Too Busy For Words - The PaulWay Blog

Sun, 04 Nov 2012

Why ask the question?

A friend at work mentioned that his daughter had been given an assignment in maths to find a series of five numbers such that the median is less than the mode, and the mode is equal to the mean. Naturally, I couldn't let this rest until I'd worked it out, and eventually I got to proving that it's impossible. Here's my proof - if someone finds a hole in it please let me know :-)

Let the five numbers be a, b, c, d, e, in ascending order. For there to be a mode that is not the median, two numbers have to be the same and every other number is different - those two numbers have to be a and b or d and e. Let's consider the case where they're d and e - the other case is symmetric. For the mean to equal the mode:

  1. (a+b+c+d+e)/5 = d. In other words:
  2. a+b+c+d+e = 5d. Since d = e,
  3. a+b+c = 5d - 2d. Therefore:
  4. (a+b+c)/3 = d.
Now, we know that a, b and c are all less than d. This means they can never sum to be equal to d, and thus it's impossible to find such a sequence.

Hopefully the next person who gets given this rather bizarre question will find this and get the answer without straining their brain coming up with cases. It is, of course, quite possible that the question had been garbled in between the teacher and me - it is, of course, trivial to think of a five number series where the median is less than the mean which in turn is less than the mode. Ah well, that's that off my brain now... :-)

posted at: 21:17 | path: /personal | permanent link to this entry

Sun, 12 Aug 2012

Satisfying Sudokus

I do like Sudoku puzzles. There's something satisfying about the types of logic, the positive and negative inferences, one uses to solve it. I have several processes I use, depending on whether I'm using a paper and pen or a computer or a phone. I'm up to solving some of the "Very hard" in GNOME Sudoku - in SudokuWiki terms I can usually solve anything that doesn't need one of their "tough" strategies, although I've had a couple of times when I've recognised e.g. a unique rectangle as well.

But some puzzles are more satisfying to solve than others. I hate ones where you have to use any kind of guesswork - in other words, trying out one number in a position and seeing if it breaks any rules anywhere. I don't like having to find positions where there's a unique number as a result of box, row and column intersection. Not being able to solve a puzzle that should be solvable at my skill level is frustrating - especially as I suspect that some puzzle setters rate things I find hard as easy. And there's a nagging doubt that, for some puzzles, my way of solving a Sudoku occasionally leads to it being harder to solve than if I just, for example, turned on GNOME Sudoku's "show possible numbers" display and filled in the places that only listed one possibility.

Incidentally, this is why I find it amusing that someone wrote a program to solve Sudokus as fast as possible by trying possible combinations in turn, as a kind of "so there" to all those humans who toil away thinking them so smart to solve a Sudoku. The point of climbing Mount Everest, Mount Kosciuszko or Mount Painter is simply because it's there; the amazing thing about a dog that walks on its hind legs is simply because it can do it at all. Computers might be much faster at solving virtually any logic puzzle than humans, but that doesn't diminish the satisfaction of doing one in the meaty confines of ones own brain.

And, strangely, the ones that are satisfying to solve also display a level of symmetry to the eye. One I solved just tonight looked a bit like a fylfot, and it was pleasing the way lines of two and three numbers would provide some insight into solving the next box. I could use one or two techniques for a while, and then switch to another couple of techniques later in the process. Others I've solved have looked like crosshatchings, or have many numbers clustered in boxes one and nine and have boxes three and seven blanks.

So I started wondering about writing my own Sudoku generator that would take five by five matrices listing the order in which cells were to be filled, and two symmetry options for horizontal or vertical: as is, mirrored, rotated clockwise, anticlockwise or 180 degrees. Use a character: 0, 1, 5, 2, 3. The cells could either be lettered A-Z or blank, so, for example:

ABCG____H____I_DEFJ______55 would indicate:

So the square pattern in the top left quadrant has been turned by 90 degrees clockwise ('5') to make the top right quadrant; this then gets turned 90 degrees clockwise again ('5') to make the bottom right quadrant and thus, symmetrically, the remaining quadrant is the last rotation of the quadrant. The overlapping in the fifth row and column is handled by not filling in a number if that cell already has one. Sudokus need at least 17 clues to be solvable, from Wikipedia, but with twenty-five to thirty-two clues being the more usual range, having letters A-J with four areas for symmetry should be enough.

Now to sit down and work out how to write a program to generate this.

posted at: 21:33 | path: /personal | permanent link to this entry

Sat, 07 Jul 2012

The lightbulb moment

Tony, the other person in Canberra building an electric motorbike, came over last night. We were both keen to try out the new 150W DC-DC converter I'd got recently to augment my auxiliary battery when supplying power for the headlights (permanently on, at the moment) and other systems. Each headlight is about 55-60W, with one for main drive and two for high beam. Having crashed the bike in part because the light was just not strong enough, I wanted to kick it up a notch and make sure I had enough light to drive safely.

