Variable-Nozzle Ducted Fan Provides Fluid Dynamics Lessons

Any student new to the principles of fluid dynamics will be familiar with Bernoulli’s principle and the Venturi effect, where the speed of a liquid or gas increases when the size of the conduit it flows through decreases. When applying this principle to real-world applications, though, it can get a bit more complex than a student may learn about at first, mostly due to the shortcomings of tangible objects when compared to their textbook ideals. [Mech Ninja] discovered this while developing a ducted fan based around an RC motor.

The ducted fan is meant to be a stand-in for a model jet engine, based around a high-powered motor generally designed for drone racing. Most of the build is 3D printed including duct system, but in order to improve the efficiency and thrust beyond simple ducting, [Mech Ninja] designed and built a variable nozzle to more finely control the “exhaust” of his engine. This system is also 3D printed and can restrict or open up the outflow of the ducted fan, much like a real jet engine would. It uses two servos connected to collars on the outside of the engine. When the servos move the collars, a set of flaps linked to the collars can choke or expand the opening at the rear of the engine.

This is where some of the complexity of real-life designs comes into play, though. After testing the system with a load cell under a few different scenarios, the efficiency and thrust weren’t always better than the original design without the variable nozzle. [Mech Ninja] suspects that this is due to the gaps between the flaps, allowing air to escape and disrupting the efficient laminar flow of the air leaving the fan, and plans to build an improved version in the future. Fluid dynamics can be a fairly complex arena to design within, sometimes going in surprising directions like this ducted fan that turned out better than the theory would have predicted, at least until they accounted for all the variables in the design.

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Wall-climbing Bot Does It With Ease

Paraswift is a robot that can climb vertical surfaces with ease. Here you can see the robot motoring up the side of a building with a parachute packed on it’s back for use on the way down. The team that built the robot is calling it a base jumper, but after seeing them catch the falling robot in a net we’d say it’s still a bit too fragile to make that claim.

The parachute isn’t the only way for this guy to get down after a long climb. As you can see in the video after the break, it has no trouble driving in any direction on a wall. Like other wall-climbers the Paraswift is using air to stick to the surface. A vortex of air, similar to a tornado, generates a large amount of negative pressure, sucking the body of the robot to the surface it is climbing. I you’re the one who traded a good portion of your life to spend building the Paraswift we’re guessing you added the parachute to hedge your bets against a power failure.

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Wall Climbing Robot Uses Supersonic Grippers


Watch out Spidey, there’s a new wall climber in town!

Researchers [Matthew Journee, XiaoQi Chen, James Robertson, Mark Jermy, and Mathieu Sellier] recently unveiled their wall climbing wonder bot at the 2011 IEEE International Conference on Robotics and Automation. Like most other wall climbing bots, theirs operates on the Bernoulli principle to keep it stuck to the surface, but that’s where the similarities end.

Unlike other Bernoulli-based climbers, this robot’s gripper never actually touches the surface it is climbing. The researchers were able to accomplish this feat by designing a specialized gripper which forces air through a 25 μm gap, creating a very powerful low pressure vortex. The gripper’s design compresses the air by shape alone, causing the air flow to reach speeds of Mach 3, without relying on powerful pumps or increased air volume.

The researchers state that their supersonic gripper can support about five times the weight of a conventional Bernoulli gripper, and as you can see in the video below it also has no problem climbing a wide variety of surfaces.

Window-washing Roomba, here we come!

[via Make]

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