PT2.1 Engineering Goals

Competition Criteria

     - Car can only use the mousetrap as its power source

     - Car has to fit following dimensions
       Length: 30cm
       Height: 15cm
       Width: 15cm

     - Mousetrap must set of from rest position without any push or pull from student

Engineering Objectives

     We decided that the way we wanted to get our car to travel the furthest, speed was not an issue, rather the efficiency of our spring release mechanism to transfer rotational energy to the axles was more important.

Ideas

Idea #1
     Our initial idea was to have an escapement system that slowly released the wound up spring of the car with a pallet fork that flips from one side to the other, stopping the gear in periods.

     Using the physics simulation app Algodoo, we developed a mechanism to do just that, inspired by escapements found in mechanical time pieces. Both gears in the video are set to the same speed and torque.

video


     After we had started building the car, we realised that the feasibility was very low. We did not have the time to fabricate a calibrated pallet fork out of a strong enough material in enough time. The pallet fork in this situation had perfectly bite into every teeth of the gear in order to stop/slow it down.

Idea #2
     A gear train of 2 or more could be used to increase amount of rotations for every little distance the spring bar releases. This would mean having a large gear connected to the release mechanism which would then connect to a smaller gear. This is increases the amount of rotations per minute (RPM) e.g. A larger gear with 30 teeth that drives a smaller gear with 10 teeth would have a ratio of 3:1. For every 3 times the small gear rotates, the large gear makes 1 rotation.


Original Sketch

Energy Efficiency

     In Idea #1, the escapement mechanism is designed to slowly release the energy so that our car would be able to use up all of the spring's energy, without the help of friction, that would waste energy. If there was not a release system that slowly released the spring, a lot of the energy may be wasted as the wheels may slip/burnout on the ground, and friction may slow down the product RPM.

     For Idea #2 however, we used gears to help increase the product RPM per amount of spring released through the gear train. (reasoning explained above)

Speed

     Speed was not the main point of concern, we were more concerned with how well our car was able to use the available energy. But, using a gear train such as idea #2 would help increase the wheel's RPM, therefore increasing speed.

     In Idea #1 however, the set up was not designed to travel fast at all, rather to travel slowly so as the be more energy efficient (reasoning explained above)

Torque

     For both ideas, the outcome torque would be low, in order to extend the amount of time the car would run for. Therefore, for our car to have enough force to move, it would need smaller wheels. this would increase the product RPM by a lot, as less force is used to rotate the wheel and would then allow the wheels to roll faster with lesser force.

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