Hackaday Links: December 25, 2022

December 25, 2022 by Dan Maloney 21 Comments

Looks like it’s lights out on Mars for the InSight lander. The solar-powered lander’s last selfie, sent back in April, showed a thick layer of dust covering everything, including the large circular solar panels needed to power the craft. At the time, NASA warned that InSight would probably give up the ghost sometime before the end of the year, and it looks like InSight is sticking to that schedule. InSight sent back what might be its last picture recently, showing the SEIS seismic package deployed on the regolith alongside the failed HP3 “mole” experiment, which failed to burrow into the soil as planned. But one bad experiment does not a failed mission make — it was wildly successful at most everything it was sent there to do, including documenting the largest marsquake ever recorded. As it usually does, NASA has anthropomorphized InSight with bittersweet sentiments like “Don’t cry, I had a good life,” and we’re not quite sure how we feel about that. On the one hand, it kind of trivializes the engineering and scientific accomplishments of the mission, but then again, it seems to engage the public, so in the final rinse, it’s probably mostly harmless.

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Comparing 3D Printed Tires: Resin Vs. TPU

June 16, 2022 by Lewin Day 24 Comments

Many robot builders and RC enthusiasts find themselves turning to 3D printed tires. The benefit is you can make them in any size and style you want, and they’re as readily available for as long as your home printer is still working. [Michael Rechtin] printed some up and decided to see how long they’d actually last in use.

[Michael] printed a pair of tires for the test. One was made in TPU on a typical FDM printer, while the other was printed in flexible resin. The tires were then installed on hubs and fitted with gear motors for drive. The assembly was then fitted to the end of a test tether that would turn in circles for hours to put mileage on the tires.

After many hours and around 10 miles of testing, both tires were showing signs of wear. Notably, the resin tires showed a lot more wear than the TPU version, suggesting the latter material is a better choice for printing hard-wearing tires.

Overall, it’s reminiscent of the tether testing we saw from [rctestflight] recently. There’s something compelling about thrashing something round in circles to learn something in the process! Video after the break.

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Do Flat Tyres Make Your Speedo Lie?

May 22, 2022 by Jenny List 45 Comments

There are some engineering questions that may not have huge importance in the world, but which become the subject of intense idle speculation. A good example is the question of whether a lower tyre pressure on a motor vehicle would make a difference to the indicated speed. There are several contrasting intuitive theories as to what should happen, so [mechatronicsguy] has taken the time for a bit of experimentation in order to find out what really happens.

At stake were the change in effective radius from a flattened portion of the tyre, the so-called tank tracks effect in which the entire circumference of the tyre is still traversed, and the prospect of a change in circumference due to the different pressure. The test wheels were made from foam, and were found to give a different reading when compressed. This might solve toe problem, but of course real car wheels have radial wires to give them stiffness. When these were simulated on the foam wheels with packing tape, the difference evaporated. Later this was confirmed by GPS-measuring a real car with deflated wheels.

All this makes for a fascinating read, because after all, there’s sometimes no substitute for a real-world test.

Header image: Gerlach, Public domain.

Solid Tips For Casting Colored Silicone Tires

April 5, 2021 by Donald Papp 13 Comments

For people who work with wheeled robots or RC vehicles, sooner or later one gets interested in making custom tires instead of dealing with whatever is available off the shelf. [concreted0g]’s preferred method is to design and 3D print wheel hubs, then cast some custom silicone tires to fit over them. Of course, the devil is in the details and this process can be a bit messy, so he’s shared useful tips on how to get reliable results with simple materials.

The casting material is cheap silicone caulking from a hardware store, and color can be added with a small amount of cheap acrylic paint. A few drops of glycerin added to the silicone thins it out slightly and helps it flow into a mold better. Mix well (the paint will also serve as a visual indicator of how well it is mixed), then scoop the mixture into the mold while trying to avoid creating air pockets. If your mold is in two pieces, assemble the mold and remove any overflow, then let it sit undisturbed for at least several hours while it cures.

Mounting the resulting tire to a wheel hub can be done with a thin film of super glue, which seems to work perfectly well for small tires and is easy to apply.

The rules are going to be a bit different for big objects. We know that silicone caulking can have difficulty fully curing when it’s applied thickly, especially when sealed into a mold with little to no airflow. In such cases, adding cornstarch (in about a 5:1 ratio of silicone to cornstarch by volume) is all that it takes to cure even thick wads of goop in less than an hour. Stirring cornstarch in tends to introduce more air bubbles into the mixture, but for larger pieces that can be an acceptable tradeoff. Cheap silicone caulking is versatile stuff, one just needs to know what to expect, and take a few steps to deal with the messiness.

