Do You Need A Cycloidal Drive?

A cycloidal gear drive is one of the most mesmerizing reduction gears to watch when it is running, but it’s not all just eye-candy. Cycloidals give decent gearing, are relatively compact and back-drivable, and have low backlash and high efficiency. You probably want one in the shoulder of your robot arm, for instance.

But designing and building one isn’t exactly straightforward. Thanks, then, to [How To Mechatronics] for the lovely explanation of how it works in detail, and a nice walkthrough of designing and building a cycloidal gear reducer out of 3D printed parts and a ton of bearings. If you just want to watch it go, check out the video embedded below.

The video is partly an ad for SolidWorks, and spends a lot of time on the mechanics of designing the parts for 3D printing using that software. Still, if you’re using any other graphical CAD tool, you should be able to translate what you learned.

It’s amazing that 3D printing has made sophisticated gearbox designs like this possible to fabricate at home. This stuff used to be confined to the high-end machine shops of fancy robotics firms, and now you can make one yourself this weekend. Not exotic or unreliable enough for you? Well, then, buy yourself some flexible filament and step on up to the strain wave, aka “harmonic drive”, gearbox.

Thanks to serial tipster [Keith] for the tip!

Continue reading “Do You Need A Cycloidal Drive?”

Oh Deere, Is That Right To Repair Resolution Troubling You?

Over the years a constant in stories covering the right to repair has come from an unexpected direction, the farming community. Their John Deer tractors, a stalwart of North American agriculture, have become difficult to repair due to their parts using DRM restricting their use to authorised Deere agents. We’ve covered farmers using dubious software tools to do the job themselves, we’ve seen more than one legal challenge, and it’s reported that the price of a used Deere has suffered as farmers abandon their allegiance to newer green and yellow machines. Now comes news of a new front in the battle, as a socially responsible investment company has the tractor giant scrambling to block their shareholder motion on the matter.

Deere have not been slow in their fight-back against the threat of right-to-repair legislation and their becoming its unwilling poster-child, with CTO Jahmy Hindman going on record stating that 98% of repairs to Deere machinery can be done by the farmer themself (PDF, page 5) without need for a Deere agent. The question posed by supporters of the shareholder action is that given the substantial risk to investors of attracting a right-to-repair backlash, why would they run such a risk for the only 2% of repairs that remain? We’d be interested to know how Deere arrived at that figure, because given the relatively trivial nature of some of the examples we’ve seen it sounds far-fetched.

It’s beyond a doubt that Deere makes high-quality agricultural machinery that many farmers, including at least one Hackaday scribe, have used to raise a whole heap of crops. The kind of generational brand loyalty they have among their customers simply can’t be bought by clever marketing, it’s been built up over a century and a half. As spectators to its willful unpicking through this misguided use of their repair operation we hope that something like this shareholder move has the desired effect of bringing it to a close. After all, it won’t simply be of benefit to those who wish to repair their tractor, it might just rescue their now-damaged brand before it’s too late.

Curious about previous coverage on this ongoing story? This article from last year will give context.

Header image: Nheyob / CC BY-SA 4.0

Marble-elevator dot-matric display

Simple Design Elevates This Mechanical Dot Matrix Display

Don’t get us wrong — we love unique displays as much as anyone. But sometimes we stumble across one that’s so unique that we lack the basic vocabulary to describe it. Such is the case with this marble-raising dot-matrix alphanumeric display. But it’s pretty cool, so we’ll give it a shot.

The core — literally — of [Shinsaku Hiura]’s design is a 3D-printed cylinder with a spiral groove in its outside circumference. The cylinder rotates inside a cage with vertical bars; the bars and the grooves are sized to trap 6-mm AirSoft BBs, which are fed into the groove by a port in the stationary base of the display. BBs are fed into the groove at the right position to form characters, which move upwards as the cylinder rotates. Just watch the video below — it explains it far better than words can.

The clever bit is how the BBs are fed into the groove. Rather than have a separate mechanism to gate the feed port, there’s a backlash mechanism that opens the port when the motor powering the drum runs in reverse for a bit. It’s a clever use of cams to get the job done without adding an extra servo, which sort of reminds us of the design parsimony exhibited in his one-servo seven-segment display.

It’s not clear that this would be a very practical display, but that doesn’t stop it from being cool. Although, [Shinsaku Hiura] just released a follow-up video showing a bigger version of this used to display upcoming events from Google Calendar, so perhaps we’re wrong. Continue reading “Simple Design Elevates This Mechanical Dot Matrix Display”

Capstan Drive Is Pulling The Strings On This Dynamic Quadruped

When it comes to legged robots, it’s easy to think that the complexity and machining costs would keep these creatures far away from becoming anyone’s garage hobby. But, through a series of clever design choices, [Damian Lickindorf] has found a way to beat the odds and give life to Stanley, a low-cost, dynamic quadruped with some serious kick!

As if building a working legged robot weren’t already a tricky task, [Damian] has made some classy design choices to keep the price low and reduce fabrication complexity without sacrificing performance. Keeping up with the latest trend in Quasi-Direct Drive legged robots that started with the MIT Mini Cheetah, [Damian] constructed a small transmission with a gear reduction under 1:9. This choice slightly reduces the amount of heat produced by operating the motor at low-speeds with high torque without sacrificing too much control bandwidth (think: “leg responsiveness”).

