Engineering the Perfect Throw for Rock Skipping

Summer is here (at least in the Northern Hemisphere) and World’s Greatest Uncle [Mark Rober] is at it again with his nieces and nephews. This time he’s all about skipping stones, that shoreline pastime that kids sometimes find frustrating and adults find humiliating when trying to demonstrate the technique.

But what exactly is the proper technique? [Mark] didn’t know, so he built a robot to find out. Yes, we know it’s not a robot – it’s just a commercial clay pigeon launcher with a few modifications — but work with us here. His idea is to build a rig that can eliminate as many variables as possible when a human tries to skip a stone, and work back one variable at a time to find the perfect set of factors. The prototype in the video below did a respectable job skipping stones, but it was nowhere near optimal. [Mark] then engaged the kids on a careful exploration of the mechanics of rock skipping using the rig, eventually going so far as to eliminate variability in the rocks by making clay pigeons of his own. The results are fantastic; at a 20° approach angle and a 20° tilt of the rock relative to the water, those artificial stones just seem to go on forever. Even skipping natural stones was much improved by what they learned, which is completely counter to the age-old advice to release as low and as parallel to the water as possible.

The real gem in this video, though, is [Mark] describing his engineering design process. Watch and learn, because he clearly knows a thing or two about turning ideas into fun stuff, such as enormous Super Soakers, fully automatic snowball guns, and dart-catching dartboards.

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Custom LCD Module is Unexpectedly Cheap and Easy

Looking to take your project to the next level in terms of functionality and appearance? A custom LCD display might be the thing that gets you there, at least compared to the dot-matrix or seven-segment displays that anyone and their uncle can buy from the usual sources for pennies. But how does one create such a thing, and what are the costs involved? As is so often the case these days, it’s simpler and cheaper than you think, and [Dave Jones] has a great primer on designing and specifying custom LCDs.

The video below is part of an ongoing series; a previous video covered the design process, turning the design into a spec, and choosing a manufacturer; another discussed the manufacturer’s design document approval and developing a test plan for the module. This one shows the testing plan in action on the insanely cheap modules – [Dave] was able to have a small run of five modules made up for only $138, which included $33 shipping. The display is for a custom power supply and has over 200 segments, including four numeric sections, a clock display, a bar graph, and custom icons for volts, amps, millijoules, and watt-hours. It’s a big piece of glass and the quality is remarkable for the price. It’s not perfect – [Dave] noted a group of segments on the same common lines that were a bit dimmer than the rest, but was able to work around it by tweaking the supply voltage a bit.

We’re amazed at how low the barrier to entry into custom electronics has become, and even if you don’t need a custom LCD, at these prices it’s tempting to order one just because you can. Of course, you can also build your own LCD display completely from scratch too.

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Wireless Charger Gives a Glimpse into Industrial Design Process

Almost every product on the market has been through the hands of an industrial designer at some point in its development. From the phone in your pocket to the car in your driveway or the vacuum in your closet, the way things look and work is the result of a careful design process. Taking a look inside that process, like with this wireless phone charger concept, is fascinating and can yield really valuable design insights.

We’ve featured lots of [Eric Strebel]’s work before, mainly for the great fabrication tips and tricks he offers, like how to get a fine painted finish or the many uses of Bondo. But this time around, he walks us through a condensed version of his design process for a wireless phone charger and stand. His client had specific requirements, like being able to have the phone held up in landscape or portrait mode, so he started with pen and paper and sketched some ideas. A swiveling cylinder seemed to fit the bill, and after a quick mockup in PVC pipe, he started work on a full-size prototype in urethane foam. There are some great fabrication tips in the video below, mainly centered on dealing with not owning a lathe.

The thing for us with all of [Eric]’s videos, but especially this one, is seeing the design process laid out, from beginning to (almost) the end. He sure makes industrial design look like a cool gig, one that would appeal to the Jacks- and Jills-of-all-trades who hang out around here.

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3D Printering: When an STL File is Not Quite Right

STL files are everywhere. When there’s something to 3D print, it’s probably going to be an STL. Which, as long as the model is good just as it is, is no trouble at all. But sooner or later there will be a model that isn’t quite right in some way and suddenly project progress hits a snag.

