Flywheel Trebuchet Spins Right Round

Most of us gained a familiarity with siege weapons from Age of Empires, and the march of technology has meant these relics aren’t typically seen on modern battlefields. However, development continues apace in the enthusiast community, and [Tom Stanton]’s latest trebuchet design puts a different spin on launching projectiles at speed.

The design takes advantage of the flywheel as an energy storage device. The flywheel is spun up to speed using a hand crank, through a timing belt and a set of hybrid 3D printed and CNC aluminium gears. Once spun up to sufficient angular velocity, a trigger releases the tennis ball payload from a sling, flinging it forth at speeds over 180 miles per hour.

Moving on from classical materials such as wood and nails, [Tom]’s latest design relies on aluminium in an effort to build something that won’t rot when left outside in the rain. The use of aluminium profiles also makes adjustment and redesigns easy, while providing the necessary adjustments to dial in things like release point and belt tension. We’ve featured a few different designs over the years; the walking-arm trebuchet is perhaps the most oddball of all. Video after the break.

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Hackaday Podcast 079: Wobble Sphere, Pixelflut, Skeeter Traps, And Tracing Apps

Hackaday editors Mike Szczys and Elliot Williams gaze upon the most eye-popping projects from the past week. Who would have known that springy doorstops could be so artistic? Speaking of art, what happens if you give everyone on the network the chance to collectively paint using pixels? There as better way to catch a rat, and a dubious way to lure mosquitoes. We scratch our heads at sending code to the arctic, and Elliot takes a deep look at the contact tracing apps developed and in use throughout Europe.

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!

Direct download (~65 MB)

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Alexa, Shoot Me Some Chocolate

[Harrison] has been busy finding the sweeter side of quarantine by building a voice-controlled, face-tracking M&M launcher. Not only does this carefully-designed candy launcher have control over the angle, direction, and velocity of its ammunition, it also locates and locks on to targets by itself.

Here comes the science: [Harrison] tricked Alexa into thinking the Raspberry Pi inside the machine is a smart TV named [Chocolate]. He just tells an Echo to increase the volume by however many candy-colored projectiles he wants launched at his face. Simply knowing the secret language isn’t enough, though. Thanks to a little face-based security, you pretty much have to be [Harrison] or his doppelgänger to get any candy.

The Pi takes a picture, looks for faces, and rotates the turret base in that direction using three servos driven by Arduino Nanos. Then the Pi does facial landmark detection to find the target’s mouth hole before calculating the perfect parabola and firing. As [Harrison] notes in the excellent build video below, this machine uses a flywheel driven by a DC motor instead of being spring-loaded. M&Ms travel a short distance from the chute and hit a flexible, spinning disc that flings them like a pitching machine.

We would understand if you didn’t want your face involved in a build with Alexa. It’s okay — you can still have a voice-controlled candy cannon.

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Flywheel Stores Energy To Power An Airplane – Eventually

Question: Can a flywheel store enough energy to power an airplane? Answer: Yes it can, for certain values of “flywheel” and “airplane.”

About the only person we can think of who would even attempt to build a flywheel-powered airplane is [Tom Stanton]. He’s a great one for off-the-wall ideas that often pay off, like his Coandă effect hovercraft, as well as for ideas that never got far off the ground, or suddenly met it again. For most of the video below, it seems like his flywheel-powered plane is destined to stay firmly in the last category, and indeed, the idea of a massive flywheel taking flight seems counterintuitive. But [Tom] reminds us that since the kinetic energy stored by a flywheel increases as the square of angular velocity, how fast it’s turning is more important than how massive it is. The composite carbon fiber and aluminum flywheel is geared to the propeller of a minimal airplane through 3D-printed bevel gears, and is spun up with an external BLDC motor.

Sadly, the plane never made it very far, no matter how much weight was trimmed. But [Tom] was able to snatch victory from the jaws of defeat by making the propeller the flywheel – he printed a ring connecting the blades of the prop and devised a freewheel clutch to couple it to the motor. The flywheel prop stored enough energy to complete a few respectable flights, as well as suffer a few satisfyingly spectacular disintegrations.

As always, hats off to [Tom] for not being bashful about sharing his failures so we can all learn, and for the persistence to make his ideas take flight.

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Peculiar Radial Mill From Car Parts

Whether 3D printer, lasercutter, or mill, most CNC machines use human-friendly, square-angle Cartesian geometry. This intriguing concept mill instead uses radial axes where motion is derived from scrap Chevy flywheels. It may look and feel weird at first, but it works – sort of.

Cartesian axes are intuitive. If you want to go to the right, increase X. If you want to go to away from you, increase Y. If you want to lift, increase Z. On a manual mill this is easy for making rectangles and blocks, or, with creative clamping, straight lines of any sort. But if you want to carve a circle? As we all learned on an Etch-A-Sketch, you increase your swearing and then throw it in the corner.

HAD - Radial Mill2[Jason] knew that with a CNC machine all geometry problems are reduced to math done by software. With two offset discs, any position is possible by rotating both the correct way. It may look odd that both plates drunkenly meander about just to draw a straight line but the computer is ambivalent. Software can be complicated without penalty and is free once written – more on that later. If a machine is physically simple then it can be built and repaired easily and cheaply. This design does away with almost all the familiar – and [Jason] argues complicated – components of normal hobby CNC machines. No slides, rails, carriages or belts here. His design uses only about a dozen parts.

Because automotive flywheels are made from cast iron the machine is rigid and naturally dampening. Sticking with the junkyard theme he pulled bearings from an F-450 truck, good for a few thousand pounds. Some steppers and a Raspberry Pi and he was done – well, sort of.

[Jason] let us know that his project has sat for long enough that he has become passionate about other things and decided to move on. He documented his progress and submitted the tip in hope to inspire someone else to continue the design further. Any type of CNC is possible, not just a mill. 3D printer perhaps?

Two big caveats: it needs a Z-axis (linear, probably standard) and there appears to be deeper-seated-than-expected G-code demands to chit-chat about rectangles and only rectangles. Nothing insurmountable, just nothing he has solved yet himself.

[Jason] said not to expect any further updates from him but he would love to see what the next person could do with it.

See the video after the break of the mill drawing our skull and wrenches logo, (soft of, without a Z-axis to lift).

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LEGO Automatic Transmissions

[AviatorBJP] is building some impressive automatic transmissions using LEGO parts. Your best bet is to check out his YouTube channel as he’s got a slew of videos related to topic. We’ve embedded test footage of first and second generation vehicles as well as the most recent flywheel design after the break. But we’re getting ahead of ourselves, let’s look at how the system works.

Each transmission centers on a mechanism that includes hinged arms attached to a central axle. The arms are held together with a rubber band but as the axle spins faster, they overcome the elastic force of the band and begin to pivot outward. This pulls the shaft in one direction, moving its gear up to the next position in the transmission box. To test the system [AviatorBJP] uses a treadmill. A string is attached to the front of the vehicle to keep it in place and the treadmill is switched on to simulate engine power.

This design is quite brilliant, and he’s not keeping it to himself. If you’ve grown tired of the manual LEGO transmission you built, you can follow his multi-video build process to make one of these for yourself.

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