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Mouse Trap Cars: Tying a Loop Knot

January 19, 2012

An important part of a mousetrap vehicles propulsion system is the loop-knot. Learn how to make and attach a loop-knot in order to propel a mousetrap racer.

A mousetrap powered car is a vehicle that is powered by the energy of a wound-up mouse trap's spring. The objective with all mousetrap vehicles is to turn the potential energy of a wound-up mouse trap's spring into kinetic energy of motion. The most common way to propel a mousetrap car is to attach one end of a string to a mouse trap's snapper arm and the other end of the string to an axle hook. There are many different ways to make an axle hook but the most important part to any propulsion system is for the string to properly release it's self from the drive axle. If the string does not properly release from the drive axle the string will rewind around the axle and cause the mousetrap car to come to an instant stop.

how it works: The most basic mousetrap vehicle propulsion system is to tie one end of a string to a mousetrap's snapper arm and then wind the other end of the string around a drive axle

How to Make a Loop Knot

It is important for the pulling string to have a correctly tied loop knot in order release itself from the axle hook or the mousetrap vehicle will come to an instant stop. Learning how to tie knots brings me back to my Boy Scout days but is also an extremely important part of building a successful mousetrap powered racer.

To start with need to talk about string. The string is used to transfer the pulling force of the mouse trap to the drive axle. The string has to be strong enough to handle the pulling force but flexible and thin enough to wind tightly around the drive axle. We recommend using a Kevlar based fishing line because its high strength. You should stay away from nylon fishing line and dental floss, these do not work well with mousetrap racers.

bonus tip: Essential Project Packet contains all the small parts that you need to get your project from the start to the finish. The Essential Project Packet includes all the hard to find parts that are included in each of our Doc Fizzix's mousetrap powered car and rubber band racer kits. The Essential Project Pack includes eight DVD/CD wheel spacers, four thrust bearings, one axle hook, and one meter of high-tech kevlar string.

Try to carefully study the images on how to tie a loop knot as seen bellow. Please note that the string being used if ONLY for illustrating how to tie the correct knot, it is NOT recommended to use a thick string with mousetrap racers. Also, the loop knot should be large enough so that it releases from the drive axle without snagging on the axle hook (see images).

step #1: Fold the string over and then tie a traditional knot with the folded part of the string.

step #2: pull loop tight

step #3: the finished product

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