Introduction: Rat Trap Car

Picture of Rat Trap Car

This project was inspired by LarrySDonald's Mouse Trap Car. I give him full credit for the idea. Anyway, this is a very similar thing except with a twist. My car is made with a rat trap instead of a mouse trap. I had some knex lying around and I thought that they could make great wheels and axles. This car goes pretty far and fast so be careful. You also need to be careful of the rat trap because it is on a hair trigger and can release at any moment. I take no responsibility of damage to any property, body parts or animals hehe. Make sure nobody is in the path of the car when it is being launched.

Let's get started!

Step 1: Gather Materials

Picture of Gather Materials

To build the Rat Trap Car you will need the following:


1-rat trap
4-eye hooks
10 inches of fishing line


4-large knex wheels
4-grey connectors
4-tan connectors
2-red length rods


Drill bits

Step 2: Mark and Drill

Picture of Mark and Drill

Mark 1/2 inch marks from the edge on both sides of the trap

Drill two holes using the 5/64 drill bit on the 1/2 inch marks you made on both sides.

Step 3: Insert Eye Hooks

Picture of Insert Eye Hooks

Screw in the eye hooks into the four holes you made in the last step. Make sure that the hooks are perpendicular to bottom of the trap

Step 4: Front Axle

Picture of Front Axle

Now its time to make the front axle. Get one of the red rods and put one grey connecter on the end. Next slide one of the wheels on and snap in a tan connector behind the wheel slide this into the whole to lock the wheel to the rod. Now slide the axle through on of the eye hooks on the front end (the end with the bar down when not in use) Next put the other end of the rod (the one without the wheel) through the next eye hook. Put the second wheel on using the method above. Now your done with the front axle.

Step 5: Rear Axle

Picture of Rear Axle

The rear axle is the same as the front but the rod needs a hole driled through it. Use your 1/64 drill bit.

Step 6: Fishing Line

Picture of Fishing Line

Now get your fishing line and measure out ten inches and cut with your scissors and burn the end with the lighter. Tie one end of the line onto the main arm of the trap. You should have about 9 inches of line on the other end.

Step 7: How to Launch

Picture of How to Launch

First you need to put the long end of the string through the whole drilled in the knex rod. Next, spin the rod backwards (on the trap there is a rat, the rat's nose is pointing in the direction you want to spin the rod in). When the string is taught and you cannot turn it anymore without pulling back the arm, pull the arm back and spin the rod again until you have used all the string. Now arm the trap as you regularly would. To trigger the trap get a long object like a ruler or something and tap it and quickly pull away.


GraceH17 (author)2015-10-27

Dear bakenbitz, I have to do a project in physics where we have to make a homemade car that has to go up a 23 degree ramp without using chemicals or electricity. I thought this car would work, but I'm just wondering, do you think it will be able to go up the ramp?

puppy theu (author)2014-11-22

I really enjoyed making this design:)

CraZeD MuSiCiaN (author)2011-10-11

Does this design get both distance AND speed??? or does it just get one or the other? o.0

CraZeD MuSiCiaN (author)2011-10-11

hahaha that made me smile

goldfishisback (author)2011-08-28

man this was so simple yet really well written, thanks heaps and keep writing :D

eestrada11 (author)2010-10-19

where did you get the knex items from??

josh2k (author)2010-06-14

how can you calculate the force of the spring?? or the force that the car is released

liltheo25 (author)2010-03-02


james.mcglashan (author)2009-11-20

throw a  rat at it to start it hehe.

pindalanderz (author)2008-09-16

I've found it to work even better if you use a broken rubber band instead of a string.

An Villain (author)pindalanderz2009-05-15

i have a lot of broken rubber bands

pindalanderz (author)An Villain2009-05-15


An Villain (author)pindalanderz2009-05-15

that really depends on your point of view, all of the rubber bands that i need whole are broken

An Villain (author)2009-05-15

not a rat trap car, call it a rat rod

kelseyyyyy (author)2009-03-30

where do you find knex wheels?

