Oliver Kuttner on Very-Light-Car

Last year, I met Oliver Kuttner, who led the team to win the Progressive X-Prize to build the most efficient and practical car over 100mpg. Oliver's Edison2 team won with the VLC (Very Light Car) and surprised everybody by doing it with a liquid fuel engine. There was a huge expectation that an electric car would win the prize, and in fact the rules had been laid out to almost assure it, granting electric cars an advantage over gasoline that I thought was not appropriate.

The Edison2 team made their focus on weight, though they far from ignored drag. Everybody made an aerodynamic car, but what they realized was that making the car light was key. And batteries are heavy, heavier than efficient liquid fuel engines. Hybrid systems, with both batteries and two motors are even heavier than what they built. They also developed a new type of suspension which was much lighter and allowed a simpler car.

Since the X prize, they have built electric cars as well -- their techniques still work there, even if that's not where they found the greatest X-prize results -- and recently showed of their latest 1,400lb model which seats 4. (Though I can't say I think it's comfortable with 4.) Equally impressive, Oliver reports they have done succesful forward offset collision tests, and done well at them, contradicting a popular impression that small, light cars must be death traps on the road.

This bodes well for robocars. As I wrote 2 weeks ago, I think the small, light car is the future of transportation if we want it to be efficient, and the robocar can, by delivering such vehicles for people making shorter solo or 2 person trips -- ie. the vast majority of all trips -- make this happen.

Earlier, I brought Oliver in to give a talk at Google in the Greeen@Google series. Here is a video where I host him describing the car and their thinking around it. His thinking on cars is fresh and while it's very challenging to start a new car company, here's somebody who might just do it.

We've often said that in the most distant future, when car accidents are very rare, we will be able to make our cars lighter because over 30% of the weight of a modern vehicle goes into safety features. I think we can get those light vehicles even sooner.


There are quite a number of reasons we can see car weights reducing because of robocars.
- Reduced requirement for crash protection.
- With or without V2V, we can expect better synchronization of vehicles, similar to bird flocking. This in turn should lead to reduced requirement for acceleration and braking, reducing weight. If that vehicle is electrically powered, then the reduction in trip times synchronization brings could reduce required battery size.
- Suppliers of driverless cab services are likely to concentrate on urban, low to moderate speed vehicles, again reducing weight of vehicles, not to mention all these vehicles require 1 fewer passenger space. Private vehicle owners may still buy one higher performance long range vehicle for the odd occasion where this is required.
- Robo cabs will be made in a number of sizes to suit a dispatch passenger number distribution. Even if the averge robo-car capacity is higher than 4, the expected dead mass per passengers should reduce.

Apologies if you have already raised each of these points, and I'm probably errg on the side of optimism as usual, but it will be facinating to see how much of this comes to pass.

Very cool.

It's good to know that someone is trying to build an ulta-light *safe!!!* car that doesn't require everyone to be robotic yet.

I wish them the best!

Ok, this is a question about basic physics.

Why does weight matter so much in vehicle efficiency? Here are the principles:

1. Energy is lost through non-regenerative braking, rolling resistance of the tires, air resistance, drive train friction, and engine waste heat. Anything else significant?
2. Braking depends on the driving course and is dominated by hills and traffic stops.
3. Rolling resistance depends on tire size and pressure, which do depend on vehicle weight but do not result in much lossage.
4. Drive train resistance and engine waste heat scale with engine size, but are they that significant?
5. Air resistance heavily dominates energy lossage above about about 30 mph. (Is this the correct number?) So again the driving course is important. But once the vehicle has accelerated to speed, weight is not so important.

Am I missing anything, or does this combination of considerations in fact account for such a strong effect for reducing vehicle weight? When I'm on my bicycle, it's the wind I curse, not my tires.

Rolling resistance is dominant over drag at lower speeds, drag is the big factor at higher speeds. Rolling resistance is directly proportionate to weight. Regenerative braking is good, but Oliver has a bunch of charts to show it's not nearly as powerful as you imagine, so total power for acceleration is also proportionate to weight.

Yes, engine waste is not really related to weight of the vehicle.

But no, at speed the losses are the weight-based rolling resistance and the profile/size based drag.

This has definitely reshaped my thinking out of the "electric car box".. time to think again :P

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