Introduction: 3D Printed Mouse-trap Cars

I have been a Technology Educator for ten years. When we first received 3D printers I was very excited to develop new curriculum for my courses. After some thought on how to incorporate the 3D printers I put a new twist on an old project. In this instructable I will be covering the steps on how to design and build a 3D printed mousetrap car.


- 3D printer

- 3D printer Filament

- 3D modeling software (TinkerCAD // Autodesk Inventor)

- Conventional mousetraps

- Dowels (1/8 inch and 1/4 inch)

- Rubber bands

- Hot glue

- Straws

- String

- Zip ties

(substitute metal rod for 1/8 inch dowel for axles of car)

Step 1: Explanation of Unit

If you are using this project in a classroom this step will describe the components of the project to the students. The attached document is a packet that can be given to students to fill out throughout the project. The packet explains:

- Problem Statement

- Competition Dates // Rules

- Engineering Journal

- Supplies // Building Instructions

- Calculations for competition

- Assessment Rubric

- Criteria and Constraints of project

NOTE: If you are not using this as a unit in a classroom you can skip this step and get to designing!

Step 2: Design

- We will begin by modeling the car in Autodesk Inventor. Although you may design the car however you would like it is practical and less frustrating to put constraints on particular sizes. The constraints I have come up with for my students are as follows:

- Overall Body of the car is 19cm x 6cm x .635 cm

- The front wheel of the car has a diameter of 3.8 cm and a thickness of .63m cm

- The back wheels of the car will have a diameter of 8.89cm and a thickness of .635cm

- The body as well as the wheels must have a 0.3175 cm hole for the axel

When you have finished the various parts for the car you can export the files as an STL which will then be able to be used on a 3D printer. I have also uploaded the sample STL files for testing.

NOTE: Encourage students to design the car further without breaking the constraints. Students should think about DRAG as well as WEIGHT when designing the interior of the components.

NOTE II: I have also put together a Autodesk Inventor tutorial YouTube series. If you or your students are unfamiliar with Autodesk Inventor you can get started here. I have also uploaded the accompanying drawings for each Autodesk Part for the tutorials.

Step 3: 3D Print

Now is the time to take the STL files to the 3D printer. I have had the best luck with positioning the wheels in a vertical way, as well as putting the body of the car in a perpendicular position relative to the bed.

Once the prints have completed you can take some time to remove the support material and prep the parts for assembly.

Step 4: Clean Up 3D Prints

Now comes for the more laborious portion of 3D printing, cleaning up the parts. I find that using an x-acto knife or a pair of needle nose pliers works well. As I do this unit with Junior High students some portions of the support material is difficult for them to remove on their own so I assist them with specific portions.

Step 5: Assemble the Axles

We are now going to start to prepare and assemble all of our components to assemble the 3D printed mousetrap car.

First we will begin by cutting our axles from either metal rod or dowel. We will be cutting the axle to 3 and 3/4". We will need two axles.

Next we can cut the straw, which acts as a spacer, to a half inch. We will need a total of four spacers.

Next we will assemble the axle. Start by placing a wheel on the end. The rolled up tape should hold the wheel in place. You may add hot glue at this point to add stability if necessary. Add a spacer and then insert the axle into the body of the car. On the other end add a spacer and roll another piece of tape on the end. Finish the first axle by placing the second wheel on the tape.

Step 6: Prepare the Mousetrap Mechanism // Dowel

We are now going to modify the mousetrap so that it works well to power our car.

First we can remove pieces from the mousetrap that we will not be utilized using a pair of pliers.

Next we can attach the dowel to our mousetrap. You can do this by simply taping or gluing the dowel to the mechanism on the mousetrap, or you can 3D print the adapter I have designed. This adapter allows for secure connection to the mousetrap as well as a a place to glue in a 1/4 dowel. I have attached the .STL file for 3D printing.

Next we can cut our dowel to length and attach to our mousetrap. I have cut mine to 9 inches but you can change this variable to net different results from the car. If you are using the adapter I suggest filling with a little hot glue.

Step 7: Finishing Touches

For the last few steps we will start by hot gluing the mousetrap mechanism to the top of the body of the car.

Once it is dry we will drill an 1/8 inch hole at the end of the dowel to attach a string.

Tape one end of the string so that it will fit through the drilled hole more easily and tie a small knot on the other end of the string. This will be used to "attach" to our axle and power the car.

Put a couple rubber bands around the back wheels to add traction to the car.

Finally we are going to attach a zip tie to the rear axle to give a attachment point for the sting. You may use a little hot glue if the zip tie is too loose. Cut the excess from the zip tie so you are left with a small attachment point.

Now you are ready to race!

Step 8: Race!

If you are using this as a unit for students you may set up an area to begin trials. Students can use a stopwatch and a tape measure to calculate speed. Distance may also be recorded and used to determine the winning car. Allow students to experiment with their car after a couple of trials. They can alter the "arm" of the car, which in this case is the dowel, or they may want to use other techniques to improve their cars abilities.

STEM Contest

Runner Up in the
STEM Contest