I don't know why you guys keep saying a frame made from 1.25 X .049 tubing
is only good for 2 years. I'm now graduated but every car my team made
since 1996 is still running and the 96 car was much lighter than today's
cars. If youre not careful about what you say the judges will impose even
more roll cage restrictions.
John
>From: "Eric Hutchenreuther" <emhutchenreuther@hotmail.com>
>Reply-To: "Eric Hutchenreuther" <emhutchenreuther@hotmail.com>
>To: <mini-baja@Autox.Team.Net>
>Subject: Re: weight problem!
>Date: Sun, 14 Nov 2004 19:33:51 -0500
>
>"weight problem!" I thought that was junk mail so I didn't read it. If you
>post something like that it may be a good idea to include Baja somewhere in
>the subject line.
>
>What is the difference between ASTM A36 and ASTM 53?
>
>Last year we switched to 1.25 dia x .049" wall tubing for our frame. It
>lasted through one season alright. I actually couldn't spot any damage to
>the tubing at all after competition. When you design your suspensions, how
>high is the frame off the floor when bottomed out? We are somewhere about
>three inches. At Midwest I know we were bottoming out the rear suspension a
>lot more than we should have been, we still didn't have any problems with
>crushed tubing. Their is little reason to build a competition vehicle that
>lasts more than two years anyways... Perhaps I should hold my tongue
>until
>the car has been rolled a few times.
>
>Another arbitrary number: Our frame weighed 75 pounds when I weighed it. At
>that time I had about half of the brackets and tabs on it. I was really
>surprised at how light the rollcage was. In Solidworks the frame itself was
>only 60 lbs. As we got closer to competition, we had less time to fabricate
>lightweight parts, so the weight did increase to make our car about average
>weight.
>
>Forget about the frame, the best way to cut weight is to be more
>intelligent
>about how all that stuff is mounted to the frame. Why use thick material
>when you can bend a piece of sheet metal to be just as stiff. You would be
>surprised at how little metal it actually takes to support an engine or a
>driver's seat if you use structural shapes instead of .25" plate. If the
>rollcage were designed around the parts inside there would be no need for
>large awkward brackets.
>
>Until you get the rest of the vehicle in good working order, loosing a few
>pounds here and there will not have a very large effect on performance.
>
>Eric Hutchenreuther
>Kettering University
>
>
>
>
>----- Original Message -----
>From: <susantoa@pdx.edu>
>To: <mini-baja@Autox.Team.Net>
>Sent: Friday, November 12, 2004 8:00 PM
>Subject: Re: weight problem!
>
>
> > Please take into account that when people tell you what the weight of
> > their frame/roll cage is you can't really compare them directly. You
> > need to know whether they're giving you the weight of the roll cage
> > with or without the mounts, is it just the cockpit area or the
> > complete frame, how big is the car, etc. If you can weld it and you
> > don't mind the frame be a "throwaway" frame, use 1.25x0.049 in ASTM
> > 53, considering the same frame it will save you around 20% in weight.
> > We used A36 in 1.25x0.049 and it locally deformed (not bent but
> > crushed) where we hit obstacles. It last through two competitions,
> > but now it's pretty shot.
> >
> > Our frame with 1.25x0.049, complete front to back with all of the
> > mountings weighed around 90lbs or so. A different year's frame with
> > 1"x0.083 weighed around 75lbs or so but it was a smaller car. Total
> > vehicle weight in the last 4 years have been anywhere from 450lbs to
> > 520lbs. Then again we used pretty big tires (24x9 in 12 inch rims)
> > and each tire/wheel combo is around 27lbs by themselves.
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