Re: XO-1.75 - Flash, Java?
On 04/13/2011 05:47 PM, Carlos Nazareno wrote: Will Flash Flash Player Java SE (not JavaME) run on the XO-1.75, it being non-x86? You may look into trying to get Java SE For Embedded working. It supposedly supports ARM architectures, but that's all I know about it. http://www.oracle.com/technetwork/java/embedded/overview/index.html#FAQ I did some work on getting Java to work correctly on my XO-1.0 and added the information that I discovered to the Wiki: http://wiki.laptop.org/go/Java The biggest problems were that the Java distribution available from Yum didn't pull in the fonts that its font configuration file actually used (making everything show up in an odd italic font,) and some problems with the display not being repainted properly on rotate. I considered it also a serious problem that the then-shipping configurations of the OLPC completely lacked fonts with glyphs for many languages (e.g. there were no fonts with Chinese or Japanese characters) so these languages could not be rendered in any application on the OLPC, including in the browser. This should probably be considered to be a bug in a supposedly-internationalized platform, and affects language learning, or even seeing what another language looks like. -- Alan Eliasen elia...@mindspring.com http://futureboy.us/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: foot power
On 01/26/2011 10:05 PM, Carlos Nazareno wrote: Hey guys. I haven't taken that much look into foot pedal chargers and do know what their internals look like -- I just remembered coming across the link I posted so I shared The efficient way to do a foot pedal powered generator would probably be to have a small weighted wheel spin as a dynamo when you step on it? You just keep pumping on the pedal to keep the wheel spinning and it shouldn't take much effort, the wheel's momentum should keep power flowing. A lot of these ideas have been analyzed in detail. Hardly any of them except the bicycle idea would be feasible at our power levels: http://tinyurl.com/6zozbcn I would note that in your sample above, the reverse EMF from the generator will be significant; the wheel will slow down rapidly. There's no such thing as a free lunch. It seems that the only thing that's feasible to make the XO kid-powered is to significantly lower its power usage. -- Alan Eliasen elia...@mindspring.com http://futureboy.us/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: foot power
On 01/27/2011 04:08 PM, Sameer Verma wrote: Looking at this thread reminded me of clocks with weight pulleys. I saw one recently outside UCSF hospital. http://www.flickr.com/photos/revger/4381874187/ The weight unwinds the pulley slowly. This is also seen on roasting jack (For those who attended the OLPC SF dinner/bbq, the Kleiders have this at their house) All of these questions are easily answered with some basic physics. E = m g h will calculate how high you need to lift a mass to get a certain amount of energy. I wrote some analysis of a gravitational system in the OLPC wiki: http://wiki.laptop.org/go/Battery_and_power#Pulley_Power I'll quote it here: The physics of such a gravitational potential energy system are easily analyzed. Assuming the figures on this page of ~6 W draw are reasonable, one would need to haul a 5 kg (11 pound) bucket to a height of 440 meters (1445 feet) feet every hour, and that's assuming perfect conversion of potential energy to electrical energy. The reality would be probably more like 25% efficient, or less, so assume a 2 km-tall tower. Not very realistic. Does the kid carry around and erect an immense derrick of that height every time they need to charge? Alternately, you wouldn't have to lift it as high if you lifted a larger mass. If you only wanted to lift it, say, 3 meters into the nearest strong tree, you could instead carry around an immense, sturdy bucket capable of holding 734 kg (1620 lb) of sand or water, fill that full of sand or water every time you stopped, rig a complex set of pulleys to give sufficient mechanical advantage so that the bucket's weight doesn't fling the child into the low stratosphere, and then haul it up those 3 meters into the tree every hour. Again, I will note that the only way to make the XO reasonably powerable by a child (or an adult) is to reduce its power consumption. -- Alan Eliasen elia...@mindspring.com http://futureboy.us/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: foot power
