Introduction: Large Snowball Slingshot
This is the snowball slingshot that Dylan MacIsaac and I, Jacob Inglis, built for our second year Engineering Dynamics course. The project was to design, analyze, build, and test a working snowball launcher to use in a giant snowball fight between the entire class. The fight went well with this device scoring in all three competitions (Capture the Flag, Dodge-ball, and Free for all), and now our professor has asked us to make an instructable explaining how to re-create our device. This device was designed for long range accuracy, after we made our final adjustments, these were the key features:
- Shot snowballs a range of 50-60 feet.
- During controlled indoor target practice, this device scored 8/10 shots landed.
- Horizontal range of motion of 40 degrees.
To recreate this robust slingshot, you will need the following materials:
- Lumber - Our analysis showed that you can use almost any size lumber to build but we used an assortment of 1x2's and 1x4's, we used about 12 meters of scrap.
- Two long bungees - Ours were around 60 or 70 cm (a lot gets used in knots).
- Screws- We were working with what we had (a mixture of random screws and nails), but I would recommend drilling pilot holes and using wood screws for all connections (will need 30 or 40).
- A large can - For the cup.
- 1.5 x 1.5 foot piece of cloth - supports the snowball so the hard can does not crush the ball.
- Elastic band- For the cup - Holds the cloth in place.
- Zip ties- For the bottom of the cup, used to pull back the sling shot.
- Duct tape- was put over the sharp edges the drill left on the can, a dremel tool could achieve the same effect.
- Drill, various bits.
- Impact gun, various bits (for screwing).
- Protractor (for angled cuts)
- Tae Measure
- Table saw
- Miter saw
Step 1: Assemble T
- Cut two center posts 0.75m long. Drill a hole through the center about two inches from the top, make sure its large enough to feed your bungee cord through. See the two middle boards in the first picture.
- Cut two Bottom Runners 0.92m long. See the two outer boards in the first picture
- Screw the center posts into the bottom runners, use at least two screws.
- Make sure that the center posts are in the center of the bottom runners. The wide face of the center post should be parallel to the length of the bottom runner, as shown in the fourth picture above.
- Try to keep them flat because the structure is not very strong until it is entirely assembled.
Step 2: Assemble A-Frame
- Cut four lengths of lumber at a length of 0.865m
- On each piece, cut one end at a 60 degree offset and the other end at 30 degrees. as seen in the first picture.
- Take the two T's built in the previous step and complete the a frame by lining up the slanted cut lumber pieces on each T, drilling a pilot hole through the bottom and the top and screw into the bottom runner and the center post. Long screws will be necessary for this
- Try not to poke the screw through the bottom of the runner.
Step 3: Join the Two A-Frames
- Cut three lengths of lumber 1m in length, these will be the bottom joists. See first picture
- Line up the a frame on the three joists as shown in the second picture
- Leave a 0.5m gap between the bottom two runners.
- drill pilot holes (12 total) through each side of both bottom runners and all three joists.
- Attach with wood screws. It will be easier to put in the screws in between drilling the pilot holes.
- The frame is now strong enough to support a load, but we decided to add side braces in the next step to support against wind and moving the device.
Step 4: Side Braces
- Cut two pieces of lumber length 0.42m. See pictures 1 and two.
- Cut two pieces of lumber length 0.21m. See picture 4.
- on all four pieces, cut one end at a 60 degree offset and the other end at 30 degrees.
- Cut two blocks (must be same lumber as bottom runners) of any size for the inside braces.
Attach Outer Side Braces
- Attach the long braces to the outside of the frame the same way as finishing the A-frame. Drill a pilot hole at the bottom and the top and screw into the center post and the edge of the bottom joist. See pictures 1 and 2.
- Make sure the 60 degree cut is on the bottom.
Attach Inner Braces
- Screw blocks onto the inside of the middle bottom joist, this should make the joist planar with the bottom runner.
- Attach inner braces the same way as the outer braces now that the joist is planar with the bottom runner.
- The frame is now complete! We will now focus on the bungee and cup apparatus.
Step 5: Cup Preparation
- Drill a large hole straight through both sides of the can about an inch or so from the opening, as shown in the first picture. Make sure it is large enough to feed your bungee through.
- Drill two more large holes through the bottom of the can, about an inch apart. As shown in picture two
- Make sure while drilling to start with a small bit and work your way up, or else you could hurt yourself with the drill because the can is metal.
- using small pieces of duct tape, tape around the drill holes.
- This is an important step or your bungee cord and your pull tie will shear off with use.
- Take three zip ties and feed them through one of the holes on the bottom of the can.
- Feed the ends back through the other hole and close the loop on all three ties. As shown in picture two
- Duct tape the connectors of the zip ties together to make a handle for the Pull Tie. As shown in picture 3.
Step 6: Attach Bungees to Cup
- Cut hooks off both ends of both bungee cords.
- on each cord, peel back the fabric about two inches (enough to tie a reef knot) and trim down the elastic bands.
- Do this only on one end of each cord.
- Feed the fabric ends of the bungees into the cup and tie them together with a reef knot. As seen in picture one.
- To tie a reef knot, hold a cord in each hand and over lap the cords left over right, go under, and then over lap right over left go under and pull. This can be seen in the attached video.
- Alternatively, you could tie the knot and then feed the cord.
- Take your piece of cloth and drape it over the open end of the can. Attach with an elastic band.
- This cloth allows for a soft exit for the snowball, instead of having a hard can smash through the ball. The cloth is where you load the snowball
Note: I did not make the reef knot video. all credit goes to Youtube user Forrest Trenaman.
Step 7: Final Step: Attach Bungees to Frame
- Feed a bungee through each of the holes drilled in the center posts of the frame.
- Tie the bungees off, be careful to leave equal length on each bungee or the slingshot will not fire straight.
The slingshot is now complete! I will add one final step explaining how to set up and operate the device.
Step 8: Set Up/Operation/Tips/Safety
- Place the device on the ground in an open area.
- It is very important that you have something to use as a counterweight. In the video above we used my friend, Sam.
- During our class snowball fight we used a large bag of books and it worked well.
- Place counter weight/s on the end joists. The opposite end that you will be standing.
- This is important because pulling the bungees makes the device want to flip, and the weight counter-acts that.
- The device is now ready for operation.
- Kneel or sit behind the device
- Pull the can back by the zip tie using both hands, the further back the bungee is pulled, the further and faster the projectile will go.
- Adjust vertical and horizontal angles.
- Place snowball into cloth on top of cup, careful not to knock the ball out. T
- In one smooth motion release the zip ties.
- The elastic energy in the bungees will accelerate the snowball forward and it will launch from the device.
- Sit down with your legs pushing against the device while operating and use your back muscles to pull the bungee back.
- Have a friend load snowballs for you.
- Make sure counterweight is heavy enough to balance the moment created from the bungees. This means stronger bungees require a larger counterweight.
- If anyone has any questions, send me a private message on instructables.