SPRING 2006
ENGINEERING FUNDAMENTALS 151 PROJECT
Andrew Z. Jackson
Curtis Huddle
Josh Kerr
Sam Moss
Objective
To turn off that stinking alarm that wakes us up for Engineering Fundamentals 151 every Monday, Wednesday and Friday morning.
Process and Design
The system is designed to turn the alarm clock off. Once the alarm sounds, the winding dial on the bag unwinds, wrapping a string that has been strung around the base of the dial. The other end of the string is attached to the trap-tripping mechanism we like to call, the “trap-tripper.” Once the clock’s dial winds enough to take the slack out of the string, what results is that the trap begins to pull follow the string. We placed a small weight next to the trap, which prevents it from scooting after the string. Because of the opposing force, the string pulls the trap-tripper, tripping the rattrap. The bar of the trap has a string tied to it, which is also tied to the middle of a domino. That domino is one leg of a two-legged domino structure. It stands parallel to another domino; both together hold a single domino, which lay across the top. Another weight identical to the other, lay on top of the horizontal domino. A string runs from the weight to the underside of a clamp that supports a Hot Wheels Ferrari. The string is set with enough slack so there is no tension on the string, resulting in no force pulling downward on the lever resisting the car.
Once the trap is sprung, the string attached to the domino leg pulls the domino, causing the simple structure to fall, which releases the weight, pulling the lever to release the car down the track. The car then accelerates down the track, continues around a curve, and heads towards a jump. The car continues over the jump and flies into the back of the clock, hitting the button to stop the alarm.
The point? It allows the student to continue sleeping without worrying about turning off the alarm, and getting up in time to make it to Dr. Bennett and Professor Schleter’s 151 lecture.
Calculations
The first thing that happens is the winding.
We didn’t count that but the next thing is the spring goes off and pulls out the block. The force of the spring is 9.5 lb. We estimated the distance of the trap bar to the middle of the trap to be 3" and multiplied that by pi. Then we put that into the equation 9.5 lb * 3" * pi =7.46 ft-lb.
The next thing to happen is the weight on top of the dominos drops. Its height is 2.25". Its weight is 6.7 ounces. Its mass is .013005 slugs. Its potential energy equals 2.25" * .013005 slugs * 32.2 ft/s2 = .079 ft-lb.
Next is the car running down the track. The height is 36" and the mass of the car is 1.7 ounces or .0032997 slugs. The calculations for velocity which are used in the next calculation are v1=(2 * 32.2ft/s2 * 3ft)^1/2 =13.9 ft/s. Potential Energy equals mgh = .0032997slugs * 32.2 ft/s2 * 3 ft = .31875 ft-lb.
The last thing that happens is the car goes from the ground up the ramp. The velocity as it leaves the ramp is v1-v2; v2=(2 * 32.2 ft/s2 * 2")^1/2 = 3.2767 ft/s; v1-v2=10.6235 ft/s. The KE=.5 * (.0032997 ft/s) * v22 = .017527 ft-lb.
All of the works added up are .017527 ft-lb + .078516 ft-lb + .31875 ft-lb + 7.46128 ft-lb = 7.876066 ft-lb
The work in = .8 lb * (.25/12) ft = .01666666667 ft-lb.
Efficiency=Work Out/Work In = .0166666666667 ft-lb/7.876066 ft-lb = .0021161157*100 = .21161157 % efficient. The efficiency is very low because the system is doing a lot of work just to push a ¼” button.
Design Process
Our design was not conceived by any preexisting thoughts. We simply came up with the idea. Initially, we were going to attempt to use balloons to lift a gate, releasing the car. However, we scrapped the idea because we figured there wouldn’t be a realistic way to control the release of the balloons.
Bill of Materials
All of the materials we used in our design were not bought, but brought from our own household. Our estimates for the price of each of the materials will be the price of the same item in a general store today.
Set of Hot Wheels track: $7.00
One rattrap: $2.00
One Hot Wheels Ferrari: $0.89
An ancient alarm clock: $5.00
One roll of string: $3.00
A box of dominos: $1.00
Two weights: $3.00
Success on the first try: Priceless
Total Price: $21.89…+ tax
Conclusion
We were impressed by the success on our first and second tries, the only two attempts we made in class. In essence, we had a 100% performance rate. We learned that there is more work involved to turn off an alarm clock using a complex process than initially suspected, as well as an incredible usefulness.