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Fasttrack
05-01-2006, 05:31 PM
What would you guys recommend as a good material to build an HMV car? I know i posted here previously about high mileage vehicles - the goal is to make a super efficient gas vehicle (essentially a go-kart) and i've been looking around at aluminum. I'd really like to find the dream alloy - cheap, easy to machine and weld, and super lightweight. I know there is no such thing :) but what kind of recommendations do you guys have? I don't think i have a particular priority as to which quality i'd preffer - i guess the cost is the biggest issue at this point. Thanks for any input!

Millman
05-01-2006, 05:43 PM
FT, try to find Upsadasium in larger quantities; all I can find are "Billets" of 2.546oz., so it would take quite a few even for a go cart. I like the anti-gravity properties. Keep up the good work.

Weston Bye
05-01-2006, 05:58 PM
All materials have trade-offs. Aluminum - for all the qualities you listed, but did you ever squash an aluminum beer can with your bare hand? I know that cars, like airplanes, are not supposed to crash, but what if...?

Most people (other than bikers) perfer to have a little mass around them for safety.

Seems these days that cars are subject to conflicting requirements; transport yer carcass from point a to point b, but cocooned in safety, in air conditioned comfort, entertained, informed and with convenient cupholders in any and all possible positions. I maintain that drivetrain efficiency has reached a plateau and now the automakers add cupholders and entertainment items to "improve" the vehicle.

Twern't much help, mostly rant. Sorry.

lbender
05-01-2006, 06:11 PM
Fasttrack,

AZ31B-H24 will give you lightweight, easy to weld and a joy to machine. Sorry about that fourth thing.

http://www.magnesium-elektron.com/data/downloads/DS482.pdf

topct
05-01-2006, 06:19 PM
All I will say is Aluminum alloys like the steel alloys we work with are made with differant properties in mind. Depending on there use.

There is no one alloy of aluminum that is perfect for everything. Niether is there one kind of steel, brass, whatever.

Study the properties and uses of the most common sorts. They are the cheapest and therefore most available.

Look up, the 2XXX, 5XXX, 6XXX, and 7XXX series.

Duct Taper
05-01-2006, 06:36 PM
Fastrack, check the Formula SAE rules regarding materials. This is the guide for all the university teams that get involved in building the Formula SAE race cars and you probably would be doing basically the same thing. Here is the Formula SAE website and the PDF of the rules:
http://www.sae.org/students/fsaerules.pdf

Evan
05-01-2006, 07:08 PM
I just had a look at the regs. The roll bars must be steel, no exceptions. The rest can be what you like but you must supply information and documentation as to the strength equivalent to specified steel sections.

I would use graphite epoxy spars for many of the components. They aren't extremely expensive and are readily available as power stunt kite spars in sizes big enough to be useful.

Fasttrack
05-01-2006, 08:27 PM
wow the sae competition is pretty intense - ours only requires three wheels, a body to enclose driver (can have open or closed style cockpit) a roll bar of any material that can handle a static load of 280 lbs, kill switches, a 50 foot turning radius, ability to stop from 15mph in 15 feet (or something like that) and the vehicle must not tip w/ driver and vehicle at some degree incline (again can't remember specifics).

Evan- i like the idea of the graphite epoxy resin - a team this year used graphite resin poles to form there body; the deflection in the poles allowed them to form some really nice curves. After everything was in place they covered it with monocoat. That stuff really works great for the body - we've been using some similiar stuff donated to us by a place that uses shrink wrap to store boats over the winter.

p.s. where can i find that upsadasium? Anti-gravity sounds like a pretty sweet idea... :D

QSIMDO
05-01-2006, 08:34 PM
A good place to start is the "Racer's Encyclopedia of Metals, Fibers and Materials" by Forbes Aird and published by Motorbooks International.

Border's, Barnes & Noble maybe even Amazon will have it.

Fasttrack
05-01-2006, 09:01 PM
Great! Thank you for the suggestion - this kind of leads me off on a tangent which i may post as a thread later on, but anyone have any suggestions for good reading/reference material for designing cars, engines, etc? Any kind of Audel's type handbook for racing? That would be awsome; i've looked around at the local book stores but haven't turned up anything besides Monster Garage Weld Anything and etc type books.

Evan
05-01-2006, 09:18 PM
If they were able to deflect graphite epoxy rods they must have been using tiny sections. Don't confuse it with the same looking fiberglass epoxy resin rods. Graphite epoxy hollow tubes are incredibly lightweight yet incredibly strong and stiff. I used .5" tubes with .030 wall on my telescope for some of the truss. On a length of 2 feet supported on the ends with a one kilo weight suspended in the center they deflect about .010" but only weigh about 30 grams.

