Electric motorcycle race in Isle of Man TT

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Postby EVguru » Thu Aug 14, 2008 8:31 am

PHEV wrote:What a strange idea to be forced to offer your bike for sale. Are there any precedents for this in the racing world?

Yes, it's been used quite a few times. It's to prevent factory teams entering budget limited privateer classes.

Although I wouldn't mind myself, I can think of any number of reasons why teams wouldn't want to sell thier entry (secrecy not least, many teams may be racing in order to get a product to market later down the line, and be forced to part with all thier design secrets?)


Then they enter the Pro class. The whole point of the Open class is to use readily available components.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
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Postby Jeremy » Thu Aug 14, 2008 11:43 am

Looking further into how light a bike could be has thrown up a design by Derbi, intended as a proof-of-concept design for a light weight dirt bike. The bike is the Derbi DH2.0, a 100cc, 8hp bike that weighs just 39.9kg. It looks like my idea of using top end downhill racing mountain bike components has already been done by Derbi. (see here for pictures and details: http://www.derbi.com/int/index.php?option=com_content&task=view&id=146&Itemid=283).

Assuming that the 100cc motor in this bike weighs around 15kg to 20kg, then it looks like the rolling frame only weighs around 20 to 25kg. Add in a couple of 1.5kg, 11kW motors, a couple of big RC brushless controllers and a LiPo battery pack that's good for around 6kWhrs (which I think should be more than enough for a bike of this weight) and the bike total weight comes in at around 70 to 75kg.

It wouldn't take much to redesign the DH2.0 concept into a road racer, either, I would have thought. If nothing else this seems to show that a 75kg electric bike may well be feasible, even without using something as novel as a monocoque frame.

Jeremy

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Postby EVguru » Thu Aug 14, 2008 3:02 pm

If you're looking for a really lightweight solution how about using a Plettenberg Predator (http://www.plettenberg-motoren.com/UK/M ... /motor.htm)


Do please remember that these motors operate with a

VERY LARGE

supply of cooling air.

8Kw input power at 88% efficiency is nearly 1Kw of waste heat. The 1.5Kg mass is going to heat up fast and it has very little surface area to dissipate the heat.

Many an Etek motor has met its demise due to a missunderstanding of thermal ratings. If you are running close to the continuous rating (reasonably likely on a bike at 60mph), then you have no extra peak power available.

Some of the problems that Tessla have been having are because they didn't understand the thermal ratings.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
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Postby Jeremy » Thu Aug 14, 2008 3:59 pm

Cooling is just something that needs to be engineered in at the design phase, but it's no great shakes to get right. People are now beginning to use these RC model outrunners in small EVs and they are proving to be pretty good.

It a mistake to think that the propeller of a model aircraft provides effective cooling for these motors - it doesn't. In fact the prop actually impedes airflow at it's centre, as it tends to just throw air outwards at this point. The solution some big outrunners adopt is to have a second, concentric, cooling fan fitted behind the prop to draw air into the motor. Alternatively the engine cowl can be designed so that it has powerful extractor vents at the rear that do the same job.

Getting rid of heat efficiently is always a challenge, even with a bigger motor. The only real difference with these light RC motors is their low thermal mass, which just means they heat up more quickly. They do have some definite advantages though. Firstly they are often outrunners, so tend to have a higher natural airflow as the spinning can draws air through the motor. Secondly, they are made of light alloy, which conducts heat away from the core fairly well.

Given the experience of this chap: http://www.wisil.recumbents.com/wisil/shumaker/default.htm it looks as if these motors can be run in lightweight EVs and still be kept cool. He's not drawing maximum power from his motor for long periods, but then these motors are so light that it would be possible to fit several, only using them all at full power for acceleration. Fitting a decent high pressure fan with good ducting to the motors would fairly easily deal with the heat problem.

They don't need to be as pricey as the Plettenberg motors either. These 6.5kW ones: http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142 are only about £75 each, which makes an array of them an interesting and affordable proposition.

I'm near-certain that these motors will be the basis for my next project - all I need to do is find some affordable HV controllers that are reliable enough. The Castle Creations ones seem to be the best, but are a bit expensive in comparison to the motor cost at the moment.

Jeremy

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Postby EVguru » Fri Aug 15, 2008 10:52 am

It a mistake to think that the propeller of a model aircraft provides effective cooling for these motors - it doesn't.


I was thinking more of forward motion.

but then these motors are so light that it would be possible to fit several, only using them all at full power for acceleration.


Isn't this getting away from light weight, it's certainly getting away from the KISS principal. There is sometimes a packaging argument for a two stage reduction drive. On the Freccia I mounted the motor up high in order to get a lead acid battery down low. Ideally you want a single stage for efficency, which means a reasonably low motor shaft rpm.

Lemco do a small version of their motor and AGNI do also, might this be a a better match.
Paul

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Postby Jeremy » Fri Aug 15, 2008 4:33 pm

The prop actually blocks airflow in the centre, so the slipstream isn't very effective either. This is one reason that aircraft tend to use cooling intakes that are spaced some distance out from the prop centre. The slipstream can be used very effectively to pull air through a cowl, using an extractor system, and this is common practice on most aircraft cooling systems. Something similar could be used on a bike, but it's unlikely to be that effective as maximum cooling will be needed at low speeds, during the hill climb sections.

Certainly multiple motors is complicating things, but it's a trade off, both with cost/complexity and weight/complexity, isn't it? I don't know how much a Lemco or Agni motor costs, but suspect that I could buy around 10 or 12 of those HXT motors for the same sort of price.