So, we clipped off the strange proprietary connector on the DC-DC converter, fitted a pair of Anderson connectors for the 120V end (to match those on the 120V fuse box) and a pair of female spade lugs for the 12V end (to match the fittings on the auxiliary battery wiring. We plugged it into the battery pack and all that happened was that the green LED came on. That was all we were expecting; sure enough, a multimeter showed it was outputting 12.5V on the output stage. This obviously wasn't impressive enough for us.

Tony had the bright idea of plugging it into the headlights of the old bike, still in their boxy plastic housing. The high beam worked. The high beam side of the dual-output lamp worked. The low beam worked - but showed us a very interesting thing. The output was noticeably dimmer than the high beams, even though it should only be 92% as bright (barely noticeable).

We pulled the bulb out and tried a couple of other experiments. We plugged it into the small 12V battery, and it did the same thing - low beam was definitely dimmer than the high beam. And a careful examination of the actual bulb showed that the filament was damaged - it looked rough and slightly irregular compared to the smooth, regular coil of the high beam - and there was a small amount of soot on the inside of the bulb near the low beam coil. So it was definitely physically damaged. Even the small battery would still give full output brightness if the bulb had been working correctly.

This made me feel a bit better about the accident. I was still riding beyond the range of the headlights, and it's still my fault. But it wasn't that the bike electrics were incapable of driving the bulb. If I'd noticed, and turned on my high beam, I would have been fine. I'd charged the auxiliary battery in the bike the previous night; it definitely would have given me full range of vision if the bulb had been working. I feel a lot more confident that the bike will give me full range of light, even if the traction battery or DC-DC converter dies and I have to run on auxiliary battery alone.

I'd also started to wonder whether I should put an external switch, or full DC relay, on the auxiliary 12V systems - the input from the battery charger, the output to the battery monitor, and the DC-DC converter. If the DC-DC converter is draining 150W from the traction battery pack continuously, it'd last about 48 hours from full charge to dead; I didn't want to find out that the converter had killed the $4000 battery over a weekend. But we realised that once the DC-DC converter has brought the auxiliary battery back up to 12.5V, the load on that circuit would be quite low - the DC-DC converter simply isn't going to be able to push 12.5V against a 12.7V auxiliary battery. It might be worth putting a suitable 15A diode in series with the lead to the battery, just in case the DC-DC converter doesn't have back current protection, but I kind of doubt that that'd be left out.

Of course, disconnecting all the auxiliary electrics is a good thing to do if I'm going away for a while anyway. The auxiliary 120V system connects from the battery to the fuse box via an Anderson connector that I can pull out. It's easier and less prone to Catch-22 problems than a relay.

posted at: 16:53 | path: /personal/ebike | permanent link to this entry

Tue, 26 Jun 2012

Not taking the bad with the good

I finally looked my TV recording schedule in the face and decided to delete all my recordings of Top Gear, and remove the schedule so it never records again. Why? Mainly because I realised that I actually hate it.

The main thing I hate is actually Jeremy Clarkson. It took me a while to realise, but it really hit home when I was watching the episode where they race across Japan. Clarkson is shown speeding more or less the entire journey; speed cameras in Japan allegedly require a photo of your face, so he holds up a picture of Bill Oddie. This made me realise what he really is: a bully. He can't stand losing, he cheats outrageously, he then denies it, and he puts everyone else down - even his guests, when he thinks he can get away with it, but mostly his co-hosts. Watching Clarkson for five minutes fills me with a burning desire to find some way of putting him in his place.

And then there's the whole "we're naff" theme. When set any of their usual construction or adventure challenges, they act completely hopelessly. After a while you realise that this is a calculated thing - they're not, actually, really that clumsy, idiotic or clueless, they're actually putting it on as a kind of act. Yes, they've made moronic caricatures of themselves, which they then fit themselves into. This, to me, is not humour; it's infantile. How any Briton can hold their head up and say "Yes, Top Gear really represents the best of British television" is beyond me.

It was in the episode when the three (first season) Top Gear Australia hosts took on the UK team that the two of these congealed unpleasantly together. The first challenge has the UK team driving cars where the pedals are in one car and the steering is in another car welded on top. Only - in a pathetic, tired attempt at humour - the Australian top cars are turned upside down. Ho ho ho, those funny Australians, upside down on the other side of the world, they'd be used to it, ho ho, oh my aching sides.

You can see the three Australians are clearly pissed off at this; they know that they've been handed a teaspoon and asked to shear a sheep, only they can't complain lest they look unsporting. It's the same with the other challenges - each one that Clarkson comes up with is off-beat, and has a twist deliberately designed to give the UK team an advantage. Even when the Australian team organises a fairly straight-up competition at using motorbikes to round up sheep, Clarkson thinks he's been clever by purchasing "Austrian" bikes, rather than "Australian" ones.

Only, yes, that's the "we're naff" side coming through again - as it becomes obvious that not only have they bought really good bikes to ride (KTM), but that the UK team's idea of being able to work together is not merely non-existent, but in some weird negative state: they almost spend more time criticising eachother and 'accidentally' being stupid than doing anything else. And, yes, in another event Hammond and May 'accidentally' give the Australian team more points than the UK team - in fact, enough points to even them up after the previous rounds.

