This is a detailed procedure for creating the prototype dragster and the actual wooden dragster. As of July 2012, this page is still under construction. Look for added details and pictures in the near future.
Before you begin, complete the design process before you begin working on the prototype. That is basically the whole point of the class, learn about your topic, create a design based on what you have learned and then build that design. Don't have a final design? Then you are missing a fundamental part of the class. Besides, how are you going to ensure that your prototype and wood dragster are the same if you don't have a singular design to work from? - Once you have finished your design, get it graded and approved by Mr. E. Then you can retrieve a polystyrene blank, the pink stuff. This is what you will make your prototype out of.
- The setup the prototype blank is important, there are some parameters your dragster needs to fit. The location of the axels is important, if you don't place your axel holes 1/4" up from the bottom of the blank, then your dragster won't fit in the launcher like all the other race cars. This is less important on the prototype, but extremely important on the actual wood block, so try to get it right on the prototype. Also, you can cut through the hole in the back of the dragster. Mark the location of the hole on the side of your prototype. After you have established the axels and engine hole, you can layout your design on the side of the blank. DON'T draw the top view on now as it will be cut away at the band saw, you can draw it on later.
- HINT: Over the years I have found that students tend to cut too much off of the prototype, try to make sure you don't make this mistake. Perhaps you can oversize your design a little bit when you transfer it to the profile on the blank to allow for this tendency.
- Drill the prototype, make sure you have the holes placed 1/4" up from the bottom of the blank, remember?
- After you have drilled, you can cut the profile of the prototype on the band saw. CUT OUTSIDE YOUR LINES. Don't cut on your lines, you need to outside your marks so you have some material to sand back.
- File and/or sand the cut surface, then draw your top view onto the top of the prototype.
- Cut the top of your prototype on the band saw.
- File and/or sand some more to finalize your design.
- Measure and record the drag in your packet.
- Measure and record the volume in your packet.
- Calculate your estimated mass and speed on the prototype worksheet.
- See the Prototype page for more information on drag, volume and speed calculations.
- Once you have a prediction recorded on your prototype worksheets, you can setup your wood blank. The setup is similar to the prototype setup except that you need to a great deal more precise. Establish markings for the axels and the engine hole on the side of the wood blank. Transfer your profile design from your working drawing to the blank.
- Drill the axel holes on the basswood blank.
- Cut the profile on the band saw. Remember to cut outside your marks so you have material to sand later.
- Sand the dragster at the BOSS and disc sander. Make sure you sand away the blade marks, ripples in the wood left by the band saw blade. File and sand as needed.
- Transfer the top view onto your dragster and cut again.
- HINT: When you transfer the design to the top of your dragster, be sure to keep track of where you drilled your axel holes. You want the axels to be at the wide part of the front, you can easily misalign the wide part and the axels and have a major goof on your hands.
- Again, sand and file as needed. Some students will take a day or two just sanding their dragster. Make sure you don't skip this. You need sand away flaws in the wood or they will be visible through the paint later on a detract from the overall quality of your work. If you can't sand part of your dragster with a machine, you can use the rough 100 grit sand paper.
- Up to this point, you've been sanding your dragster to remove flaws in the wood. Once ALL the flaws have been removed, you want to prepare the surface for painting. You want your dragster to be as smooth as possible for painting. To make the wood smooth, sand with the 100 grit sand paper if you haven't already. You might think the surface to be smooth after the 100 grit sand paper, but you can get it smoother. Now sand with 220 grit sand paper. The higher grit paper will remove less wood, but the resulting surface is noticeably smoother. Now sand with 400 grit paper. The higher the grit, the less wood get sanded off, but the smoother the wood gets. It is important to note that you can skip right to 400 to save time. 400 grit paper can't remove scratches or blade marks from your dragster, you need to use the lower grit paper to remove flaws. You also can't back track to fine tune, if you have sanded properly, stepping through the three grits, and you want to round an edge, you use 100 grit again, but you'd need to step back through 220 and 400 again.
- After you are don't sanding, you should blow off any sanding residue that might be on you dragster before you paint it.
