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Parametric airless tire

by tjhowse, published

Parametric airless tire by tjhowse Feb 13, 2012

Description

This design is inspired by Bridgestone's airless tire concept:

physorg.com/news/2011-12-bridgestone-airless-concept-tokyo.html

Using the natural springiness of plastic, this design can absorb shock and vibration in a manner similar to a pneumatic tire, but cannot be punctured.

Videos here:
youtube.com/watch?v=3LctFwZhY1M
youtube.com/watch?v=sXBgaaI7dHY

This design is fully parametric.

Update: Added tiny (0.001) offset between spirals. Openscad errored when trying to export an STL otherwise.

Recent Comments

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TETRIX, We use ROBOTC or Labview to program LEGO Mindstorm controllers to interface with TETRIX electronics and parts.
Is this for Vex?
With a grip_depth of 1, and a grip_density of 0.5, 50% of the outer circumference of the wheel will be raised, and 50% will be lowered.

Make sure you're rendering the model in openscad before the export. Do this by pressing F6. Also make sure you're using the latest version of openscad.

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License

GNU - GPL
Parametric airless tire by tjhowse is licensed under the GNU - GPL license.

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Instructions

Tweak values to suit your application, compile, slice and print! If you're having traction problems, I suggest a zig-zag of hot glue around the circumference to give it a more frictious surface.
does any one have any experience with printing Polycarb? Is it similar to PLA but stronger, or more similar to ABS? I would like to try using this as a replacement wheel for a Robotics competition, but I dont want to use PLA because it would probably break if another robot accidentally hit our bot. I know I could get good results with Nylon if there were enough "spokes" i guess you could call them, but I would like to know more about the properties of printing Polycarb.
Is this for Vex?
TETRIX, We use ROBOTC or Labview to program LEGO Mindstorm controllers to interface with TETRIX electronics and parts.
Thanks for posting this! I'm trying to use the SCAD file in OpenSCAD, but am having some trouble rendering with the grips setting. I'd like grips to have a 50% density along the outer wheel. Do I need to enter a fractional amount (e.g. 0.5)? Also, what does grip_depth mean? I'm also having trouble exporting a .stl file for printing. It exports, but when I open the .stl file, it is empty.
With a grip_depth of 1, and a grip_density of 0.5, 50% of the outer circumference of the wheel will be raised, and 50% will be lowered.

Make sure you're rendering the model in openscad before the export. Do this by pressing F6. Also make sure you're using the latest version of openscad.
Nice! :)

Ron Arad made a bicycle with spring-steel tires based upon a similar concept:

core77.com/blog/materials/ron-arad-designed_bicycle_with_spring_steel_wheels_up_for_auction_20994.asp
Cool! It would be neat to make one that could interface with LEGO axles . . .
Any guess if this design is strong enough to replace a 32cm (12-13inch) wheel for a light-weight (aluminium) wheelbarrow? (Pumping the tire every time before use tiring :-P)
If you make it out of Nylon and have enough "spokes" I wouldn't doubt it
Though getting a printer with that build volume capable of printing nylon would be a trick...
Neat! I played with this a while back but mine was too stiff and I never tried again. How does this work?

Also, I designed mine just like yours, but later noticed that the tweel and others have spirals that go both ways. Prevents deformation both front and back.
Oops, and then I read the other comments.
This is called a tweel for posterity.
Very cool!

Have you made a double spiral like Bridgestone's airless tire? A small change to the code but not printed yet:

for (i = [0:spoke_count-1])
{
rotate([0,0,i * (360/spoke_count)]) translate([(spoke_dia/2)-(dia_in/2)-hub_thickness,0,0]) spoke();
rotate([0,180,i * (360/spoke_count)]) translate([
(spoke_dia/2)-(dia_in/2)-hub_thickness,0,-height]) spoke();
}

Probably much less soft.
I think the reason they have two counter-rotating spirals is such that the characteristics of the wheel don't change too much under torque. If the hub is accelerated quickly it tends to twist independently of the rim, splaying or twisting the spokes, changing the spring constant. Stiffness isn't an issue with my design, since you can add spokes or make them thicker until you reach the desired stiffness.

I added a "double_spiral" boolean so people can generate counter-rotating spiral wheels if they want.
At a guess, the two separate spring sections also serves to decouple the rim and hub, reducing resonance around a particular frequency/speed at higher speeds. For a small plastic version that will (presumably) not be run at very high speeds, this advantage is probably not very relevant though.
I'm guessing that it's simply that double spiral breaks the 'flex' up into many short sections, which is needed for a large wheel, because the total 'flex' for a single spiral spoke for a full sized tire would be so long (perhaps 1.5 feet long in a 2' diameter tire) that the wheel would be unusably floppy, while the single spiral leaves the flex in one piece, which is perhaps 1.5" long on a 2" diameter toy wheel. So if the two opposing spirals intersect to break up the 1.5' into a dozen, 1.5" segments, with cross-bracing, the result would be perhaps roughly comparably 'springy'.
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