Hackaday Podcast 032: Meteorite Snow Globes, Radioactive Ramjet Rockets, Autonomous Water Boxes, And Ball Reversers

Hackaday Editors Mike Szczys and Elliot Williams recorded this week’s podcast live from Chaos Communication Camp, discussing the most interesting hacks on offer over the past week. I novel locomotion news, there’s a quadcopter built around the coanda effect and an autonomous boat built into a plastic storage bin. The radiation spikes in Russia point to a nuclear-powered ramjet but the idea is far from new. Stardust (well… space rock dust) is falling from the sky and it’s surprisingly easy to collect. And 3D-printed gear boxes and hobby brushless DC motors have reached the critical threshold necessary to mangle 20/20 aluminum extrusion.

Take a look at the links below if you want to follow along, and as always tell us what you think about this episode in the comments!

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Putting The Coanda Effect To Work On A Quadcopter

The Coanda effect is an aerodynamic principle regarding the way fluids tend to flow along curved surfaces. This can be used to direct a flow, and [Tom Stanton] wanted to try out its application on a quadcopter. (Video embedded below.)

The project began by firing up the 3D printer, which made experimenting with a variety of different aerodynamic forms easy. Wishing to avoid simply putting a large obstruction in the way of an otherwise efficient propeller, the experiment first used impellers to direct flow sideways, over the edge of the Coanda domes. The impellers, combined with the Coanda domes, were a factor of 5 less efficient at generating thrust compared to a standard prop setup, but [Tom] persevered.

In testing, the drone was unable to fly outside of ground effect, with its weight exceeding its maximum thrust. However, [Tom] noted that the Coanda domes helped create a cushion of air when flying in this ground effect region that was far more than experienced with a typical prop drone.

Wanting some further success, [Tom] then replaced the impellers with standard drone props. This greatly improved performance, with the drone now able to fly out of ground effect and use far less power. However, its performance was still worse than a standard drone without Coanda domes fitted. [Tom] suspects that this is due to the weight penalty most of all.

While it’s unlikely you’ll see Coanda effect drones going mainstream anytime soon, [Tom]’s project goes to show that you can perform viable aerodynamic research at home with little more than a 3D printer and a fog machine. There’s plenty more fun you can have with the Coanda effect, too. Video after the break.

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Compressed Air Levitation And The Coanda Effect

What do you want to levitate today? [Latheman666] uses his air compressor to make all kinds of stuff float in mid air. Light bulb, key chain, test tube, ball bearing, tomato… pretty neat trick to try in your shop.

It is interesting to see what physics explain this behavior. The objects do not float just because they are pushed upwards by the airflow, that would be an unstable equilibrium situation. Instead, they obtain lift in a very similar way as the wings of an airplane. Not all objects will levitate using this trick: the object has to be semi-spherical at the top.

[Applied Science] nicely shows this behavior by levitating a screwdriver first, then an identical object but with a flat top. The flat top screwdriver fails to levitate. The curvature provides the path for a smooth airflow, because of the Coanda effect, creating a zone of low pressure at the top, making the situation analogous to that of an airplane wing. Therefore, for this to work, you need an object with some kind of airfoil shaped surface. Another great demonstration is that of [NightHawkInLight], using a high speed camera.

A very impressive experiment that needs nothing more than an air compressor!, we are sure you will try it next time you work with one. For more on this topic of levitation with air streams, check the ping pong ball levitation machine.

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