Your science teacher has organized a toy car race made with a mousetrap: the one that can go farthest wins, and of course you want to win. These simple steps will teach you how to build your own toy car and will help you with useful tips to reach the greatest possible distance in the shortest possible time.
The ways to achieve maximum distance are: reduce weight, reduce axle friction and use a long lever for the best mechanical advantage. Give the car an aerodynamic, tapered and elongated shape. Use an axle with a narrow diameter and large diameter wheels. Each time the axle turns, it spins the wheel - a wider wheel means the car can go farther for each turn of the axle.
Using a longer lever than the original mouse trap rod increases the length of the rope used and conserves energy (slows down the trip of the trap). The machine moves slowly, but goes farther because the spring force is used more efficiently.
Even if the materials you will use will be different than those proposed, you will still have to deal with the limited force of the spring, you will have to overcome the friction, use the traction, take advantage of the "mechanical advantage" and minimize the mass to reach the maximum distance with your racing "car".
Steps
Step 1. Create a lightweight body for the toy car
The trap and the wheels are attached to this "body". As you can see in the pictures, the bodywork can be smaller than the mousetrap. Reduce it: the lighter the structure, the better! However, keep in mind that styrofoam boards break more often than wooden boards.
Step 2. When placing the trap check that the spring is facing the correct direction so that the lever arm rotates forward
Make sure the trap is as far away from the front wheels as possible without touching them. The greater the distance between the trap and the wheels, the better! But up to a certain point.
Step 3. Know that wheels are a determining factor in distance
No matter the size or the number of front wheels, you can even have just one. As for the rear ones, however, make sure they are as large as possible, while the rear axle must be as thin as possible. Two old CDs work pretty well. A hydraulic washer can be used to reduce the size of the hole in the middle of the CD (to make the axle fit better).
Step 4. Create traction by covering the wheels with tape, rubber bands or balloons
If they are slippery, energy is wasted. Adding tape to the rear axle can reduce rope slippage.
Step 5. Use glue instead of screws to attach the mousetrap to the structure
The glue will hold just as well and the screws only add unnecessary weight! Make sure you have positioned everything optimally before gluing. With a screw you can still change your mind, the glue on the contrary is practically permanent.
Advice
- If the rope is just wrapped around the axle, the car can barely move. Adding a larger drive hub can improve towing capability. In some images there is a rubber tire on the axle, this acts as a "gear" and reduces the slippage of the rope.
- You can reduce the bump by using a piece of sponge to simulate cheese. This reduces the bounce of the car when the lever arm snaps onto the base.
- You can reduce friction on the axle by minimizing the surface of the support in contact with the drive axle. A thin steel support has less friction than a hole in a block of wood.
- If you buy a gasket bring a CD with you and drive it to the store. It can help you get the right size on the first try.
- Use the longest lever available to extend the mouse trap arm as much as possible and thus allow more turns of rope. The antenna from a broken portable stereo was used as a lever. Anything that is long, light and not too flexible will work as leverage.
- You can see the work completed by other students on the] Mouse Trap Car Challenge website.
- Increase friction where needed by using a rubber tire or tape around the axle where the rope is wrapped. The rope should turn the axle and not slip.
- The alignment of the axles to the supports is essential to reduce friction and increase performance.
- Reduce the bulk by using a simple lightweight wood for the bodywork. Reducing mass also reduces friction on the axle supports.
- Increase the friction by covering the string with candle wax. By waxing it, the rope has better traction on the axle.
- Reduce friction by applying Molykotè®, a powdered lubricant based on molybdenum disulfide, on the axles, wheels and spring of the mousetrap.
Things to Consider
- Axle - wheel ratio: To cover a greater distance use large wheels and a small axle. Think of the rear wheel of a bicycle; a small transmission gear and a large wheel.
- Inertia: how much energy does it take to start your car? A light car requires less energy. Reduce the mass of your vehicle to cover a greater distance.
- Energy release rate: If the energy is released slowly, the force is used more efficiently and the machine will go further. One way to slow the release is to extend the lever arm. A longer arm travels a greater distance and allows for more turns of rope around the axle. The car will go far, but slower.
- Friction: minimize the friction on the axle by minimizing the contact surface. A thin steel support was used in this example. Initially a hole was used through a block of wood to support the axle. This method has been abandoned because the larger surface area causes the machine to use energy to overcome friction rather than drive forward.
- Traction: this is what friction is called when it is used to one's advantage. Friction should be maximized where necessary (where the rope wraps around the axle and where the wheels touch the ground). Slipping rope or wheels mean wasted energy.
Warnings
- There is a limit to the amount of energy available: the force of the spring. The machine presented is close to the maximum. If the lever arm were longer or the wheels were larger, the machine would not move at all! In this case the energy release can be adjusted by shortening the antenna a little (i.e. shortening the lever).
- Be careful when using tools, cutting wood, or handling any hazardous materials. Ask for adult supervision when needed.
- Mouse traps are dangerous. You could break your finger. Use adult supervision. You could get hurt and break the trap!
