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
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
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
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
Shiny Stuff!
I got my battery frame panels at the end of the weekend, and they look really
cool:
To get these I had to:
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:
"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
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
Wishful thinking
My current "it would be so cool but it will never happen" fantasy project
idea:
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
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.
Sigh.
posted at: 17:12 | path: /personal/ebike | permanent link to this entry
Unexpectedly finding oneself playing 'Mao'
One of my favourite games, when I get to play it, is ' Bartok' - a Nomic-like card game where you
start with an initial set of rules (similar to the popular card game 'Uno') and
each time someone wins they get to add a new rule and another round is played.
After a number of rounds, remembering what rules are in play, and what you have
to do to obey them at any one time, can be an interesting challenge. I usually
don't play with the question rule ("asking any question is illegal") because it
makes the game a silent, tense affair.
Next up the scale, then, is "Mao", where one person decides a secret set of rules that no-one else knows. Players try playing and are told whether their play is allowed or not, and they have to try and work out the rules. Of course, not telling the other people what you've worked out is a standard way of getting ahead in the game. I like Mao less than I like the question rule, because it's all about trying to work out everything in your head and saying anything is a distraction. And, as the name implies, throwing in one or two nonsensical or counter-intuitive rules (e.g. "it is illegal for someone to play a jack and not immediately play another legal card") is just part of the fun.
So I was somewhat disturbed to realise, in trying to book international flights recently, that I was in the middle of a game of Mao without realising it. Airlines have an extremely complex, ever changing, and sometimes completely bizarre rules about what flights are offered and how much they cost. Then each of the many flight searchers - Zuji, Skyscanner, Expedia, Lastminute, etc - has their own way of combining these options. Seemingly sensible outward journeys will be combined with ludicrously long returns; prices will suddenly seem to jump up for no given reason, and route options you'd think were right there - indeed, that you can easily prove exist with other queries - are ignored.
The nonsensical rules I've discovered so far are:
The site that I have to give most credit to - including a link - is Skyscanner. It has a good range of flight options and sort options - total travel time and departure time are very useful, for example. And then tonight, after I'd near given up in despair, I found the options on the left-hand side that I'd ignored, which allowed you to set a maximum journey time, remove airlines, and (most importantly) choose an outgoing and return flight in separate lists. If only I'd spotted that yesterday!
They still need flight details expanding on the page, the ability to limit flight selection by price, and to realise that for some routes - e.g. CBR to just about anywhere - you're going to have to pull together a couple of separate flight options rather than only go with carriers who fly the whole distance or with code-shares.
And still, I had more success with a travel agent - in fifteen minutes she
could find all the options, try every possible combination out, eliminate
the obvious wrong ones, and present me with a simple list of the best options
available - including a 'Y' journey where we go to one destination and return
from another nearby. And at a competitive rate, too.
posted at: 23:24 | path: /personal/rants | permanent link to this entry
Great minds think alike
The next major task for the electric motorbike is to build a frame that
can store the battery. They need to be held in place with a lot of
strength - the battery frame and its contents need to be able to withstand
a 20G impact from the front, for example, and it needs to be able to fit
the 38 cells I have as low as possible to make the bike handle well. I'd
made up some cardboard mock-up cells and had worked out a way to get them
into the frame - just.
Then I'd realised that I'd forgotten the space on top of the cells - there needs to be about a three centimetre gap above the top of the cell for the interconnects and cell management module. And then I needed to include the thickness of the actual frame. And I realised that one of the frames would be sticking right where my toes were supposed to be. This needed a rethink.
I've found that I get a lot better results and ideas when I brainstorm with friends, so I invited my two brothers-in-law to come over and play with some cardboard boxes. I showed them what we had to work with and, between drinks, we started rearranging things. We also talked about the actual requirements, and we started discarding the ideas which had been limiting me - like whether we used the side fairings I'd bought for it.