On 01/27/2011 08:18 PM, Nathaniel Theis wrote: On Thu, Jan 27, 2011 at 07:54:16PM -0700, Alan Eliasen wrote: Again, I will note that the only way to make the XO reasonably powerable by a child (or an adult) is to reduce its power consumption. Well, this isn't entirely true. For example, something like a potter's wheel pedal could potentially generate sufficient (25+ W) amounts of power, given a reasonably efficient dynamo (and a reasonably efficient child!) However, the endurance problem is still *huge*. The XO-1 takes about 2-3 hours to charge from 10% battery level. If you have a foot-pedal system that generates 25 watts, you still need the child to do this for _several hours_. I've seen a huge deal of confusion in the human-powered discussions here and on the Wiki; there seems to be some sort of strange idea that having a flywheel lets us get out more energy than we put in. The potter's wheel example above is one such example. It seems to neglect the idea that drawing off 25 watts of power from the flywheel's rotation means that we have to put in (more than) 25 watts of power to keep it from stopping. Anyone who has ever used a generator on a bicycle knows that you can *feel* the drag from the reverse electromotive force as soon as you turn on the light. It will stop you. And those generate maybe 3-6 watts. The braking force from pulling off 25 watts of power is huge. Alright, you may say, maybe you make it ultra-efficient and very easy to push the pedal down (repetitively, for hours on end!) But that's just the tip of the iceberg. I'd never say such a thing, because I realize that if I'm going to be getting 25 watts out, I need to be putting in more than 25 watts, constantly, to keep the flywheel from stopping! There's no such thing as a free lunch, or a magical linkage that puts out more power than it takes in. It doesn't matter if it's a treadle, a kickwheel, a playground carousel, or whatever... that kid has to be sustaining more than 25 watts or the wheel will stop very rapidly due to the significant drag from the generator. No amount of magical efficiency will make it easy to push the pedal down. The kid has to be constantly putting out an average of 25 watts (or significantly more, due to friction and generator efficiency.) Anything less and the wheel stops. Rapidly. Just how rapidly? It's calculated below. Let's analyze the above situation mathematically. We're not doing any justice to the cause of education if we can't analyze these situations with basic physics and real calculations. Let's take a pretty hefty potter's wheel. I looked up some on the web, and we'll use the figures of a 130 lb concrete kickwheel with diameter 30 inches (radius 15 inches.) I'm going to put the following equations in Frink notation, ( http://futureboy.us/frinkdocs/ ) Frink is a programming language/calculating tool I've developed for just this sort of purpose. It tracks units of measure through all calculations and ensures that answers come out right, even when mixing units. The moment of inertia, I, of the disc is given by: I = 1/2 * 130 lb * (15 in)^2 Let's say that the kid is able to spin it to a rather high rotation rate of 120 rpm. (This is quite high for a foot-powered potter's wheel.) omega = 120 rpm The kinetic energy of the spinning wheel is given by: E = 1/2 I omega^2 Which gives 338 joules of energy. We're now going to draw this energy off with a generator. Let's say the generator produces 25 W of power and is, very generously, 60% efficient. (A bicycle hub generator that efficient is very expensive.) The wheel will then come to a complete stop after: E / (25 W / 0.6) Or a dead stop after only 8.1 seconds if we stop adding power. This is significant braking. Note also that the kid has to be putting in 41.6 watts of power for the generator to produce 25 watts, due to its efficiency. If the kid lets it slow down at all, they'll have to put in more than 41.6 watts to accelerate it back up! We're also neglecting the significant amount of energy that was needed to spin the wheel up to get it to this point, or any other frictional or electrical losses. A flywheel does *nothing* to reduce the amount of sustained power that someone has to produce. Especially if we can't posit some sort of magic source of energy to spin it up in the first place. If you disagree with any of this analysis, please respond with physical equations. Engineering is done with numbers. Analysis without numbers is only an opinion. --Akin's Laws, #1 http://spacecraft.ssl.umd.edu/old_site/academics/akins_laws.html -- Alan Eliasen elia...@mindspring.com http://futureboy.us/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Font problems (affecting Java and others?)
