Monday, March 7, 2011

Homebrewn 1960's style nettop

The screen on my Atom N270-based Acer ZG5 netbook died and I decided to take it apart and put the guts in a different case. It gets used for daily browsing and some light torrenting and movie watching, driving a 1920x1080 display over VGA without issue. The case I used is one intended for storing photographic slides, made by the Smith-Victor company which I discovered still operates today. The dimensions are somewhere around 14" by 7" by 2" deep, big enough that the motherboard takes up about half the footprint. In keeping with the 1960's-ish audiovisual theme I added some 3/4" high rubber feet for clearance.

Using a dremel, I made cutouts for VGA, ethernet and one USB port. Not accessible without opening the case are the power button, audio jacks and the other two USB ports. The power brick is mounted internally and there's a cutout for the AC cord as well. The DC line is soldered directly to the motherboard's input, bypassing a dodgy section of cord that had been causing problems since before the screen broke. The motherboard rests on the battery at one end and the power brick at the other, both of which are conveniently around the same height. Unfortunately the battery is no longer recognized, which hasn't ended up being a big issue because the computer generally stays in one place.

I also had an idea that I would replace the stock hard drive with a 3.5" desktop drive, since there's plenty of unused space on the right hand side of the case. To that end I installed a power supply pulled from an old cd burner enclosure, and made another cutout for the power cord jack. I bought a molex to SATA power adapter to hook up the drive, but haven't got around yet to ordering a gender changer to allow plugging a SATA data cable to the motherboard. It would only be a 2 or 3 dollar part but I'd have to send away for it and at the moment I don't have a spare hard drive to use with it anyway. So, for the moment the cutout is just used for USB and audio cables. There's one 6" USB extension and one 4-port "squid" hub, an essential component since the keyboard, mouse and other devices are all over USB.

The mini-PCIe slot of the computer is not in use at the moment, as using it would require some alternate means of holding the card down. If you wanted to get fancy with the original wireless card, I guess you could wire up the internal antenna connectors to connect to standard RP-SMA connector antennas through additional holes in the case, but instead I have been using a USB adapter or wired ethernet. USB 3.0 or gigabit ethernet are other possibilities for the mini-PCIe slot but neither seem to be very affordable at the moment. I can understand that since adding either to a typical laptop would be impractical.
There remain some idiosyncrasies with the design (primarily that the case needs to be opened to use the power button etc.) but I'm pretty happy with it as a first attempt. I'd like to try to construct a similar-sized case from scratch out of aluminum or maybe copper or brass, for use with a mini-ITX motherboard, picoPSU,  and maybe a full-sized 3.5" hard drive. The pipe dream is to make a few to sell but we will see.

Wednesday, September 23, 2009

Auto-Mini Executive

I've been interested in older folding bikes for a while and now have a few that I tinker with. I had one as a kid that I now think may have been an "Auto-Mini", an Austrian-made bike with 20" wheels and a large main tube that is rounded on the top and bottom but flat on the sides. Various sources refer to two different models (Junior and Executive), but the difference is unclear and both of the Executives I have with original decals say Junior on the "T" of the Auto-Mini logo. I recently picked up a few of these bikes in various states of disassembly with the idea of putting together a recumbent quad bike with two of the frames side by side. These things are pretty common in Toronto but I haven't been able to find much on them on the internet in any one place.

Folding of the Auto-Mini is done by releasing a simple clamp lever. A lot of older folding bicycles I have seen require loosening of a nut or bolt which takes longer and requires a tool in some cases. Recently I learned of another very similar-looking folder that uses the same type of clamp, the Leader Voyageur (misspelled in the link as "Voyager"). Close inspection of the decal on the front reveals that it was made (or at least assembled) by the Victoria Precision Works of Montreal. This bike looks almost identical to the Auto-Mini in most respects, but appears to have a one-piece crank and a different type of quick release for the stem. The Auto-Mini has a slot cut into the steering column and the quick-release clamps around that, making direct contact with the fragile threads. The Voyageur has a more normal-looking headset and stem with a quick release acting on the stem binder bolt, which I think may be a more durable design. Another "Canadian-made" folder, the Supercycle Traveler, looks to be pretty much the same as the Voyageur.

The Auto-Mini's hinge clamping mechanism and quick releases (for stem and seatpost) are marked "brev. stop" or "stop brevettato". It turns out that "brevetatto" is not a brand name but an Italian term meaning "patented". Is "stop" the brand name? In any case, one nice thing about these quick releases is the fact that they use a 17 mm hex nut. Similar quick releases I have seen on folders use a rounded nut with a minimal amount of knurling, making it difficult to get them very tight without marring them with a tool they weren't designed for.

Originally, these bikes game with a generator and headlight, but on all the bikes I've seen in person they were long gone, with only the generator mount built into the fork remaining. There's a mount on the back of the seat tube for a pump, also missing on my bikes. The original rat-trap style rear rack was made by Pletscher of Switzerland.

The Auto-Mini's original brakes are different in the front and back, which made me think that one set had been replaced at first. The front brakes are "Arai Gold" (appears to be chrome-plated steel) and the longer-reach ones in the back are unbranded, made of aluminum alloy and look a lot fancier. The alloy brake levers are pretty lightweight (pair weighs only 93 grams) and also unmarked.

