Build a Mousetrap Car

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Introduction: Build a Mousetrap Car

About: I am an Extension Educator for the UNH Cooperative Extension specializing in hands on inquiry based STEM education for 4-H Clubs, after-school programs and educators. I'm big on Making to help activate STEM...

I made these mousetrap car plans to be used with 4-H clubs where I live in New Hampshire. While there are several other good mousetrap car Instructables and videos to be found out there and many car designs that travel faster and farther, I like these plans for their simplicity and ability to adapt and modify. It makes a great 4-H or class project that provides an opportunity to learn some basic physics and engineering skills.

Step 1: Materials

  • 2 pieces of Cardboard (4” x 10”) many dimensions will work, but this is a good starting place.
  • 4, DVD’s (old used ones work great or new black ones from an office supply store)
  • 4, 1/4L (19/32”) Beveled Faucet Washers (found at most hardware stores in the plumbing dept.)
  • 2, 3/16” Dowels - 6” long (these will need to be longer if you use wider pieces of cardboard)
  • 1, ¼ inch dowel, 10“ long
  • 2, Straws
  • Tape – Masking & or Duct
  • zip ties (an assortment of 4” & 8” works well)
  • String
  • Hot Glue

Step 2: Car Body

Take the 2 pieces of cardboard (about 4”x10”) and cut a rectangular notch (about 1”x2“) in the center of the short side of each piece of cardboard. Be sure that the notches overlap. Then place the two pieces of cardboard on top of each other and tape the edges together to make one double thick piece of cardboard. Make sure the notches line up.

Step 3: Attach the Straws

Cut 3 sections of straw to fit on the body of the car like in the illustration. Glue them in place using hot glue. This will be the underside of the car. Be sure the straws are parallel to each other and the leading (short) edge of the cardboard.

Step 4: The Mousetrap

Take a mousetrap and remove the pieces that make up the release trigger (bait holder and wire bail, see picture). Use two or three 4” zip ties to secure the ¼ inch dowel to the snap arm and reinforce with tape or hot glue. Glue the mousetrap in place towards the front on the topside of the car with hot glue. Be sure the dowel is pointing forward away from the notch in the cardboard and that the dowel also lines up with the center of the notch when it is pulled back. See picture at the top of the Instructable for placement. Attach a piece of string to the end of the ¼ inch dowel with a zip tie. It should reach a bit longer than hook on the rear axle. Tie a small loop on the end. The loop should just reach the hook on the rear axle.

Step 5: Preparing the Wheels

Place a piece of duct tape over the hole in the center of the DVD. Turn the DVD over and place the faucet washer into the center of the DVD onto the tape. Use a generous bit of glue to hold it in place. Do this for all four wheels.

Step 6: Adding the Axles and Wheels

Place the 3/16” dowels into the straws and press the wheels onto each end. Sometimes the hubs can be hard to press onto the dowels. Rounding or slightly sharpening the ends can make this easier. At this point you should test the car to see if it rolls straight. If not you may need to straighten the straws.

Step 7: Attaching the Hook to the Rear Axle

Attach a 4” zip tie to the center of the axle exposed by the notch in the cardboard, and cut it short, about ¼ inch. This is the hook for the string. A dab of glue will help keep it in place.

Step 8: You're Done!!!

You should now have a car that looks something like the picture. Attach the string to the hook and wind it backwards. Put the car on the ground and let it go and it should start rolling away from you. Take some time to get to know your car. It will likely take some tinkering and practice to get it to roll straight and smooth. Once you’ve got it working well. Run it several more times and when it goes, watch it carefully to see if you notice anything that might be hampering its performance. See if you can tweak it to make it go better. Once you have a good idea how the car works, see if you can design another car that can travel even farther. Try different materials for the body, axles, wheels etc.

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    53 Discussions

    0
    isnp91DH
    isnp91DH

    Question 2 months ago

    How do you stop the string from wrapping around the axle and stopping the car?

    0
    CThelemarck
    CThelemarck

    Reply 2 months ago

    Great question. Tie the loop so it barely reaches the zip tie hook on the axle. That way when it releases it won't catch the hook, allowing the car to coast.

    0
    musicalclef88
    musicalclef88

    Question 4 months ago

    How long should the string be?

    0
    CThelemarck
    CThelemarck

    Answer 4 months ago

    The string should reach from the tip of the wooden dowel in its forward position, to the rear axle. I usually tie a loop just short of the zip tie hook (see step 7). that way when the dowel snaps forward, the loop won't catch on the hook allowing the car to coast.