This is pitiful. I don't care about the sportsmanship - which is still atrocious - it's just bad TV. Who wants to watch a soccer game where both teams miss the ball, 'accidentally' hit own goals, make deliberate mistakes and try to trip the other team up? No-one. By the time we get to the last round, where they 'unnoticeably' substitute The Stig for James May driving a rally car, I have ceased to care. Even if the Australians win, it'll be only because the UK team stuffs up in some allegedly humourous fashion. If the UK team wins, it'll be because they cheated. Most likely, I imagine, it was a tie some British TV producer's idea of promoting the two brands without snubbing either. I don't know, the recording cut out before the show finished, and I have as much interest in finding out as I do trying to see if I can crash my motorbike again.

Then there's the clear bias that Clarkson has against any electric vehicle, and in fact any vehicle which isn't somehow a symbol of power, and his willingness to cheat, lie, and outright make up crap about them. Tesla took the BBC to court after trying to get this straightened out for months to no response. In October, the judge in the case decided that "no Top Gear viewer would have reasonably compared the car's performance on the show's airfield track to its likely performance on a public road." Funny, that, because that's exactly what Clarkson is claiming - if he says "the range is 55 miles per charge, not 211", he's not comparing it to 211 miles on the track, is he? If the car had "reduced drive", and not "run out of charge", why did they show the film with them pushing the car back into the shed? The other four claims are still being pursued and I can't find any evidence of a decision yet on them.

At the heart of this is the dichotomy of the show: when criticised, they simply claim that they're "merely entertainment" and not a fact-based show. Funny, that, because they spend an awful lot of time talking about facts: torque, power, top speeds, times around the track, weights, lengths, etc. It fits in perfectly with Clarkson's attitude: I'm going to criticise anything I like, but you can't criticise me because my role is not to be critical. It's morally bankrupt, in my opinion.

Top Gear Australia is bearable, mainly because even when they do get set challenges - doing the Oodnadatta Track mail run in small european cars, for example - they at least give it a go. They come out looking like they've done a good job, not been told to be naff because that's what the public expects. But, no, I've got more interesting, and less personally irritating, things to do than to watch Top Gear.

posted at: 21:49 | path: /personal | permanent link to this entry

Thu, 07 Jun 2012


The electric motorbike is - was - very close. I had cut the bottom out of the fuel tank to fit around the controller and battery management system, wired everything into the 12V system, got the traction battery charging, received the replacement for the cell that had died, hooked that in without frying a BMS board, and made a mock-up of the crash protection for the traction battery. So I put the bike on the trailer on a frosty Monday morning, to take it to a couple of welding and fabrication places for quotes.

All unsuspecting.

As an aside, a friend of my brother-in-law came over to have a look at it on Sunday and suggested a polycarbonate battery case, with solid bars to hold it in position. The roll bar system I'd made up, while structurally good, would stick out quite wide, reducing my cornering angle; the mountings for the polycarbonate would be closer in. And the polycarbonate would reduce weight, would resist abrasion and rebound from an impact rather than bending permanently, and not catch fire if something catastrophic was to go wrong (the acrylic sheeting I had in mind for the covering actually burns quite well).

So after the quote from the engineering company to get the roll bars made came in about five times the price that I'd expected it to be, I went and saw a plastics company who said they could do a polycarbonate shell for more like the price I was expecting. Still, a small crowd had gathered to ask questions at the engineering company - I can definitely hear the attitude change between two years ago ("it'll never be as good") to now ("hey, that looks pretty cool!") in the questions from the greater public.

Likewise, when I took it to the Canberra Riders group meeting that afternoon there were lots of questions and lots of ... enthusiasm is too strong, but certainly a level of appreciation for the project. And, since I wanted to give the battery a bit of a work-out and generally show the project as nearly finished, I took it off the trailer and rode it around the car park a bit, then took it for a ride down a nearby disused road.

It's easy, at this point, to think about what I should have done. Should have had an escort, should have noticed my lights weren't too bright and my visibility was down. Was the controller cutting out on me as I started to accelerate because it could secretly predict the future? Unlikely. As it was, I rode the bike up the road a bit, through the two chicanes I knew were there, and started to accelerate into the main stretch.

And found the big traffic island that had been put in the road, at somewhere between 40km/hr and 60km/hr.

The trope here is one's life flashing before one's eyes. That doesn't happen for me. All I recall is seeing the traffic island, thinking "Oh no", and then being on the ground three or four seconds later. I picked the bike up and started both assessing the damage and cursing my foolhardy stupidity. I checked myself over - everything seemed to still work, no broken bones - and started picking up the pieces of the bike - the left mirror broken off, the windscreen cracked, the indicator dangling, the left handlebar control cluster broken beyond repair. A new dent in the fuel tank, just where I'd beaten out the previous one and found the repair from the one before that...

