Gear Up Your Gear Knowledge With Gears

Gears are fairly straightforward way to couple rotational motion, and the physics topics required to understand them are encountered in an entry level physics classroom, not a university degree. But to really dig down to the root of how gears transfer motion may be somewhat more complex than it seems. [Bartosz Ciechanowski] put together an astonishingly good interactive teaching tool on gears, covering the fundamentals of motion up through multi-stage gear trains.

Illustrating the distance traveled at different points on the disc

The post starts at the beginning – not “how to calculate a gear ratio” – but how does rotational motion work at all. The illustrations help give the reader an intuitive sense for how the rate of rotation is measured and what that measurement actually represents in the real world. From there [Bartosz] builds up to describing how two discs touching edge to edge transfer motion and the relationship of their size on that process. After explaining torque he has the fundamentals in place to describe why gears have teeth, and why they work at all.

Well written explanatory copy aside, the real joy in this post is the interactivity. Each concept is illustrated, and each illustration is interactive. Images are accompanied by a slider which lets you adjust what’s shown, either changing the speed of a rotating gear or advancing the motion of two teeth interlocking. We found that being able to move through time this way really helped form an intuitive understanding of the concepts being discussed. This feels like the dream of interactive multimedia textbooks come to life.

Casting Gears At Home

Automatic doors and gates are great, except when they fail, which seems to be about every three days in our experience. [MAD WHEEL] had just such a failure, with a plastic gear being the culprit. Rather than buy a new drive unit, they set about casting a replacement in metal.

The video is light on instructions and heavy on progressive rock, and may be a little difficult to follow for beginners. The process begins by gluing the original plastic part back together, and filling in the gaps with epoxy putty. A mould is then created by setting the gear in a gelatine/glycerine mixture. This mould is then filled with wax to create a wax copy of the original part. The wax gear is fitted with cylindrical stems to act as runners for molten metal, and then a plaster mould is made around the wax positive. Two plaster moulds are made, which are placed in an oven to melt out the wax.

The aim was to cast a replacement part in aluminium. The first attempt failed, with the aluminium cooling too rapidly. This meant fine details like the gear teeth simply didn’t cast properly, creating a useless metal blob. On the second attempt, the plaster mould was heated first, and this kept things hot enough to allow the aluminium to fill in the finer details. With that done, it was a simple matter of some post-processing to remove the runners, clean up the gear teeth and refine the shape of the gear on the lathe.

The resulting part does its job well, meshing properly with the other gears in the drivetrain and moving the gate effectively. Many in the comments have stated that the original gear being plastic was likely as a safety measure, to strip out in the event the gate is jammed. While this may be true, it’s a far more robust design practice to instead use a breakable plastic key rather than breaking an entire gear in the event of a problem.

Casting is quite accessible to the dedicated home maker. It’s a great way to make custom metal parts once you’ve learned the fundamentals! Video after the break.

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A (Mostly) 3D Printed Servo/Gear Reduction

This servo/gear reduction was assembled with almost all 3D-printed parts. Apart from a brushed 36 V DC-motor, a stainless steel shaft, and screws for holding the servo together, the only other non-printed part is the BTS7960B motor driver.

Some interesting stats about the plastic servo – its stall torque is about 55 kg/cm, reaching a peak current draw of 18 A when using a 6s LiPo battery outputting 22-24 V. The shaft rotates using two 20 mm holes and lubrication. (Ball bearings were originally in the design, but they didn’t arrive on time for the assembly.)

The holes of the gears are 6.2 mm in diameter in order to fit around the shaft, although some care is taken to sand or fill the opening depending on the quality of the 3D print.

This isn’t [Brian Brocken]’s only attempt at 3D-printing gears. He’s also built several crawling robots, a turntable, and a wind up car made entirely from acrylic. The .stl files for the project are all available online for anyone looking to make their own 3D-printed servo gears.

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(Mis)use This Part To Attach 3D Printed Stuff To A Shaft

Interfacing a shaft to a 3D printed gear doesn’t have to be tricky. [Tlalexander] demonstrated a solution that uses one half of a spider coupling (or jaw coupling) to create an effective modular attachment. The picture above (and this older link) shows everything you need to know: the bottom of the coupling is mounted to the shaft, and a corresponding opening is modeled into the the 3D printed part. Slide the two together, and the result is a far sturdier solution than trying to mate a 3D printed gear directly to a motor shaft with a friction fit or a screw. This solution isn’t necessarily limited to attaching gears either, any suitable 3D printed part could be interfaced to a shaft in this way.

These couplings are readily available, and fortunately for hobbyists, come in sizes specifically designed for common stepper motors like NEMA 17 and NEMA 23. Ironically, these couplings are often used when building custom 3D printers for those same reasons. With this method interfacing anything at all to a motor shaft becomes mostly a matter of modeling a matching hole out of the part to be 3D printed. One coupling even provides two such attachments, since only one of the two sides is used.

