Differential Drive Doesn’t Quite Work As Expected

Placing two motors together in a shared drive is a simple enough task. By using something like a chain or a belt to couple them, or even placing them on the same shaft, the torque can be effectively doubled without too much hassle. But finding a way to keep the torque the same while adding the speeds of the motors, rather than the torques, is a little bit more complicated. [Levi Janssen] takes us through his prototype gearbox that attempts to do just that, although not everything works exactly as he predicts.

The prototype is based on the same principles as a differential, but reverses the direction of power flow. In something like a car, a single input from a driveshaft is sent to two output shafts that can vary in speed. In this differential drive, two input shafts at varying speeds drive a single output shaft that has a speed that is the sum of the two input speeds. Not only would this allow for higher output speeds than either of the two motors but in theory it could allow for arbitrarily fine speed control by spinning the two motors in opposite directions.

The first design uses two BLDC motors coupled to their own cycloidal drives. Each motor is placed in a housing which can rotate, and the housings are coupled to each other with a belt. This allows the secondary motor to spin the housing of the primary motor without impacting the actual speed that the primary motor is spinning. It’s all a lot to take in, but watching the video once (or twice) definitely helps to wrap one’s mind around it.

The tests of the drive didn’t go quite as planned when [Levi] got around to measuring the stall torque. It turns out that torque can’t be summed in the way he was expecting, although the drive is still able to increase the speed higher than either of the two motors. It still has some limited uses though as he notes in the video, but didn’t meet all of his expectations. It’s still an interesting build and great proof-of-concept otherwise though, and if you’re not clear on some of the design choices he made there are some other builds out there that take deep dives into cycloidal gearing or even a teardown of a standard automotive differential.

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Ingenuity Completes Fourth Flight On Mars, Gets A New Mission

It’s the same on Mars as it is here — just when you’re getting used to your job, the bosses go and change things up.

At least that’s our read on the situation at Jezero crater, where the Mars Ingenuity helicopter has just had its mission upgraded and extended. In a Friday morning press conference, the Ingenuity flight team, joined by members of the Perseverance team and some NASA brass, made the announcement that Ingenuity had earned an extra 30 sols of flight time, and would be transitioned from a mere “technology demonstrator” to an “operations demonstration” phase. They also announced Ingenuity’s fourth flight, which concluded successfully today, covering 266 meters and staying airborne for 117 seconds.

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Unique Planetary Gearbox Can Be Custom Printed For Steppers

Stepper motors are a staple in all sorts of projects, but it’s often the case that a gearbox is needed, especially for applications like the linear drives in CNC machines and 3D printers. In those mechanisms, a high-torque, low backlash gearbox might be just the thing, and a 3D printable split planetary harmonic drive for the popular NEMA 17 motors would be even better.

Right up front, we’ll say that we’re skeptical that any plastic gearbox can stay as backlash free as [SirekSBurom] claims his creation is. But we can see the benefits of the design, and it has some nice features. First off, of course, is that it’s entirely 3D printed, except for a few screws. That it mates perfectly with a NEMA 17 motor is a really nice feature, too, and with the design up on Thingiverse it shouldn’t be too tough to scale it up and down accordingly. The videos below show you the theory: the stepper drives a sun gear with two planet gears orbiting, each of which engages a fixed ring of 56 teeth, and an output ring of 58 teeth. Each revolution of the planets around the fixed ring rotates the output ring by one tooth, leading to almost 100:1 reduction.

We think the ‘harmonic’ designation on this gearbox is a little of a misnomer, since the defining feature of a harmonic drive seems to be the periodic deformation of a flex spline, as we saw in this 3D-printed strain wave gear. But we see the resemblance to a harmonic drive, and we’ll admit this beastie is a little hard to hang a name tag on. Whatever you call it, it’s pretty cool and could be a handy tool for all kinds of builds.

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Rope Braiding Machine Built Entirely From LEGO Technics

If you’ve ever seen a rope-braiding machine in action, you know they’re amazing machines where bobbins of thread whirl and spin in a complex dance to weave the threads under and over each other. Building one of these machines must be incredibly difficult; building one out of LEGO Technics pieces is darn near insane.

[Nico71], as hardcore a Technics builder as they come, tackled this complex build and made it work. A large drum spins horizontally and carries three groups of three planetary-mounted thread bobbins. The entire drum spins in one direction while the bobbins and another die with three holes spin the other way. The resulting braids are then fed through another spinning die, and the resulting 9-strand rope is taken up by a winding drum. The drum has a self-reversing feeding mechanism to keep the finished spool neat and tidy. The most impressive thing about the build, though, is the fact that it’s all powered by a single motor, and that everything is synchronized via gears, shafts, sprockets, chains and clutches. It’s a Technics tour de force you can see in action after the break.

[Nico71]’s build are pretty amazing. Some are pure art, others are models of classic cars and motorcycles, but things like his loom and the calculator he’s working on now are remarkable. Of course if you need to see more of the mesmerizing ballet of rope-braiding machines, check out this 16-bobbin hand-cranked version.

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Gears Embedded In Business Cards

In [Bre Pettis]’s latest “things” video, he talks with [Adam Mayer] about his geared business cards. [Adam] has designed several versions of these cards that have functional gear systems in them. There appears to be a simple two gear one and a more complicated planetary gear set up. The designs have been uploaded to Thingiverse, so you can download and build your own.