At this point two of the Canberra Riders came looking for me, probaby because I'd been gone for some time. They made sure I was OK, then one stayed with the bike while the other took me back to the car. Then a couple more riders followed me down and helped me lift the bike onto the trailer. Actually, they did the lifting, because my left shoulder really wasn't up to bearing weight. And the front wheel wasn't turning either. They tied it down, made sure I was OK, and followed me some of the way home. Those guys - I don't know their names, and I only vaguely remember their faces - helped me out when I most needed it without being asked or expecting reward. That's what motorbike riders do.

The rest is mainly painful. Three fractured ribs, a non-dislocated fractured collarbone, and some grazes to my knees. A worse-for-wear helmet, jacket and gloves. A lot of guilt and self-blame for being such a stupid, overconfident, unthoughtful idiot. A lot of thanks to luck for my injuries being that minor. Care from a beautiful, kind, thoughtful woman who never once reiterated what my conscience was already beating into me. Several days of rest, not being able to lie easily or get up simply. Another three to six weeks of healing before the shoulder knits together.

I can cope with the financial outlay. I can cope with the pain. We all do stupid things, and we move on from them. I don't dwell on it, really. I'm really more inclined to look at the things that somehow, amazingly, survived. Me, basically intact, with no ambulances or surgery. The battery, with not a single scratch or BMS board damaged. The rest of the bike is still sound. The bike actually worked. It's a temporary set back - life still goes on.

And only today I got an email from a guy doing an electric motorbike conversion in Sydney wanting to know some details about the project. Yep, life still goes on :-)

posted at: 22:37 | path: /personal/ebike | permanent link to this entry

Thu, 05 Jan 2012

Time to make something better

I've just managed to release the magic smoke from some or most of my battery management modules - the little boards which sit on each cell and make sure that it doesn't over-charge and notifies you when the cells are getting low. Unfortunately, EV Power's basic design has a fundamental flaw: they require two through-hole soldered connections which are very close to the cell terminal. With the large cell interconnect blocks, this makes it rather easy to end up with one cell's sensor wires touching the traction battery. When another cell somewhere else also has its sensor wires touch the traction battery, the tiny MOSFETs that do this switching end up with a potential difference of several tens of volts with over a hundred amps ready to gleefully emit magic smoke.

I consider it a basic flaw in EV Power's design. They could supply the modules with wires already soldered in and epoxied over. They could have supplied explicit instructions about how to wire them up which warned me of this possibility. The most recent design had an even worse flaw in my opinion - the holes which you feed the sensor wires through to provide some strain relief on the solder joint were on the wrong side. Earlier designs had it so the insulation of the wire would be the bit touching the terminals if things went wrong; the new design makes sure that you put the solder joint is right there to contact the traction battery.

In addition, the circuit board didn't go all the way across, instead using a wire and a lug (in some kind of supererogatory effort to save a fraction of a cent in circuit board cost, as far as I can see). This means that the sensor wire solder joints are literally pressed against the terminals unless you turn the board sideways. I did try to avoid this, but apparently not fervently enough, and the result seems to be numerous module boards with scorch marks and (in the next-to-most-recent design) burned-off heat-shrink.

Now I have to find another BMS, because there's no way I'm paying for any more EV Power products. I would strongly recommend anyone considering using them on 60AH Thundersky cells look elsewhere. I will now be ordering a Lithiumate Lite BMS from Elithion - the communications interconnect is top-soldered only. EV Power's BMS probably works fine for 90AH cells and anything larger than a 61mm between-centres connection. But for me this is definitely a dud.

posted at: 23:58 | path: /personal/ebike | permanent link to this entry

Thu, 25 Aug 2011

Git for Nomic

I read of an interesting project today: Open Knesset (in Hebrew). It takes the laws created by the Knesset (the Israeli parliament) and checks them into Git, an open-source, distributed version control system. Other people can then get those versions and modify them to their own preferred wording. Because git provides information about what lines of each text file have changed, it's easy to see where people agree and disagree, and to see what improvements people might have. By merging and copying from other people's work, you can converge on a more universally applicable system of laws.

Long ago I started playing Thring Nomic, and I and some friends created Mornington Crescent Nomic. Nomic is a game where you start with an initial set of rules and people propose modifications to the rules; the modifications get voted on and the ruleset changes. You can win either by satisfying some condition in the rules, or by proving that the game is in a state of paradox. It's an amusing system for exploring how rules work and what makes rules function - you get very good at coming up with loopholes and thinking of problems with the way rules are worded.

The fundamental burden of traditional Nomics is that the ruleset changes and other game mechanisms have to be coordinated by a person, usually designated "the Speaker". I wrote a system of Perl scripts and a database to encode and automate some of this (it's not worth linking to, it's mainly defunct). The type of game you play, of course, depends in part on the functionality of the system implementing it; in CGI Nomic there's no point in proposing a rule that states there's a fourth sub-level of rules, because the system was only ever designed to cope with three. (Well, you could propose it, but it would be impossible to implement in the game system with out me revising the code.)

