Inventing wheels.. with built-in suspension =p

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

Post by sgrogan »

Very interesting topic as usual DeepSOIC.
An interesting thing is that the "spokes" did not break at the hub or rim, but slightly above, maybe at the transition from the fillet. The optimal curvature is not circular even for equal sections. In your case, from a thick to a thin section, the curvature should be more elliptical, or even parabolic, to distribute the stress.
Given that you were successful on the floor and not on asphalt, Frequency amplification is probably also involved. Given the amount of damping you have, by design, the amount of amplification about resonance will look more like a bell curve than a delta function.
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Re: Inventing wheels.. with built-in suspension =p

Post by tom »

That is a very cool project! How about using the FEM workbench in order to find the most stressed points?
A_3
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Re: Inventing wheels.. with built-in suspension =p

Post by A_3 »

I agree with ezzieyguywuf and sgrogan related to the function of suspension built into the wheel and design. (But it's your wheel and project :) )
Solution of the problem is a combination of design and material (wow, very wise ;) ).

I'm not familiar with 3D printing, but I see that there are flexible materials similar to rubber. Although there is not much material characteristics except flexibility and price of 60$. Some of them have high hardness and could be used for bearings and couplings cartridges. Maybe you could do something with that material, but for 60$...
polarized
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Re: Inventing wheels.. with built-in suspension =p

Post by polarized »

Nice project, I really enjoyed it. Reminds me this kickstarter startup: https://www.loopwheels.com/
ulrich1a
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Re: Inventing wheels.. with built-in suspension =p

Post by ulrich1a »

DeepSOIC wrote:Fatigue may indeed be the culprit. I have made the radii of spokes to the very limit of plastic deformation, to maximize stored energy density. As it may be obvious, I don't have much room for more spokes, which means if I need to reduce the strain to avoid fatigue by more than two times, then I'm screwed :| and there is no way apart from using different material. Which will not be 3d-printable, most likely.
I did today some web research regarding design with plastic material because I need some more knowledge at work about this topic. I came across those two pages which I thought to post here:
Here is a design guide for plastic snaps, that gives some guideline how to avoid concentration of stress at the root point of a cantilever.
http://www.plastics.covestro.com/Librar ... hures.aspx
Look at "Schnappverbindungen für Kunststoffe – Ein Konstruktionsleitfaden Titel: Schnappverbindungen für Kunststoffe – Ein Konstruktionsleitfaden"
it is in english.

Here is a page about plastic hinges, that recommends two materials for it: polypropylene or polyethylene.
http://www.efunda.com/designstandards/p ... /hinge.cfm
I do not know, if these materials are available for 3D-printing, but it is a hint for another trial. ;)

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

Post by A_3 »

Materials that I mentioned in one of the previous posts:
http://www.stratasys.com/materials/polyjet/rubber-like
https://www.matterhackers.com/3d-printe ... nt-compare for example> Section 2: Flexible Filaments
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DeepSOIC
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Re: Inventing wheels.. with built-in suspension =p

Post by DeepSOIC »

ulrich1a wrote:Here is a design guide for plastic snaps,
Nice, thanks. Might come in handy for designing actual plastic snaps :P . As for the wheel, I would probably use FEM rather than those application-specific equations.
A_3 wrote:Materials that I mentioned in one of the previous posts:
http://www.stratasys.com/materials/polyjet/rubber-like
https://www.matterhackers.com/3d-printe ... nt-compare for example> Section 2: Flexible Filaments
I have some flexible filament. It is probably the worst flexible filament in the world! It doesn't stretch, it doesn't fully recover from a deformation and the recovery is slow; it has poor self-adhesion (I can unwind a spiral-vase mode printed thing, as if it was a coil of copper wire wicked by lacquer). Some others might be better, but after experience with this one, I don't even want to consider making a suspension from this material. I would rather think of using silicone sealant as elastic part of the wheel, as it has some pretty amazing elastic properties.
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bernd
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Re: Inventing wheels.. with built-in suspension =p

Post by bernd »

DeepSOIC wrote:
ulrich1a wrote:Here is a design guide for plastic snaps,
Nice, thanks. Might come in handy for designing actual plastic snaps :P . As for the wheel, I would probably use FEM rather than those application-specific equations.
Should we give it a try with FEM ?
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DeepSOIC
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Re: Inventing wheels.. with built-in suspension =p

Post by DeepSOIC »

bernd wrote:Should we give it a try with FEM ?
Catch the model!
swheel v06.FCStd
Requires Lattice2 and Module container
(318.26 KiB) Downloaded 97 times
The final shapes are "ModuleXXX - ???". The shapes should be available even if you don't have Module containers (you don't ;) ). If you want them, you'll need to compile https://github.com/DeepSOIC/FreeCAD-ell ... DeepSOIC10

This isn't the latest model I've printed. That was very different from the actual wheel. This should have all the necessary geometry.
You'll have to fuse spokes to the wheel (I didn't because I needed them as separate STL for printing).

EDIT: material = PLA.
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Re: Inventing wheels.. with built-in suspension =p

Post by DeepSOIC »

Closeup pictures of spoke attachment
Attachments
spoke attachment g-code.png
spoke attachment g-code.png (371.1 KiB) Viewed 3394 times
WP_20160904_20_47_05_Pro_.jpg
WP_20160904_20_47_05_Pro_.jpg (204.56 KiB) Viewed 3394 times
WP_20160904_20_43_05_Pro_.jpg
WP_20160904_20_43_05_Pro_.jpg (173.83 KiB) Viewed 3394 times
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