It's often said that progress doesn't happen with the word 'Eureka' as often as it does with the phrase 'that's interesting...'. And sure enough, Trev came up with the break-through idea by just rearranging things and observing, testing and improving. Then I made a few suggestions, then Rob made a few more, then we talked about how to build it, and before an hour was up we had a pretty much complete idea of how to construct the whole thing. And it all fits lower than the original fuel tank!
The key insight, as it later appeared, was that making room for the cell interconnections inside the frame chews up lots of space. Turning the cells on their side used horizontal space, which is less constrained. By putting the interconnects on the outside, I can see every cell's monitoring state and check the connections easily. The only variation is the bottom row, which faces forward because that way I can fit six batteries across the bottom row and still have room for my toes.
This photo illustrates the whole thing. The bottom layer is six cells across (facing forwards), and each other layer is made of eight batteries facing side-out. (The smaller squares are one cell, then I made three- and four-wide groups for ease of construction and reduction in cardboard). You can see on the right the rear upper engine mount which sticks into the second layer of cells - when this is removed that row can move an inch back; this in turn allows the front group to move down, which then in turn allows the top group to move forward. There is plenty of room there even with plates between each row.
Then the whole outside is covered in a solid plate of something - we're currently debating whether steel, aluminium or acrylic is better - that provides water and abrasion resistance. Steel plate with laser cut holes with an acrylic plate behind it is my current favourite - the holes provide viewports through to see the battery management system, and also mean that the bike has pinpoints of green light glowing from it at night. Inside the plate there are rubber offsets which both keep the plate away from the interconnects and press the cells into their niches. The outside plates attach at hinge points at the bottom and bolts go through from the top to a central plate which holds the whole thing together.
If the outer plate isn't seen to be enough to hold the cells in place, I have idea to fix that as well: put a steel strap around each group of cells and, on the ends, attach a flat plate to which a bolt has been attached. This then bolts down to a rod attached to the plate in the middle. The steel strap will sit inside the channel on the side of the batteries, holding them just as well as the frame I made up before.
The method of construction is still a little up in the air. Rob likes the idea of just bending acrylic into place around wooden moulds. Trev likes aluminium for lightness and for the horizontal plates to support the cells I think that's good. The central vertical plate I think I would make from steel and I would definitely prefer the outer plate to be steel for abrasion and impact resistance. All these can be cut from plate using water jet cutting - in fact, this design lends itself much more to water jet cutting than other designs I've considered. That makes it cheaper, as well as much more awesome.
Hopefully I'll have some plans together this week and I can start taking
them around to fabrication places to see what they'd charge to make. The
other good thing about this plan is that it's probably even possible for
me to make it so that I can simply bolt the bits together myself, rather
than having to pay someone to put it together. It feels like I've got
the whole project back on track!
posted at: 21:31 | path: /personal/ebike | permanent link to this entry
I should be more electrified?
Last weekend I got the electric hub motor running. You'd think this would
be the cause for great celebrations, fireworks and national days of
rejoicing, but strangely it leaves me feeling like it's a fairly hollow
victory.
I'd spent the week assembling bits and pieces, soldering and crimping, fixing things and getting things running. I managed, somehow, to avoid frying the DC-DC converter supplying the 12V power for the controller and contactor after connecting its 12V leads to the 130V battery. I checked everything with a multimeter. I ran through every possible combination of wires and, on the very last possible sensible combination got the motor turning over without sounding like it was trying to chew up a cheese grater. I uploaded a video at the time. It was still sounding a bit odd and the controlle was occasionally cutting out when I backed off the throttle, so I got a friend with an oscilloscope to come over and have a look at the signal. I also layed out the controller flat on the table, which meant I could get the power wires straight rather than crossing over eachother. We fired up the motor on Friday and had it running for five minutes or so. The waveform looked OK, but since neither of us really knew what a bad or good waveform looked like it was somewhat moot.