Most games, and most Nomics in my experience, work on having a common, single set of rules. But what if everyone worked on their own personal set of rules, and could request updates from other people? I would say "I've got a new rule that allows people to collect a point for each new rule they've created that gets into another person's ruleset", and people would choose whether to add that rule to their ruleset or not. Rules would be numbered by the ID of the commit that first introduced them, to avoid overlap. And there would have to be some understanding of 'consensus' in the game - for instance, you can only declare a thing to be true if two thirds of all the rulesets allow for it to be true. So I can create a rule saying "Paul wins the game", but it only becomes true if two thirds of the people then copy that rule (verbatim) into their ruleset.

The automatic versioning might also come into play with fixing rules. One of the traditional problems in Nomics is that a rule might be proposed which has a flaw that the author missed but that's obvious to someone else. Usually you can't change your proposal, so while there's some incentive to get it right first time, there's also an incentive to vote against version A and then propose version B. With git, however, you can see what someone else has done and say "hey, I like that, but I think it could be better written like this". And then the other person can see your improvement and might think "that version really is better, although it misses out a thing I wanted to avoid", and changes their old rule to a new version. Then you might copy that because it has the best of both authors, and others might do the same. That way you can collaboratively work on fixing rules rather than being limited by the fixed interaction of traditional Nomics.

It'd be an intriguing game to play, that's for sure. One where everyone has a copy of the rules that is divergent to a lesser or greater extent, yet one where there is a growing consensus about what's going on in the game. Would it inevitably fracture, or would it keep a core of rules that kept on working and people kept on using?

If only I had the free time to try it out.

posted at: 14:34 | path: /personal | permanent link to this entry

Fri, 10 Jun 2011

CodeCave 2011 wrap-up

After a hectic two evenings preparing for CodeCave 2011 and a morning that seemed full of reasons to stay at work, I picked up James and Rusty and we headed up to Yarrangobilly Caves with Tridge and Ian in convoy. After a small panic of me not remembering the landscape (and trusting my memory rather than e.g. a map or a GPS) we arrived. Andreas had got there beforehand and unlocked so we moved in.

I was immediately very pleasantly surprised - Caves House is really well appointed, with an excellent kitchen, nice wide corridors, plenty of heating and great facilities all round. I had been worried about finding a forty year old oven and one knife (I brought my own favourite cleaver and carving knife just in case) but it was excellent.

The other thing that was good was that everyone pitched in and helped in the cooking and cleaning. I wasn't surprised by this - I think open source people generally expect to pull their weight and contribute, and I think everyone understood that I was only passing on costs rather than making a profit. But I had been a little worried that I'd have to set up rosters and roust people out from under their laptops to help me, and that wasn't the case at all. I had planned a group menu that pretty much everyone joined in with, and I really enjoyed having help as I cooked (as much as I also enjoyed the process of cooking for friends). Another win.

We had quite a variety of projects being worked on. Andreas was working on an Arduino home alarm system, Ian was continuing to work on his password manager integrating with the arcane complexities of XWindows' clipboard, Andrew and Tridge worked on getting SaMBa to talk to various Windows servers via IPv6 (you can guess where the problems lay), James continued ironing out the wrinkles in Zookeepr, and Rusty took up Tridge's challenge to write an algorithm that could find a bright dot reliably in a picture, not easy when the actual source is a quarter of a pixel wide - this was for the UAV Challenge: the bright dot is an infra-red light source, the picture is a IR-bandpass image of a field with that source in it, and each quarter of a second a new picture is taken, during which time the plane can move over twenty metres.

I was learning Go, something I had wanted to attempt at the previous CodeCon but had failed to get the compiler correctly installed before leaving contact with the internet. This was a general theme in the background of the weekend - nice as it was to be away from all the quotidian distractions of life, including those of the internet, it would have been rather useful in certain circumstances: looking up Wikipedia articles, for example. While Tridge's grand plan of taking his quad-copter up high enough to get his phone in contact with the 3G network, and then to use it as a wifi access point for emergency internet access, didn't eventuate, it was wished for on more than one occasion.

In between hacking and feeding ourselves, we watched Tridge fly his quad-copter (briefly) and went for tours through the three main cave systems at Yarrangobilly. I'm always left in wonderment at the amazing beauty and delicacy of the cave formations: flowstone, straws, helictites (which grow against gravity), shawls, and more, all solid, real examples of the amazing processes of crystals, physics and time. Fractals so perfect in their execution they make computer-generated ones look fake; persistent, unfathomably patient processes eroding away and building up in intricate, complex sculptures. Places where you can see these geologically slow processes already subsuming the man-made fittings that have been there for a blink of an eye. Caves really do have an aura of wonder to me that awakens the scientist in me.

Tridge had the good idea of each of us giving a talk about what we'd learnt so far and what we were working on and still to overcome, in a convenient spot in the self-guided cave. We didn't disturb anyone else and it was quite wonderful to have that completely different setting for something as interesting and familiar.

We packed up by about 11AM on Sunday to go on the final cave tour, and then to have lunch at the thermal pool. Sadly it wasn't warm - it was tolerably cool; with a cold Winter upon us there was nothing about it to entice one to stay in. Still, it was kind of fun to do something different again. And there was still one treat in store - we found an open place on the snow plains south of Kiandra and Tridge flew his model plane. It went very well despite the wind, which would have been at gale strength in scale and had the motors struggling to keep it going upwind.