Joel
05-01-2006, 09:36 PM
Engineer to Win by Carroll Smith
Any other book by Carroll Smith, like Prepare to Win and Tune to Win

How to Make Your Car Handle by Fred Puhn
Chassis Engineering by Herb Adams

Engines are a broad subject, but a good book with a fair amount of explanation as to why certain modifications help is Power Secrets by Smokey Yunick

Fasttrack
05-01-2006, 11:07 PM
Evan - yeah i did a little research online about graphite epoxy rods and realized that they must have had fiberglass. Shoot it all looks the same to me :)

Joel - Thanks for the recomendations; those will go on my growing wish list of tools and literature!

john hobdeclipe
05-01-2006, 11:42 PM
"Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook"

SJorgensen
05-02-2006, 04:10 AM
Machine it out of heliuminimum. This metal is very easy to work with except that you have to vacuum the chips off the cieling. Care must be taken. Don't let go of the part when you are outside. You'll never see it again.

Spence

Duct Taper
05-02-2006, 12:04 PM
Fastrack, I just checked with my son who was in the Supermileage program in high school and the Formula SAE in college.

The supermilage car that they built in high school had an all aluminum frame and only weighed about 75lbs. I do recall going to the high school competitions and seeing some of their aluminum welds break. They had to repair them on-site with that perforated strap that plumbers use to hold up pipe sometimes.

In the Formula SAE car they used mild steel tubing, that way it was easy to repair with a torch.

Evan
05-02-2006, 12:39 PM
Here is a little trick to recover a bit more energy from the engine. Naturally you would point the exhaust out the back to gain the small amount of thrust it produces. That can be considerably augumented by using a simple arrangement to cause the exhaust to entrain additional air. The mass of the air entrained will more than double the thrust from the exhaust. It's the same principle that bypass jet engines use compared to pure jets.

http://vts.bc.ca/pics/exhaust.jpg

Scishopguy
05-02-2006, 01:35 PM
You may want to avoid aluminum in the frame and support members and opt for the carbon fiber material. The folks who made bicycle frames from aluminum tubing soon found that it hardens with age and after a few years, tend to fail at bad times.

Jim (KB4IVH)

abn
05-02-2006, 04:30 PM
As others have stated I would consider the whole Smith lineup immediately, I've seen some specials if you buy them all at once:

http://www.CarrollSmith.com/main.html

I'm lucky to have Cerritos Community College relatively nearby, it has the only Community College based composites curriculum in California, I still have a sample of kevlar/aluminum honeycomb I stand on once in a while to amaze myself at how light/strong/stiff it is.

In some situations steel can actually be the best material, especially if you are limited in cross sectional area and you have the time to machine the part and remove material in un-needed areas.

I have some AZ61 magnesium it's easy to work with, but I don't know a cheap source.

Fasttrack
05-02-2006, 06:50 PM
Hey evan - i don't think 2.4 hp will generate a very noticeable amount of thrust...but do you have some dimensions for that? Looks like a fun little thing to whip up - i love finding tiny little projects to do on a lathe because the small projects are pretty much right at my skill level :)

I like the idea of using some kind of composites except for the money involved and the difficulty of construction (that is difficulty in constructing a vehicle on the fly with composites - read w/o any plans :) )

Also - i realize aluminumm will work harden but these frames won't be used more than two maybe three years anyway - thats only one to three races which means max of 75 miles on the frame. (thats with practice runs added in)

Evan
05-02-2006, 07:05 PM
i don't think 2.4 hp will generate a very noticeable amount of thrust...
I wouldn't ignore it. A ten cubic inch engine running at 2000 rpm will be pumping about one half pound of air through it per minute. It isn't much thrust but in your application every tiny bit helps and it costs basically nothing to implement. If you can double that to one pound per minute out the back at maybe 100 mph exhaust velocity it isn't negligible.

Dimensions? Nope, you will have to experiment.

topct
05-02-2006, 07:53 PM
Do not attempt to free up the exhaust.

You want to keep as much heat in the engine as possible. A more restictive exhaust is the way to go.

As far as an aluminum chassis goes. Look at how long a welded boat can last. They flex a bunch and seem to hold together.

Using the proper alloy, a 5xxx series, and proper welding techniques your chassis would be strong enough.

What do the rules say for materials?

Evan
05-02-2006, 08:14 PM
Yep. The above trick will not only provide some back pressure but it also will use some of the exhaust heat to provide additional thrust. That idea is what made the P51 the fastest aircraft around in WWII. They used the waste heat from the radiator to overcome nearly all the cooling drag of the system by expanding the cooling air and expelling it out the restricted exit of the cooling shroud.