First, a word (make that words) about transmissions: in the most general sense, a transmission is the thing that turns the power output of a motor into some combination of speed and torque. Usually, the way a transmission works is that you can trade torque for speed (or vice versa) while optimizing the efficiency of your motor: in automobiles, a low gear gives you lots of torque but limits your top speed, while a high gear gives up torque to let you go faster.
Most automobiles have discrete gearboxes, where you can choose from some number of fixed gear ratios. Inevitably, this means that most of the time, the transmission is not optimized for what you want to do. A continuously variable transmission, on the other hand, offers an infinite number of gear ratios over a fixed range.
Unlike most automobiles, most robots don't bother with transmissions at all, because they're heavy and complicated. This means that robots have to be designed to either move fast (which doesn't require a lot of torque), or haul stuff (which does), but they're not great at doing both.
The researchers designed an origami wheel that can do both, by simply changing its radius, and thanks to its origami design, it does this by itself. It's a completely automatic continuously variable transmission, which allows a small robot to either move fast or haul stuff without requiring any additional complexity beyond an origami wheel.
There are three robots in the video below. There's one with big fixed wheels (high speed, low torque), one with small fixed wheels (low speed, high torque), and then one with origami wheels that can expand and shrink. No adjustment is necessary: if the origami wheels have too much load on them to rotate, they stall, and as the wheel hubs continue to turn, the wheels collapse, which increases their torque until they can move:
To reiterate, this transmission is both continuously variable and completely automatic. The wheel can adopt any effective gear ratio in the range between its minimum and maximum diameters, and it does this passively like a spring, as it responds to loads on it by shrinking its diameter until it achieves the maximum diameter at which it can consistently rotate.
The cost of the origami wheel is 70 percent of the cost of a fixed diameter wheel, less whatever it costs to hire someone who knows what they're doing to fold it up for you. The researchers suggest that it would also be ideal for applications where weight and volume are issues, like interplanetary rovers, as the wheel can be folded up and then deploy itself.
Get more from IEEE Spectrum
Original article appeared on IEEE Spectrum; all rights reserved.