We have been asked to compete in a United Way Soapbox derby at work. We are up against a few aerospace companies, and some companies with some major engineering. We want to take no prisoners. It is going to look sweet and be very very fast. Here is the help I have enlisted: Composites engineer who can do fluid dynamic models, this guy used to work for Canondale, and has built ralley cars, and human powered vehicles. Industrial Designer to make the body shape and grapics, Myself, model maker, prototype maker, painter, casting specialist, layup artist, machinist. Manufacturing engineer/machinst has machined titanium, incanel,and can make anything out of aluminum. Here are the thoughts we had. Something similar to the Volvo Gravity Car http://www.3autos.com/20050...e-Gravity-Race,3215/ Three wheels a backwards trike design with tilt steering, and aluminum backbone, with a carbon tube front suspension. No more than 2 inches off the ground, weighing less than 77 pounds. The shell will be hand laid carbin fiber. Here is the kicker.....we are fishing reel/rod company. We want to come in there and surprise everyone. Yes we make fishing reels with carbon fiber. Cool thing is our salt water rods stripped down are perfect carbon tubes that will hold tremendous weight. Heck they haul in 400 pound marlins. So any thoughts tips things to keep in mind??

[This message has been edited by Curlrup (edited 10-14-2008).]

Pointers, hmmm go down hill.


Sorry, couldn't help myself.

Ron

Reducing rolling resistance. Low friction bearings will be very important. I

It this meant for one person to ride in or more?

+ One on the low friction bearings, all I can think of right now is very good roller blade bearings cause the spin so fast and barely weigh anything. I'm sure theres something better out there.

Make sure your alignment is perfect (this is going to need to be taken care of in the early stages of development if you are running a fixed axle). Keep your center of gravity low, use big skinny wheels.

Of course the classic; measure twice, cut once.

Good thing is the guy from Canondale has tons of race proven bicycle wheels. We are thinking about doing a carbon fiber disk around the spokes to eliminate the wisking effect through the air. Also being a fishing company we have access to every bearing known to man so if we need to put some ceramic compsite bearings in those bike hubs we will be able to do it. Canondale guy is also the pilot he is small but dense. I was thinking baout enlisting my friend who works for the Renalt F1 team. I wonder if that would be fair?

Brakes?

The single rear wheel will be outfitted with a hydrolic disk bicycle brake, the squeeze handle will be on the steering wheel. Our driver thinks that will be enough. I'm picturing a red hot stream of smoke behind him as he burns the rotor up. I guess we will find out when we do our first test run.

quote Originally posted by Curlrup: ... being a fishing company we have access to every bearing known to man ...

Think air bearings. In this design realm, friction and aerodynamic drag rule ... and not necessarily in that order.

when you've won, you're going to share the design with us, right? RIGHT?

A 350 swap.

I was thinking about a reverse polarity magnetic bearing.......but air could work too.

I guess I could share the design, this won't exactly be for a profit. However, if we ever meet at a race you will take a penalty of a christmas ham being drug behind you.

You want the lowest narrowest profile you can get. The less air resistance the better. Is there a weight limit or minimum weight that has to be met?

quote Originally posted by Curlrup: I guess I could share the design, this won't exactly be for a profit. However, if we ever meet at a race you will take a penalty of a christmas ham being drug behind you.

can we swap it for a big rock? it seems a shame to waste a good ham.
i'm only really interested in the aerodynamics. i have this project in mind, a couple of years down the line. it's going be underpowered, and will need a sleek body.

DON'T USE A SOAPBOX!

quote Originally posted by avengador1: You want the lowest narrowest profile you can get. The less air resistance the better. Is there a weight limit or minimum weight that has to be met?

Max weight without the driver is 170 lbs. Using carbon fiber, and fiber glass for the majority of it we expect weight to be between 50 and 80 lbs.

"Go that way, really really fast. If something gets in your way....turn"

Better Off Dead.

make it electric powered, its quiet enough that noone will know

quote Originally posted by Curlrup: Max weight without the driver is 170 lbs. Using carbon fiber, and fiber glass for the majority of it we expect weight to be between 50 and 80 lbs.

Do you realize that the lighter the car is the slower it will go downhill?

