You find them everywhere from 3D printers to jet airliners. They’re the little switches that detect paper jams in your printer, or the big armored switches that sense when the elevator car is on the right floor. They’re microswitches, or more properly miniature snap-action switches, and they’re so common you may never have wondered what’s going on inside them. But the story behind how these switches were invented and the principle of physics at work in the guts of these tiny and useful switches are both pretty interesting.
For the last few years, very well-informed people have been able to tell if an alkaline battery is good or not simply by dropping them. When dropped from an inch or two above a hard surface, a good battery won’t bounce, and will sometimes land standing up. A dead battery, on the other hand, will bounce. Thanks to [Lee] and a few of his friends, we now know why this happens.
While hanging out with a few of his buddies, [Lee] was able to condense all the arguments on why dead batteries bounce to two theories. The first theory, the ‘bounce theory’ said dead batteries had an increase in outgassing in the battery, increasing the pressure in the battery, which increases the spring constant of the battery itself. The second theory, the ‘anti-bounce theory’, said the gel-like properties of the electrolyte worked as a sort of mass damper.
[Lee] designed an experiment to test the outgassing ‘bounce theory’ of bouncing batteries. Instead of dropping a battery, an object – in this case a brass slug – was dropped onto both good and bad batteries. There was no difference. Even after holes were drilled to vent any gasses inside the battery, the brass slug bounced off both good and bad batteries the same way.
This means the reason dead alkaline batteries bounce is due to the electrolyte. [Lee] cut open a few AA cells and found the electrolyte in a good battery was a mushy mess of chemicals. In the dead battery, this same electrolyte hardened into a solid mass. [Lee] compares this to an anti-bounce hammer.
Finally, more than a year after most of us learned about bouncing dead batteries thanks to [Dave Jones]’ video, we have an answer. It’s a chemical change in the electrolyte that turns it from a goo to a solid that makes dead batteries bounce.
[Nigel’s] been trying out a series of designs and materials to make his own bounce flash. He set out on this mission because most of the images he used flash on ended up washed out with dark shadows. The flash add-on seen above seeks to curb the harshness of the direct light but shielding the subject.
What you see above is just a couple of pieces of paper. [Nigel] put together a template so that you can cut your own. Although the design is his favorite, he also put together a second generation that is built from hobby plastic with a piece of aluminum tape as the reflecting surface. The main link at the beginning of this feature leads to that version, but after the break we’ve included direct links to each article he published during his experimentation.
The Blind Juggler is a robot that juggles or bounces balls in a controlled manner without any sensory input. It is basically just a linear actuator with a paddle on the end to smack the ball back into the air as it returns to the ground. The crazy thing is, it is doing this based purely on pre programmed math. There are no sensors telling it to make any adjustments. While we could envision this functioning, we would never have expected it to be as stable as it is. You can see in the video above that they can actually move the entire robot around while maintaining the bounce. Also check out the pendulum version, instead of just actuating vertically, it is mounted as a pendulum allowing the ball to travel back and forth in an arc.