It is sometimes a surprise in our community of tinkerers, builders, hackers, and makers, to find that there are other communities doing very similar things to us within their own confines, but in isolation to ours. A good example are the modified vehicle crowd. In their world there are some epic build stories and the skills and tools they take for granted would not in any way be unfamiliar to most Hackaday readers.
As part of a discussion about electric vehicles near where this is being written, someone tossed an interesting link from that quarter into the mix; a two-part treatise on building ultra-light-weight tubular frame vehicles. Or space frames, as you might know them.
You might think that making a tubular framed for a vehicle would be a straightforward enough process, but as the article explains, it contains within it a huge well of geometry and metallurgy to avoid a creation that is neither too heavy nor contains excessive weakness. Part one deals mainly with prototyping a frame, the selection of materials and joining tubes, while part two goes into more detail on fabrication. The author likes brazing which may offend the sensibilities of welding enthusiasts, but you can substitute your jointing tech of choice.
A particularly neat suggestion, one of those simple ideas that make you wish you’d thought of it yourself, is to prototype a frame in miniature with copper wire and solder to evaluate the effect of different forces upon it before you commit your final design to steel.
The articles are a few years old, but no less pertinent in the information they contain. Meanwhile if you are a spaceframe veteran, then you may have your own suggestions for the comments below. And if you’d like some tips on how not to build a spaceframe, have a look at this motorcycle.
Thank you [JHR] and [Jarkman] for the tips.
Beware if you are welding Cr-Mo or otherwise high-strength tempered steel; its strength is incredibly dependent on the heating/cooling profile that you subject it to. Unless you preheat before welding, you are likely to have cracking under load in the heat-affected zone adjacent to the weld. The preheat needs to be warm enough to prevent fast-freezing (and therefore large crystals) in the HAZ, but not so much that you anneal the tube and make it soft.
This cracking effect is more pronounced with thicker-wall tubing, so you will find great disagreement online about whether per-heating is necessary. Arguably it is maybe not necessary for super-thin-wall stuff, but many people claiming “it’s fine” have not actually tested that it is fine, and there were a few fatal drag-racing crashes in the 2000’s eventually attributed to HAZ cracking in Cr-Mo.
Post-weld heating/annealing of a welded area is popular but also foolish: it will prevent HAZ cracking, but returns the metal to the same annealed/untempered softness as mild steel, in which case you just wasted all your money on buying high-strength Cr-Mo steel, unless you have the means to temper your entire assembled frame. Which, let’s face it if you’re reading HAD, you don’t have a vehicle-sized vacuum chamber.
For tempering a vacuum chamber is not used. A high temperature oven flooded with an inert gas is much cheaper, and in reach of a hobbyist.
And an (inert) gas fill helps very much in heat convection and distribution. In a vacuum you have to rely only on radiative heat transfer, which can be very inconsistent and uneven and difficult to control.
I tend to work with CDS on my lil projects for this reason, its within my means to make the best of that material, can be plenty strong. just not as light for a given strength as Cr-Mo.
Soda straws.
How do you join them together? Blutac?
hot glue?
I’ll give you a tip for one: Cyanoacrylates
Soda straws might be a little on the flimsy side, however you probably have access to a near infinite supply of plastic tubing you have been discarding for years.
In every bottle of liquid soap, and every kitchen and bathroom spray bottle there is a length of plastic tubing. There is often a small glass bead, a metal spring, and a plastic or silicone washer, depending on the construction of the sprayer.
I liberate these before consigning the rest of the bottle to the recycling bin.
They are surprisingly useful and can be worked a little like glass tubing, using a hot air gun. If you need a pipette or small syphon, they are just the ticket. The tubing is also impervious to most solvents, and acids.
You can also join them using heat, epoxy or plastic dowels.
Short lengths make good screw fixing plugs for wood and plaster too.
I might add building a space frame to my list of uses.. perhaps a spray bottle tubing hexacopter chassis.
nice tip, any idea what material they are made of?
Problypropelene :)
I lol’d.
Well, for an “idiot”, you have posted a very good idea,
so maybe you are an “ideait”.
B^)
W’s comment shows the reason to love brazing. If you can keep down the joint temperature, you don’t wreck the temper of the steel/
What do you use for the alloy? Tempering starts to affect hardness above 200 C
Bike frames have been brazed since there have been metal bike frames, using everything from straight brass to nickle-silver.
http://www.phred.org/~josh/build/brazing.html
https://youtu.be/LdOWRbk5x-Q
But bike frames aren’t particularily high strenght alloys, and brazing is used mostly to avoid the deformation caused by welding that would complicate the assembly. You can see they happily heat it up to red heat, which, if done on a high strength alloy would mess up with the tensile strength and hardness depending on the cooling rate – it may end up soft or brittle, depending on the cooling rate.
I like your first paragraph about these communities with similar goals yet different culture, jargon, and membership. I myself am from the custom motorbike side of things originally. I got drawn into electronics when I was dissatisfied with a turn signal relay which depended on the ohms of the lamp to maintain a proper blinking rate. I wanted to combine input from the turn signals, brake switches, and running lights switch to control just two tail lights. I ended up designing my own 12v circuit to combine the functions into one unit, and thus I began my EE hobby. I did it all with relay logic. It’s hideous, but it works. I’m learning to use solid state stuff now.
I’m a freak in that respect, though. Most of the other gearheads stay away from their vehicle’s electrical system with a ten-foot pole, regarding it with a primal mixture of hatred and respect like a caveman watching a thunderstorm. I still see it that way sometimes. We’ve heard of communities of hackers and makers, and had great respect for their ability to do all sorts of things with a box of dumpster-sourced capacitors and transistors. We always thought it was silly to call oneself a “maker.” Who doesn’t make things? Everyone is a maker. But you guys build some things we could scarcely imagine.
I think the divide is closing. One of my buddies recently took a class in building an analogue synth, and is tackling a weird short on his new motorbike with gusto and confidence. This article has me considering bronze-brazing my new exhaust system together instead of welding it. I think the coloration would be better, too. Thanks for writing this up.
Back in college our slodrering excercise was to construct a cube with tinned wire. After sevéal months of our tutor rejecting our work werre required to construct our cube inside a larger cube and fix the corners. Taught a massive lesson in heat transfer of materials and basic patience, something lacking in youth at the time. Put me in good sted for future work. Great excercise for anyone starting out in soldering IMO.
For information on building space frames look no further than the world of motorsports. This is a big deal in many different types of racing as many types of race cars use tubular frames. in oval track racing just about every kind of race car has a tubular chassis, all the way from go karts and mini-sprints to nascar. Tubular chassis are also used in drag racing. In fact top fuel dragsters probably are the area where this is most important. In these cars you have a long skinny frame which is being subjected to tremendous forces from the rear wing that is being counter balanced by forces from the front wing to keep the nose from lifting into the air and added into this equation is the torque reaction from the rear wheels which are applying up to 11000+ horsepower to the sticky VHT treated track surface. If you watch videos in slow motion of these cars going down the track, you can see how heavily the frames are loaded as the cars actual arch up in the middle like an angry cat. There have been instances of failures where the cars actually broke in half in the middle of a pass, like Cory McClenathans crash at Bristol in 2006. So, building strong yet lightweight space frames is definitely an area of expertise that race car chassis builders must be proficient in.