A diode allows current to travel in only one direction. With that in mind, [Alex] built a mechanical diode that will only allow gear rotation in one direction to be transmitted through the system. But wait, by connecting two of these devices together he’s built something of a mechanical rectifier. An electrical rectifier converts alternating current to direct current and this mechanical version outputs clockwise rotation no matter what direction of rotation is coming into the device.

There’s video which we’ve embedded after the break as well as many pictures on his site but not much explanation. Here’s what we’ve deduced. The two large gears are inputs. Mounted on top of them is a smaller ratcheting gear that will only turn in one direction. This ratcheting gear selects whether the smallest gear on the left or right will rotate, which then feeds the output gear at the top of this image.

Yesterday we mentioned the Woot! sale of the Didj, and we had some comments and emails from readers who had purchased one. We couldn’t resist either, and ordered a couple to take apart and modify. We will probably be following the work laid out by [Claude Schwarz], who seems to be one of the leading hackers on the scene. [Claude] has done some work in porting the GP2x libraries to the Didj, which gives a tremendous head start to anyone looking to have a working game system any time soon. There will also be a build log for everyone to follow along at home, and contribute what you want and have, as well as a follow up How-To when a working system is attained. Happy Hacking, everyone.

If you think there’s never enough computerized numerical control in your life perhaps the pizza plotter should be your next project. This is a large 2-axis machine that shoots pressurized sauce onto a pizza crust. It’s a food-grade RepStrap and appears to use a garden sprayer as a reservoir. They learned their lesson when a loose hose clamp sprayed sauce around the room. We’re thinking this is a bit of reinventing the wheel as pizza-making factories but it’s fun nonetheless.

[MkMan's] LEGO spider robot combines pieces from a Mindstorm kit with a few milled plastic parts. The legs are a locomotive concept called a Klann Linkage. They operate in pairs and convert the rotational force from one motor into movement for two legs. Here, a total of four rotating gears moves eight legs, besting the hexapods we saw a couple of weeks ago in both leg count and motor economy.

Each limb is made up of five pieces plus one base for each pair. That makes eleven pieces per pair and a total of 44 for the entire robot. [MkMan] milled these parts out of 3/8″ HDPE stock. He’s made videos of forward motion and turning which we’ve embedded after the break. Even on a polished surface the bot looks fairly efficient at getting around.

Walking forward

Turning

It’s pretty creative to use a 9v battery as an enclosure. That’s what [Osgeld] did when building this amplifier. There are several advantages; they’re easy to find, it keeps a bit of the dead battery out of the landfill, and this method provides a built-in connector for a 9v power source. In this case the circuit is built around a LM386 audio amplifier. It’s glued to the back of a potentiometer and wired up with the other components for a package smaller than a quarter. A stereo jack reside in the side of the battery case with a cable and alligator clips for connection with a speaker. Now the amp can be quickly connect to any 4-8 ohm speaker.

Not too long ago we asked our readers what they would like to hear about from the PUSH N900 winners and their hacks. We got some silly questions, and some serious, we asked both and now the PUSH teams have answered.

Solderin Skaters are really making progress. They’ve gotten their printed circuit boards and mounting equipment all set to go, and the code and algorithms are really shaping up. All that and more updates are seen in their latest video, and blog entry.

>Thank you for taking the time to answer some questions for HackaDay. We love when a hacker is willing to share their work with us.

>How did you and your team get together? Any fun backstory you care to share?

[Keywan] came back from Amsterdam with an N900 and everybody here was
envious. We saw the PUSH N900 project as an opportunity to equip
everybody with such a device. Because we couldn’t think about a hack
needed other ideas. We remembered funny things we did as
youngsters and *bam* there was the skateboard idea. We called
friends here (University of Bielefeld) and there (Berlin),
*tada* there was the team.
When we started working on the project we soon realized
we would need additional help to tackle such a big
project in such a short time (6 weeks), so we asked
three more highly qualified friends to join the team.

> Have you and your team worked on any other projects? Cellular related
> projects? N900 projects?

No, this is our first project together. [Jan] and [Sebastian] worked both on
different hardware projects. [Keywan] and [Flo] worked together a
shirt design and other non-technical stuff. [Nick] is involved in
a startup developing mobile applications. He sometimes suffers from
badly designed and closed source APIs during the development on other
platforms.