Similarly, IIRC a Lemco 200 weighs around 11kg, which is the same as about 5 of those 6.5kW HXT motors (or about 7 of the 6kW, higher Kv, HXT motors). I can't recall the max power of the 200, but would guess that it isn't as high as 32kW (or 42kW for the smaller HXT motors).

Assuming that a light weight bike application might need around 15 to 20kW, then the multiple small motor approach is both significantly lighter and also much cheaper. This may well be a trade off that makes sense for a budget limited privateer entry.

Finally, these model motors are brushless, so as long as they are kept cool they will run for very long periods with good reliability; no worries about brushes wearing or arcing under high loads. Their timing can also be adjusted on the fly from the controller, so they can be optimised for a wide speed range.

Obviously they are still an unknown quantity and may not suit a wide range of projects, but they may well be the most appropriate solution for the particular point solution I have in mind.

Jeremy

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Postby EVguru » Fri Aug 15, 2008 5:33 pm

I'd be very interested to see results, certainly. Synchronising the controllers might be a bit of a challenge.

One more thing to consider is torque at zero rpm. Some controllers, particularly the sensorless designs generate almost zero torque at stall. The Corbin Sparrow prototye had that problem (and had acoustic noise probelms from the drive) and the Sheffield University F3 car was just a joke. You had to push start it! The Bluebird team used the Sheffield motors/drives and we know how well they did!

As to your Mountain-bike component ideas. For road use the tyres wouldn't be legal and for certain shouldn't get through MSVA. For track use, you've got to convince the Scruitineer and they can be a very conservative bunch. I wouldn't invest any time in the idea until I'd run it past the ACU, likewise the brakes. I doubt if the tyre manufacturers would approve of their tyres for this application and that may be the deciding factor.

I know Cedric runs Mountain bike slicks on heavy duty bike rims, but I also know he's had side-wall problems with some of them. If anyone took a close interest in his bike, they'd probaly take a dim view of bicycle tyres on a motor vehicle the exceeds the 50cc class power limit.
Paul

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Postby Jeremy » Fri Aug 15, 2008 6:18 pm

Synchronising is a doddle, modern brushless controllers self-synch exceedingly well, even if the motors are locked onto a common shaft, with no pole alignment.

Starting performance is dependent on the particular controller start algorithm, but Castle Creations seem to be on the ball and currently appear to have the best way of doing this. This may well be because they are actively developing controllers for EV applications of RC model motors, so have put some effort into this aspect. Certainly Matt Shumaker (who is using a CC controller) has found that his bike launches off the line very quickly, I think he commented on the ES forum that he had to back off the throttle to keep the front wheel down.

I have a few fairly low power (up to about 1kW) RC model brushless controllers and most of them start pretty well. The only one that's a bit iffy is a no-name one from the far-East. My recumbent ebike has a sensorless, brushless, geared hub motor and starts very well indeed, so there is plenty of evidence about that this particular problem has been hacked.

The tyre problem depends entirely on the regulations. My intention wasn't to use mountain bike tyres, as they would obviously not pass scrutineering. All along I was looking at fitting moped tyres to lightweight wheels, something that has been done on heavy-weight bicycles, like tandems, for years. Similarly, brakes aren't really an issue either. A downhill mountain bike will run at similar speeds, require better brakes and won't be that much lighter. Also, tandem bikes work OK at far greater weights with just decent bike brakes. The brakes on that Derbi link I posted are just big mountain bike ones, from the look of them, yet Derbi seem to think they are OK.

Although energy absorbed from braking is very much speed dependent (being proportional to V²), it's also linearly proportional to mass. The combination of light weight, regenerative front wheel braking and modest mechanical brakes should be adequate, based on the sums I've done so far.


Jeremy

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Electric TT or GP? "Junkyard Dog"-Owner's musings

Postby ex925 » Mon Aug 18, 2008 8:34 pm

HEALTH WARNING: Author has difficulty with sensible thinking - the following is intended to stimulate responses - hopefully "more light than heat"

1 "Green TT" or is it a "GREEN MANX GRAND PRIX"?
If the latter, then rider licenses might be less problematical

2 Scrutineering - "SERIOUS" I expect......
Having experienced (admittedly in the distant past) the finely balanced care by the scrutineers to ensure maximum safety without unduly stifling ingenuity, I expect there will need to be some very informative guidelines. These will need to be available SOONEST - SO: Should the BVS immediately agree among ourselves and ASAP after that make representations to the scrutineers to enable safety and ingenuity in TWEVs, so builds can start, with some assurance of reliable regulation parameters?

3 Pedal cycling round the I.o.M. in the sixties taught me:
a] Manx racing cyclists were, (and still are...) formidable riders
b] good braking and steering in the I.o.M. are vital to continuation of life

4 Motorcycling round the I.o.M. back then taught me
c] Manx racing motorcyclists were, (and still are...) formidable riders
d] road-holding, braking, and steering are endurance-tested beyond anywhere else I have experienced

5 If any of the above prohibits - or even dissuades - a racing entry, maybe keen TWEV people could take their UK-road-legal TWEVs to the Island for an Electric (not quite so...) Mad Sunday

6 Anyone contemplating even just 5 above should still up-rate the handling, braking, and steering qualities of their machine, a lot, in my opinion.................

7 I should also admit that I have a history of over-strengthening Mk.I projects, then gradually following the Colin Chapman route… (“simplicate, and add lightnessâ€Â

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Postby EVguru » Fri Aug 22, 2008 9:47 am

From the TTXGP forum;

Qualification minimum will be average 50mph.

Our expectation is an average speed of between 70-90 mph. On the straights we would expect 100mph+.

These are the performance figures gained from consultation with teams and engineers.

This will be a race and not an exhibition lap. Performance is the focus. We are looking to reward the winners.

Thanks,

Team TTXGP
Paul

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