The bike's crankset is a 2-piece cottered system (only the left crank is detachable from the spindle) with an unthreaded bottom bracket. Apparently this is what's known as a "Thompson" style bottom bracket. I find the original pedals a bit small but that might just be me. There is a 44 tooth chainring in the front, and both of the original rear wheels I've got have 18 tooth sprockets on different 3-speed hubs. One is a Sachs Torpedo Dreigang 415 and the other is a Sturmey-Archer AW. Martin Bergman's tables list the 415 with ratios of 0.73, 1.00, and 1.36 (total range 1.87), and the AW's ratios are 0.75, 1.00 and 1.333 (range of 1.78). According to the late Sheldon Brown, the AW line was introduced in 1936 is "far and away the most common model" of hub made by the S-A company. I think the "W" refers to the "wide" spacing of gear ratios.

Another commentator describes an Auto-Mini with a Sachs Torpedo Duomatic hub. The Duomatic is a 2-speed hub with a coaster brake that is easily mistaken for a single speed. After reading the above article I realized that I had one of these on another folding bike, an Italian-made "Amica" that I got in 2005 or so. The Duomatic is shifted by backpedaling, and a related 2-speed model, the Torpedo Automatic, shifts at around 16-18 km/h using a centrifugal clutch. The 2-speed Torpedo models' top gear has a 1.36 ratio just like the Dreigang, so the only difference apart from the coaster brake appears to be the absence of the lowest gear. With a small-wheeled bicycle the distance traveled per rotation of the wheel is much smaller than on a regular bike anyway, so second gear is usually low enough for even a steep hill.

The bigger problem on a small-wheeled bike in my experience is mediocre performance in the top end. Three possible solutions come to mind: a larger drive wheel, a smaller gear in the back, or a larger gear in front. The auto-mini's frame does have enough clearance to allow a somewhat larger drive wheel, but 22" wheels are not common and 24" would be too big. A 22" wheel with internal gearing might need to be custom built. Brakes would be another issue. Sounds like a lot of effort overall for only a 10% gain.

Replacing the cog on a the stock hub with something smaller than an 18T may be the cheapest and simplest option. A 14 tooth cog would give 28.6% more distance with every stroke, and nothing else would need to be changed on the bike.

The third option, replacing the crankset, is complicated by the weird bottom bracket but not impossible. The user "zepi" on added a custom-machined 72T chainwheel to his Auto-Mini using a 40 mm Shimano BB pressure fit to the shell. The bike's owner is identified on Mark Rehder's Auto-mini page as Martin Zeplichalt.The rear hub is a Duomatic with coaster brake, and 16 and 19T cogs are mentioned at different points in the forum discussion. The 72T gear is so big it looks almost comical, probably 2/3 the diameter of the wheel, but I bet the thing flies.

Thursday, October 30, 2008

va3bay update, ide hd media player review

Haven't been posting to this thing in a while.  That amateur tv station va3bay that I mentioned before seems to have gone offline within the last couple of weeks, which is too bad. Since I first posted on it, the station switched to a more detailed powerpoint-style broadcast on the physics of radio signals and the ionosphere and other topics related to amateur radio. Later, it switched to what looked like a satellite feed of a nasa space mission. This was cool in a way but not really that exciting to watch. The earlier broadcasts were at least educational. I may try to get in touch with the guy who was doing this and find out what happened. Hopefully it wasn't that nasa shut him down.

I thought I might try a little product review for a media player/usb hard drive enclosure (model HM2-U2TV) I picked up a few weeks ago. It's made by a company called mediasonic which does a line of similar enclosures; the 2.5" IDE version I got is the cheapest (C$50) and offers the lowest resolution (480p.) It has coaxial sound and component outs but I use a tv of the era with regular rca a/v jacks so I have not made use of these. 

I had a 160gb IDE wd hard drive around from a laptop I had that died, so that is what I used. There were already some movies and tv shows on there so I had thought to just leave things more or less as they were, but the media playing capabilities only work when the hd is in FAT format so I used partitionmagic to change the format from ntfs. As far as I know even FAT32 will not work, so longer file names will end up being truncated and I believe the size limit is 4gb.

When I first hooked the machine up to a tv I was not impressed at all with the startup time (5+ minutes.) When it starts up it seems to do a scan of all the files, so when I deleted the windows folder and everything else other than the movies it started up in only a few seconds. The compatibility with the video files I had was decent but not amazing, as some xvid files will refuse to play, including whole seasons of shows. I haven't had much luck figuring why this is but in some cases (not in others) it seems to have been solved by deleting the files and re-copying. Another thing that happens occaisionally is that the names in a directory will be garbage characters, which was definitely the result of a copying error as re-copying always fixed the names.

Overall I'm reasonably happy with this device for the price I paid (and considering that the company was one I'd never heard of): for playing downloaded video on a tv it has advantages over the two main alternatives, using a computer tv-out (much less portable, even with a laptop) or re-encoding and burning to dvd (time-consuming and wasteful for one-time use). The 2.5" SATA version is only a little more expensive and offers more resolution and potential storage space, so it probably makes more sense if you don't have a reason to use IDE like I did.