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Post Info TOPIC: Frame Material


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Frame Material
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Down here in Tampa a lot of cars are made of EMT conduit, especially the Robinson cars (Meangreen). But my teacher is very hesitant with it because it is galvanized and creates toxic fumes when welding, but it can be MIG welded. But aluminum is also popular but we don't have the money for a TIG welder or the skill. So what other materials are used in car that can be MIG welded? What is used at the schools in the NW?



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Middleton High School, Tampa

 



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Nearly all of our cars have frames, rollbars, etc. made out of mild steel tubing. We use 1 X 2 0.083 for the Axle. Then for the rest round or square 1" to 1/2" tubing, most of it is 0.049 wall with some 0.065.

We also sometimes build them out of Chrome Moly and have gone as thin as 0.032 on that.

The frame built this way usually weighs about 12-20 pounds not counting wheels, etc. So I can not see spending that much on Al and if it breaks or wrecks at a race you can not weld it unless you bring a portable TIG. Most of our finished cars weigh from 90 to 110 pounds with everything but batteries. Aluminum etc. is not going to make them that much lighter. My car is a tank and weighs about 130 pounds but I got tired of bending it over continual seasons so I use 0.123 wall tubing for my axle and most of it is 0.065 or 0.083 wall tubing.

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I have used EMT conduit in various sizes for years. Yes, the fumes from welding it can be hazardous if inhaled. Therefore, I keep a fan blowing across my work area at all times when I'm welding so the smoke does not come up into my welding hood. Since a breeze is the enemy of normal MIG welding because it blows away the shielding gas, I use a flux-core wire feed welder.

EMT conduit is light weight, relatively cheap, readily available at any hardware store, and can be cut and bent with inexpensive common tools. Welding it without blowing holes in it takes a little practice for beginner welders, but it's cheap enough you can practice on it a little before beginning actual construction.

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Jim Robinson


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In the past before we purchased TIG welders for aluminum we had a MIG welder with aluminum wire and an Argon tank on it and it did OK welding aluminum for some of our earlier cars. We had to really watch the heat as it was easy to overheat and cause the aluminum to be brittle.This is an option, if you want to spend the money on Aluminum. Like I said we have gone almost exclusively to mild steel tubing most of it with 0.049 walls. Like EMT it is light, strong, cheap, and it welds easily. It is also not galvanized and so does not have Zinc fumes to kill brain cells of my students.

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I can say I have an aluminum framed car.  Before the new year, my car turned seven years old.  In the entire time I've driven it I've never had something break on the frame due to a weld issue.  The majority of the frame was welded together using a spool gun while the critical areas for the front steering and where the rear wheel sits was done using a TIG.  The other thing to keep in mind if you are planning to build a alloy frame car would be make sure you've got enough bracing throughout the frame.  If you don't, the frame will twist causing increased fatigue on critical sections of the car (front end, mid section, rear end).  

This was the main reason Centennial switched to steel framed cars a few years back because their aluminum framed cars kept breaking on them due to not building a properly strengthened frame.  The other issue was they would simply re-weld over cracks that showed up in the frame and not find out why the cracks kept showing up.  Those two main causes were the main reason for the switch of materials.  I've checked for cracks after a race and the entire time I've only ever found three cracks in the weld.  Two were by the steering rack which lead to me adding bracing to the area to prevent the rack from twisting, and the other was on the steering shaft support.  I could take the steering out of my car on the support that had a needle bearing pressed into it.  The part with the needle bearing had the crack in it which was simply not enough weld for that area.  

Other than checking for cracks and having a properly braced frame while building, aluminum is pretty easy to work with for the most part.  As Mike said, just watch how much heat you have going into parts and make sure you clean the area with a stainless steel brush before welding.  If you have a issue with weld taking, use a propane torch to heat the area up, that way you're not wasting time letting the TIG do all of the work.  



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Zaine, I have always been curious how much does your car weigh? With everything but the batteries, you and ballast in it. Mike

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Mike, around six years ago before the summer races started up after winning the 2010 series, we did actually weigh the car.  With me, ballast, and red or yellow tops we got some numbers.  Total weight with me, ballast and reds was around 405 pounds.  Total weight with me, ballast and yellows was around 410 pounds.  Without the batteries (reds or yellows), ballast and myself in the car; dry weight was around 150 pounds.  The frame itself I'd need to look at my notes to find that number since I'd need to weight the wheels, tires, tubes, sprockets (wheel and motor), chain, chain tensioner, meter, seat belt, windshield and the tail cone to determine the frame weight without taking everything out of the car to find out.  I know I have the weight of the frame written down.  

Zaine 



-- Edited by Zaine Stapleton on Monday 2nd of May 2016 03:22:00 PM



-- Edited by Zaine Stapleton on Monday 2nd of May 2016 03:22:48 PM



-- Edited by Zaine Stapleton on Monday 2nd of May 2016 03:23:19 PM

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The dry weight is what I was wondering. My car is heavy by Willamette standards. Just the complete car without me or the batteries is about 130 pounds--so about 400-415 with those--depending on my fat content...... Many of our student cars are in the 95 to 110 pound range. Gary Dull's #49 car is I think 92 pounds.

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Ron


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I recall the first year I was involved in electrathon (2004) weighing the car my daughter drove "empty" (no batteries, ballast,etc.) it weighed 214lb.

as I recall Caity finished 7th in her first race, 3rd in her second race and 2nd (or tied for second) in all other races (before our accurate computer lap timing)

and I once drove that car and came in 4th open class (6th overall) @ Corvallis.

seems like we should worry less about weight (only important on tracks with a lot of elevation change)

and worry a lot more about getting the car "in rig" (tire scrub, ackerman angles, bearing/tire design) than weight savings...

there is a LOT more energy lost in these areas (and driving style) than parasitic weight.

just my two cents worth.

Ron

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For a second car, I'd like to make a copy of my current car (see avatar picture) in a different material.
More as an experiment car to see what that weight difference actually makes.

Material I would most likely use would be kevlar honey-comb board for the base and main sides.
To round it off on the edges and corners, most likely either fiberglass, kevlar, or carbon fiber with foam underneath to pull a mold from.

We'll see what happens when I get to that point.

Zaine

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