Mousetrap Vehicle

Mousetrap Vehicle is a two person building event in which teams build a vehicle powered by one or two mousetraps. The vehicle must be capable of pushing a plastic cup 3 meters or more down a track, reversing direction, and stopping as close to the vehicle target point as possible. It is a Division C event for the 2019 season, and it has been an event in both Division B and Division C in the past.



How It Works
1 or 2 mousetraps are mounted on the car. Most often, a long dowel or other type of rod is attached to the mousetrap, so that when the mousetrap is triggered, it pulls the rod and the attached string, which unwinds from around the axle, which turns the wheels, propelling the car.

Building
The building materials that can be used vary greatly depending on the builders' skill level. Experienced builders might use lightweight balsa wood and carefully crafted plans. Many different kits and books are available in hobby stores to help educate participants on how a mousetrap vehicle works. These kits are usually made of balsa wood, but some kits are available that are made of plastic for home experimentation. Careful examination should be made to ensure that these kits do not have any illegal parts. It is also possible to 3D print a car, but this is expensive. Many methods can be used to build a mousetrap vehicle, and it is suggested that anyone interested go to the Mousetrap Vehicle Forum for more tips and information.

Number of Winds
To figure out the number of winds needed, all that must be done is get the circumference of the drive wheels and divide the distance by the circumference. However, due to inertia and other factors, many test runs must be performed to find out exactly how many winds the car's string initially needs. Some vehicles need more or less than others, even with identical wheels and axles. Careful attention should be taken to ensure that the track is free of debris that could affect the vehicle. High-caliber teams should take every detail to attention to help ensure a winning score.

Adjusting the Vehicle
To reach the next level, the vehicle's design should be adjusted to better fit a variety of properties. There is no single strategy that will yield a perfect vehicle, and adjusting one element to fix one property of the vehicle may cause a negative change in another property. This is all part of the design process. All of the following tips require testing to reach the vehicle's full potential.

Making The Vehicle Go The Distance
If for some reason the car cannot travel the minimum distance, try the tips below. If the car does not move at all under its own power, go to the next section. It most likely will need more power.


 * Make the car's drive axle thinner. This will allow more winds of the string around the axle, making the car go farther.


 * Make the drive wheels larger. Wheels with a larger circumference will travel a greater distance with each revolution.


 * Make the drive string longer. This will also require a longer lever arm.

Warning: The first three suggestions will reduce the car's torque as a side effect.
 * Make the car lighter.

Making The Vehicle Faster
Making the car travel quickly is an important factor in the score. Follow these tips to make the car go faster. Please note that the first two are the opposite of the distance tips, so the participants will need to find a balance between the distance the car will travel and speed. They will generally want to just be able to make the distance, with a little wiggle room.


 * Thicken the axle: Wrapping some tape radially around the axle or adding a spool. It may be surprising as to how much faster this makes the vehicle. This also helps if the vehicle will not move at all.


 * Use smaller wheels. They will require less force to complete a rotation.


 * Make your vehicle lighter.

Making The Vehicle Accurate
Another factor in the score is the accuracy of the car when stopping at the stopping point. It is common to include a braking system in mousetrap vehicles to ensure the car's stopping on the right spot. Especially common are wingnut brakes. Please see the brakes used in the previous event, Scrambler, for an example, or the picture at the link in the next section.

Making Your Car Go Straight
In the 2018 competition, the track must be at least 1 meter wide, therefore, traveling straight is important. If you cannot build the axles to be exactly parallel, then there are some other options. One commonly used solution is to build the car in two halves. The front axle will be part of the front half, and the rear axle will be attached to the back half. The two halves of the vehicle are connected together with a bolt that runs to the middle. Here is a modified example of this method. To adjust the path of the vehicle, simply loosen the bolt, turn the front half, and lock it in place by tightening the bolt again. Now you can adjust how straight or curved the path of the vehicle is.

Note that the picture is from the event Battery Buggy, and electricity is not allowed in Mousetrap Vehicle!

General Tips

 * 1) CDs or vinyl records are common wheel ideas. Rubber bands or balloons can be placed around CDs to add traction. Also, good wheels can be found at local hobby stores. Airplane wheels are often light and come in a variety of sizes. The only main problem is they can sometimes be expensive.
 * 2) If possible, try to test the vehicle on a surface similar to the one that will be encountered at the next competition. Testing on tile and then competing on hardwood will affect the vehicle's performance. The best way if the competition surface is unknown is to test on multiple surfaces and keep data for each one. Also, the importance of clean floors cannot be emphasized enough: the results will be varied if the floors are dusty or have small pieces of trash on them.
 * 3) Possible places to practice can be:
 * 4) a school gym
 * 5) a school cafeteria
 * 6) school hallways
 * 7) For string, Kevlar fishing line works quite well. Sewing thread breaks fairly easily, and regular monofilament fishing line will stretch under stress. It is best to have a thin string, so that the thickness of the string does not interfere with the winding of the string.
 * 8) When building, it may be best to move the mousetraps as far from the driving wheels as possible. This enables the participants to maximize the length of the lever arm and drive string. If the lever arm sticks beyond the axle, the string must extend back to the axle to wind around it, meaning that any additional string is wasted. Furthermore, the initial power from the trap will be wasted until the lever arm is vertically positioned over the axel.
 * 9) It is recommended that the drive string be wound around the axel, and then lock the trap(s), eliminating the requirement to pull the string tight as you wind it.

Scoring
The goal is to have the lowest final score. Each team is given a total of 8 minutes to attempt 2 runs. The lower score of the 2 runs will be the team's Final Score. If a team cannot successfully complete a run in the 8-minute block, they are given participation points and scored in a lower tier, but they are still scored above no-shows.

The run score is calculated as follows: 2*(Vehicle Distance in cm) + Cup Distance Score (300 + the distance in cm to the ctl, 0 if the entire cup is beyond the ctl) + Run Time in secs + Penalties

Vehicle Distance
Vehicle Distance is calculated as the distance from the VTP to the closest part of the dowel, to nearest 0.1 centimeter. If the dowel covers the VTP, the Vehicle Distance is 0.

Cup Distance Score
The Cup Distance Score is the distance of the cup to the CTL when it has reached the final resting position. A score of 0 is given if the entire cup ends up past the CTL. If the cup does not pass the line, the score is the distance to the nearest 0.1 cm from the cup furthest from the CTL to the CTL + 300.

Run Time
The run time begins as soon as the mousetrap is released, and is measured until the mousetrap stops completely for 3 seconds.

Penalties
A penalty of 250 points is given for teams with incomplete practice logs. A penalty of 500 points is given for teams that do not impound their practice logs. A penalty of 2,000 points is given for every competition violation, with a max of 8,000 points. A penalty of 5,000 points is given for every construction violation, with a max of 15,000 points. A penalty of 10,000 points is given for every run with a vehicle not impounded during the impounded period.

Ties
Ties are broken in the following sequence: 1) Lower Cup Distance Score 2) Lower Vehicle Distance 3) Lower Run Time 4) Lower Run Score of the other run

Resources

 * Several sections of the Scrambler wiki
 * Mark Rober's Video feat. Troy