A Compact Strain Wave Gear Assembly

May 20, 2019 by Jenny List 8 Comments

Strain wave gearing is a clever way to produce a high-efficiency, high ratio gearbox within a small space. It involves an outer fixed ring of gear teeth and an inner flexible ring of teeth which are made to mesh with the outer by means of an oval rotor distorting the ring. They aren’t cheap, so [Leo Vu] has had a go at producing some 3D-printable strain wave gearboxes that you could use in your robotic projects.

He’s created his gearbox in three ratios, 1:31, 1:21 and 1:15. It’s not the most miniature of devices at 145mm in diameter and weighing well over a kilogram, but we can still imagine plenty of exciting applications for it. We’d be curious as to how tough a 3D printed gear can be, but we’d expect you’ll be interested in it for modest-sized robots rather than Formula One cars. There’s a video featuring the gearbox which we’ve placed below the break.

This certainly isn’t the first strain wave gearset we’ve brought you, more than one 3D printed project has graced these pages. We’ve even brought you a Lego version. Continue reading “A Compact Strain Wave Gear Assembly” →

Power Wheels Gets Real With Real Wheels

December 19, 2018 by Tom Nardi 10 Comments

We’re no stranger to Power Wheels modifications, from relatively simple restorations to complete rebuilds which retain little more than the original plastic body. These plastic vehicles have the benefit of nostalgia to keep the adults interested, and naturally kids will never get tired of their own little car or truck to tear around the neighborhood in. Many toys come and go, but we don’t expect Power Wheel projects to disappear from our tip line anytime soon.

Today’s project starts with a straightforward Power Wheels restoration story: [myromes] picked up a well-worn Jeep and decided that it needed a fresh coat of paint and some tweaks before handing the keys over to the next generation. But in an interesting spin, he decided to try mounting proper pneumatic tires on it in hopes they might imbue the pint-sized Jeep with some of the abilities of its full scale inspiration. But as it turned out, the project wasn’t quite the Sunday drive he was hoping for.

For one thing, the new wheels were much thicker than the old ones. This meant cutting away some of the plastic where they mounted so he could get the shafts to slide all the way through. At 5/16″, the original Power Wheels shafts were also thinner than what the axle the wheels were designed for. Luckily, [myromes] found that a small piece of 1/2″ PEX water pipe made a perfect bushing. Then it was just a matter of buying new push nuts to lock them in place.

That got the front wheels on, but that was the easy part. The rears had to interface with the Jeep’s motors somehow. To that end, he cut out circles of plywood and used an equal amount of Gorilla Glue and intense pressure to bond them to the new wheels. He then drilled four holes in them which lined up with the original motor mounts so he could bolt them on.

Things were going pretty well until he tried to replace the Jeep’s rear axle with a length of threaded rod from the hardware store. It wasn’t nearly strong enough, and sagged considerably after just a few test rides. He eventually had to place it with a correctly sized piece of cold rolled steel rod to keep the car from bottoming out.

While the new wheels certainly perform better than the original hard-plastic ones, there’s a bit of a downside to this particular modification. The slippy plastic wheels were something of a physical safety to keep the motors and gearboxes from getting beat up to bad; with wheels that have actual grip, the Jeep’s stock gears are probably not long for this world. But [myromes] says he’s got plans for future upgrades to the powertrain, so hopefully the issue will be resolved before the little ones need a tow back home.

For more tales from the Power Wheels garage, you might want to take a look at this fantastic rebuild complete with digital speedometer or just head straight to the big leagues with some seriously upgraded rides.

A DIY Balcony Crane Lifts Groceries For The Lazy But Patient

September 9, 2018 by Dan Maloney 39 Comments

If necessity is the mother of invention, then laziness is probably its father. Or at least a close uncle. Who hasn’t thought, “There has to be a better way to do this, one that doesn’t involve me burning precious calories”?