At this point we noticed the cheap plastic caps that came with the lugs that I'd bought for the power leads were melting. Then the solder in the power wires started melting (why they put solder into the wires is beyond me). I went and got my thermometer cable for the multimeter and determined that the power wires were sitting at about 70°C! And that was only running for five minutes! This raises all sorts of questions.
Anyway, I decided to get a better video than the previous one. Armed with the knowledge that my phone had a high-definition video camera, I tried taking videos with that. Kate suggested putting light on the motor so you could see it moving rather than just a dark blob. I tried my other video camera, a ContourHD unit that I bought for attaching to the front of the bike, on helmets, and so forth - but the field of view is too wide and the sound is pitiful. And in a burst of idiocy I deleted the good video and kept the eight second out-take. (As strange as it may seem, these weren't excuses to start the motor up again.)
So now that I've got the video uploading away I thought I'd write this update. I should feel happier - a major milestone has been passed, and theory has turned into practice. But the major work now is to try and get a battery frame welded up on the bike; I want to use a professional metal fabricator for that. That has to go past the engineer to get his approval. Then I have to get all the batteries, controller, contactor and other parts actually in it, and attach all the cables. Then I have to get the 12V system working. Then I might be ready to actually run it down the street.
So it still feels a long way off. And I'd like to get the bike at least running in some fashion for the first practice event of the TTXGP at Wakefield Park near Goulburn at the end of April. And there's that cable heating problem to watch, or better yet fix. And how does one register an electric motorbike anyway? It still feels like a long way to go.
Here's the 'better' video:
posted at: 02:43 | path: /personal/ebike | permanent link to this entry
A crimp in my plans
Well, yesterday I hooked all of the cells up and installed and wired up all
the BMS modules. That's 76 wires about three centimetres long, 76 crimp
connectors and 76 solder joints - two per cell module. I used crimp
connectors because I had a bunch of them from hooking up the controller
cables - Jaycar has 100 packs of connectors for about double what a pack of
12 cost - and so that I could disconnect and rearrange every module if
necessary (i.e. I wouldn't have a mess of cables when I disconnect it).
After a while I got a technique up. I borrowed a friend's crimping tool (I tried pliers and they either didn't get enough force or cut straight through the connector), but because it's fairly cheap it tends to bend out of line when you squeeze it as the normal hand motion applies sideways force (due to the way your fingers curl). Solution: put the bottom half in the vice. This way I could exert all my force straight on and the tool itself wouldn't twist in my hand. This reduced the number of bad crimps down significantly. I also got into a bit of a production line - cut a number of segments of wire, trim all the insulation with a stanley knife, then crimp all of the segments and arrange them. This meant less tool swapping and allowed me to get a good technique on each operation.
I worried a bit as I was soldering everything up, but not because I thought that I would accidentally adger the circuit on the BMS modules. They're copy-protected in a crude but effective way - a blob of translucent epoxy on the centre of each module. You can see the LEDs shining through but nothing of the circuit or components. It wouldn't stop a dedicated counterfeiter for a second, of course, but it's enough to stop me making my own. I don't really care about this - if I need one I'll buy one, and if the company that makes them goes out of business I'll just cut the epoxy off one and figure it out on my own - or just buy a new circuit. I like the ones Elithion make - expensive compared to an analog BMS but you get so much more neat information!
No, I worried because I was hovering over a bunch of exposed metal connectors that could easily kill me if I was stupid enough to make a good circuit between two ends, or even parts, of the battery. It's only 130V, but if it gets a low resistance connection it can do 180A for as long as you please - about a quarter of a second will do it to stop your heart permanently. Fun, eh? The problem is in getting too used to handling them, too blazé about the accidental touch, until I do something stupid.
Anyway. There was a fraught moment getting the charger working. The charger takes a feed from the battery that goes through the relay in the BMS, it recommended hooking it up on the positive side (why?). I then proceeded to attach the other lead of the charger to the positive terminal, and wondered why it wasn't charging. Moving the connection to the negative terminal started it up just fine.