Tmbo17932 (author)kelseyyyyy2009-05-11

yannyboy (author)kelseyyyyy2009-03-30


cjgirl (author)2009-05-09

how far did this go

gamefreek (author)2009-03-27


cartmanblues (author)2008-11-09

Does it go like 10m? That's how far mine has to go for a class.

bakenbitz (author)2008-10-09

What do you need help with?

pinkpooj (author)2008-09-17

I just posted a design for a window shade car. Check it out! Pull down window shades give the car a lot more torque and distance than mouse traps because the torque spring is several inches long.

bitesnkisses (author)2008-08-30

awesome, how far does this go?

bakenbitz (author)bitesnkisses2008-08-30

30 feet or so. Why did you comment twice?

bitesnkisses (author)bakenbitz2008-09-01

sorry, my internet crashed and i thought it hadn't sent it >.<

bitesnkisses (author)2008-08-30

this looks nice? how far did it go?

BuangAyam (author)2008-03-16

Nice work, you really do it great. maybe I'll try to make one too. But, I'll try to make mine with some car parts to make it look like a true car and some art and modification. So the rat will surely be inside and really trapped.

bakenbitz (author)BuangAyam2008-03-17

Stop advertising.

I_am_Canadian (author)bakenbitz2008-03-26


thepaul93 (author)2007-11-10

cool you should find out how fast it goes

zeeky zeeky bomb!


A_squared (author)2007-11-21

very good i made one in grade eight. Best in class of course : )

I made one w/ a mousetrap in my 7th grade tech ed class I cant wait to make one with the all-powerful rat trap!

dannosliwcd (author)2008-01-14

I remember when I was assigned to make a mousetrap car a few years ago. One group used a rat trap and knex and got an A. My group got a B because we followed the rubric Our fault I guess. That teacher never really seemed to grade on any specific standards.

Hyper_hurdler3 (author)2007-11-16

Thanks soo much! =D
lots of help!
fo sho!

Hyper_hurdler3 (author)2007-11-16

I have to make one for science;;
pretty sure mine's gonna suck.
Most definitely!

LarrySDonald (author)2007-11-08

Pretty badass, rat traps have a lot more spring for sure. It's certainly not my idea as such though (though thanks for the kudos), people have been building these since probably like the Jurassic period - I just wrote it up. Don't even remember where it came from. Man, now I want some knex. I'm reverting to childhood I tells ya..

bakenbitz (author)LarrySDonald2007-11-08

Hey, thanks for the comment. I was just saying that I saw yours and that gave me an idea. You can get lots of knex on ebay for cheap, if you were wondering.

LarrySDonald (author)bakenbitz2007-11-12

Certainly not baggin' just not wanting to take undue cred 'cos certainly I've seen most of the ideas I used somewhere. They don't seem to sell rat traps around here, guess not enough rats in suburbia. I did order a bit of knex, but, well, wife, kids, work, things come up. I do have a few ideas up my sleeve, guess perhaps another sometime if they work.

Brandon121233 (author)2007-11-11

You should use bearings for the axles to reduce friction.

Olaf One-Brow (author)2007-11-09

NO it does not have a purpose thought that was cool.

i make shooting things (author)2007-11-07

cool thanks one of the shop teachers at my school has us make these unfortunately i dont have him. so iv been wanting to build 1 but i didnt know how untill now

John Smith (author)2007-11-06

Huh, that's pretty cool. I'd be a better instructable with a video, though.

bakenbitz (author)John Smith2007-11-07

I think I will do that soon, expect it within the next few days if not less.

joejoerowley (author)2007-11-07

The way the picture is taken on the 3 step it looks like your trap is really big or your feet are really small.

04bobby1 (author)joejoerowley2007-11-07

its on a table i think

bakenbitz (author)04bobby12007-11-07

Yep, it's on a table

awoodcarver (author)2007-11-06

Nice work ,good use of knex.... these are always fun to make , I haven't used a rat but a mouse trap , how far did it go ?

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