Overall it was a really great weekend, full of interesting talk, cogently argued ideas, personal insights and wonder-generating surroundings. I was really glad to have been a part of it and I hope to run another one next year!

posted at: 09:18 | path: /personal | permanent link to this entry

Tue, 17 May 2011

Catching the EV bug

In the past year or so there's been a fair number of people who have come along to one Canberra EV group meeting and never come again. Based on what they were interested in and what the meetings have consisted of, I suspect they saw that we were (at the time) more dealing with the theoretical and policy ideas rather than practical vehicle making - Canberra EV has a vague idea of running a group project but no actual plan, no shed to build stuff, few tools, and most of the people are either not building one or have already built their own. Seeing what they perceive to be a lack of practical action on our part (myself, possibly, included), they go away again.

(Or maybe they realise that it's a bit more difficult than just having someone invite them over to convert their old vehicle in a weekend for the price of a couple of beers and a few lead-acid batteries. But who knows?)

Recently, a young guy has started coming along who's dead keen and a tinkerer besides. He built his own electric go-kart out of an old frame, a bunch of second-hand free starter motors, a bunch of second-hand free lead-acid batteries, and an on-off switch. It fuses starter motors fairly quickly but he's worked out its something that he can do. And I, in my own way, am keen to see him not leave because we're not doing enough to help new people - and I'm also interested in building an electric go-kart, too.

He lives in Goulburn and commutes to Canberra each day, and he wants an electric vehicle to do that. I've suggested to him that he gets an old ute - something with a bit of carrying capacity for the batteries. To give him some leeway in his journeys - no good having to do a run to the post-office at lunch and finding out you can't make it home - I've suggested to calculate for 300Km and a top speed of 140Km/hr. But how do we actually convert those abstract numbers into an idea of what to actually buy?

Well, let's do a bit of research. From the Green Vehicle Guide we know that the Tesla Roadster uses 231Wh/km (watt-hours per kilometre) and the Mitsubishi i-Miev uses 132Wh/km. So let's settle on 200Wh/km as a rough guess of how much our car conversion is going to use. We need to go 300km, so that's 60Kw that we need to store in the batteries. Picking 192 amps as a reasonable maximum for our motor - the Kostov 11" motors are rated at 192A - we can then derive from W=VA that we need about 312.5Ah in the batteries.

Picking two 160AH Thunder-Sky LFP160AHA cells to supply 320AH, we need 120 cells to provide 192V at the battery pack's standard resting voltage. That would deliver 960A continuous and up to 6400A peak, making the pack able to deliver 184 electrical kilowatts continuously. The whole pack would weigh about 660kg and cost about $24,960 from EV Works - or possibly less if you bought direct from the manufacturer.

Then you've got to buy the motor, controller, wiring, and various electrical accessories to run the traction side as well as the accessory side. And the car, of course. So you're easily looking at the thick end of $30,000 to do the whole conversion. It's not a way to save money, by any stretch of the imagination. But I think I've got the EV bug pretty badly, because calculating this kind of stuff is interesting to me.

Aside: Steve Walsh has taken the time to correct my statement that going at 120km/hr would use 'a lot of' petrol. In analysing this graph from this page on fuel economy in automobiles, we determined that for most of the cars on that graph there was about a 10% drop in fuel economy at 120km/hr compared with going 110km/hr. Someone going 130km/hr would be losing about 22% or so. The average loss between 55mph (~88km/hr) and 75mph (~120km/hr) is around 25% (taken from the study that the graph gets its data from).

Our car does about 15km/l in a 300km journey from Canberra to Sydney - with fuel at about $1.40/l, it costs about $28.00 for that journey. An extra 10% on that is about $2.80 - 25% would be about $7 extra. So not, perhaps, the 'lot more' that I'd speculated, but still needless. Instead of 2h43m to do 300km, it's about 2h30m - so they've saved 13 minutes for about $2.80. If that gives them a smug feeling of pleasure at being faster than those other mundane people that just do the speed limit, then I suppose it's cheap entertainment - unless they pick up a speeding ticket, where it gets a lot more expensive.

posted at: 22:03 | path: /personal/ebike | permanent link to this entry

Tue, 10 May 2011

Shiny Stuff!

I got my battery frame panels at the end of the weekend, and they look really cool:

Shiny aluminium plates

To get these I had to:

That cost around $650. While expensive, it totally feels worth it. I was worried that the 3mm aluminium plate would be too soft - my experience with aluminium pieces like window frames and so forth led me to believe that I would have to go with 5mm plate just to get something that didn't flex under my fingers. That experience is clearly with inferior products - I can put as much pressure as I like on even the largest plate with my hands and it doesn't even give in the slightest. I am totally confident that this plate, held securely in the frame, will easily be able to support the weight of the batteries.