I have never built a sopbox car (the car you are describing sounds quite different then what I was told the rules were for soapbox a couple years ago when I looked into it) but have built numerous wining pinewood cars. Also look up Electrathon cars, I have built a number of winning cars in it.

My input: I am assuming you can do about anything you want and are not bound my soapbox rules. It would be great to see the rule set that you are building to. You win by pushing the limits of what is allowed.

The heavier the car is the faster it will roll down hill. If your track is a constant incline you should speed up all the way. Heavier is faster with this style of track.

The lighter weight the wheels the faster it will accelerate. The higher the tire pressure the easier it will roll.

Take the grease out of the bearings and use ATF or possibly tri-flow. Grease will slow you down. Pull out the plastic lip seal in your bearings, it will add drag.

You really should rethink about a single brake on a single rear wheel. If you go into a skid you will likely flip the car. Seems strange, but I have seen it a number of times on Electrathons.

Right more weight = more potential engery. However, wouldn't maxing out the weight make the acceleration off the line slower? Especially on something that size? We were planning on a few practice runs while adjusting position and amount of weight to get the fastest acceleration, and the fastest speed down the hill. We are hoping to find that butter weight.


Here are the rules:

1. can't weigh more than 177 lbs ( does not include driver )- must have one driver - can have ONE passenger ---

2. no longer than 20 feet and 1 inch,

3. no wider than 6 feet and 1 inch,

4. must be steerable,

5. have some form of brake system.

6. no taller than 7 feet and 1 inch---

7. minimum of 3 wheels -- wheels can be from bikes, trailers, trikes, inflated, or hard wheels,

8. NO, pushing

9. NO PRE FABRICATED CAR BODIES


Pretty lax rules

[This message has been edited by Curlrup (edited 06-10-2008).]

It is my understanding that the heavier the better, period. This would possibly change if there was an uphill or an extended flat track, but for downhill heavier is faster. It is best to build your car overweight and then on check in have them make you remove weight. If their scale is off you will possibly get to carry a couple extra pounds of weight. Every ounce added to the car makes it faster.

1- So you can have 2 very heave riders? Do it.

2- Longer is more stable at speed. Imagine a dragster compared to a jeep on a drag strip.

3-Wide is more stable in turns, but you are not turning. It also crates more frontal surface area to open up the airstream on. Keep it as narrow as you can and still maintain stability.

4-Basic go cart steering will work. Keep the steering ratio very slow. You do not want a small movement from the driver to make a big movement in turning. You are going straight, so geometry is a minor issue. Toe in adjustment is critical.

5- If you are using two front wheels and one rear, brakes go on the front. Also, keep the controls independent left to right. It may help you steer and is far safer if you have a failure you will not loose all brakes.

6- Low is better. The higher it is the higher you need to lift the airstream. Visibility is a minor issue when going straight only.

7- 20' bike BMX wheels. The strongest lightweight ones you can find. Find a set of hubs that use 17mm axles. Maxis hookworm tires work good for us but you may be better off with Kevlar slicks. Use rigid plastic sheets and make spoke covers, both sides of the wheels. At least 100 psi on the tires, more is better. The less the tires touch the ground the better.

quote Originally posted by Curlrup: Right more weight = more potential engery.

But also consider that more weight => more mass, which takes more energy to accelerate. Disregarding aerodynamic drag and mechanical friction, you want to maximize the ratio of "linear" mass to rotational mass ... i.e. heavy body, lightest possible wheels and tires. More formally, you want to have the lowest possible moment of inertia in the rotating components.

[This message has been edited by Marvin McInnis (edited 06-11-2008).]

Make it a tube just wide enough to lay down in, and just tall enough to cover your butt. Put a curved window in the nose of it so you have a near perfect missle shape. You could get fancy and put the wheels inside the body, then less drag.

I would really reccomend braking on the front wheels, if nothing else you wont end up dragging the rear wheel allong as you go blasting into a forest. You might even be able to do a skid steer system, depending on your manuvering needs.

So yea, low, thin, long, pointy. Personally Id probably rummage around and find some sort of premade tube and put a nosecone on it.

