Wednesday, December 11, 2013

VDSKart: TIG Welding Aluminum Frame

I've been meaning to build an electric vehicle a bit more exciting than my Electric Orbit Wheels. And by a bit more exciting, I mean ridiculous acceleration, drifting, and driving around MIT campus at odd hours of the night. It's about time I built something that I could bring along and race Ben's trike in the Stata basement. I've accumulated a few very nice parts from the recently deceased club in N51, Vehicle Design Summit (VDS). Most of this kart will be assembled from parts I scrounged from VDS: hence the name VDSKart.

Due to the ridiculous size of the solar car axial flux motor that Ben generously donated, this vehicle is going to be a full sized racing go-kart, a slight deviation from MITER's smaller electric vehicles. It's probably going to weigh upwards of 150 lbs and won't fit through doorways, but it will go really really fast and accelerate like a sports car. I'm using aluminum round tubing for the frame to decrease weight, to learn how to weld aluminum, and because it's available.

After looking at many different designs for racing go-karts, I came up with this frame.
                                                                                                                

More on practice welds and crufted parts after the break. 



Mars had the rear-axle of a racing go-kart laying near his shelf. It's about 3'6" wide (small enough to fit through Stata elevators), 1.25" in diameter, has a keyway cut along its entire length, includes spherical bearing hubs, and has clamp hubs for both the brake disc and drive sprocket. 


As for welding, I talked with Jack Whipple and he kindly taught me how to TIG weld in his shop, D-Lab. 


Before tackling the whole frame, I welded some small aluminum scraps together in order to get a feel for TIGing aluminum. From my short experience, I've noticed it's very different from welding steel. There's more cleaning involved due to the oxidation layer aluminum makes almost instantly, and aluminum doesn't cool as rapidly as steel does. Steel is also much more forgiving. It doesn't take much to melt through the aluminum piece. 




After welding, I broke it to test my welds.



I bent the plate quite a bit, but it just tore along the welds. This indicates that I didn't melt enough of the base material and added to much filament.


Excited after welding, I went and CADed a rough frame in SolidWorks.


I soon learned that the joints containing four different aluminum pipes would be extremely hard to weld with my current welding ability. 

Next I tried TIGing a mitered edge to a pipe.


Welding the inside of the right angled miter joint was very difficult. I definitely don't want to weld joints with more than two pieces intersecting. I do want the challenge of welding my own frame, but I don't want building the frame to take up most of my time on this project. After welding the mitered edge at a right angle, I went and changed my initial frame design significantly to reduce any joints to two members and most angled joints to right angles. In this case, practicing welding a few scraps together helped constrain the design.



It took a bit more force with the wrench to break the weld. However, it still broke at the weld. I'll need a bit more practice getting the balance between using the existing material and not burning through it.

For safety considerations and to make welding the joints a bit easier, I pondered buying aluminum pipe fittings. That way, I could just weld a two-dimensional circle rather than a three-dimensional mitered edge path. However, they're cost is almost an order of magnitude more expensive than copper fittings.



Just as I was getting the hang of TIG welding aluminum, I borked my collarbone fractured my left clavicle skating really fast into walls playing hockey. This delays everything, including welding the frame. On the pain medication it says, "Do not operate lathes, mills, bandsaws... heavy machinery." I guess that is actually relevant now.

Here's a cool X-ray of my broken body. I'm going to have to get surgery so they can implant a titanium plate. Step one of becoming a robot... check. 



Though I might not be able to machine or weld things at MITERS with a borked bone, I can still CAD. Here's a somewhat pretty finished frame with the added design constraints.


More to come on machining a mount for the pancake motor and welding the frame. 

1 comment:

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