And how much is that? Well, according to NCOP 14, the frame has to hold the batteries against 20 Gs of force from the front, 15 Gs from the side, and 10 Gs from rear, top and bottom. With 83 Kgs, this means I have to support about 1245 Kgs from the side. In other words, I have to imagine the bike hanging on its side and 1.2 tonnes hanging directly from the central battery frame panel.

And, you know, I'm pretty confident of that. Most of that weight is going to be directly transferred to the frame, which is already designed to take that carrying the combustion engine anyway. The panels feel strong enough to hold that load and transfer it to the bike frame easily. The edges, from the water jet, feel a bit rough but the corners are sharp and there's no tearing or wavering. Now to actually get enough time to start putting bits of it in the bike! (I need to find a tame person with a decent metal brake to do some of these bends, though...)

posted at: 15:54 | path: /personal/ebike | permanent link to this entry

Performance Pay for teachers considered harmful

Mikal Still blathers about performance pay for teachers - he thinks that "the only people who object to performance pay are those who secretly know they under perform?".

Well, I for one object, and they're worth a blog post.

The problem is: how do you judge the teacher's actual performance? How do you separate this from the abilities of their class? How do you know, empirically and repeatably, that they're better than another teacher?

The answer is: you can't. A teacher's ability to teach is an intangible thing, like an artist's ability to create. It covers not only the obvious skills of passing on information and concepts, but also their ability to engage the class, work with good and bad students, and to keep the whole group interested and active. The best teachers I've had have not been those in which my entire class did brilliantly, or where our class's results were demonstrably better than the others. They've inspired me, sure - but maybe other people in the class still found it a chore, or just didn't care that much about the subject.

And we've already seen teachers cheating on marking students' work to make sure their class gets a better grade. Link that to pay and there will be a much bigger reward for that kind of bad behaviour. Then you have to have all sorts of extra supervision and suspicion, which costs money to implement and hurts morale. And exactly how do you say "this person's artwork isn't as good as you marked it"?

And how do you reward the teacher aide who got given the entire year's worth of difficult students to babysit while the teachers went off and rewarded their talented students? By assessing how their problem children went? This happens even now.

Morally, judging one person by the performance of other people is wrong, especially when those other people are affected by a lot of other factors besides the teacher's 'ability to teach'. Would one suggest performance pay for police based on the amount of crime in their suburb?

And practically, no-one who suggests 'performance' pay for teachers also suggests increasing their average pay. So it's only rewarding those that artificially do well by cutting pay from those who already can't afford it. This doesn't trim the fat, it only makes the back-stabbing and cheating pay off more.

The larger question is really "what will it take to get teachers to be better respected in our society?". The answer, in my opinion, is three fold:

  1. Take back the control of how things are taught from people in the education department, who may never have taught in a classroom or done an education degree, and give it to a body of teachers who have real-world experience.
  2. Pay the teaching profession in proportion to the amount of work they actually do now. Teachers are treated as if their job is simply from nine to three, but in real life every teacher I know has spent countless hours before and after school and on weekends preparing lessons, doing research, marking, helping some students, training, watching over the children outside of lessons (e.g. 'playground duty') and more. Teaching is paid as a thirty hour a week job where it's more like a sixty hour a week job.
  3. Don't make education the forgotten cousin in the budget. We waste billions of dollars on defence projects that never see the light of day, millions are spent commissioning great swathes of reports which are never acted on, yet the increase in actual school funding is minimal.
In short, as it is said:

"It will be a great day when schools get all the money they need and the army has to run a cake stall to buy a tank."

posted at: 14:36 | path: /personal/rants | permanent link to this entry

Tue, 03 May 2011

TTXGP Round 1 - Wakefield Park

On Saturday afternoon I rode up to Wakefield Park for the first round of the TTXGP in Australia - the electric motorbike racing series. I joined Tony, who is also building an electric motorbike and who had ridden up the day before. (Aside: riding the GS-500 long distance isn't really comfortable, and what is it with all these people that do 120Km/hr? Here's a hint, going that much faster will get you a fine and waste a lot of petrol but won't get you there any appreciable amount faster). We were staying at the on-site cabins, a cheap accomodation for race crews, which was simple, clean and pretty decent. The Formule One is not as nice, and a bit more expensive. But anyway.

I got to meet the team from Catavolt, who've been putting together a race bike and had set the record (for a while) for land speed on an electric motorbike. They're running a forced-air cooled version of the Enertrac hub motor I'm using, and are looking at the dual coil version. Team Ripperton lead by Daniel (who finally got sick of all the usual hassles of petrol engines and decided to go electric) was also there, as was Anthony, the guy (I think) who's making the electric drag car up in Sydney. Going out to dinner with them was an experience - this is car talk as you'd hear in any Goulburn pub, but fully technical and all about electricity and construction. Then back to the cabin to talk more technical stuff before bed.

