I’m new here and have just introduced myself in the “new guy post here” thread couple of weeks ago.
As a DIY community, I think you may find this very interesting.
This is my little project, self promoted for now, of new frame concept. The latest update is of the actual hardware assembly: http://dosimplecarbon.com/first-frame-assembly/ And the loading test is really promising: https://www.youtube.com/watch?v=tUHVNc1hJkM
That’s very interesting - one of my projects this summer is to build an ultra-light board - these are some good ideas. Please let me know how the PLA parts work out. What % fill did you use? And is it just regular PLA or did you use carbon infused or high temp?
If the PLA cracks it might be interesting to see if you could epoxy aluminum ribs into it.
@DougM - this can be you next light frame, or at least a guideline. My background is aerospace structures so I’m used to making them as light as possible.
The parts were printed with 15% infill, which is enough for now, I tried breaking them with reasonable force but failed to do so. I’m pretty comfortable with the analysis results, so there is no benefit with aluminum ribs, you might just add PLA ribs and get the same result. I will keep this thread posted with the updates.
@gee - This is interesting, however these tubes have only 12mm inside diameter. But, you can take bigger tubes and do this if you don’t mind the added stiffness.
@thisguyhere - In the youtube video you can see the rotation of the frame on the trucks, the frame should rotate as one and it does that without problem. Torsional rigidity is needed if there is a loading in torsion, like trying to rotate each side in the opposite directions… This is not the case here.
I think you’re on to something here. I’ve been playing around with carbon infused PLA and it is incredibly strong. I found the material details on your website so I hope you don’t mind if I use similar to your designs for a one-off build.
@DougM - Don’t mind at all, please use these numbers as you wish, I’ve myself found them online.
If you go with aluminum, there are two things to consider regarding the end units:
First, you really don’t need the extra material as in the PLA version, please do not do it as is from aluminum, you will end up with unnecessary heavy part.
Second, the interface between the carbon tube and aluminum will have to be considered. The stiffness of aluminum is in the same ball park as carbon, so the transition need to be looked at, you don’t want any biting and hot spots there.
When I started this project, I thought of aluminum with carbon structure - neat, straightforward and very hi-tech looking.
And now I’m rethinking this, I’m leaning (strongly) towards carbon-PLA structure. I think there is a lot of things that remain unexplored there. I think that with smart design you can do a much more beneficial structure.
This frame is the first effort in this direction. Now I’m working on designing a folding hinge that will eventually make the board even more useful in everyday life
This requires some effort and is not that simple, but I’m a structural engineer and I love doing this
My goal (as for now) is to get to the point when a kid with 3d printer will buy some carbon parts, print the rest and will end up with useful, hi-tech-cool looking, and light board/scooter that will serve him daily.
I’m not doing footpads, standing on the tubes. Surprisingly very comfortable.
Another thing that has my focus is to design an attachment/fit in part that will interface with any truck and will give you more spacing to mount bigger wheels, for pneumatic wheels 5-6" for example.
While searching this forum I’ve seen that the common practice is to add kind of tube extensions to the axes or spacers and mount the bigger wheels that way. I don’t think this is the correct way, as you end up loading the axes beyond the design point. I believe that I’ve seen some reports of this method to fail.
I understand there are several dedicated designs with wider trucks, but wouldn’t it be neat to have any regular/non-proprietary trucks and just add the width that you need? I believe it would.
That being said, I’m talking from structural point of view, as I’m the furthest from experienced skateboard user there is. So if I’m talking nonsense, please correct me.
on a long day of riding you might find the tubes get uncomfortable after a while. But a small carbon fiber footpad with grip tape on it will resolve that. Also, if your shoes get even slightly wet it’s all over.
I only do drop decks. I severely dislike regular skateboards because I think they are unstable and not sufficiently carvy. So my aluminum portion will mostly address the transition from the carbon tube drop portion to the carbon tube (or perhaps aluminum plate) risers. The nice thing about this is it makes it modular so you can change the risers if you want to go to bigger tires. If you engineer a clamp into the aluminum you can swap risers for different drop configurations.
Good advice on pinch points, should be easily addressable by rounding over the exit portion of the tube hole?
yes - a block of aluminum the size of your PLA part would weigh a lot
Good advice on the foot pads, thanks. I’m not at all experienced in skateboarding so not thinking about this right now. Also, this is an evolving project, if it will feel awkward, I will add some foot rests.
You are right, an ability to swap parts and to play with them is a really cool idea, you can think of something modular to address this.
Regrading the transition/pinch points, it is slightly more complicated. Think of this this way:
you have a tube (no matter which material) stuck in a large massive block and you bend it. Where will it break? Right at the transition between the large block and the tube, this is the point of a sudden drop/rise of stiffness - not healthy. For this matter it is less significant if the actual edge is rounded or not.
Now take the same tube and insert it into slightly larger diameter tube and bend it. Both tubes will bend and the transition point will be smoother, the breaking point will no longer be at the transition. In an optimal design it will not be at the very transition. Now in your case you will want to design something that will increase in wall thickness/stiffness gradually for this purpose. Several FE iterations should get you there.
Another issue with carbon/aluminum is the galvanic corrosion in the interface. I though of fitting a glass fiber sleeve on the carbon tube and bond this to aluminum, but his idea is not baked up yet.
I really looking forward for your variation of this frame idea
I got some of my carbon fiber tubes in, will post piccies of the drop mount blocks as soon as I get the rubber (tomorrow) and get them made (probably not until this weekend at the earliest)
The tubes I found on Amazon are 500mm, which are too short for the drop-part of the deck, so I’m seriously toying with the idea of a variable length board or even possibly a breakdown board using hexagonal tubes such as below, but with thicker walls:
This requires some effort and is not that simple, but I’m a structural engineer and I love doing this 