When models interface with other physical things, those other components may not always be exactly as the designer expected. Being mindful about such potential inconsistencies during the design phase can help prevent problems, but it’s not always avoidable. The reason it’s a problem is because an STL file represents a solid model as a finished unit; it is not really intended to be rolled back into CAD programs for additional design changes.

STL files can be edited, but just like re-modeling a component from scratch, it can be a tricky process for those who don’t live and breathe this stuff. I’ll describe a few common issues related to STLs that can hold up getting that new project together, along with ways to deal with them. Thanks to 3D printing becoming much more commonplace, basic tools are within reach of even the least CAD-aware among us.

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Cams and Pushrods Improve 3D-Printed Compressed Air Engine

Some folks just can’t leave well enough alone, and that often ends up being a good thing. Such is the case with this 3D-printed compressed air engine, which just keeps getting better.

The design has changed a lot since we first covered [Tom Stanton]’s attempts at reviving the powerplant from the glory days of the Air Hogs line of toys, which he subsequently built a plane around. The engine was simple, with a ball valve that admitted air into the cylinder when a spring mounted to the top of the piston popped it out of the way. That spring has always bothered [Tom], though, compelling him to go back to the drawing board. He wanted to replace the ball valve with one actuated by a cam and pushrod. This would increase the complexity of the engine quite a bit, but with the benefit of eliminating the fail point of the spring. With a few iterations in the design, he was able to relocate the ball valve, add a cam to the crankshaft, and use a pushrod to open the valve. The new design works much better than the previous version, sounding more like a lawnmower than a 3D-printed engine should. Check out the design process and some tests in the video below.

And speaking of lawnmowers that run on compressed air

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Smart Outlet Cover Offers Lessons on Going from Project to Product

Going from idea to one-off widget is one thing; engineering the widget into a marketable product is quite another. So sometimes it’s instructive to take an in-depth look at a project that was designed from the get-go to be a consumer product, like this power indicating wall outlet cover plate. The fact that it’s a pretty cool project helps too.

Although [Vitaliy] has been working on this project for a while, he only recently tipped us off to it, and we’re glad he did because there’s a lot to learn here. His goal was to build a replacement cover for a standard North American power outlet that indicates how much power is being used by whatever is plugged into it. He set constraints that included having everything fit into the familiar outlet cover form factor, as well as to not require any modification to the existing outlet or rewiring, so that a consumer can just remove the old cover and put on the new one. Given the extremely limited space inside an outlet cover, these were significant challenges, but [Vitaliy] found a way. Current is sensed with two inductors positioned to sense magnetic flux within the outlet, amplified by a differential amp, and power use is calculated by an ATmega328 for display on 10 LEDs. Power for the electronics is tapped right from the outlet wiring terminals by spring clips, and everything fits neatly inside the cover.

It’s a great design, but not without issues. We look forward to seeing [Vitaliy] tackle those problems and bring this to market. For more on what it takes to turn a project into a product, check out our own [Lewin Day]’s story of bringing a guitar effects pedal to market.

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Learn What Did and Didn’t Work In this Prototyping Post-Mortem

[Tommy] is a one-man-shop making electronic musical things, but that’s not what this post is about. This post is about the outstanding prototyping post-mortem he wrote up about his attempt to turn his Four-Step Octaved Sequencer into a viable product. [Tommy] had originally made a hand-soldered one-off whose performance belied its simple innards, and decided to try to turn it into a product. Short version: he says that someday there will be some kind of sequencer product like it available from him, “[B]ut it won’t be this one. This one will go on my shelf as a reminder of how far I’ve come.”

The unit works, looks great, has a simple parts list, and the bill of materials is low in cost. So what’s the problem? What happened is that through prototyping, [Tommy] learned that his design will need many changes before it can be used to create a product, and he wrote up everything he learned during the process. Embedded below is a demo of the prototype that shows off how it works and what it can do, and it helps give context to the lessons [Tommy] shares.

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