Even before the Industrial Revolution, gears of one kind or another have been put to work both for and against us. From ancient water wheels and windmills that ground grain and pounded flax, to the drive trains that power machines of war from siege engines to main battle tanks, gears have been essential parts of almost every mechanical device ever built. The next installment of our series on Mechanisms will take a brief look at gears and their applications.
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.
Here on Hackaday, too often do we turn our heads and gaze at the novelty of 3D printing functional devices. It’s easy to forget that other techniques for assembling functional prototypes exist. Here, [Reuben] nails the aspect of functional prototyping with the laser cutter with a real-world application: a roll-pitch friction differential drive built from just off-the shelf and laser-cut parts!
The centerpiece is held together with friction, where both the order of assembly and the slight wedged edge made from the laser cutter kerf keeps the components from falling apart. Pulleys transfer motion from the would-be motor mounts, where the belts are actually tensioned with a roller bearing mechanism that’s pushed into position. Finally, the friction drive itself is made from roller-blade wheels, where the torque transferred to the plate is driven by just how tightly the top screw is tightened onto the wheels. We’d say that [Reuben] is pushing boundaries with this build–but that’s not true. Rather, he’s using a series of repeatable motifs together to assemble a both beautiful and complex working mechanism.
This design is an old-school wonder from 2012 uncovered from a former Stanford course. The legendary CS235 aimed to teach “unmechanically-minded” roboticists how to build a host of mechanisms in the same spirit as MIT’s How-to-make-almost-Anything class. While CS235 doesn’t exist anymore, don’t fret. [Reuben] kindly posted his best lectures online for the world to enjoy.
After a couple of millennia of fiddling with gears, you’d think there wouldn’t be much new ground to explore in the field of power transmission. And then you see something like an infinitely variable transmission built from nested pulleys, and you realize there’s always room for improvement.
The electric motors generally used in robotics can be extremely efficient, often topping 90% efficiency at high speed and low torque. Slap on a traditional fixed-ratio gearbox, or change the input speed, and efficiency is lost. An infinitely variable transmission, like [Alexander Kernbaum]’s cleverly named Inception Drive, allows the motor to stay at peak efficiency while smoothly changing the gear ratio through a wide range.
The mechanism takes a bit of thought to fully grok, but it basically uses a pair of split pulleys with variable spacing. The input shaft rotates the inner pulley eccentrically, which effectively “walks” a wide V-belt around a fixed outer pulley. This drives the inner pulley at a ratio depending on the spacing of the pulley halves; the transmission can shift smoothly from forward to reverse and even keep itself in neutral. The video below will help you get your head around it.
We’ve seen a couple of innovative transmissions around here lately; some, like this strain-wave gear and this planetary gearbox, are amenable to 3D printing. Looks like the Inception Drive could be printed too. Hackers, start your printers and see what this drive can do.
Small DC motors are easy to find — you can harvest dozens from old printers and copiers. You might even get a few with decent gearboxes too. But will you get exactly the motor with exactly the gearing your project needs? Unlikely, but you can always just print a gearbox to get exactly what you need.
There’s nothing fancy about [fortzero]’s gearboxes. The motors are junk bin specials, and the gears are all simple spur gears 3D-printed from PLA. There are four gears in the train, each with a 2:1 reduction, giving a 16:1 overall ratio. The gears ride on brass shafts that are press-fit into the housing, and there’s not a bearing in sight — just a few washers to keep the gears spaced apart and plenty of grease. Despite the simplicity, the gearboxes turned out to be pretty capable, lifting a 3.5 kg load. The design files are available and should make it easy for you to get just the ratio you want for the motor you have.
Of course more complicated gearboxes are possible with a 3D printer, including a split-harmonic planetary gear, or a strain wave gear using a timing belt. No 3D printer? No problem! Just build a LEGO gearbox.
Even if you’re reading this on a piece of paper that was hand-delivered to you in the Siberian wilderness, somewhere someone had to use energy to run a printer and also had to somehow get all of this information from the energy-consuming information superhighway. While we rely on the electric grid for a lot of our daily energy needs like these, it’s often unclear exactly how the energy from nuclear fuel rods, fossil fuels, or wind and solar gets turned into electrons that somehow get into the things that need those electrons. We covered a little bit about the history of the electric grid and how it came to be in the first of this series of posts, but how exactly does energy get delivered to us over the grid? Continue reading “How Energy Gets Where Its Needed”
Do you have a car? Does that car have a manual transmission? Do you want to beautify your shifter knob, while simultaneously gaining mad street cred, yo? Well, you’re in luck, because all of that can be done for the low, low price of a couple old skateboard decks, a lathe, and a lot of glue.
This project, from [basiltab] illustrates how you can use old skateboard decks to create really cool looking custom shifter knobs. The process starts with cutting the decks up into uniform strips, which are then glued and clamped to form small planks. Sections of the decks were alternated, to create a visually interesting pattern. The planks are then sanded so that they’re smooth and flat, and then glued up in a jig to form blocks with a threaded aluminum insert in the center. Optionally, aluminum can be used for some of the layers to add a little flair (2-part epoxy was used in place of glue for the aluminum).
After the glue has dried, the blocks can then be turned on a lathe to create the desired shape of the knob. As you can see, the results are pretty darn nifty. And, they certainly have a little more artistic credibility than the giant acrylic shifter knobs you normally find at your local auto parts store. Don’t worry, if you thought this article was about shift registers, we’ve got you covered there too.