New York City’s L train carries about 400,000 passengers a day, linking Manhattan and Brooklyn and bringing passengers along 14th Street, under the East River, and through the neighborhoods of Williamsburg, Bushwick, Ridgewood, Brownsville, and Canarsie. About 225,000 of these passengers pass through the Canarsie Tunnel, a two-tube cast iron rail tunnel built below the East River between Manhattan and Brooklyn in 1924. Like many other New York City road and subway tunnels, the Canarsie Tunnel was badly damaged when Hurricane Sandy’s storm surge inundated the tubes with million of gallons of salt water. Six years later, the impending closure of the tunnel is motivating New Yorkers to develop their own ambitious infrastructure ideas.
Few things are as frustrating as a WiFi signal that drops in and out. On a public network it is bad enough but at home? Even if you can live with it, your cohabitants will certainly impune your technical abilities if they don’t have solid WiFi. One solution is a WiFi repeater. You can buy one, of course. But you can also make one out of an ESP8266 and some code from GitHub. There is also a video about the project, below.
[Martin Ger’s] code implements NAT, so it isn’t a true WiFi repeater, but more of a bridge or router. Of course, that means performance isn’t stellar, but tests show it can sustain about 5 Mbps, which isn’t bad for a little board that costs a couple of bucks. There is a limit of 8 clients, but that’s more than enough for a lot of cases. Even if you don’t want to use it as a router, it has a mesh mode that could be a basis for some interesting projects all by itself.
There is definitely a passion for detail and accuracy among LEGO builders who re-create recognizable real-world elements such as specific car models and famous buildings. However, Technic builders take it to a level the regular AFOLs cannot: Not only must their model look like the original, it has to function the same way. Case in point, [Wolf Zipp]’s version of a massive bridge-building rig. The Chinese-built SLJ900 rolls along the tops of bridges and adds ginormous concrete spans with the aplomb found only in sped-up YouTube videos. It is nevertheless a badass robot and a worthy target for Technicization.
[Wolf]’s model is 2 meters long and weighs 10.5kg, consisting of 13 LEGO motors and a pneumatic rig, all run by a handheld control box. The rig inserts LEGO connectors to a simulated bridge span, lifts it up, moves it over the next pier, then drops it down into place. The span weighs 2.5kg by itself — that ain’t no styrofoam! There are a lot of cool details in the project. For instance, the mechanism that turns the wheels for lateral movement consists of a LEGO-built pneumatic compressor that trips pneumatic actuators that lift the wheels off the ground and allows them to turn 90 degrees.
Sometimes it blows the mind what can be built with Technic. Check out this rope-braiding machine and this 7-segment display we’ve posted. Continue reading “Functioning Technic SLJ900 Bridge Builder”
Infrastructure seems so permanent and mundane that most of us never give it a second thought. Maintenance doesn’t make for a flashy news story, but you will frequently find a nagging story on the inside pages of the news cycle discussing the slowly degrading, crumbling infrastructure in the United States.
If not given proper attention, it’s easy for these structures to fall into a state of disrepair until one suddenly, and often catastrophically, fails. We’ve already looked at a precarious dam situation currently playing out in California, and although engineers have that situation under control for now, other times we haven’t been so lucky. Today we’ll delve into a couple of notable catastrophic failures and how they might be avoided in future designs.
Gaining Weight While Delaying Repairs
Most of us take infrastructure for granted every day. Power lines, roads, pipelines, and everything else have a sense of permanence and banality that can’t be easily shaken. Sadly, this reality shattered for most people in Minneapolis, Minnesota in August 2007.
[Afonso]’s 77-year-old grandmother lives in a pretty remote location, with only AM/FM radio reception and an occasionally failing landline connecting her to the rest of the world. The nearest 3G cell tower is seven kilometers away and unreachable with a cell phone. But [Afonso] was determined to get her up and running with video chats to distant relatives. The solution to hook granny into the global hive mind? Build a custom antenna to reach the tower and bridge it over to local WiFi using a Raspberry Pi.
The first step in the plan was to make sure that the 3G long-shot worked, so [Afonso] prototyped a fancy antenna, linked above, and hacked on a connector to fit it to a Huawei CRC-9 radio modem. This got him a working data connection, and it sends a decent 4-6 Mbps, enough to warrant investing in some better gear later. Proof of concept, right?
On the bridging front, he literally burned through a WR703N router before slapping a Raspberry Pi into a waterproof box with all of the various radios. The rest was a matter of configuration files, getting
iptables to forward the 3G radio’s PPP payloads over to the WiFi, and so on. Of course, he wants to remotely administer the box for her, so he left a permanent SSH backdoor open for administration. Others of you running remote Raspberry Pis should check this out.
We think it’s awesome when hackers take connectivity into their own hands. We’ve seen many similar feats with WiFi, and indeed [Afonso] had previously gone down that route with a phased array of 24 dBi dishes. In the end, the relatively simple 3G Pi-and-Yagi combo won out.
Part two of the project, teaching his grandmother to use an Android phone, is already underway. [Afonso] reports that after running for two weeks, she already has an Instagram account. We call that a success!
The gist of the idea is to suspend an underwater tunnel from floating pontoons. By the time you finished reading that sentence, you probably already had a list of things in your head that seem to make this a terrible idea. After all, it does seem to combine the worst aspects of both underwater tunnels and bridges. But, the idea may actually be a good one, and it’s already being seriously considered in Norway.
The TP-Link TL-WR703n is the WRT54G for the modern era – extremely hackable, cheap, and available just about everywhere. Loaded up with OpenWRT, it’s capable of bridging networks: turning Ethernet into WiFi and vice versa. This requires reconfiguring the router, and after doing this enough times, [Martin] was looking for a better solution. The SOC inside the WR703n has two exposed GPIO pins, allowing [Martin] to choose between WiFi access point or client and between bridged or NAT/DHCP.
According to the OpenWRT wiki, there are a few GPIOs available, and after connecting these pins to a DIP switch, [Martin] could access these switches through the firmware. The hard part of this build is building the script to change the settings when the system boots. This script looks at the state of the GPIOs and changes the WiFi into client or access point mode and tries not to muck about with the DHCP somewhere off in the cloud. Yes, we just used cloud in its proper context.
The only other hardware to complete this build was a simple USB to serial converter that should be shoved into the corner of everyone’s workbench. Not bad for an extremely minimal soldering and configuration required for a something that’s extremely useful.