Build a Mousetrap Car

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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. Lately I've been on a Maker kick to hel...

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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    20 Discussions

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    CThelemarcklittler_lopez

    Reply 8 days ago

    It needs to reach from the end of the dowel and be long enough to reach the rear axle. you can either wind the string directly onto the axle making sure that the string overlaps as it winds. or tie a loop onto the string and fashion a small hook from a zip tie on the rear axle as shown in the instructable.

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    mtumenas

    Question 6 weeks ago on Step 1

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

    1 answer
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    CThelemarckmtumenas

    Answer 8 days ago

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

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    SavannahL7

    Question 2 months ago

    what sizes do you have to cut out for the little piece in the cardboard?

    1 answer
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    CThelemarckSavannahL7

    Reply 2 months ago

    I usually make the notch in the back about 2 inches deep, by about 1 1/4 - 1 1/2 inches wide. If you make it too narrow, the string tends to rub on the side and slow it down. If you make it too wide then the cardboard loses strength and might bend.

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    SavannahL7

    Question 3 months ago

    What is the metal rod at the end of the wood stick that the string is on?

    1 answer
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    CThelemarckSavannahL7

    Reply 3 months ago

    Oh, Good catch. That is the metal bail wire from the mousetrap that usually holds down the snap arm. I just zip tied it to the end of the wooden dowel.

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    CThelemarckDanielJ301

    Answer 6 months ago

    When I work with youth, they can regularly get it to go about 50-60 feet without modifications. Mine will go about 100 feet. I think wit some tweaking and more modifications we can do better. My 4-H Makers club will be experimenting with some 3-D printed parts this spring.

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    ChanceD7

    3 months ago on Introduction

    Btw. This is very important. The diameter of the straws matter. A LOT. If the diameter is too small, the dowels will be too tight, and they will not spin. I wish i could tell you what size straw you need, but i can't. I had to sand the dowels down to where they would spin, causing the car to wobble, and causing the diameter of the dowels to not be snug in the washers, but i got it figured out. Expect to spend more time on this car than you are probably thinking. I thank CThelemarck for the simple design, and we will get a passing grade, but that's ABOUT it.

    2 replies
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    CThelemarckChanceD7

    Reply 3 months ago

    Thanks ChanceD7. Yes Friction matters a lot. I've never run into straws that were too narrow for the 3/16 inch dowels, but I'm sure they're out there. There are many other ways to make hubs to run the dowels through, but aligning them is key, that's why I like the straws so much, because they are much easier for youth to line up and get relatively straight.

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    ChanceD7ChanceD7

    Reply 3 months ago

    Also, instead of cutting the straw in 3 pieces, cut it into 2 equal lengths and cut the 1 AFTER you glue it on. If the 2 small pieces aren't lined up perfectly, friction will be met, and the dowel will not spin correctly.

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    JeniferT3

    Question 3 months ago on Introduction

    can you tell me how far away the straws are placed from the edge of the cardboard? Thanks!!

    1 answer
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    CThelemarckJeniferT3

    Answer 3 months ago

    Hi There,

    I'm assuming you mean from the front and rear of the car. I typically align the straws about 1/2 inch to 1 inch from the ends. Then I cut them so they are the exact width of the car. You can play around with the distance, I have even glued them to the very end. They key is that they are parallel to each other and the ends of the car.

    Good Luck

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    dezicat

    5 months ago

    this car is made of the exact same materials that i am using in science class!!!!!

    1 reply
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    Swansong

    1 year ago

    Those are fun cars, this would be a neat class project!

    1 reply