Need something tougher? Maybe check out using slices of automotive silicone hose for robot wheels to get something that works just as well, but is a lot more durable.

3D Printed Wheels Get Some Much Needed Grip

January 30, 2019 by Tom Nardi 11 Comments

You’d be hard-pressed to find more ardent supporters of 3D printing then we here at Hackaday; the sound of NEMA 17 steppers pushing an i3 through its motions sounds like a choir of angels to our ears. But we have to admit that the hard plastic components produced by desktop 3D printers aren’t ideal for a number of applications. For example, the slick plastic is useless for all but the most rudimentary of wheels. Sure there are flexible filaments that can give a printed wheel a bit of grip, but they came with their own set of problems (not to mention, cost).

In the video after the break, [Design/Forge] demonstrates a clever method for fitting polyurethane rubber “tires” onto 3D printed hubs which is sure to be of interest to anyone who’s in the market for high quality bespoke wheels for their project. The final result looks extremely professional, and while there’s a considerable amount of preparation that goes into it, once you’re set up you should be able to pump these out quickly and cheaply.

The process begins with a 3D printed mold pattern, which includes the final tire tread texture. This means you can create tire treads of any design you wish, which should have some creative as well as practical applications. The printed part is then submerged in silicone rubber and allowed to cure for 8 hours. Once solidified, the silicone rubber becomes the mold used for the next steps, and the original printed part is no longer needed.

The second half of the process is 3D printing the wheels to which the tires will be attached. These will be much smaller than the original 3D printed component, and fit inside of the silicone mold. The outside diameter of the printed wheel is slightly smaller than the inside diameter of the mold, which gives [Design/Forge] the space to pour in the pigmented polyurethane rubber. The attentive viewer will note that the 3D printed wheel has a slight ribbed texture designed into it, so that there will be more surface area for the polyurethane to adhere to. Once removed from the mold and cleaned up a bit, the final product really does look fantastic; and reminds us of a giant scale LEGO wheel.

Whether you’re casting metal parts or just want a pair of truly custom earbuds, creating silicone molds from 3D printed parts is an extremely useful skill to familiarize yourself with. Though even if you don’t have a 3D printer, there’s something to be said for knowing how to mold and cast real-world objects as well.

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Will Your Next Whip Pack Memory Chainmail Tires?

December 2, 2017 by John Baichtal 37 Comments

NASA’s Glenn Research Center is experimenting with nickel-titanium memory alloy tires that resemble chain mail. It’s an intriguing angle — the tires can withstand heavier loads and at higher speeds. They’re airless and immune to puncture. Presumably they’re not literally chainmail but closer to a sweater in construction.

This tire is a culmination of a number of fascinating research drives. NASA has been experimenting with tensegrity structures as a means of building in space without spending a ton of rocket fuel on heavy hardware. These structures use tensioned cables to maintain a three-dimensional structure. The tires use the stiffness of the wire as well as internal stiffeners to maintain shape, without the need for a whole rim.

In addition to structural tensegrity, the memory alloy also helps keep its original shape by resisting deformation — it springs back into its original shape. When ordinary materials are stretched, you’re stretching the bonds between the atomic structures. NASA’s NiTi alloy goes through an “atomic rearrangement” when stressed, easing the forces put on those structures. As a result, the alloy can withstand 10% deformation versus 0.3% for spring steels, or about 30 times the deformation that a normal alloy could withstand without having permanent deformation occur — dents, basically. NASA’s tires can actually compress down to the axle and then pop back.

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Cheap And Effective Dune Buggy Wheel Chair

July 6, 2016 by James Hobson 14 Comments

[masterfoo]’s mother-in-law suffers from a bad hip which would have sidelined her participation in the Fourth of July festivities. As a testament to the power of family and ingenuity, [masterfoo] built her a beach-capable wheel chair to give her some off-roading capability.

The frame is built out of 1.5″ PVC piping and the tires are 20×8-8″ inner tubes for ride-on lawnmowers. The lawnmower wheel inner tubes were cost-effective and fit the purpose, saving the need for the more expensive purpose-built-for-the-beach Wheeleez tires. They also have a fluid inside that plugs small punctures which will come in handy against he beach’s small cacti and other flora. This video was their guide for the foam insulation and plywood wheel assembly, also employing the handy man’s secret weapon to protect the tube from the rim’s plywood edge. Check it out in action!

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