Speedy Gonzales: How to Make a Mousetrap Racecar

Oh, what better a way to start off the new semester than by building a racecar? Why, building a racecar using a mousetrap, of course!

In this Instructable, I will not only show you how to build a mousetrap car, but also some tips and tricks that I learned in my own building process.

Back off, PETA. No animals (or pet rocks ;]) were harmed in the making of this Instructable.

Step 1: Gather Thine Materials

In order to built your Mousetrap car, you will need:

1. (2) Balsa wood side rails (8" x 1/2" x 1/4") - mine came pre-drilled; but you'll have to drill holes (slightly larger than 3/16") in yours for the axle

2. (2) Brass axles (6" x 3/16" tube)

3. (1) Brass lever arm (6" x 1/8" Tube)

4. (4) CD's to use as wheels - I used those clear things that you get when you buy a pack of black disks; these work fine, too

5. (8) Rubber CD spacers

6. (4) Metal thrust washers

7. (1) Victor Mousetrap

8. (1) Zip tie to use as axle hook

9. 36" Kevlar String - if you can't find Kevlar, any type of thin string, even fishing wire, works well enough

Note: In class we were provided with these kits; you can order them rather than trying to gather all the parts individually.

You'll also want these tools:

1. A hot glue gun and hot glue or super glue

2. Needle-nose pliers

3. Wire cutter

4. Scissors

5. Protractor, optional

6. Sandpaper, optional

Step 2: Mousetrap Surgery

1. Use your wire cutters to sever the mousetrap's snapper arm at the point where the spring is pushing the snapper arm. Discard the snapper arm.

2. Use the wire cutters again to remove the mousetrap's locking bar. You'll need to save this for the next step.

3. I used my needle-nose pliers to straighten the locking bar's tip, but if you'd like you can just cut it off with the wire cutters; take care not to take off too much.

4. Slide the locking bar into either end of the brass lever (the smaller tube) and glue into place.

5. Put a dab of hot glue into the other end of the brass lever and slide it over the mousetrap's snapper arm.

Step 3: Fabricating the Chassis...

...out of balsa wood... Now we're rollin'...

1. If you want to, go ahead and sand the balsa wood side rails and the axle holes.

2. Glue the side rails to the bottom of the mousetrap, NOT the sides. Gluing the rails to the side of the mousetrap will not allow your brass axles to make it through the axles holes... Not good, assuming you want the car to go. :]

Step 4: Time to Kick Some Axle

1. Place the brass axles (the larger two tubes) through the front and rear axle holes of your car's frame.

2. Slide on a metal washer on each side of the axles. Then, slide on a rubber CD spacer.
(Actually, I guess I should say 'force on a CD spacer', because they're tricky little things. Try coaxing them into place with a little dish soap. Or, try to drive the brass axle through the CD spacer rather than the vice-versa, if that makes sense)

Heads up! Loose axles? That's good, provided they're not too loose. They do need to be able to rotate, remember? Later if you find out that your car doesn't go straight, you can always adjust - I'll show you how :]

Step 5: Wheel Installation

1. Pop a rubber CD spacer into the center of each CD wheel.

2. Pop a CD wheel onto each end of the axles. Voila! You now have motion.

It should be noted that by adjusting the wheels' camber, you can help your car to go straight, even if your axles are uneven. It's just a matter of finding that sweet spot.

Step 6: Time to Hook Up Your Ride With an Axle Hook

This is gonna be one of those steps where you just really want to thank Eric for comments on pictures...

Step 7: Adding the "Chain"...

err... string, rather.

Uh, sorry about the lack of visual aid on this one, guys...

1. Tie one end of the string into a loop knot.

2. Put the loop around the ring of the locking bar.

3. For the next few parts, you'll have to guesstimate. With the brass lever in the resting position and the loop still in the locking bar ring, pull the other end of the string down to where the axle hook is. The idea is to make a loop on this end of the string, too, to put around the axle hook. You don't want there to be too much slack in the line and you don't want your loop to be too big. This takes some fumbling with; just don't cut anything until you're satisfied.

Step 8: Start Her Up

Yes. After hours of toil, you now have in your own possession a mousetrap racecar. What are you waiting for? Start her up!

1. Make sure you've got your string attached to both the locking bar and the axle hook.

2. Pull the brass lever arm all the way back.

3. Wind up the string around the back axle.

4. Let go.

5. Sometimes I like to make Vroom vroom noises right about now.

Sorry I don't have any shots or video of my car in motion. Here's the finished product, though.

Step 9: Aftermarket Modifications

Now the whole point of Engineering class, as my instructor explained, was to find ways to make things better. The purpose of our making these cars was to tweak it and win a race that we had at the end of class.

She also mentioned something about re-purposing things...