How Retractable Pens Work

[Bill Hammack], aka the [EngineerGuy] is at it again, this time explaining how retractable ballpoint pens work.

pen-thumbIn this excellent video, he describes the simple (but remarkably sophisticated) engineering of the mechanism that allows a pen to pop the ballpoint mechanism out, then back in again. It is a great example of how to illustrate and explain a complex concept, much like his videos on how the CCD sensor of your camera works.

Perhaps the most interesting part of the video is an off the cuff observation he makes, though. The Parker company, who first developed the retractable mechanism, were worried that this new design might flop. So they didn’t put the distinctive Parker arrow clip onto the pen until a few years later, when the pen was a big seller. It seems that while some engineering problems are easy to solve, short-sighted accountants are a harder problem.

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Chicken-powered Pendulum

Every once in a while we get sent a link that’s so cute that we just have to post it. For instance: this video from [Ludic Science]. It’s a wind-up chicken toy that kicks a pendulum back and forth. No more, no less.

But before you start screaming “NOT A HACK!” in the comments below, think for a second about what’s going on here. The bird has a spring inside, and a toothed wheel that is jammed and released by the movement of the bird’s foot (an escapement mechanism). This makes the whole apparatus very similar to a real pendulum clock.

Heck, the chick toy itself is pretty cool. It’s nose-heavy, so that under normal conditions it would tip forward. But when it’s wound up, tipping forward triggers the escapement and makes it hop, tipping it backward in the process and resetting the trigger. The top-heavy chicken is an inverted pendulum!

And have a look, if you will indulge, at the very nice low-tech way he creates the pivot: a bent piece of wire, run through a short aluminum tube, held in place by a couple of beads. Surely other pivots are lower-friction, but the advantage of using a rod and sleeve like this is that the pendulum motion is constrained to a plane so that it never misses the chicken’s feet.

Our only regret is that he misses (by that much) the obvious reference to a “naked chick” at the end of the video.

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Bike Pedals in Both Directions, Gets You to Your Destination AND Back

[punamenon2] has built an interesting bike that moves forward regardless if it is pedaled forward or backwards! What? Yes, you read that correctly. Pedal forward or backwards and the bike goes forward. This project started off as any old cruiser with a free-wheeling rear hub. To pull off this mod a second free-wheel and sprocket had to be added to the current wheel assembly. One free-wheel and sprocket set is used when pedaling forward, the other set is used when pedaling in reverse. There is also a new chain tensioner that serves to not only keep the chain taut but also allows for the chain to change directions which ultimately allows this novel idea to work.

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Hackaday Links: August 25, 2013


[Adrian] came across a treasure trove of 507 mechanical device designs. It didn’t seem quite right for a Retrotechtacular post, but we wanted to share it as it’s a great place to come up with ideas for your next Rube Goldberg machine.

Biking with headphones is dangerous. That’s why [J.R.] built a handlebar enclosure for his Jambox Bluetooth speaker.

While dumpster diving [Mike] found a Macbook pro. It was missing a few things, like a keyboard, touchpad, battery, ram, and storage. He borrowed a power supply to test it out but without the keyboard there’s no power button. He figured out the traces on the motherboard which turn it on when shorted.

[Mateusz] want to let us know about the Hercules LaunchPad. Like the other TI Launchpad offerings it’s an all-in-one dev board. The Hercules line features a couple of flavors of dual-core ARM chips. Can you believe the dev boards you can get for under $20 these days?

After seeing the ammo can sound system about a month ago [Ilpo] was inspired to share his ammo can PC case with us.

And finally, here’s a way to display your Bitcoin mining rig for all to see. This system was laid out in an antique frame and hung on the wall.

Mechanical engineering primer

So you’re master of electrons; able to program multiple chip architectures without batting an eye. Good for you. The only problem is that blinking LEDs gets boring after a while and you’re going to want to do something else. Here’s a chance to expand on your physical construction skills. Make: Skill Set is sharing the first chapter from the book Making Things Move by [Dustyn Roberts].

This chapter, which comes in PDF form, covers simple machines. It’ll guide you through the three different types of levers, including examples of how you use these in your everyday life. Next it’s on to pulley systems, wheels and axles, inclined planes and wedges, screws, and gears. [Dustyn] rounds out the chapter by talking about how these concepts are combined into machines like the Rube-Goldberg device seen above. Take some time to look this chapter over and then put it on the holds list from your public library if you’re interested in reading more.

Parallel parking system


Autoblog dug up this classic mechanical engineering project from 2006. A team of five University of Toledo students constructed a system to help parallel park a car. First, you drive nose first into the space. Hydraulic rams then lower the drive wheel out of the trunk, raising the rear of the car. The single wheel is also hydraulically driven and moves the car into the space. They have a blog documenting the six week build. Have a look at the demonstration video below.

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