# How The Turntable Paradox Works

Leave most objects on top of a turntable, and set it spinning, and they’ll fly off in short order. Do the same with a ball, though, and it somehow manages to roll around on top for quite some time without falling off. [Steve Mould] set about unpacking this “Turntable Paradox” in a recent YouTube video.

In the basic case, the fact that the ball rolls is what keeps it on the turntable. As the turntable spins, the ball spins in the opposite direction, as per Newton’s first law of motion. As long as the ball is allowed to roll up to the same speed as the turntable, it will pretty much stay in place in the absence of any other perturbing forces. In the event the ball is nudged along the turntable, though, it quickly ends up in a more complicated circular motion, orbiting in a ratio to the speed of the turntable itself. [Steve] explains the mechanisms at play, and dives into the mathematics behind what’s going on.

Sometimes, demonstrations like these can seem like mere curiosities. However, understanding physical effects like these has been key to the development of all kinds of complicated and fantastical machinery. Video after the break.

# Put A New Spin On Your 3D Printed Parts

Once you get tired of printing keychains and earbud holders with your 3D printer, you’ll want to design things a bit more sophisticated. How about things that rotate? [3DSage] has a good how-to about how to integrate a simple motor and controller into a few different size boxes. Combined with some 3D printed linkages, these boxes can turn your project — printed or otherwise — into something that spins.

To demonstrate, he created a few cat toys, played with an idea for a magic trick, and refit a selfie light into… something. We have no doubt you can find something to do with these little motor modules. The boxes vary mostly in how big the battery packs are. There are also several interesting side pieces like a 3D holder for rechargeable button cells and their charger.

In addition, he also demonstrates how to use the motor as a (rather poor) generator. Attaching a water wheel wasn’t a success until he used compressed air to run the wheel. You would have thought water would have done the trick.

The video stresses that you should solder connections, but you don’t have to. Honestly, we think if you are building moving stuff with a 3D printer, you should probably just go ahead and learn to solder. It isn’t that hard and there are plenty of reasons to learn.

Of course, you could 3D print the motor itself. Adapting motor modules for different uses isn’t a new idea, of course, but it is always great to see more ways to apply basic components.

# Piezoelectric Gyro Shows How They Rolled Back In The Day

There’s no doubting the wonders that micro-electromechanical systems (MEMS) technology have brought to the world. With MEMS chips, your phone can detect the slightest movement, turning it into a sensitive sensor platform that can almost anticipate what you’re going to do next. Actually, it’s kind of creepy when you think about it.

But before nano-scale MEMS inertial sensing came along, lots of products needed to know their ups from their downs, and many turned to products such as this vibrating piezoelectric gyroscope that [Kerry Wong] found in an old camcorder. The video below shows a teardown of the sensor, huge by MEMS standards but still a marvel of micro-engineering. The device is classified as a Coriolis vibratory gyroscope (CVG) which, as the name implies, uses the Coriolis effect to sense rotation. In this device, [Kerry] found that a long, narrow piezoelectric element spans the long axis of the sensor, suspended from what appears to be four flexible arms. [Kerry] probed the innards of the sensor while powered up and discovered a 22 kHz signal on the piezo element; this vibrates the bar in one plane so that when it rotates, it exerts a force on the support arms that can be detected. Indeed, [Kerry] hooked the output of the sensor to a wonderfully old-school VOM whose needle wiggled with the slightest movement of the sensor.

Sadly, MEMS made this kind of sensor obsolete, but we appreciate the look under the hood. And really, MEMS chips are using the same principle to detect motion, just on a much smaller scale. Want the MEMS basics? [Al] has you covered.

# Couch Potato Refined: Self-Rotating TV Uses Plywood Gears

When we first saw [Mikeasaurus’] project to rotate his TV 90 degrees in case he wanted to lay down and channel surf we were ready to be unimpressed. But it grew on us as we read about how he fabricated his own gearing system to make a car seat motor rotate the TV.

The gearing system is made from plywood and the design was from geargenerator.com, a freebie design tool we’ve covered before. You’d think you’d need a laser cutter, but in this case, the gear forms were printed out, glued on the plywood and then cut out manually. Each gear is made of several laminated together.

# 12-axis Sensor Adds Auto Screen Orientation To This Older Tablet PC

[Mal’oo] has one of those laptop computers whose screen swivels to turn it into a tablet. But the thing is a few years old and didn’t come with an orientation sensor that changes the screen between landscape and desktop, but also knows which side is up. His solution was to add a 12-axis sensor via the mini PCI express header.

The hardware comes in two pieces. The first is a mini-PCIe card to USB interface. This is handy if you want to add a Bluetooth dongle permanently to your computer. But he’s got other things in mind for it. After hacking the BIOS (which for some reason limits what you can plug into this slot) he moved onto the second part which is a USB 12-axis sensor. This picture shows the wires before they were soldered to the USB card. [Mal’oo] couldn’t just plug it in because the sensor wouldn’t have been oriented correctly in relation to the computer. The final product is quite response, as shown in the clip after the jump. Continue reading “12-axis Sensor Adds Auto Screen Orientation To This Older Tablet PC”

# Modifying A Servo For Continuous Rotation

[robomaniac] shows us how to modify a standard servo to allow continuous rotation. This is a classic robotics hack and has been around for a while, but we really like the way he put this together. Although you may need some soldering and desoldering tools to open the servo up, the hack is a physical one. All you really need to do is cut off a plastic tab on one of the gears. If you want to see an example of a bot you can build with one of these CR servos, he just posted this one motor walker.