CO2 Dragster Design

Technology Education Eighth Grade SSA+S Mr. Footland

Dragster Unit Outline

What is CO2 and what is a CO2 dragster? Background information Engineering principles Design your car Build your car Race!

What is CO2

CO2 is a dry gas with properties similar to the air you breath. CO2 gas is actually carbon dioxide. It can be compressed or perhaps squeezed into cylinders or cartridges.

What is a CO2 Dragster?

When the cartridge is placed into your car and a hole is poked into one end of the cartridge, the compressed gas rapidly escapes out of the hole.

The gas will continue to escape until the pressure inside the cartridge is the same as the pressure outside the cartridge.

Newton’s Third Law

For every action, there is an equal and opposite reaction.

As to Newton's third law.... The gas is forced out of the cartridge in one direction directly out of the hole in the cartridge.

Background Information What is the Best Design?

The best design is the one that wins. I know that's not what people want to hear, but it's true. There is no "one design" that is best. Generally though, the two best indicators of a good car are clean aerodynamics and high craftsmanship. I've seen really good designs built poorly lose to so-so designs built well.

Background Information Design Tips

Everyone wants to design a CO2 car that will scream down the track and leave his or her classmates in the dust, right? In order to do well, you have to know what your doing, and this requires some homework.

Remember: It's your car. If you don't care about any of this, then you just won't do very well, giving your classmates the power to crush your car come race day. Can you say embarrassment, boys and girls?

Making a super fast car involves learning about the principles behind CO2 cars, the engineering factors involved, and the envelope the project must remain within. Read, learn, and crush the opposition!

CO2 Car information

Although CO2 cars are raced 2 at a time like fuel dragsters they ride differently.

Run on the same principle that propels rocket or jet powered land speed record vehicles.

More info can be found in your design packets.

Engineering principle #1: Mass

CO2 cars are quite a bit lighter than barbells but they still have weight or mass.

What do suppose would be better for a car design lighter or heavier?

How would you achieve a lighter or heavier design?

Principle #1 Balancing Act

Advantage.- Cars with less mass go much faster.

Disadvantage.- Cars with less mass are less stable and less durable.

Engineering Principle #2: Drag

Which shapes do you suppose would have the least amount of Drag?

What would be another way of saying this?

Engineering Principle #2: Drag

Take a piece of wood, throw wheels on it, shoot it down a track at 40 MPH and the air rushing over the body and wheels will slow it down.

Make the body as aerodynamically clean as possible.

Principle #2 Balancing Act

Advantages: Aerodynamically shaped cars are less “draggy”, so they go faster.

Disadvantages: Aerodynamically “clean” cars are more difficult to build.

Engineering Principle #3: Friction

Due to gravity, everything has friction.

CO2 cars have 3 sources. – Wheels and ground – Axles and car body – Eyehooks and fishing

line. Although you can’t get

rid of friction you can reduce it.

Engineering Principle #3: Friction

What are some ways that we can reduce friction?

Principle # 3 Balancing Act

Advantages: A friction filled car is easy to build. A friction filled car is slow, so it tends to be more durable.

Disadvantages: Reducing friction takes more time and patience.

Engineering Principle #4: Design Envelope

In the real world everything has limits.

Our cars have min. and max. dimensions.

Without a design envelope competition would be unfair and unsafe.

Principle #4 Balancing Act

Advantages: Cars that follow a design envelope can compete equally and safely.

Disadvantages: Cars may go faster without following the specifications but will be disqualified. (so they won’t race!)

Designing your car!

Step # 1: Thumbnail Sketches

Thumbnails are quick, sketchy, doodles.

They don’t need to be perfect or have too much detail.

The purpose is to get your ideas on paper.

Step # 2: Rough Sketches

Rough sketches are more detailed than thumbnails but are still “rough”.

They should be sketches but be neat, have detail and refine your ideas into a drawing that you can use to discuss your ideas with classmates.

Step #3: Working Drawings

1st pick your favorite rough sketch.

These are final drawings that will be used directly in the construction of your cars so they must be neat and accurate.

Step 4: Drilling Axle Holes

First we will tape our working drawings onto our block of wood.

Using a 3/16” drill bit we drill the front and rear axle holes.

Very important not to make crooked holes.

Step 5: Cutting

1st we will cut the side view using coping saws.

Careful not to over cut, you can always sand the last little bit.

2nd we cut the top view into the block

Step 6: Shaping

We will use wood files and sandpaper to round and smooth your edges.

After you get the shape that you want and it is smooth we are then ready to paint.

Step 7: Painting

Using either a dowel or paint stand we will be able to paint our cars without touching them.

Remember a couple light coats will dry better and be more effective than a really heavy one.

While waiting for paint to dry you can get ready for assembly.

Step 8: Axles

Using a hack saw or pipe cutter we will cut our steel axles to length.

Axles should be the same dimension as your car body at the axle hole plus an extra ½”.

After cutting sand the axle to remove any pitting.

Step 9:

After your car is cut out, sanded, painted, and assembled it is next time to verify that we followed all the design contraints from the design envelope and give it a “dry run” to see if it goes straight and smooth.