Hello everyone. I have a project idea that I’d like your feedback on.
For years I’ve been attempting to build a pedal / electric trike from various materials with varying degrees of success. Recently I started thinking, why not 3D print a trike? There are a number of physical and technical hurdles, but it should not be outside the realm of possibility given sufficient time, effort, and funds.
The first hurdle is getting a 3D printer large enough to create the frame in a single piece. The largest single part would be approximately 3ft long, 2ft wide, 1ft tall. As far as I can find, there is no commercially available printer with those dimensions. I’m going to have to invent one.
My goal right now is to develop and build a 3D printer of at least the above dimensions. I will open source the entire design, and would like to work with others who are interested in developing such a machine.
My questions for are:
How feasible does this project sound? Is it doable with current technology?
Are there any existing printers that can handle objects of this scale? Are there any open source ones that could be adapted to it?
What technical and physical hurdles are inherent to printing at larger sizes? I understand that larger printers tend to be less accurate. What other problems will there be? How can they be overcome?
It isn’t that larger printers inevitably become less accurate, it’s that the longer an unsupported span is (so, assuming you’re talking a cartesian printer, your x/y gantry) the more it will want to flex so the more rigid it will need to be. The usual solution is to scale it up, using larger rods or aluminum extrusions or whatever your gantry is made out of, which in turn increases the weight of the gantry and the momentum of it which means you need more powerful motors in order to overcome that momentum (both in starting and, somewhat more importantly, in stopping).
Basically, the challenge of scaling up a printer isn’t just getting longer rods/extrusions/whatever. There are fancy engineering tricks that can help with the challenge, but those are the sorts of things people working as professional engineers pick up over years of experience… so I don’t really know many of those tricks.
But more basically than that I have concerns about the ultimate strength and longevity of a fully 3D printed trike. There are materials available now that have very good interlayer adhesion, but even in a best case scenario of good material choice and optimal layer orientation I would wonder if it would be strong enough to be of real use. I can’t answer that question, but it’d be worth trying to figure out the types and magnitudes of the forces the frame would experience and compare those to the interlayer adhesion strengths of different printing filaments to see if it would work for you.
Thank you for your reply! I was thinking that a honeycomb internal structure for the tubing might make it strong enough while still lighter than a solid beam. I’d need to find some structural / mechanical engineers to brainstorm that part. I’m a software engineer, so I understand engineering processes, but not so much the workings of forces.
The weakest part of a print tends to be the junctions between the layers, so you generally want to orient the print in such a way that the part experiences compression forces on those joints.
Basically, if you 3D print a tube oriented straight up and down (so the openings are pointed more or less up and down) then try to bend it by grabbing the two ends and pushing it over your knee the tube will snap along one of the layer lines.
If you print that same tube oriented horizontally, so the hollow central space is parallel to the print bed, then repeat the bending test it will fail when the plastic itself gives out and won’t snap along a layer line.
That makes a printed part very different from a metal part or even an injection molded plastic part.
So what you’d need to do to figure out if it’s feasible to print a trike is to work out what sorts of forces the different components experience and if there are ways to orient the print such that those forces don’t act primarily along the layer lines.
Torsion is exactly what I was thinking while reading Stephen’s last comment. The majority of stresses on a trike are torsional rather than linear. I guess that means I’ll need to find a frame builder to weld a metal frame for me. I’d rather not learn to DIY welding.
The second stage of this project was going to be building a full fairing for the trike, similar to the aerorider concept trike which is no longer in production. Would 3D printing be suited to fabricating the body panels?
Yeah, I can draw it. All of my modeling experience is in 3D Studio Max, so as long as the interface is even remotely similar I’ll figure it out. There’s already an almost identical model on 123d that could serve as a template: http://www.123dapp.com/123C-3D-Model/Velomobile-Closed-Top/1490040
I looked up the Big E, and it looks like exactly what I had in mind. How much did it cost you to set it up? Is it cheaper if you build it yourself? Can the parts be downloaded and printed on another machine?
I open source everything so of course. It will be cheaper to order the water jet parts from me probably. Amazon.com has extrusion we used. The more the merrier. It is still in development but we print w it almost every day… The learnings are still coming!http://amazon.com
Perhaps, but I’m interested in printing more than this trike, and I wouldn’t be interested in welding anything other than the trike. Also I’ve got zero depth perception, so trying to make things accurately by hand is very difficult for me. That’s why I want a 3d printer, so I can create things and let the computer take care of the accuracy.
OK, think more about it this way, a 3d printer is an enabling tool that can create one off enabling tools. For instance (off the top of my head) it could make the mold for something so the material molded would still be to your design, but made from something substantially stronger than slightly melted plastic
