Radial Vector Reducer Rotates At Really Relaxed Velocity

December 5, 2022 by Ryan Flowers 15 Comments

When [Michael Rechtin] learned about Radial Vector Reducers, the underlying research math made his head spin, albeit very slowly. Realizing that it’s essentially a cycloidal drive meshed with a planetary gear set, he got to work in CAD and, in seemingly no time, had a design to test. You can see the full results of his experiment in the video below the break. Or head on out to Thingiverse to download the model directly.

[Michael] explains that while there are elements of a cycloidal drive, itself a wonderfully clever gear reduction mechanism, the radial vector reducer actually has more bearing surfaces, and should be more durable as a result. Two cycloidal disks are driven by a planetary gear reduction for an even greater reduction, but they don’t even spin, they just cycle in a way that drives the outer shell, setting them further apart from standard cycloidal drives.

How would this 3D printed contraption hold up? To test this, [Michael] built a test jig with a NEMA 23 stepper providing the torque, and an absurd monster truck/front loader wheel — also printed — to provide traction in the grass and leaves of his back yard. He let it drive around its tether for nearly two weeks before disassembling it to check for wear. How’d it look? You’ll have to check the video to find out.

If you aren’t familiar with cycloidal drives, check out this fantastic explanation we featured. As for planetary drives, what better way to demonstrate it than by an ornamental planetary gear clock!

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Magnetic Gearbox Can Go Fast But Not Hard

September 2, 2022 by Danie Conradie 13 Comments

3D printed gearboxes are great for experimental designs, but due to roughness and inaccuracies in the printed surfaces, they can wear quickly and be rather noisy. As a possible alternative, [Resetman] is experimenting with magnetic 3D printed gearboxes that work without physical contact between the rotating wheels, and can also be “geared” for different ratios in some interesting ways.

Naturally, two closely spaced wheels with magnets will interact with each other, with the ratio defined by the number of magnets on each wheel. A much less obvious implementation is a second-order radial flux coaxial magnetic gearbox. It works similar to a normal planetary gearbox, with an outer and inner wheel containing magnets, and an intermediate ring known as a flux modulator, containing equally spaced pieces of ferromagnetic steel metal. In [Resetman] demonstration, the flux modulator is just a 3D printed ring screws around its circumference.

The most obvious disadvantage is of course severely limited torque transfer. [Resetman] could easily accelerate the sun wheel to 12,000 RPM if the flux modulator is accelerated slowly, but any sudden changes in speed would cause it to lose synchronization. Of course, you can consider this a torque-limiting feature for certain use cases. With a bit of testing, he determined the torque limit at a 1:4 ratio was a meager 0.05 Nm. This could be increased by some optimization, for example rearranging the magnets to form Halbach arrays, and reducing the air gaps between the components.

Magnetic gearboxes are nothing new, we’ve featured another demonstrator before, and even did an “Ask Hackaday” on the subject. What would you use these for? Let us know below.

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Stackable 3D-Printed Gearbox For Brushless Motor

July 24, 2022 by Danie Conradie 11 Comments

Affordable brushless motors are great for a variety of motion applications, but often require a gearbox to tame their speed. [Michael Rechtin] decided to try his hand at designing a stackable planetary gearbox for a brushless motor that allows him to add or remove stages to change the gear ratio.

The gearbox is designed around a cheap, 5010 size, 360 KV, sensorless motor from Amazon. Each stage consists of a 1:4 planetary gear set that can be connected to another stage, or to an output hub. This means the output speed reduces by a factor of four for each added stage. Thanks to the high-pressure angle, straight-cut teeth, and fairly loose clearances, the gearbox is quite noisy.

To measure torque, [Michael] mounted the motor-gearbox combo to a piece of aluminum extrusion, and added a 100 mm moment arm to apply force to a load cell. The first test actually broke the moment arm, so a reinforced version was designed and printed. The motor was able to exert approximately 9.5 Nm through the gearbox. This number might not be accurate, since sensorless motors like this one can not provide a smooth output force at low speeds. As [Michael] suggests, adding a sensor and encoder would allow for better testing and low speed applications. Check it out in the video after the break.

We’ve featured a number of [Michael]’s projects before, including a bag tracking corn hole board, and a 3D printed linear actuator. Continue reading “Stackable 3D-Printed Gearbox For Brushless Motor” →

Cheap Big Servo For Robot Arm

November 19, 2021 by Lewin Day 10 Comments

[Skyentific] is looking to push the hobbyist robotics state of the art. Motors and their gears, the actuators, are typically the most expensive part. For his build, he realised he needed big servos capable of delivering plenty of torque. Thus, he set about creating a 3D-printed design to get the job done on a budget. (Video, embedded below.)

Stepper motors are the order of the day here, chosen for their low cost compared to brushless solutions, particularly when taking control hardware into account. In this design, the stepper motor drives a sun gear as part of a bigger planetary gearbox with a high gear ratio. Cross-roller bearings are used to allow the servo to effectively handle both radial and axial loads. The servo as a whole is designed to fit neatly into the joints of the robot arm itself, and has external mounting points provisioned as such.