Michael Stone wrote: Alan, Thanks very much for the detailed writeup of your findings (and for your efforts make OLPC's software distribution more friendly to people who like Java). I can't personally resolve any of the questions which you raise with any authority but I can direct you toward the people who might be able to -- those people tend to live in #fedora-devel and on [EMAIL PROTECTED] might. (In particular, you'll find the Fedora OpenJDK packagers among them.) Thanks for the suggestions. So is all RPM packaging done by the Red Hat team? Do we have any control about what shows up in those repositories? That is, if we have a patch specific to the OLPC, are we dependent on Red Hat to approve/reject it and get it incorporated? I'll also pose a few related questions that pertain to OLPC philosophy, and not Red Hat philosophy: 1.) Is the OLPC expected to contain at least one font containing a glyph for all Unicode characters? Right now, I'm not sure we even have one complete font, even if we pick and choose between fonts. This affects many Activities; I tried to show people one of my web pages (using the Browse activity) that tests your recognition of Chinese numbers, and none of the glyphs for the Chinese characters appeared, indicating that we have font problems even in the Browse utility. See http://futureboy.us/fsp/chinesenumbers.fsp and http://futureboy.us/fsp/ChineseWorksheetGenerator.fsp And I know Firefox tries *hard* to find fonts with glyphs for each character it displays, and succeeds well on most operating systems. It would seem that a world-friendly OS should contain at least one font with glyphs for the majority of Unicode codepoints, or at least a bunch of fonts that can be searched for a glyph. This affects language learning and makes or breaks applications. 2.) If internationalized applications like Java or GTK or Browse have pointers to font files that are missing, is it considered an OLPC bug that we forgot to distribute those files? Or considered a bug in that Java distribution that needs to point at the fonts we already have? What if they're incomplete? Or is it a space-saving consideration? Or a free font availability consideration? If it's one of the latter, do we declare that we won't fully internationalize so platforms like Java and internationalized applications (like Browse) will be forever broken? 3.) Should it be considered a bug if an existing, central application like Browse or Firefox can't find a glyph for many Unicode codepoints, and thus fails to display many languages? Or do we just ship the fonts most used in our customer countries? (The latter seems a bit cynical... :) ) By the way, I've made a major rewrite to the Java page of the Wiki, hoping to bring it up to date, and provide links to Java-blocking bugs, Java issues, benefits of Java, and my own research into improving Java footprint and usability. Updates or discussion are highly welcomed. See http://wiki.laptop.org/go/Java -- Alan Eliasen | Furious activity is no substitute [EMAIL PROTECTED]|for understanding. http://futureboy.us/ | --H.H. Williams -- Alan Eliasen | Furious activity is no substitute [EMAIL PROTECTED]|for understanding. http://futureboy.us/ | --H.H. Williams ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Font problems (affecting Java and others?)
of packaging the OpenJDK distribution? I can probably create a patch for it. By the way, I haven't verified if *all* fonts in our fontconfig file exist, such as Sazanami, Lohit, Baekmuk, etc., or if we should point it at other files on the OLPC. By the way, what's the best way to: a.) Create a patch for a *new* file b.) compile a resource file to that .bfc format? -- Alan Eliasen [EMAIL PROTECTED] http://futureboy.us/ ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Font problems (affecting Java and others?)
Alan Eliasen wrote: I'm working on making it possible to get Java to run on the OLPC, and have a solution to what many of you may have seen: the problem that any Java program uses a strange italicized serif font, no matter what font you request. This odd font is used everywhere, and no other fonts seem to work. Update: I have filed bug http://dev.laptop.org/ticket/8348 for this issue, if you'd rather respond there. I have also done further research, and OpenJDK's font configuration file points at many fonts that aren't distributed on the OLPC, including fonts for Bengali, Malayalam, Tamil, etc. These will need to be fixed or added also. -- Alan Eliasen | Furious activity is no substitute [EMAIL PROTECTED]|for understanding. http://futureboy.us/ | --H.H. Williams ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