    0
    tlangstonstbs
    tlangstonstbs

    Question 5 months ago on Step 1

    Hello! I can't wait to complete this with my students. Can you provide some suggestions for adding additional friction to the CDs/DVDs so that they can "grip" the tile floor? What works well/is easy? Thank you so much!

    0
    CThelemarck
    CThelemarck

    Answer 5 months ago

    Great! Hope it works out and you all have fun learning. You can stretch balloons over the wheels to add a little grip. but if you use similar dimensions for the cardboard and wooden dowel, the cars start slowly enough that the wheel wont slip. I have a curriculum guide that lets students use mousetrap cars to explore the engineering design process at https://extension.unh.edu/resource/4-h-mousetrap-car-curriculum-guide.

    0
    lop24jq
    lop24jq

    6 months ago

    i got mine to go 500 ft with ball barrines

    0
    CThelemarck
    CThelemarck

    Reply 6 months ago

    Wow. Nice work. that exceeds many cars on even the Doc fizzix webpage which specializes in mousetrap cars.

    0
    ponyboi808
    ponyboi808

    6 months ago

    How do you keep the wheels from rubbing against the cardboard frame?

    0
    CThelemarck
    CThelemarck

    Reply 6 months ago

    There are a couple of things to think about if the wheels are rubbing against the frame.
    First, look closely to see if the wheels are straight or wobbly when they spin. If they are wobbly, you have to address that first by trying to straighten them.
    Then look closely at the axles. Do they slide back and forth so that one wheel or the other rubs? To keep the axles centered you can cut the straws wider than the body so the axles don't go back ad forth so much or you can add extra rubber washers to the axle to keep it centered and move the wheels wider apart so they won't rub against the body.

    1
    CThelemarck
    CThelemarck

    Reply 6 months ago

    the average car for a first time builder goes between 20-50 feet. I have gotten them to go up to 100 feet.

    1
    oliviagaddy
    oliviagaddy

    Question 7 months ago

    When I roll it, the weels are crooked and I have been trying to fix but its not
    working so what do I do?

    0
    CThelemarck
    CThelemarck

    Answer 7 months ago

    There are a couple of possibilities for crooked wheels.
    1. the straws may be glued on crookedly so that the axles are not parallel. this would cause the car to roll to the side or turn.
    2. if the washers (hubs) are not mounted flush on the CD's the wheels will wobble, slowing the car down and perhaps making it turn. - Make sure they are flat and in line with the CD before taping or gluing them
    3. if the wheels are crooked and/or pushed in too far they can rub on the car body making the car drag or turn.

    These are just a few things that might make them crooked. I would take a good look at the car turning the wheels and observing what is happening to see if you can find the cause of the crookedness. you may have to take things apart and re-glue them to get a car that rolls better.

    Good Luck

    0
    experilab
    experilab

    8 months ago

    I believe the first (similar) mousetrap car design was by Prof Jeff Bindon in the '70s who was teaching mechanical engineering at the University of Kwa Zulu Natal (Durban, South Africa) at the time. We still sell the kit which is supplied to us by UKZN (see attached). His designs for elastic cars, bottle jet racers, steam cars, pop-pop boats etc. were widely copied all over the world. He was a remarkable inventor with other projects such as a marshmallow gun powered by a vacuum cleaner etc.

    MouseTrapCar_01.JPGMouseTrapCar.JPG
    0
    jlewis0033
    jlewis0033

    Question 9 months ago on Introduction

    What theory can be proven, after doing this project

    1
    CThelemarck
    CThelemarck

    Reply 9 months ago

    Well, it's not about proving a theory, but there is lots of science to be learned. by building and working to improve your car you can explore some basic concepts of physics. Three common concepts that can be explored with Mousetrap[ Cars are friction, torque and inertia. You can read more about this on the web page I manage for UNH Cooperative Extension
    https://extension.unh.edu/resource/how-build-mousetrap-car

    0
    UkeDog
    UkeDog

    Reply 8 months ago

    What a great physics project! Besides the concepts you mentioned, you could add potential energy as well. I wish my kids had a physics teacher like you!

    1
    mtumenas
    mtumenas

    Question 1 year ago on Step 1

    Is there a reason to use the beveled washers vs the flat ones?

    0
    CThelemarck
    CThelemarck

    Answer 1 year ago

    no both work fine. the beveled washers seem to fit easier though. but I've used both successfully.