- Plan you finish, too often we have students that plan poorly and ruin their dragster because they don't paint in the proper order and aren't careful enough about what they are doing. You should plan on painting your car a bright color like yellow, red, orange, or pink. Avoid the aspiration of painting your car dark blue or even black, how well will the Sharpie show up on a black car? If you are planning on painting multiple colors you have to plan for that. Painting more then one color means that you'll need to mask off one color before you paint the second, hence "masking tape." Maybe you want to paint your car blue and yellow or green and white. Can you paint whole dragster blue first, mask it, then paint yellow over the blue? No, yellow won't cover over the blue very well, you'd need two or three coats of yellow and even then it would look a little drab because of the blue underneath. You'd want to paint two coats of yellow on the car first, then mask the parts of the body you want to remain yellow and then paint blue. The blue will cover the yellow much better and you may even get it on in one coat. When planning for multi-color cars, plan to paint the lighter of the two colors first, then paint on the darker color and you'll be much happier with the results. A word on masking, you'll want to make sure the edges of the tape get pressed down and smoothed over really good. If you tear the tape, that ragged edge will make a similar impression on the body of the dragster.
- We use spray paint to paint the dragsters. Mr. Eldred will retrieve your desired color from the office. You'll need to paint the very back of your dragster first. Hold the dragster at the front and spray the back on an angle so as to not spray onto your arm. Then place the dragster on the painting stand and paint the rest of the body. When painting you'll need to stay 7 to 10 inches away and don't linger on any one spot too long. If you spray too much paint on, it will run down your car and drip, that's very bad. Don't try to get the paint 100% solid the very first time. You will paint your dragster at least twice. Once you paint your dragster during class, you put it up to dry and you can't handle the dragster again during the hour, it needs time to dry.
- When you come in the next day and retrieve your dragster from the drying area, you may notice that the body is a little rough. Lightly, very lightly, sand the painted body with 600 grit sand paper. If you are removing paint from the dragster, you are sanding too much. This should be the last time you'll be sanding the body of the dragster. Blow off the residue as before and prepare for your second coat of paint.
- Paint your second coat of paint and allow to dry as before. You shouldn't need to sand after your second coat of paint.
- Draw number, sponsor and other embellishments on with different colors using the Sharpie markers. Try to make your dragster as attractive as you can. It should be bright and flash. Most importantly, it should be something you can be proud of and want to put on your book shelf at home.
- Now you can start to add the hardware to your dragster to prepare it to race. The first thing you'll want to add eye hooks on the bottom of the dragster. The hooks are used to control the dragster as it races down the track. When we race, the dragsters are strung up on fishing line that run the length of the track. This fishing line is what keeps the cars on the track. If we didn't do this, the dragsters would likely veer off the track and kill students. You could twist the hooks into the bottom of the dragster by hand, but that would be difficult. Instead, take a hammer and small nail and tap a small starter hole for each of the hooks. You'll want to place the hooks as far apart as you can get them in the center of the body of the car. You should also be certain not to place the hooks directly under the axels you drilled. The hooks are long enough to poke through the axel hole interfering with the operation of the wheels.
- Before you install the wheels, use a steel axel to check the your axel holes. You want to make sure the axel can move freely in the axel hole. If the hole seems too tight or the axel catches somehow, you'll want to use the hand tap tool with the drill bit on it to ream the axel holes to clear them out.
Also before assemble the wheels, you should sand off the little nubs that are left on the wheels from the manufacturing process. These nubs will interfere with your dragster and could prevent our car from finishing the race. Use a file or rough sand paper the grind the nubs off, be sure not to create a flat spot on the wheel when you do this.- To install the wheels, place the dragster on it's side on a piece of scrap wood and place a steel axel in the hole. Now take a wheel and lightly tap it onto the axel with a hammer. Hold the wheel in place and turn the dragster over and tap on another wheel. When both wheels are on, make sure the wheels spin freely. If the wheels don't spin, you probably pressed the wheels together too hard squeezing on the body of the car. Pull and twist on the wheels to loosen them up. If you find that the wheels are too far apart, too wide based on the width of your car, you can push one wheel in, letting the excess axel hang out one side of the dragster. This excess axel can be trimmed back with the mini bolt cutters. Repeat the operation for the second set of wheels. Set your dragster on the table to make sure your hooks don't touch the table, if they do, twist them in a little more.
- Now that the dragster is complete, you can put your dragster in the wind tunnel and measure the drag. Make sure to record the drag in your packet and also the official time sheet for the race.
- Finally, measure and record the mass of your completed dragster on the scale. Record the mass on both your packet and the official time sheet.
- Place dragster in the box so it is ready to race the following day!
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