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How to Build a Mousetrap Car: Step-by-step Directions

Mousetrap cars are one of the most common projects in schools. Here are step-by-step directions to help you build this car, quickly and easily.
Mayuri Kulkarni
Last Updated: Apr 20, 2018
Schools and colleges often assign the task of building a mousetrap car as a part of science fair projects, because they help demonstrate the application of the various concepts of physics. Besides imparting knowledge, building a mousetrap car is also fun. Not only kids, but adults also enjoy building their own little car and participating in races. However, first let us understand the working of this car.
Working of the Mousetrap Car
The mousetrap car works on basic physic laws. In the design, the snapper of the mousetrap is tied with a string; the other end of which is tied to the axle at the rear end of the car. The car is then wound in the reverse direction with the help of its hind wheels, much like a pull-back car. This will pull the string, and in turn, open the snapper of the mousetrap. When the jaw trap closes, it pulls the string along with it. The string that is wrapped around the rear rod gets pulled, and in its motions, the rod rotates too. The wheels that are fixed onto the rod also rotate, thus giving the mousetrap car its motion.
mousetrap car animation
Mousetrap Car
Step-by-step Guide to Build a Mousetrap Car
  • Wooden mousetrap
  • Four eye screws
  • Plywood board
  • Drafting compass
  • Two rods
  • Drilling machine
  • Epoxy glue
  • Lots of rubber bands
  • Strong string (about a foot long)
  • Measurement tape
Step 1: Removing the Bait Holder
Removing the Bait Holder
Before building the mousetrap car, you will have to make certain modifications to the mousetrap. Be careful while handling the mousetrap, as you may hurt yourself. Remove the bait holder of the mousetrap and take out the wire catch (the wire that keeps the mousetrap open) with the help of pliers. Do not use your hands. You may risk hurting yourself.
Step 2: Attaching the Eye Screws
Attaching the Eye Screws
In this step, you will prepare the assembly for installing the axles for your mousetrap car. Take two eye screws and insert them at the corners of the rear end of the mousetrap. Place these eye screws at a distance of 8 mm to 1 cm from the respective corners. While inserting the eye screws, take care that the wood does not split in the process. Similarly, screw the remaining two eye screws at the front end of the mousetrap. Align the eye screws properly so that you can slide the rods through them.
Step 3: Inserting the Axles
Inserting the Axles
After the eye screws have been aligned, insert the rods into the hooks. These rods can be of any material. The important point is that the rods should be of a thickness that can comfortably fit into the eyes. They should be small enough to easily fit, but big enough to keep their alignment. Once you have inserted the rods, cut them at half-an-inch distance from the hook at both ends. Repeat the procedure for the rear end too.
Step 4: Making the Wheels
Making the Wheels
Now, it's time to prepare the wheels for the mousetrap car. Take the plywood boards and draw four circles. Make two circles a bit smaller than the other two. You can use a compass to draw these circles. Drill holes with a drill machine in the center of the circles. Correspond this hole with the diameter of the rod. Cut the circles from the plywood with the help of a knife or a saw. To smoothen the wheels, use a flat file or sandpaper.
Step 5: Creating Traction
Creating Traction
After the wheels have been smoothed, it is time to coat them with plastic. This is done to help create traction. Use rubber bands for this purpose. Wide and stretchy rubber bands of superior quality is the best option. You can also use balloons. Cut thick strips out from the widest section of big balloons. Secure them around the wheels as shown in the image.
Step 6: Fixing the Wheels
Fixing the Wheels
In this step, we will attach the wheels to the rod that is inserted between the eye screws. Insert the wheel into the rod with the help of the hole that was drilled in step 4. If the measurements are correctly followed, the rod should fit exactly into the wheel. Secure the wheels into the safety of the rod by tying rubber bands at the ends. Glue them with some epoxy glue.
Step 7: Attach a String to the Mousetrap Jaw
Attach a String to the Mousetrap Jaw
The outer body of your mousetrap car is ready. It is now time to work on the mechanism. Take a piece of string and tie it to the middle of the mousetrap jaw. Make it strong by winding it around the rod a few times. Measure the length from the jaw to the rear rod of the car.
Step 8: Tie a String to the Rear Axle
Tie a String to the Rear Axle
Tie the end of the string to the rear with the help of a loop knot as shown in the diagram. Make sure that the knot is tight. If you're doubtful, use some glue on the knot. Your mousetrap car is now ready to race.

To wind the car, pull back the rear wheels in the reverse direction, like you would do with a pull-back car. This will wind the string on the rear rod and the jaw trap will open. Be careful while handling it. Now slowly release the wheels. As the jaw trap will force shut, your mousetrap car will speed into motion.