There is a rule of thumb to follow when looking at product announcements at the fringes of the motor industry that probably has something in common with crowdfunding campaigns. If the photographs of the product are all renders rather than real prototypes, walk away. It is said that small volume vehicle production is a space that attracts either crooks or dreamers, and parting with your money to either can be a risky business. So when yet another electric vehicle platform makes its debut it’s always worth looking, but too often the rendered images outnumber anything from the real world and you know you’ll never see one on the road.
It is with interest then that we note an exciting announcement made last week at CES, that the French carmaker Renault are to release an open-source vehicle platform. It is called the POM, and it is based upon their existing Twizy electric buggy platform. If this last point causes you to snort with derision because the Twizy is a tiny and not very fast in-line two-seater with awful weather protection better suited to the French Riviera than an American Interstate, remember that the car itself is not the point of this exercise at this stage. Instead the access to the technology will spark fresh innovation in the open electric vehicle sector that will transfer into better systems for more practical open source vehicles in the future. (Incidentally, we’re told by people who’ve tried the Twizy that it can be something of an unexpected gem to drive. It seems the lowish top speed doesn’t matter in the twisties when you have a low centre of gravity and quite impressive acceleration in a tiny machine.)
Partnered with Renault are OSVehicle, ARM, Pilot Automotive, a manufacturer of automotive accessories, and Sensoria, who will be working on wearable accessories. It’s probable that you won’t see many POMs on the road if you don’t live in a territory that already has the Twizy, but it’s certain you’ll see its technological legacy in other vehicles.
We’ve covered plenty of electric cars in the past here at Hackaday, and this isn’t the first one with an open source angle. We’ve had a very nice Mazda-derived ground-up build, and an astounding home-made hub motor.
Delrin, Acetal, and its many trade names is a material properly known as Polyoxymethylene or POM. It is one of the strongest plastics and is a good go-to material when you want the best properties of plastic, and don’t need the full strength of a metal part. It was originally formulated to compete with Zinc and Aluminum castings after all.
I won’t go too deep into the numbers behind POM. If you need the Young’s Modulus, you probably don’t need this guide. This is intended to be more of a guide to its general properties. When you’re looking for something to fit an application it is usually easier to shift through the surface properties to select a few candidates, and then break the calculator out later to make sure it will work if you’re uncertain about the factor of safety.
The most popular property of POM is its ease of machining. While doing this research every single site I came across referred to it as the most machinable plastic. That’s about as objective as subjective praise can get. It doesn’t tend to grab tools like, for example, HDPE. It also chips nicely unlike UHMW and Nylon. Some plastics, like UHMW, have the unfortunate tendency to render the dials on a mill or lathe meaningless as the plastic deflects away from the tool. POM does not do this as much. Of course these other plastics have their strengths as well, but if any plastic will do, and you’re machining, POM is a very good choice.
Continue reading “Materials to Know: Acetal and Delrin”
[Philysteak527] modified a Nerf rifle, making it semi-automatic thanks to the powers of compressed air. This is not a simple change to make, and rests on his ability to design and manufacture a bolt-action that fits in the gun, works with the Nerf ammo, and uses a CO2 canister and solenoid valve for the firing action. Knowing that, it’s not surprising to find that he’s an engineering student at Stony Brook University. He started with some POM, or polyoxymethylene plastic sold under the brand name Delrin, and used a CNC lathe to machine the parts for the bolt. Add in some brass fittings, a solenoid, tubing, and the electronics and you’re in business.
We’ve embedded the test footage after the break. Looks like the new internals allow a rather fast firing rate (maybe 2-3 shots per second?) and achieve a distance between seventy and one hundred feet.
Continue reading “Nerf gun converted to CO2 powered semi-automatic”