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0 pointssjtgraham9y ago0 comments

> Semis spend a large part of their time driving at highway speeds where air resistance is at a maximum.

Why would a self-driving cargo vehicle drive at highway speeds? A human truck driver can only drive 11 hours/day, an autonomous vehicle can be on the move 24/7 and so could travel at slower, more efficient speeds while completing trips on similar time scales.

> To achieve useful performance an electric semi will need a lot of batteries which will reduce its cargo capacity (Federal law regulates the maximum gross weight), which reduces its value to freight companies.

Don't forget about the solar roof unit. There is a lot of surface area on a trailer. This could offset some of the energy requirements along with other technology such as regenerative breaking. Also consider that a supercharger network might be constructed.

> Autonomy. I think this will take a lot longer to achieve than planned, both technically and socially.

I disagree. The evidence is to the contrary technically speaking. The matter is more subjective on the social front, but we've seen how popular attitudes change to technology. It might be a fatuous example but consider how it was once uncool to be online and then MySpace happened, and consider how it was anathema to be anywhere near online dating, the archetypal hallmark of a loser, then Tinder happened and now it's almost de rigueur in the mainstream.

> Enable your car to make money for you. I don't want anyone using my car. Legal liability is one reason. As owner of the car, I am liable for damage it causes.

Insurance (including public liability insurance) is already a thing. Insurance is priced according to risk, so when autonomous vehicles are here and much safer than human drivers the insurance will be priced as such.

> If I need to go somewhere, and my car is not here, I don't want to wait for another one.

The post alluded to making your car available when you're at work etc. I expect the intention is ensure it has returned to you by the time you want to go home.

> I don't want to get my car back from another user and find food wrappers strewn about and used condoms under the seat.

These are valid concerns I share too.

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chiph9y ago

Even though he said Semi, I don't think he meant an interstate tractor-trailer. I expect to see a replacement for the typical urban box truck, that is used to make local deliveries.

1. It's local, so it's always near a charger 2. They're smaller, so easier to build in their existing factory space 3. Possibly the biggest perceived win for the environment, as people wouldn't see exhaust soot anymore right outside their window 4. Stoplights - the box trucks spend more time accelerating from a light, so they need torque. Something that electric motors have from a dead stop.

Vik1ng9y ago

A semi travelling a very slow speeds would need his own lane or it would significantly increase the risk of accidents (unless every car on the road is autonomous).

Solar on the roof is most likely rather insignificant and will also just add weight.

seanp2k29y ago

Re: solar on the roof, agreed that it wouldn't do much:

An ISO container that could fit on a truck trailer is typically 40'x8'. Solar panels are, on the sunniest of days, making 10-14 watts per square foot. This gives us:

40x8=320sqft assuming panels with no borders.

Assuming 14 watts per sqft (optimal conditions) we'd end up with 4,480 watts. Assuming 100% efficiency converting this into usable motion, we'd get 6 BHP. A normal semi truck has 350-600HP, so this is a drop in the bucket compared to their normal output power. As far as how much of that they use while cruising, I'd wager that it's much more than the 1-2% boost which solar-powered electric would provide (again remember that my calculations assume cloudless sky, no dust on panels, no weight or aerodynamic penalty, no maintenance costs, 100% conversion efficiency, etc).

They reason you don't see them is because it's not worth it. The aero mods under and behind the trailer on the other hand ARE worth it, and this claims that a specific version of a "trailer tail" gives a 6.6% boost to fuel economy at 65MPH: http://realtruckdriver.com/what-do-i-think-about-semi-truck-...

Eiriksmal9y ago

Thanks for this math, which really demonstrates how... er, pipe-dreamy Musk is on this.

The truck logistics industry has been struggling with this problem for years. How do we increase fuel efficiency from the days of 90s Caterpillar engines dragging 80K lbs at 4.3 mpg while simultaneously decreasing emissions while simultaneously figuring out how to make the truck itself lighter and able to move more cargo in a single load?

Autonomous electric trucks would improve "fuel" economy and minimize downtime caused by the limits of human endurance, but at what cost? How many miles of range would the batteries have to have to compensate for the slower cruising speed and additional stops needed to recharge them? How much DOT downtime has to be eliminated to make up for being able to pull a few thousand pounds less on each trip, owing to the massive number of LiOn batteries scattered around the truck and trailer?

When I worked at Penske Truck Leasing in the late aughts, I'd have fascinating conversations with truck drivers on the math they were doing to optimize for fuel economy and load capacity. The switch one of Penske's clients made in changing their fleet to DEF Volvos with 240 gallons of diesel capacity compared to the classic Detroit Diesel Freightliner Centuries with dual 150-gallon tanks caused many an angry tirade.

Many of the drivers were constantly juggling juuuuuust enough fuel to make it to the destination and back; the trailer they were headed to pick up was so heavy they couldn't have more than ~200 gallons of fuel or they'd be over 80K and fined accordingly at the scales. Good luck making that 1200 mile round trip on your 200 gallons, driver.

I'm not sure trucks are the answer. We'd need too much overhauling of the current system to make it worthwhile. Without increasing weight loads, which destroys our infrastructure even faster, as well as rethinking how trailers are loaded and unloaded to maximize the 24/7 automated nature of autonomous fleets... We're a long way off.

And, anyways, aren't cargo ships and trains basically already electric and their massive diesel engines are just powering the electric motors? No weight limits or problems caused by slow cruising speeds in those applications, that I'm aware of.

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codeulike9y ago

Who said anything about solar on the roof of a truck? I think you are misunderstanding.

coredog649y ago

Use solar on the roof for reefer trailers (similar to 3rd Gen Prius option)?

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