Using Vibration To Make Stuff Stick Contact-Free To Ceilings

Generally making stuff stick to something like a ceiling requires resorting to suction cups, glue or something much more permanent, but [Steve Mould] starts his video featuring a playing card that is clearly defying gravity with no such measures. All that it seems to take is the small vibration motor placed on said playing card, with its vibrations making the card stick like a kind of magic trick.

Although the easy explanation would be that it creates a kind of Bernoulli grip – a common pneumatic, contactless gripping device – [Steve] explains how it’s more complex than that. This vibration adhesion effect doesn’t rely on the same constant pressure drop that a Bernoulli grip experiences within the small gap between the surface and the object. Although a gap is present, it’s much smaller in this case.

Of note is that this effect only occurs when the object is made of a flexible enough material that can vibrate along with the vibration source, in the form of a motor or transducer. As demonstrated in the video, this creates standing waves that affect the surrounding air. When pushed against a rigid surface, these standing waves change into travelling waves, which result in the air that enters this small gap constantly being pushed out and thus lowering the air pressure.

The air pressure between the rigid and flexible surfaces thus becomes lower than that of the surrounding air, creating the resulting suction effect without touching the surface as something like a suction cup would.

One can imagine practical uses for this effect much like with Bernoulli grips. These are especially common in the semiconductor industry for handling delicate items like silicon wafers with zero risk of contamination. In the video it’s shown how you can use the effect to even hold the weight of a person, though they failed to get past a few dozen kilograms with the used setup involving a 400 Watt transducer, possibly due to their ‘ceiling’ not being rigid enough, leading to energy loss.

There are also papers such as this 2025 one by [Siquan Li] et al. who suggest a ‘Micro-Vibration Adhesion’  (VBA) system to help small robots climb up walls for use in repairs and inspection. In their experimental setup they found an adhesion-to-weight ratio exceeding 51 times, making it an interesting way to have small robots defy gravitational pull without a complicated mechanism.

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Space Shuttle Model In A Hypersonic Wind Tunnel

Mach 20 In A Wind Tunnel: Yes, It’s Rocket Science

Hypersonic speeds are defined by those exceeding Mach 5, and lately there’s been a lot of buzz about unmanned hypersonic vehicles making test flights. Vehicles returning from orbital flight also travel at hypersonic speeds as they do their best to transition back to the terrestrial realm. Before anything leaves ground though, these machines are tested in wind tunnels. [Scott Manley]’s video “How Hypersonic Wind Tunnels Recreate Mach 20” (embedded below) does a wonderful job of explaining the engineering behind wind tunnels for testing hypersonic vehicles.

While the earliest wind tunnels such as that used by the Wright Brothers were powered by simple fans, it is not possible for any propeller to surpass subsonic speeds. This is evidenced by there not being any propeller driven aircraft that can exceed Mach 1. Since an aircraft can’t reach those speeds with a propeller, it follows that a wind tunnel cannot be driven by propellers, fans, or any such device, and exceed Mach 1 wind speed, either. So it begs the question: Just how do they do it?

You might think that the answer lays in Bernoulli’s law – but it does not. You might think it involves compressing the air into smaller and smaller tubes and pipes. It doesn’t. As [Scott Manley] so expertly explains in the video below the break, it has quite a lot in common with actual rocket science.

You may be interested to know that we’ve covered some DIY wind tunnel builds as well as a small desktop wind tunnel in the past. While not hypersonic, they’re exactly what you’d want to have if you’re an aerospace hacker of any kind.

Thanks [Zane Atkins] for the tip!

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The Old Ping-Pong Ball Levitation Trick

pingpongLev

[Jacob] has put a slightly new twist on the levitating ball trick with his ping-pong ball levitation machine. We’ve all seen magnetic levitation systems before. Here on Hackaday, [Caleb] built a Portal gun which levitated a Companion Cube. Rather than go the magnetic route, [Jacob] levitated a ping-pong ball on a cushion of air.

Now, it would be possible to cheat here, anyone who’s seen a demonstration of Bernoulli’s principle knows that the ball will remain stable in a stream of air. [Jacob] proves that his system is actually working by levitating ping-pong balls with different weights.

A Parallax Ping style ultrasonic sensor measures the distance between the top of the rig and the levitating ball. If the ball gets above a set distance, [Jacob’s] chipKit based processor throttles down his fans. If the ball gets too low, the fans are throttled up. A software based Proportional Integral Derivative (PID) loop keeps the system under control. A graph of the ball distance vs fan speed is displayed on an Android tablet connected to the controller via USB.

When [Jacob] switches a heavy ball for a light one, the lighter ball is pushed beyond the pre-programmed height. The controller responds by reducing the fan speed and the ball falls back. Who said you can’t do anything good with a box of corn dogs?

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