It’s a neat servo that somewhat apes those used on full-sized industrial designs, at least in the sense of being an integrated part of the joints of a robot arm. It also comes in at a relatively-cheap $32 based on the materials used by [Skyentific].

We’ve seen some related work from [Skyentific] before, too – like this interesting cable-driven joint. Video after the break.

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A Featherweight Direct Drive Extruder In A Class Of Its Own

November 5, 2020 by Sonya Vasquez 39 Comments

Even a decade later, homebrew 3D printing still doesn’t stop when it comes to mechanical improvements. These last few months have been especially kind to lightweight direct-drive extruders, and [lorinczroby’s] Orbiter Extruder might just set a paradigm for a new kind of direct drive extruder that’s especially lightweight.

Weighing in at a mere 140 grams, this setup features a 7.5:1 gear reduction that’s capable of pushing filament at speeds up to 200 mm/sec. What’s more, the gear reduction style and Nema 14 motor end up giving it an overall package size that’s smaller than any Nema 17 based extruder. And the resulting prints on the project’s Thingiverse page are clean enough to speak for themselves. Finally, the project is released as open source under a Creative Commons Non-Commercial Share-Alike license for all that (license-respecting!) mischief you’d like to add to it.

This little extruder has only been around since March, but it seems to be getting a good amount of love from a few 3D printer communities. The Voron community has recently reimagined it as the Galileo. Meanwhile, folks with E3D Toolchangers have been also experimenting with an independent Orbiter-based tool head. And the Annex-Engineering crew has just finished a few new extruder designs like the Sherpa and Sherpa-Mini, successors to the Ascender, all of which derive from a Nema 14 motor like the one in the Orbiter. Admittedly, with some similarity between the Annex and Orbiter designs, it’s hard to say who inspired who. Nevertheless, the result may be that we’re getting an early peek into what modern extruders are starting to shape into: smaller steppers and more compact gear reduction for an overall lighter package.

Possibly just as interesting as the design itself is [lorinczroby’s] means of sharing it. The license terms are such you can faithfully replicate the design for yourself, provided that you don’t profit off of it, as well as remix it, provided that you share your remix with the same license. But [lorinczroby] also negotiated an agreement with the AliExpress vendor Blurolls Store where Blurolls sells manufactured versions of the design with some proceeds going back to [lorinczroby].

This is a clever way of sharing a nifty piece of open source hardware. With this sharing model, users don’t need to fuss with fabricating mechanically complex parts themselves; they can just buy them. And buying them acts as a tip to the designer for their hard design work. On top of that, the design is still open, subject to remixing as long as remixers respect the license terms. In a world where mechanical designers in industry might worry about having their IP cloned, this sharing model is a nice alternative way for others to both consume and build off of the original designer’s work while sending a tip back their way.

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Robot Joints Go Modular With This Actuator Project

October 22, 2019 by Donald Papp 4 Comments

[John Lauer] has been hard at work re-thinking robot arms. His project to create modular, open source actuators that can be connected to one another to form an arm is inspiring, and boasts an impressively low parts cost as well. The actuators are each self-contained, with an ESP32 and a design that takes advantage of the form factors of inexpensive modules and parts from vendors like Aliexpress.

Flex spline in action, for reducing backlash

Each module has 3D printed gears (with an anti-backlash flex spline), an RGB LED for feedback, integrated homing, active cooling, a slip ring made from copper tape, and a touch sensor dial on the back for jogging and training input. The result is a low backlash, low cost actuator that keeps external wiring to an absolute minimum.

Originally inspired by a design named WE-R2.4, [John] has added his own twist in numerous ways, which are best summarized in the video embedded below. That video is number three in a series, and covers the most interesting developments and design changes while giving an excellent overview of the parts and operation (the video for part one is a basic overview and part two shows the prototyping process, during which [John] 3D printed the structural parts and gears and mills out a custom PCB.)

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Rover V2 Handles Stairs As Easily As The Outdoors

August 15, 2018 by Donald Papp 10 Comments

Rover V2 is an open-source, 3D-printable robotic rover platform that has seen a lot of evolution and development from its creator, [tlalexander]. There are a number of interesting things about Rover V2’s design, such as the way the wheel hubs themselves contain motors and custom planetary gearboxes. This system is compact and keeps weight down low to the ground, which helps keep a rover stable. The platform is all wheel drive, and moving parts like the suspension are kept high up, as far away from the ground as possible. Software is a custom Python stack running on a Raspberry Pi that provides basic control.

The Rover V2 is a full mechanical redesign of the previous version, which caught our attention with its intricate planetary gearing inside the wheel hubs. [tlalexander]’s goal is to create a robust, reliable rover platform for development that, thanks to its design, can be mostly 3D printed and requires a minimum of specialized hardware.