Next day after a cobbled-together breakfast I walked down to where the two groups had set up. There was a lot of checking chargers, checking voltages, checking duct-tape (called 'race tape' to make it sound more authentic) and general talk. The two teams knew eachother fairly well and they obviously got on together. The biggest problem was trying to get a good supply of power - the various circuit breakers on power boards and in the shed kept on tripping as the chargers sucked down the power, competing with the tyre warmers and compressors and so forth. Finally (oh, the irony) they set up a petrol-driven generator to get clean, reliable power.

The really interesting thing was that each group had many things in common but many differences. Ripperton's bike is a Mars brushless DC motor with an A123 60AH battery pack; Catavolt uses the Enertrac motor with a Headway 38120S pack. Voltron over in Perth runs two Agni brushed DC motors with a prefabbed pouch cell battery. I suspect as we get more entries - and I'm told there will (hopefully) be six different teams competing in the next race event - we'll just see more combinations of motors, battery technologies and controllers. That's the fun of it!

The actual racing was, let's be honest, not particularly exciting. Two bikes on a 2.2Km circuit was never really going to be dramatic, and with both teams running fairly conservative throttle limits, the acceleration and top speed were sedate compared to the regular petrol bikes - around 110Km/hr top speed and 1:22 lap times for the Ripperton bike. There were a few worrying things - the Enertrac motor heating up enough to smoke the anti-corrosion compound in the motor, the controllers switching off for a variety of reasons - that made all of us that were really keen to see the bikes do well cringe momentarily. Yet for the most part it seems to have gone quite well - both crews had literally finalised their bikes in the last week before the race and were trying new things, and with no major component failures or crashes they'll be improving and perfecting for next time.

And I have to say that if that's the future of racing, then bring it on! A race where I can speak at a normal volume while competitors fly by six feet away? Awesome! The Catavolt made the barest whisper of tyre and slip-stream noise as it went by - the Ripperton bike with its chain drive was only slightly noisier. We've come to see howling exhausts as a manifestation of power, but really that's just lots of wasted energy. Light the tyres up in burn-outs, pull wheelies on the straight, and do faster times than other people - that's the real show of power. It's going to be awesome!

posted at: 07:40 | path: /personal/ebike | permanent link to this entry

Sun, 01 May 2011

Wishful thinking

My current "it would be so cool but it will never happen" fantasy project idea:

Using direct drive should be sufficient - at a tyre circumference of say 1.8 metres, at 5,500RPM the car will be going about 594Km/hr (unless I've done something grossly wrong with the units of those calculations). But getting a gearbox to reduce the ratio on those motors, say by a factor of two, puts the top speed at a more reasonable 297Km/hr and puts more of the motors peak efficiency within our standard rev range. Still, trying to find a gearbox that can deal with 900Nm of torque is a problem.

As a comparison, the Ultima GTR that has set several world records used a seven liter V8 producing 720bhp (528Kw). I'm delivering 200KW (268bhp) per wheel in a curve that flattens out at around 3500 RPM. A similar car has a torque of around 811 lb/ft - 1100Nm; I can deliver 900Nm per wheel up to around 1250RPM. It's too late and I've spent too much time browsing random stuff on the internet to work out how to convert that into an acceleration time for a 1000kg car on wheels with a radius of about 307mm. It's probably fairly big. So an electric conversion doesn't make it into a GTR-killer, but it's still pretty compatible.

So overall the UltimaWatt project would cost over $100,000. Anybody interested in sponsoring this project ☺?

posted at: 20:52 | path: /personal | permanent link to this entry

Fri, 29 Apr 2011

Constantly learning

After I build my tenth Electric Vehicle, I think I'll just start to have a basic knowledge of how to do so.

After all, just today I learnt about the Tritium Wavesculptor, a high-end controller for brushless three-phase DC motors (which aren't really DC motors, they're actually AC, it's just that the simpler controllers just output on-off square-like waves to energise each phase in turn, but that's another story). And they make a battery management system too - one that is actually formed (by chance) for the specific type of cell I have.

I learnt this not in a search for controllers - apart from already having one, I had discovered the EVnetics Soliton One (I refuse to link to EVnetics' site since it's Flash-only, but here's Rebirth Auto selling one for a mere $2,995 USD). Since that was far more controller than I needed - even the Soliton Jr doesn't really work under 240VDC, which is twice my standard pack voltage - I hadn't really looked around for more. I actually noticed a reference to a "Tritium Wavesculptor" in a post on the AEVA forums about converting (of all things) a VW Type 3.

Tritium are an Australian company that's been around and creating EV controllers for, oh, nearly a decade! How is it that I haven't heard of them?

Clearly, this is a field that needs a really good directory of motors, controllers and batteries. And, just as clearly, the market is fragmented - dozens of forums (with names from the normal to the incomprehensible and unguessable), dozens of suppliers, minimal coherence of specification (e.g. some cells are measured in grams per watt hour, some in litres per amp hour, etc.) and dozens, even, of supplier lists and directories on forums, enthusiast and club sites, and elsewhere. I feel the need to create a motor comparison and controller comparison site, if I didn't think I was already struggling for time just to do the things I want to do that are relevant to me right now.


posted at: 17:12 | path: /personal/ebike | permanent link to this entry

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