Unlike the Cheetah, though, which uses a planetary gearbox, [Damian] opts for a capstan drive, a cable-driven transmission that’s both backlash free and backdriveable: two must-haves for force-sensitive dynamic legged robots. For legs, he’s opting for 2d machined FR4 (think: circuit board material). And for motors, he’s chosen a set of brushless motors with a large gap radius and driven by Moteus Drivers. The result is high fidelity, dynamic build that’s a fraction of the cost of some of the creatures we’re seeing emerge from academic research labs.

If you’re looking to feast your eyes on some action shots, look no further than [Damian’s] YouTube and Instagram presence. And if you’re looking to follow the project, have a look at the Hackaday.io project. While we’re eager to see the project continue to unfold, we’re thrilled by how far it’s come. In the meantime, be sure to take a look at one of the project’s inspirations: the Mjbots Quad A0.

Finally, since we’ve not seen capstan drives much on Hackaday, if you’re curious about these mechanisms and can get past the paywall, these two research papers might be a good place to dig deeper.

Continue reading “Capstan Drive Is Pulling The Strings On This Dynamic Quadruped”

You Can’t Put The Toothpaste Back In The Tube, But It Used To Be Easier

After five years of research, Colgate-Palmolive recently revealed Australia’s first recyclable toothpaste tube. Why is this exciting? They are eager to share the design with the rest of the toothpaste manufacturers and other tube-related industries in an effort to reduce the volume of plastic that ends up in landfills. It may not be as life-saving as seat belts or the Polio vaccine, but the move does bring Volvo and OG mega open-sourcer Jonas Salk to mind.

Today, toothpaste tubes are mostly plastic, but they contain a layer of aluminum that helps it stay flattened and/or rolled up. So far, multi-layer packaging like this isn’t accepted for recycling at most places, at least as far as Australia and the US are concerned. In the US, Tom’s of Maine was making their tubes entirely out of aluminum for better access to recycling, but they have since stopped due to customer backlash.

Although Colgate’s new tubes are still multi-layered, they are 100% HDPE, which makes them recyclable. The new tubes are made up of different thicknesses and grades of HDPE so they can be easily squeezed and rolled up.

Toothpaste Before Tubes

Has toothpaste always come in tubes? No it has not. It also didn’t start life as a paste. Toothpaste has been around since 5000 BC when the Egyptians made tooth powders from the ashes of ox hooves and mixed them with myrrh and a few abrasives like powdered eggshells and pumice. We’re not sure what they kept it in — maybe handmade pottery with a lid, or a satchel made from an animal’s pelt or stomach.

The ancient Chinese used ginseng, salt, and added herbal mints for flavoring. The Greeks and Romans tried crushed bones, oyster shells, tree bark, and charcoal, which happens to be back in vogue. There is evidence from the late 1700s showing that people once brushed with burnt breadcrumbs.

Continue reading “You Can’t Put The Toothpaste Back In The Tube, But It Used To Be Easier”

A High Torque 3D Printed Harmonic Drive

Actuators that are powerful, accurate, compact, and cheap are like unicorns. They don’t exist. Yet this is what [3DprintedLife] needed for a robotic camera arm, so he developed a custom 3D printed high torque strain wave gearbox to be powered by a cheap NEMA23 stepper motor.

Strain wave gears, otherwise known as harmonic drives, are not an uncommon topic here on Hackaday. The work by deforming a flexible toothed spline with a rotating elliptical part, which engages with the internal teeth of an outer spline. The outer spline has a few more teeth, causing the inner spline to rotate slowly compared to the input, achieving very high gear ratios. Usually, the flexible spline is quite long to allow it to flex at one end while still having a rigid mounting surface at the other end. [3DprintedLife] got around this by creating a separate rigid output spline, which also meshes with the flexible spline. Continue reading “A High Torque 3D Printed Harmonic Drive”

Putting Your Time In

I was absolutely struck by a hack this week — [Adam Bäckström]’s amazing robot arm built with modified hobby servos. Basically, he’s taken apart and re-built some affordable off-the-shelf servo motors, and like the 6-Million-Dollar Man, he’s rebuilt them better, stronger, faster. OK, and smoother. We have the technology.

The results are undeniably fantastic, and enable the experienced hacker to get champagne robot motion control on a grape-juice budget by employing some heavy control theory, and redundant sensors to overcome geartrain backlash, which is the devil of cheap servos. But this didn’t come out of nowhere. In his writeup, [Adam] starts off with “You could say this project started when I ordered six endless servos in middle school, more than 15 years ago.” And it shows.

Go check out this video of his first version of the modified servos, from a six-axis arm he built in 2009(!). He’s built in analog position sensors in the motors, which lets him control the speed and makes it work better than any other hobby servo arm you’ve ever seen, but there’s still visible backlash in the gears. A mere twelve years later, he’s got magnetic encoders on the output and a fast inner loop compensates for the backlash. The result is that the current arm moves faster and smoother, while retaining accuracy.

Twelve years. I assume that [Adam] has had some other projects on his plate as well, but that’s a long term project by any account. I’m stoked to see his work, not the least because it should help a lot of others who are ready to step up their desktop servo-arm projects. But the real take-home lesson here is that if you’ve got a tough problem that you’re hacking on, you don’t have to get it done this weekend. You don’t have to get it done next weekend either. Keep hammering on it as long as you need, but keep on hammering. When you get it done, the results will be all the better for the long, slow, brewing time. What’s the longest project that you’ve ever worked on?