I dont know about weight, dont know which is better. Seems to me lighter would have better acceleration, but a slower terminal velocity, or at least a slower accelleration curve. You could build just a lightweight plank basically, then ring some hoops down it and stretch fabric (old bed sheets) over it to make like an airplane body. That would be light and aerodynamic.

quote Originally posted by Marvin McInnis: But also consider that more weight => more mass, which takes more energy to accelerate. Disregarding aerodynamic drag and mechanical friction, you want to maximize the ratio of "linear" mass to rotational mass ... i.e. heavy body, lightest possible wheels and tires. More properly, you want to have the lowest possible moment of inertial in the rotating components.

Correct

quote Originally posted by Electrathon: 7- 20' bike BMX wheels. The strongest lightweight ones you can find. Find a set of hubs that use 17mm axles. Maxis hookworm tires work good for us but you may be better off with Kevlar slicks. Use rigid plastic sheets and make spoke covers, both sides of the wheels. At least 100 psi on the tires, more is better. The less the tires touch the ground the better.

These are our inspriation minus one wheel of course.





Thanks for the tips folks. The design will have 20 inch tires and racing bike hubs. The spokes will filled in with a urethane foam and sandwiched with carbon fiber. When I ahve a rendering for mr. industrial designer I will post it. Brakes will go in front now. It is also expressed elswhere in the entry form that there is to be no other propulsion than gravity. So powering the front is out.

Just a thought .. have you looked at bobsled designs?
Very low center of gravity, tons of research on aerodynamics already completed

http://www.geomagic.com/en/...bobsled/software.jpg

http://www.3dcadbrowser.com...aspx?ModelCode=16300

quote Originally posted by HIOSILVER!: "Go that way, really really fast. If something gets in your way....turn" Better Off Dead.

I was thinking that too!
.
.
1. can't weigh more than 177 lbs ( does not include driver )- must have one driver - can have ONE passenger ---

Have as much of the weight over the front tires as possible or maybe in front. Have them lay next to each other, facing forward.

6- Low is better. The higher it is the higher you need to lift the airstream. Visibility is a minor issue when going straight only.

Have them look down through a mirror to the front.

20" wheels? How about 80mm? http://www.streetski.com/ Get 4 of the StreetSki FreeRide DHXRACE Skates, connect them with your fishing rods, add aerodynamic body with tubing made with your rods and increase weight to max.

[This message has been edited by Gokart Mozart (edited 06-11-2008).]

The Volvo sar is a very good design. A few of the corners could be smoothed, but as an overall it is great.

Here is some of the folks we will be up against

NORDAM (aerospoace)
Spirit Aerospace
Lufthansa

I guess there are a few others who have engineering and the means to build something awesome. So this is going to be a tough one.

Any updates?

Bump

Well I think seeing that your a fishing company get a canoe/small boat and stick some wheels on it and hold on. Way more fun and easier

------------------

You are talking about an air displacement design, not high speed aeronautics. A simple equal elliptical wing designed body is the long favored body shape.

Your wheels need to be large as is practical to lower the rpms, and the tires need to be very narrow and preferably hard. Don't worry about lowering the car. It is more important to have the air moving at equal speed over all of the body panels. You don't want to compress air under the car.

The wheels indeed need to be filled. You can fabricate discs that attach to spokes and create low drag. Incidentally, light wheels, heavy body.

Tall and narrow body allows your "skinny" driver to get behind the air foil to eliminate any wind agains his/her body if they are sitting up. You build the body to fit the driver.

If you have a length of 20 ft max to work with, you can build a prone design with a plexiglass windscreen molded into the body shape. Remember that the longer the body of a displacment boat, the faster the boat can travel. Same thing for a displacement air racer. The wing shape can be either vertical or horizontal but favor the wing over a tube, or if you can do it, an elongated tear drop.

As for the weight, you need to build it with a mind to add weights to achieve both your maximum weight and weight balance. Generally weight which is added forward so the weight distribution at the wheels is heaviest on the front wheels, will get you down the hill fastest. Your wheel base and steering ratio are pretty important. The vehicle, if designed incorrectly will become unstable if steering is applied. There needs to be some forgiveness in the steering assembly.

As for bearings, low friction is the order of the day. Teflon and light weight oil will help. Bicycle bearings are actually well designed. Using them is not a mistake, but using a heavy grease is.

Lastly, try building a small wooden model and work from the model.

Hope these suggestions help.

Arn

I say go a completely different route.

Have this guy drive it:



Then just build the vehicle around him.

Don't know if I want to bump this after that last pic, but I will.