The image up top is from [Tlalexander]’s Rover image gallery, which contains a ton of fantastic pictures of the work that went into the gearboxes, a major part of the Rover’s design that we’ve seen in the past.

Printed It: Hand Cranked Photography Turntable

Even a relatively low-end desktop 3D printer will have no problems running off custom enclosures or parts for your latest project, and for many, that’s more than worth the cost of admission. But if you’re willing to put in the time and effort to become proficient with necessary CAD tools, even a basic 3D printer is capable of producing complex gadgets and mechanisms which would be extremely time consuming or difficult to produce with traditional manufacturing techniques.

Printable bearing cross-section

Once you find yourself at this stage of your 3D printing career, there’s something of a fork in the road. The most common path is to design parts which are printed and then assembled with glue or standard fasteners. This is certainly the easiest way forward, and lets you use printed parts in a way that’s very familiar. It can also be advantageous if you’re looking to meld your own printed parts with existing hardware.

The other option is to fully embrace the unique capabilities of 3D printing. Forget about nuts and bolts, and instead design assemblies which snap-fit together. Start using more organic shapes and curves. Understand that objects are no longer limited to simple solids, and can have their own complex internal geometries. Does a hinge really need to be two separate pieces linked with a pin, or could you achieve the desired action by capturing one printed part inside of another?

If you’re willing to take this path less traveled, you may one day find yourself creating designs such as this fully 3D printed turntable by Brian Brocken. Intended for photographing or 3D scanning small objects without breaking the bank, the design doesn’t use ball bearings, screws, or even glue. Every single component is printed and fits together with either friction or integrated locking features. This is a functional device that can be printed and put to use anywhere, at any time. You could print one of these on the International Space Station and not have to wait on an order from McMaster-Carr to finish it.

With such a clever design, I couldn’t help but take a closer look at how it works, how it prints, and perhaps even some ways it could be adapted or refined going forward.

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Pushing 3D Printed Wheels And Transmissions To The Limit

What do you do if you want a robot with great mobility? Walking is hard, and wheels are good enough, especially if you use the ‘wheels within wheels’ Mecanum setup. But you need torque, too. That’s what makes this entry into the Hackaday Prize so fantastic. It’s a Mecanum wheel of sorts, with an integrated gear set that produces a phenomenal amount of torque using a small, cheap stepper motor.

The wheel itself if 3D printed and fully parametric, using nylon weed wacker filament for the treads. This allows the wheel to scoot back and forth like a Mecanum wheel, or at the very least like one of those hyper mobile wheeled robots you see from time to time. It goes backwards, forwards, and side to side, and also has a zero turn radius.

A 3D printed Mecanum wheel is great, but how on earth do you drive it? That problem is solved with this hybrid planetary/strain-wave  3D-printed gear set. [Daren] has created a very compact ‘single’ stage gear set that fits right on top of a stepper motor. It’s thin, flat, and has a gear reduction of about 66:1. That’s a lot of torque in a very small package. Both of these projects are combined, and together they represent a freaky wheel with a lot of torque.

Even though [Daren] doesn’t have a robot in mind for this build, these are most certainly the building blocks of a fantastic robot, and a great entry in the Hackaday Prize.

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Benchtop Lathe Gets An Electronic Leadscrew Makeover

The king of machine tools is the lathe, and if the king has a heart, it’s probably the leadscrew. That’s the bit that allows threading operations, arguably the most important job a lathe can tackle. It’s a simple concept, really – the leadscrew is mechanically linked through gears to the spindle so that the cutting tool moves along the long axis of the workpiece as it rotates, allowing it to cut threads of the desired pitch.

But what’s simple in concept can be complicated in reality. As [Clough42] points out, most lathes couple the lead screw to the spindle drive through a complex series of gears that need to be swapped in and out to accommodate different thread pitches, and makes going from imperial to metric a whole ball of wax by itself. So he set about building an electronic leadscrew for his lathe. The idea is to forgo the gear train and drive the leadscrew directly with a high-quality stepper motor. That sounds easy enough, but bear in mind that the translation of the tool needs to be perfectly synchronized with the rotation of the spindle to make threading possible. That will be accomplished with an industrial-grade quadrature encoder coupled to the spindle, which will tell software running on a TI LaunchPad how fast to turn the stepper – and in which direction, to control thread handedness. The video below has some great detail on real-time operating systems on microcontrollers as well as tests on all the hardware to be used.

This is only a proof of concept at this point, but we’re looking forward to the rest of this series. In the meantime, [Quinn Dunki]’s excellent series on choosing a lathe should keep you going.

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