The only minor annoyance at the moment seems to be that the BMS turns off the charger as soon as the battery reaches 3.65v per cell. This means that about seven or eight of the modules show their red "I'm diverting current around this cell to stop it overcharging" before the BMS turns charging current off. I figure I'm going to have to this cycle about half a dozen times to get all the cells up to roughly equal charge - I can see cell voltages of between 3.34v to 3.44v at the moment. It only takes about two to three minutes for it to go from starting the charge to stopping it, though, so I'll do that a couple of times this afternoon and monitor the cell voltages and see what happens. The readout on the charger isn't getting beyond around 137V anyway, so I don't think there's any damage being done.
Now to start getting the controller inputs wired up and see if I can starts the motor up!
P.S. Here
are the pictures.
posted at: 21:18 | path: /personal/ebike | permanent link to this entry
Artificial Manna
I read Marshall Brain's short story
Manna recently, and
it was a very clever articulation of the benefits and disadvantages of
automation and increasingly zero-cost matter, energy and data. At the
risk of over-analysing a fairly unsophisticated example, however, my
opinion is that his Manna-dystopia is less likely than the technology or
management profiling might suggest.
I always end up thinking about the logic and construction of plot in stories. So the section of the story where he talks about Manna, a computerised system of managing workers (first human, then robotic) by breaking tasks down and monitoring performance of every task, doesn't ring quite true. I can understand that it's possible to make a system that does this basically, but I think it's unlikely that it would ever get to the same level of control if implemented in real life.
Firstly, the inputs to these systems are never perfect. The idea of people pressing buttons whenever the bins are full implies that people care but they just don't like complaining to the staff. I think it more likely that patrons simply won't bother to press the button for something even as trivial as a waste-bin being full or as important as a flooding toilet. You've also got the social aspect - if patrons know that an automated system is going to pay attention to a call button, they're going to play with that. They may toggle it all the time; they may try to vandalise it or break it; they may press it merely to try and get attention from the staff for something else.
Secondly, the Manna system implies that everything in the restaurant can be broken down. What if a patron has an accident? What if a patron starts screaming abuse at a staff member? The more you build these edge cases into the system, the more likely people are going to try to find ways around it. The system detects raised voices? You bring in some screaming kids. The system knows about how to deal with someone who's bleeding? Try fainting. It's going to be a constant battle for the people maintaining the Manna system to encode the responses that are appropriate to the situation. Taking away people's natural ability to adapt and think on their feet and replace that with a business system will never succeed in the long run.
And thirdly, toward the middle of the book the Manna system runs everything. It pays minimal wages, calls you up whenever it needs a person regardless of time or availability, and because there's so many people unemployed it can dictate the terms on which you work or replace you. But what of unions? What of civil protest? What of consumer advocacy? What of human rights? This whole section seems to be based on the - to me rather alien - USAdian labour system, and a pretty biased view of it too. I think it ignores the whole history of the rights of workers from the industrial revolution. Admittedly, it's doing this to present why this situation is so bad anyway, but this process doesn't make the story more believable.
I've spoken to one person who believed sincerely that labour unions are a kind of evil manifestation of shiftless, devious workers attempting to get everything they can from their nice, kind-hearted employer. The fact that this same person enjoyed the luxuries of an eight-hour day, compulsory superannuation, considerable health benefits and leave allocations worked for and bargained for by those very unions he so denigrated was lost on him. I myself don't believe that all employers are heartless, money-grubbing Scrooges determined to crush their workers under an iron boot, and I believe that many modern companies point to exactly the kind of worker freedom and independence that would make the Manna system both unnecessary and overly restrictive to their growth.
The Australia Project part of the story is a vision of how life could be
if hardware and materials emulated the opening and freedom of software,
but the Manna part isn't a convincing proof of the death of capitalism.
I believe that will come as a totally unintended side-effect of the
economics of abundance...
posted at: 18:26 | path: /personal | permanent link to this entry
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