Inventing wheels.. with built-in suspension =p

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DeepSOIC
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Inventing wheels.. with built-in suspension =p

Post by DeepSOIC »

Hi!
Lately, I've been experimenting with 3d printing some wheels with built-in suspension, also known as airless tires. The ultimate goal is to make new wheels for my kick scooter.

This is the first experiment.
swheel v01.png
swheel v01.png (89.02 KiB) Viewed 15402 times
swheel v02 compact.FCStd
(216.71 KiB) Downloaded 204 times
This one has a very flexible outer surface (tire). I have glued some sandpaper to it, and got a very nice grinding/sharpening tool.
swheel v02 _small.jpg
swheel v02 _small.jpg (166.44 KiB) Viewed 15327 times
As a wheel, such a structure is obviously too gentle. But as a grinding tool, it is awesome.

More to come ;)
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Re: Inventing wheels.. with built-in suspension =p

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Slicing it was a bit tricky.
As a note, this wheel was designed for a specific extrusion width of 0.4 mm.
Slicing it as a single solid, I couldn't get an acceptable result:
slicing bad.png
slicing bad.png (267.77 KiB) Viewed 15327 times
I realized I wanted the outer ring (tire, so to say) to be a continuous loop of extrusion. Also, it as quite clear, that the springy spokes should be attached to the sides more intensely, otherwise they will just break off (ABS isn't particularly good at sticking to itself; yet ABS is the material of choice because if it's springiness).
I was able to obtain the required result, and here's how. I have taken the whole wheel apart: the spokes, the base and the tire were separate STLs. I've made the spokes go into the tire and the middle by quite a bit, in order to get them fused into the bulk as good as possible.
So I loaded all three parts into the slicer (Slic3r). That made the slicer think they were separate objects, and I was lucky Slic3r doesn't auto-arrange objects, and ignores overlapping.
The resulting slice looked like this:
slicing good.png
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triplus
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Re: Inventing wheels.. with built-in suspension =p

Post by triplus »

Looking good.
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Re: Inventing wheels.. with built-in suspension =p

Post by DeepSOIC »

Thanks triplus!
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Re: Inventing wheels.. with built-in suspension =p

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The first wheel was small, is was merely a proof of concept. And here comes the second one, a size of a real wheel.
swheel v04.png
swheel v04.png (224.19 KiB) Viewed 15310 times
File: https://drive.google.com/file/d/0B9lBm- ... sp=sharing (663KB)

There are a few design differences compared to the previous one:
* the outer ring is rigid, because the non-rigid one is too gentle to be practical. I have used an involute gear as the infill, although I probably should have simply asked the slicer to take care of that.
* the spokes are larger
* there is a raft, to fight warping forces ripping the wheel off the printbed while printing (this even was a problem with the small wheel)
* this time, knowing how to slice, I didn't even bother to fuse the wheel together.
* I've put the holes for 807 bearings, although I have no at hand (gonna buy a few).
This design turned out to be waaay too soft a suspension, I guess it is only suitable for 1-kg load. The outer ring proved to be not tough enough, I have broken it quite easily.
The purpose of this wheel is mainly to take some rigidity measurements (not done yet), in order to have a baseline for engineering the final take.

Picture of the printout:
swheel v04 _small.jpg
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Re: Inventing wheels.. with built-in suspension =p

Post by DeepSOIC »

Short video of how it flexes: https://youtu.be/J79K_1EF2Y4
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Re: Inventing wheels.. with built-in suspension =p

Post by PrzemoF »

I think it's a perfect model to do come FEM calcs and test the results with a real life measurements :D

I like that type of wheel, but it's not as flexible as yours: http://www.cnet.com/news/new-honeycomb- ... lletproof/
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Re: Inventing wheels.. with built-in suspension =p

Post by DeepSOIC »

Rigidity measurement: result is 4090 N/m, with an error of about +-10%
rigidity.png
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Update: the real thickness of the springy ribbons is about 0.36 mm
Is it time for some FEM business? ;)
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Re: Inventing wheels.. with built-in suspension =p

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Crush test results:
The wheel started to irreversibly deform (slightly) at a load of about 4.5 kg, and catastrophic failure happened at about 13 kg.
swheel v04 crushed _small.jpg
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Re: Inventing wheels.. with built-in suspension =p

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New version is being prepared... Potentially capable of bearing some 66 kg of me.
swheel v05 pre.png
swheel v05 pre.png (229.5 KiB) Viewed 15036 times
Compared to the previous design, it is:
* based on rigidity results obtained from previous wheel
* different shape of spokes, they should be much more tolerant to overload (but they allow less displacement...)
* stronger outer structure with hand-modeled infill (no involute gear abuse this time)
By the way. Does any of you have ideas of how to model the sinusoid-like infill of the "tire"? I have done it, but I can't say I like the way I did it (it's an epic mess of hard-coded angles in sketches and draft arrays). The infill itself is actually just arcs and lines, not sinusoid.
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