Motivational laziness seems to increase with potential energy, as anyone who needs to haul groceries up four flights of stairs will tell you. This appears to be where this balcony-mounted drill-powered crane came from. Starting with a surplus right-angle gearbox and drum, [geniusz K] fabricated the rest of the crane from steel plate and tubing. We like the quality of fabrication and the tip on making slip couplings from bits of square tubing. The finished product got a nice coat of brown paint to match the balcony railing; keeping the neighbors happy is always important. He tested the crane with a 20-kg weight before installing it on the balcony and put it to work hauling groceries up three stories. Check out the build and the test in the video below.

While it won’t set any speed records, at least the drill is doing the work. But what if you’re impatient as well as lazy? Aside from being two-thirds of the way to programming greatness, you may have to up the game. A heavy-lift quadcopter, perhaps?

Continue reading “A DIY Balcony Crane Lifts Groceries For The Lazy But Patient” →

Printed Part Gets Classic Truck Rolling

August 8, 2018 by Tom Nardi 19 Comments

When working on classic vehicles, and especially when modifying them outside of their stock configurations, things can get expensive. It’s a basic principle in economics: the rarer something is the more money somebody can charge you for it. But if you’ve got the skills and the necessary equipment, you can occasionally save yourself money by custom-fabricating some parts yourself.

After changing the gear ratio in his 1971 Ford F100, [smpstech] needed to adjust his speedometer to compensate. Unfortunately, a commercial speedometer reducer and the new cables to get it hooked up to his dash would have run into the hundreds of dollars, so he decided to try designing and 3D printing his own gearbox. The resulting development process and final product are a perfect example of how even a cheap desktop 3D printer, in the hands of a capable operator, can do a lot more than print out little toy boats.

The gearbox contains a large ring gear driven by a smaller, offset, spur gear. This compact inline package drops the speed of the input shaft by 25.5%, which [smpstech] mentions is actually a bit slower than necessary, but it does give him some wiggle room if he decides to change his tire size.

Even if you’re not looking for a speedometer reducer for a nearly 50 year old truck, there are some lessons to be learned here in regards to 3D printed car parts. The first version of his gearbox, while functional initially, ended up looking like a deflated balloon after being exposed to the temperatures inside the F100’s engine bay. His cheapo PLA filament, which is probably fine for the aforementioned toy boats, simply wasn’t the right material for the job.

[smpstech] then reprinted the gadget in HTPLA, which needs to be annealed after printing to reach full strength. Usually this would involve a low-temperature bake in the oven, but he found that simmering the parts in a pot of water on the stove gave him better control over the temperature. Not only did the HTPLA version handle the under-hood conditions better, it was also strong enough that he was able to use a standard die on the connections for the speedometer cables to create the threads instead of having to model and print them. Definitely a material to keep an eye on if regular PLA isn’t cutting it for you.

This isn’t the first time we’ve seen 3D printed parts used to get a vintage vehicle back on the road. Building these custom parts would have been possible without a 3D printer, of course, but it’s a good example of how the technology can make these types of repairs faster and easier.

[via /r/functionalprint]

Bomb Hoist Teardown Shows Cold-War-Era Big Iron

July 17, 2018 by Jenny List 10 Comments

Buying surplus equipment lends a frisson of excitement as you eagerly await the package or crate containing your purchase. Did you buy a hidden treasure, or has some shyster succeeded in unloading a pile of garbage onto you, their mark? [Professor Churls] shelled out $49.99 for a military surplus bomb hoist which definitely falls into the former category. His teardown reveals it to be a beautifully over-engineered piece of Cold-War-era American hardware.

As the package with its extremely heavy contents is first inspected, he reminds us just what a bomb hoist does, it is clipped to an aircraft by ground crew and serves as a small but extremely powerful crane to lift up to a 6000-pound piece of ordnance onto the wing pylon of an aircraft. This particular example dates from the 1960s, and features a 28-volt DC motor coupled to a bulky gearbox assembly on a swivel mount for attachment.

His teardown is extremely detailed, but such is the engineering and complexity of the device you’ll want to read every part of it. The motor is a fairly traditional separately-excited brushed DC design such as you’d expect from that era, but with unusual features such as brushes on pivots rather than a slide. The multiple sets of gears are packed in aged and phenolic-smelling grease, and have unusual features such as stub-form teeth for high torque at low durations. There is even an entirely separate gear train for the hex drive provided so that crews could keep the bombers rolling even when the power was out.

