Mr. Sexton Engineering Technology CO2 Dragster Cars Mr. Sexton Engineering Technology

Purpose of CO2 Activity Understand how a CO2 car works Design your CO2 car Build your CO2 car Race your CO2 car

Overview • Intro to Racing CO2 cars • Engineering Principles • Student examples • Designing your CO2 Car • Manufacturing your CO2 Car

Intro to Racing CO2 cars 2 Cars are set up Cars ride on guide wire from start of track to end of track Co2 cartridge is punctured –propelling car forward Two cars race Cars go through end gate light goes for fastest car Race time is recorded for each car

What do you use for the track? Many times when people are new to CO2 racing, they hear about cars running on a "track" and think that a track specially made for CO2 cars is needed to race them. We will race our cars on the floor. You can easily build a simple and inexpensive race track. Not as good, but a lot cheaper

CO2 Racetrack The only track required is 50# test fishing line. Fishing line is used as a guide line that the eye-hooks on the bottom of the cars attach to. The fishing line runs between the start gate and the finish gate We will likely run our races using only fishing line along the concrete floor of my lab. The smoother the surface, the faster the times will be.

length of the track The length of the track is also important. You need to have at least 60 feet without any obstructions. Any shorter distance than this, and the cars will destroy themselves upon finishing a race. The optimum track length is 66 feet (20 Meters), which is in scale with real dragstrip lengths of a quarter mile.

How fast are these things? Up to 60 mph (100 kmh)

Engineering Principles The following Engineering Principles Relate to how and why a CO2 car works Newton’s Laws of Motion Mass Drag Friction

Newton’s 2nd Law of Motion greater force = greater action. Acceleration is dependent upon the mass and force of the car. F = ma F = force m = mass a = acceleration For a fast car, you need: Big force Light car (mass)

Mass The Balancing Act: – Advantages: Cars with less mass go much faster. – Disadvantages: Cars with less mass are less stable and less durable. Does takes more or less force to push 40g than it does to push 130g?

Mass F = m* a Assuming force is the same F = 40 *1 F = 130 * 1 F would be larger with the F/40. (A piece of cake divided by 40 parts or 130 parts, which gives you a bigger piece of cake?) Therefore, the smaller mass requires less force.

Acceleration Acceleration is produced by the CO2 gas cylinder. The CO2 canister produces thrust when you puncture it – propelling the CO2 car forward It works similar to sticking a pin in a balloon - The balloon is propelled around the room by the thrust created by the escaping gas.

Forces of Resistance Drag (from air resistance) (FW) Friction

Drag Take a piece of wood, slap wheels on it, shoot it down a track at 60 MPH and the air rushing over the body and wheels will try to slow it down. Scientifically this is called drag: the resistance of wind moving over an object.

Minimizing DRAG The Balancing Act: – Advantages: Aerodynamically shaped cars have less drag so they go faster. – Disadvantages: Aerodynamically "clean" cars are more difficult to build, but worth the effort

Friction Friction is a product of gravity • On a CO2 car, Friction occurs primarily in three places: Between the wheels & the ground. Between the axles & the car body. Between the eye-hook & the fishing line.

Minimizing Friction Make sure the axle & tires freely rotate. Make sure the wheels are not rubbing on the car body. Be sure to install your eye-hooks properly. Poorly aligned eye-hooks are often the cause of a slow car.

What's the best design for a CO2 car? Your Car must meet the size and dimensional requirements of TSA. The best design is the one that wins. There is no "one design" that is best. Generally, the two best indicators of a good car are clean aerodynamics and high craftsmanship. Often, really good designs that are built poorly will loose to so-so designs built well.

Designing your CO2 car Step 1: Obtain the proper paper from me

Designing Your CO2 Car Step 2 Brainstorming (think about what you want your car to look like) Sketch 6 different possible design ideas Create drawing on the lined paper Remember, 1 square = 2 mm

Designing Your CO2 Car Step 3 Complete technical drawing for CO2 car You must have a high quality, accurate drawing Drawing must be 1:1scale (actual size) Identify the axles Check your car against the TSA specifications

Designing Your CO2 Car Step 5 Step 6 Step 4 Get instructor to look over your drawing. You must get instructor sign off before beginning to manufacture the car that you designed Step 5 Locate a piece of copy paper Trace your design onto the copy paper. Use the light table to do this. Step 6 Cut-out the tracing that you made Obtain a blank piece of balsa from me

Overview of the CO2 Car Manufacturing Process http://co2.technologyeducator.com/cars/babybro.htm - Sample CO2 car being made http://co2.technologyeducator.com/steps/steps4.htm - Step by step overview

Manufacturing Your CO2 Car Step 7 – Transfer your design to the Balsa blank Tape the cut-out onto the blank. Trace the outline onto the car. Use a Sharpie. Mark the axles.

Manufacturing Your CO2 Car Step 8 - drill the holes for the axles (using the drill press). Make sure the axle holes are in the right spot and are straight The holes should be perpendicular to the center line of the car and parallel with the bottom surface of the car. * Take care to make sure these holes line up evenly and are drilled accurately. Crooked holes mean a slow car! Use a drill press and take your time! *

Manufacturing Your CO2 Car Step 9 - Using the Bandsaw, cut out your shape. When using the band saw to cut curves, you must use relief cuts (or you will break the band). Follow the shape that is on the template that is traced on your CO2 car. Follow all safety precautions. Clean your mess

Manufacturing Your CO2 Car Step 10 – Shaping and Sanding Use a rasp or wood file to remove band saw blade markings and to round corners and edges. Also to begin the smoothing process. Hand Sand your CO2 car until you have removed the file marks with 100 grit sand paper. Hand sand with fine sand paper (>150 grit) to remove all scratches. Always clean your mess.

Manufacturing your CO2 car Step 11 – Finishing Finish cars with the acrylic latex paint we have Every brush must be cleaned out. Loss of daily points if not done so

WCHS Policy We will paint the car in class. We will not assemble with wheels, screw eyes, etc.. Until right before the race.

CO2 Designs This car was created by John Vice, Mr. Sexton’s student teacher.

CO2 Designs

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Manufacturing your CO2 car Step 12 – Assembly before the race Assemble all the parts of the CO2 car Wheels Axels Body Eyelets CO2 cartridge

CO2 Cars If you need more info on the Design and Manufacturing Process check out: http://co2.technologyeducator.com/steps/steps1.htm