My idea was to make a Hot Wheels launcher using simple materials, as a project for teaching kids in a funny way about mechanical engineering, specifically about the potential and kinetic energy concepts.
Searching on Instructables, I found this tutorial from DotatDabbled. Very interesting, cool and well executed. But considering my objective, I have the following issues:
- Materials have to be easier and cheaper to find: Getting stiff plastic and wood blocks for 20 kids can be very complicated and out of budget.
- Very basic tools: nothing more complex than a hot glue gun, scissors and maybe, a x-acto knife.
- Launching mechanism: I wanted the launcher to have a trigger.
So I created this easy-and-cheap-to-build car catapult (a "car-tapult"?). I made two prototypes and tested them with three different toy cars: a Hot Wheels "Batman Live! Batmobile", a Matchbox "MTN XT" and a generic bootleg car (suspiciously branded "Motor Wheels"). I'm in the process of improving the design, but until now, I'm happy with the results.
The mechanism is very simple: the launcher works pulling back two rubber bands and it's released when the trigger (a binder clip) is pressed. At the end, you will have a toy that you can use it science and/or for having fun with your kids!
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Step 1: Materials
- 8 wood craft sticks (Size I used: 15 cm x 1.7 cm)
- 1 corrugated cardboard or wood rectangular piece (I used 16 cm x 7.5 cm, but maybe you will have better results with one of 18 cm x 7.5 cm)
- 2 binder clips (bottom length: 3.1 cm)
- 2 paper clips
- double-sided foamy tape (it can be replaced with hot glue)
- 2 rubber bands
- Aluminum foil adhesive tape (optional; to reduce friction and improve aesthetics)
- Toy car (Hot Wheels, Matchbox or similar)
- Hot glue gun
- Hole puncher
- X-acto knife
Step 2: Using the Hole Puncher
Take two craft sticks and on each one, mark a point at 1 cm of each end. Then, use the hole puncher to open a hole on the marked spot.
Step 3: Platform
Take one of the hole-punched sticks and, using double-sided tape, tape it to one of the ends of the cardboard tablet. Use the ruler to verify the center of the craft stick is aligned with the middle of the tablet.
Step 4: Starting With the Launcher
Take the other hole-punched stick and one of the binder clips. Remove the handles and glue the body of the clip to the middle of the stick.
Step 5: Before You Continue Building This Project...
- Take your time to analyze where every part will be: the position of the rails, the launcher, the trigger and the car. On the next steps we will have to glue and stick together several parts, so it's better to apply the "measure twice, cut once" adage. Or it will become a mess.
- Check the release mechanism for the trigger: the pink binder clip (trigger) holds the green binder clip (launcher). When the handle is pressed, the pink binder clip opens and the launcher is free to go pulled by the rubber bands.
Step 6: Starting With the Rails
Place double sided tape on two craft sticks. Don't remove the plastic cover yet.
(If you don't have double sided tape, no problem. Later you can use hot glue to fix them to the launching platform).
Step 7: X-acto Knife
Take two craft sticks and cut two pieces from each one: one piece 1.5 cm long, and the other, 4 cm. Use the X-acto knife. If it's too dangerous for kids, replace these pieces with metal washers, as long as they have the same thickness of the craft sticks.
(Actually, I will build the next prototype using the washers. Sounds like a better idea)
Step 8: Creating the Rail
Using the hot glue gun, fix the previous stick pieces (or metal washers) to each end of the double sided-taped sticks. The 4 cm pieces will be in front of the rail; the 1 cm pieces, in the back.
Step 9: Again: Measure Twice...
Now, before sticking the rails to the platform, it's time to check the widths of your cars. Measuring the three test cars, I got the following numbers:
- Hot Wheels "Batman Live! Batmobile": 3.1 cm.
- Matchbox "MTN XT": 3.6 cm.
- Generic "Motor Wheels" bootleg car: 2.9 cm.
(Laugh as much as you want about the bootleg car; it got the best result in the launching test).
My first prototype was build for the MTN XT (space between rails: 3.6 cm + 0.2 cm ). This instructable is based on the second prototype, for the Batmobile and the "Motor Wheels" (space between rails: 3.1 cm + 0.2 cm = 3.3 cm)
Step 10: Fixing the Rails to the Platform
Considering the Batmobile 3.1 cm width + extra 0.2 cm (to avoid the car to be stuck between the rails):
- With the pencil, draw the center line of the platform.
- Now, draw a parallel line on each side, distanced 1.65 cm from the center line (3.1 cm + 0.2 cm = 3.3 cm between rails; 3.3 cm / 2 = 1.65 cm).
- Remove the plastic cover from the double sided-taped sticks and fix them after the parallel lines of the previous point.
(Note: I know over the platform I wrongly wrote 16.5 cm. Sorry, I was in a hurry when I took the measures)
Step 11: Launcher in Position
Place the launcher over the rails, and check it slides with no problem. The bottom of the blue binder clip must be facing front.
Step 12: Finishing the Rails
Using hot glue, fix one craft stick to each rail, trapping the launcher. The hot glue has to be carefully placed on the stick pieces (or metal washers) of Steps 7 and 8 (if you place the hot glue in any other place, you will jam the launcher).
Check the launcher is still sliding with no problems.
Step 13: Trigger
Catch the launcher with the trigger (pink bending clip) on the back of the platform. In that point, glue the trigger to the platform. Be careful of not gluing the launcher, or it will be jammed.
Step 14: Chrome and Shiny to Valhalla
Using the adhesive aluminum foil, cover the space between rails.
(I think this step would be easier to do before placing the launcher).
Step 15: Rubber Bands
On each side of the catapult, attach a rubber band on the holes of the front stick and the launcher.
- In the holes of the front stick: use a cow hitch knot.
- In the holes of the launcher, use a plastic coated paper clip to fasten the rubber band.
Step 16: Cushioning
Place a piece of double sided tape or glue a piece of foam on the binder clip of the launcher, to avoid dents when the launcher hits the car.
And it's ready!
Step 17: Testing and Improvement
After some tests, I found some instability in the launching. Even the catapult jumped twice. After checking, I corrected the problem, fixing the inferior handle of the trigger/pink binder clip completely to the platform, and not leaving any space between that handle and the floor (in the case of the prototype for Batmobile, I had to add another craft stick and glue it). Now it works great.