 3/4" bungee cord (~120cm in length)
- One hard plastic dish (~8cm in diameter, 15cm long)
- Duct tape
- Wood screws (2" and 1/2")
- Rigid thin plastic (~4x12cm)
- Wood glue
A jigsaw, power drill (with a 5/8" drill bit and screw drill bits), measuring tape, and scissors will also be used in building, but will not be consumed by the design.
Step 2: Building the Slingshot Frame
Safety glasses and steel-toed shoes should be worn throughout the build process. Expect the process to take about 1 hour.
Using a jigsaw, cut one 40cm length (the main arm) and one 20cm length (the side arm) from the 2x2" wood.
Drill a 5/8" hole in both the 40cm and 20cm pieces of wood as shown. A power drill and 5/8" drill bit was used to drill the hole centered 2.5cm from the end of the wood arms.
To connect the pieces together, first ensure that both arms are oriented properly with both holes facing toward you. The side arm is connected to the center of the main arm's length so that a "y-shaped" arrangement is created. Wood glue should first be applied to both pieces of wood at the attachment location. Once the glue has dried, slowly drill a 2" screw through main arm into the side arm. We first drilled a hole through the wood before drilling in the screw to prevent cracking of the wood.
Step 3: Adding a Thumb Protector
We added a thumb protector to the frame to protect the thumb when the slingshot is launched. To include this safety feature, cut a 4x12cm piece of rigid thin plastic (we obtained ours from a broken plastic bucket) with scissors. Before attaching the thumb protector it is time to decide which hand you will want to shoot the slingshot with. A right handed person should attach the thumb guard on the face that makes a "y" shape when held in front of you. A left handed person should attach the guard to the opposite face.
Screw the plastic piece into the front face of the frame (the side containing both holes) such that it bends into a U shape that your thumb can slide under.
Step 4: The Snowball Chamber
The snowball chamber is what holds the snowball before it is launched. For our Snowball Slingshot we used a hard plastic measuring cup (top diameter=10cm, bottom diameter=6cm, height=15cm). This shape is ideal for a snowball chamber because it allows good sized snowballs to be held and it is long enough that you have something to hold on to when pulling back. Hard plastic is essential as the chamber will be subject to wear and tear from use.
Choose your cup as close to the dimensions/shape of ours as possible (the dollar store has an assortment of cups). Drill a 5/8" hole radially through the dish about 5cm down from the top. It is critical that the holes line up exactly so that the chamber does not wobble during launching. Since you are drilling through two plastic surfaces it is best to mark both holes and drill each one separately.
As noted previously, hard plastic is essential. Upon repeated testing we noticed a small crack forming in our dish. Fortunately we repaired the dish by wrapping both the top and bottom with duct tape. On your dish, wrap several layers of duct tape around the entire dish to protect the cup and help prevent cracking.
Step 5: Securing Your Bungee
Take a standard 3/4" bungee cord (ours was 120cm in length) and cut off the hooks on the ends with scissors. The type of bungee is important for determining the power of the launch; thus the thickness of the bungee can vary based on the strength of the user.
If you are right handed, thread one end of the bungee into a hole on the front side of the frame (so that it makes a "y" when facing you). Tie a knot on the other side to secure it. The figure 8 knot is highly recommended as it is stronger than normal knots (used on ships) and is easy to tie, as shown to us by our professor.
Thread the other loose end of the bungee through the holes on your snowball chamber and then through the other hole on the front side of the frame. Secure this end with another figure-8 knot.
Apply wood glue around the holes (both sides) where the bungee cord attaches to the frame. Once the glue has dried, wrap several layers of duct tape around the knot and frame to really secure the bungee.
And that's it. Your Snowball Slingshot is ready for battle.
Step 6: Admiring the Final Device
The final product should look similar to our prototype as shown above.
Step 7: Operating the Slingshot
WARNING: Do not operate the slingshot if you have any wrist or arm injuries.
Make a snowball 6-8cm in diameter. Place it into the snowball chamber.
Hold the slingshot by the main arm with your non-dominant hand. Slide your thumb underneath the thumb protector and grip around the main frame arm.
With your other hand hold the snowball chamber taking care not to allow the snowball to fall out. Hold the slingshot straight out in front of you and pull back on the chamber.
Select a target and release the chamber. Our prototype allowed us to launch a 100g snowball 45ft.
Step 8: Reflections
Building the Snowball Slingshot the snowball slingshot was fun and we learned a lot through testing and refining the design. Although you are only seeing the final product, this project allowed us to apply dynamic analysis to real world designs and practice applying the engineering design process. Compared to other designs in the class ours device gave us a mobility advantage, while still providing us with sufficient firepower. But like any product that exists "it can always be better". Here are some of our recommendations we have for the design:
- Attach magnets to the chamber and the frame so that there is no dangling when the slingshot is not being launched.
- One of the things we would like to improve is our reload time. The Snowball Slingshot should be accompanied by a "snowball satchel" or belt with a sack to store snowballs in while you're running around. These ideas were provide by Dr. Trivett.
- Different bungee cords should be tested to maximize distance based on the user's strength.
The Snowball Slingshot is recommended to anyone who is looking to spice up their next snowball fight. The design is sustainable as the few materials required can be found lying around the house. We would like to thank Dr. Trivett for his guidance in this project. Thanks for reading and feel free to post your own recommendations or feedback in the comments!