> What was your main inspiration for your team’s project?

We wanted to enhance a real everyday activity and
create an application beyond game controllers such as
Wii-Accessories and Tony Hawks: Ride.

> How do you think people will react when you finish/release?

We recruit a security team to protect us from fans and
paparazzi. Just kidding. We are curious how/if they will react,
but hope they will like it.
As with all open-source projects, we hope that the
work we did might be useful to other applications in
the future.

> Do you have any future plans with your team? Continued N900 development?
> Update your current projects?

We have not planned past the deadline, but we sure
would like to continue working together.

> What do you think of the other winners?

We like their projects and looking forward to meet them in
London. They are very nice and we are in contact with them.
Everybody tries to help each other. We share code, thoughts and
tips.

> Questions from our commentators.
>
> What are you thoughts on Arduino? Do you intend to use one in your
> project?

The Arduino family is a great timesaver for rapid
prototyping, so we did our prototype with an Arduino. But we needed small and
tough hardware, so we decided to design and build our own PCB.
It is based on the same microcontroller, an ATMega168.

> How is working with the N900 hardware and software?

[Nick] says: It’s like a cybernetic implant which I don’t want to
miss in my life. The hardware is very powerful and to be root on
a more or less normal Linux gives you a lot of freedom. The tons
of possible frameworks are sometimes a bit confusing, but gives
you possibilities like on no other platform.

> What do you think about the movement of cell phones towards open source
> software, such as the Maemo? Do you plan to, or have you ever tried
> Android?

We like Maemo even though it still have some glitches. Open
Source phone software gives you freedom in the hand. Just see
how the community around Maemo provide solutions for problems
Nokia didn’t see as crucial. Open Source on phones rocks!
Most of us didn’t worked much with the Android, but Nick tried
Android. For him it’s pretty painful installing an app for every
single messaging service. Google maps is nicer than the Ovi stuff
though. Developing on Android is a little more fun than e.g.
Blackberry, using Linux. But coding and running for example a rails
app on the N900 in minutes just changes the way you do developing for
mobile devices. You can even code on the N900 itself.

> (If you use a secondary power source, example – to run motors) What kind
> of battery life is expected for your project?

We expect a good hour of battery life (average power consumption
of our sensors boards is about 80 mA and our batteries have 130
mAh capacity. Bluetooth, status LEDs (10 mA each) and the ATMega
drain most of the power, the sensors power consumption is almost
negligible.

> Can we get a list of what you’re using in your project? (example –
> bluetooth sets, motors, dedicated sensors, etc)

Each Skateboard is equipped with two sensor boards. On each
sensor board, an ATMega168, running at 7,3728 MHz (to avoid
transmission errors) and connected to to an RN41 bluetooth
module, samples one triple axis accelerometer (ADXL345) and two
dual axis gyrometers (LPY/LPR5150). They are powered by through
a lithium polymer battery connected with BEC plugs to a
protection module. And of course, a large number of resistors
and capacitors. We used 0603 SMT components.

> And yes, we actually had a reader (Joe) ask the following (feel free to
> omit)
>
> How often do you change your underwear?

Underwhat?!

Yes, its true. Facebook has completely rewritten the PHP runtime to make it faster and more efficient, and its completely open source. Named HipHop, its described as a source code transformer, changing PHP into optimized C++ which is then compiled using g++. Thus keeping the best aspects of PHP while taking advantage of the performance of C++. Using HipHop, the Facebook web server CPU usage has been decreased by about fifty percent! And who would have thought that this and many other cool advances in programming, started at a Hackathon.

Apparently it’s been around for fifteen years but using foil impressions to pick locks is new to us. This is similar to using bump keys but it works on locks that are supposedly much more secure. This method uses a heavy gauge aluminum foil to grab and hold the pins in the correct place for the lock to be turned. The foil is folded over and slits are cut where each pin will fall. It is then inserted into a lock on a tool shaped like a key blank. Jiggle the tool for a bit and the cylinder will turn. This just reminds us that we’re much more dependent on the good will of our fellow citizens to not steal our stuff, rather than the deterrent that a lock provides.

We’ve embedded a detail and fascinating demonstration of this method after the break. The materials in the video are from a Chinese-made kit. We’re not sure where you find these types of locks, but we don’t feel any less secure since our keys could be obtained from a distance anyway.