He leaves us with the tantalising information that there is a project awaiting this device, but doesn’t tell us what that might be. We hope we’ll get to see it, whatever it is. Meanwhile it’s great to see that this kind of item can still be found from military surplus suppliers, where this is being written they have degenerated into little more than stockists of camouflage-printed camping gear. Our colleague [Brandon Dunson] lamented in 2015 on the slow decline of the electronic surplus business in his location.

3D Printed Transmission Invented Again; This Time Continuously Variable

March 13, 2018 by Al Williams 26 Comments

We shouldn’t laugh, but we know the feeling very well. [Gear Down for What] invented a revolutionary transmission and fabricated it from scrap material when he was 16. Except he later found out the same design was the subject of a patent filed 14 years earlier. Dismayed he destroyed his prototype, but fast forward to today and he’s made a 3D model of a ratcheting continuously variable transmission. You can see a video of him explaining how it works below and put your own spin on the idea by grabbing the model from Thingiverse.

The model is just for demonstration purposes. We doubt it would wear well enough to use in practice but it’s great to get your hands on for a really intuitive understanding of the mechanism. Some modern automobiles use a continuously variable transmissions (CVT) and many recreational vehicles and motorcycles use them. Like any transmission, their job is to match the motor’s rotation to needed output torque and speed by offering different gearing ratios. Whereas a normal transmission provides a few fixed gears, a CVT changes seamlessly through a range of ratios.

Some of the design of the transmission is pretty tricky, like the cam adjustment. The video shows the rationale for how the design works and how it relates to tank steering (tank as in an Army tank; not like a gas tank). The model isn’t just plastic. It uses some screws and BBs, as well. However, if you have a 3D printer and wanted a good classroom demonstration, this is the ticket.

We’ve seen other geared variable transmissions for robots before. The planetary gears in the cam adjustment of this design are well understood. If you want to brush up your planetary knowledge, there’s no time like the present.

Continue reading “3D Printed Transmission Invented Again; This Time Continuously Variable” →

Stripping 3D Printed Gears For Science

October 17, 2017 by Tom Nardi 33 Comments

While 3D printing is now well on its way to becoming “boring” in the same way that a table saw or lathe is, there was a time when the media and even some early adopters would have told you that the average desktop 3D printer was perhaps only a few decades behind the kind of replicator technology we saw on the Enterprise. But as the availability of these machines increased and more people got to see one up close, reality sunk in pretty quickly.

Many have dismissed the technology as little more than a novelty, and even within the 3D printing community itself there’s a feeling that most printers are used for little more than producing “dust collectors”. Some would see this attitude as disheartening, but the hackers over at [Gear Down For What?] see it as a challenge. They’ve made it their mission to push printed parts to increasingly ridiculous heights to show just what the technology is capable of, and in their latest entry, set out to push a pair of 3D printed gearboxes to failure.

The video starts out with a head to head challenge between two of their self-designed gearboxes. As they were spun up with battery powered drills, the smaller of the two quickly gave up the ghost, stripping out at 228 lbs. The victor of the first round then went on to pull a static load, only to eventually max out the scale at an impressive 680 lbs.

The gearbox may have defeated the scale, but the goal of the experiment was to run it to failure. By rigging up a compound pulley arrangement, they were able to double the amount of force their scale could detect. With this increased capacity the gearbox was then run up to an astonishing 1,000 lbs before it started to slip.

But perhaps the most impressive: after they got the gearbox disassembled, it was discovered that only a single planet gear out of the ten had broken. Even then, judging by how the gear sheared, the issue was more likely due to poor layer adhesion during printing than from stress alone. No gears were stripped, and in fact no visible damage was seen anywhere in the mechanism. The team is currently unable to explain the failure, other than to say that the stresses may have been so great that the plastic deformed enough that the gears were no longer meshed tightly.