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 l…

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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    62 Comments

    0
    mojo12
    mojo12

    3 months ago

    Mouse trap trapped

    0
    s5116928
    s5116928

    Reply 20 days ago

    then just untrap it

    0
    ltzmar8703
    ltzmar8703

    8 months ago

    Trying to make this work but the wheels keep falling off. Followed the directions but cant figure it out. Seems like i need a cotter pin to go thru the dowel?

    0
    CThelemarck
    CThelemarck

    Reply 8 months ago

    Are you using the correct faucet washers? the 1/4L 19/32" faucet washers should fit pretty snugly over a 3/16" dowel. then securing the washer with some tape or hot glue should make it pretty secure.

    0
    ltzmar8703
    ltzmar8703

    Reply 8 months ago

    Yeah, figured that out after studying the pictures, as it wasn’t in the description. Now the wheels stay on but we get no traction. The CDs just spin. Not sure where to go from here.

    0
    CThelemarck
    CThelemarck

    Reply 7 months ago

    Well, on the bright side, your getting great experience trouble shooting :). Spinning wheels can be an issue for mousetrap cars. Usually because the lever is unwinding so fast, with so much force, that the wheels spin. There are a couple of approached here.
    Reduce the torque - lengthen the car body and lever. this will unwind slower and with less force.
    Increase the friction of the wheels - you can stretch balloons over the wheels, or maybe some wide rubber bands to add traction. you could also add a bit of weight over the rear wheels.
    Give these ideas a try. and also keep testing your car and make careful observations. by paying close attention to what you see you may come up with other ideas.
    Good Luck

    0
    ltzmar8703
    ltzmar8703

    Reply 8 months ago

    I ended up gluing the washer to the CD that way when the axel spun the wheel would move.

    0
    HBV123
    HBV123

    Question 10 months ago

    Does it matter what side you zip tie the dowel to?

    0
    CThelemarck
    CThelemarck

    Answer 10 months ago

    The zip-tie needs to go on the rear axle. It really doesn't make much difference how you put it on. The main point is to create a "hook" to catch the loop in the end of the string to wind the car.

    0
    isnp91DH
    isnp91DH

    Question 1 year ago

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

    0
    CThelemarck
    CThelemarck

    Reply 1 year 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 1 year ago

    How long should the string be?

    0
    CThelemarck
    CThelemarck

    Answer 1 year 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 1 year 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 1 year 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

    1 year ago

    i got mine to go 500 ft with ball barrines

    0
    CThelemarck
    CThelemarck

    Reply 1 year ago

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

    0
    ponyboi808
    ponyboi808

    1 year ago

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

    0
    CThelemarck
    CThelemarck

    Reply 1 year 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.