omenti

a candidate for urban and suburban mobility

I have a serious interest in how we get around.  Currently the tech press seems entirely focused on car sharing and self-driving cars as THE FUTURE™, but those approaches are problematic.  I've spent a fair amount of time highlighting those issues, but rather than drone on for pages and pages I'll recommend a new book from a friend - Elements of Access by David Levinson .. essential reading for anyone trying to make sense of cities and suburban areas.  It's non-technically, fascinating and humorous.  From the about:

 

Transport cannot be understood without reference to the location of activities (land use), and vice versa. To understand one requires understanding the other. However, for a variety of historical reasons, transport and land use are quite divorced in practice. Typical transport engineers only touch land use planning courses once at most, and only then if they attend graduate school. Land use planners understand transport the way everyone does, from the perspective of the traveler, not of the system, and are seldom exposed to transport aside from, at best, a lone course in graduate school. This text aims to bridge the chasm, helping engineers understand the elements of access that are associated not only with traffic, but also with human behavior and activity location, and helping planners understand the technology underlying transport engineering, the processes, equations, and logic that make up the transport half of the accessibility measure. It aims to help both communicate accessibility to the public.

 

Bike sharing is currently experiencing explosive growth in urban areas around the world.  Bikes are very efficient in terms of density - you can put a large number of cyclists on bikes on the street - and energy use.  About eight years ago I measured the cycling energy expenditure of a friend at a little better than 1,000 mpg_e at a shade over a constant 13 miles per hour.¹  An added benefit of cycling is it is good for your health (assuming your path is safe enough) - good enough the both the Netherlands and Denmark factor cycling into their healthcare cost structure as a benefit.   In Northern Europe they've been integrated as an import element of transportation.  Infrastructure, laws and the public accommodate and encourage cycling and it's dovetailed into other elements of transport - bike to the commuter train and then to your office.  But there are issues.

 

First is most people don't ride long distances.  Even the Netherlands, with the highest bicycle use in the world, reports about 76% of commuting trips are less than five kilometers (figure about three miles) and fewer than one percent are longer than 15 km (about 10 miles).  There are many reasons: bikes are too slow/ trips take too long, hills and winds, the weather, long trips and long term use are hard on the wrists, back, shoulder and crotch. 

 

The electrically assisted bike or ebike solves many of these problems..  The speed can be up to twice as fast and hills and wind are much less problematic.  You feel like superman (or woman) on one. They're quite addictive and set to be hugely important in areas that have the right infrastructure - safe path, clueful motorists, parking and charging locations, traffic calming and so on..  not difficult technically or expensive, but change is often difficult. So ebikes are great, but they still have problems for many parts of the world.

 

There are niches where electrically assisted velomobiles could come into play.  Currently the only places you're likely to spot one is the Netherlands, Belgium or  Germany.  They usually have three wheels and a recumbent riding position and have an aerodynamic fairing.  I've seen four in the US - three were made by amateurs and one was a Dutch import.  I tired one and that proved to be an eye-opener. 

 

It was homemade, human power only and very heavy at a bit over forty kilograms. The body rattled and it configuration really needed a suspension.  But wow was it fast!  A human delivers about a hundred watts to the pedals to a bike during light commuting - about the same as what it takes to keep you alive (your brain takes about 20 to 25 watts).  Up to about six miles per hour most of the drag on a bike (or velomobile) is rolling resistance - tires against the ground.  Above that and air resistance becomes more important dominating around 15 miles per hour.  If it takes 100 watts to go about 13 mph, it takes about five to six  times as much power to go twice as fast (eight times as much power to overcome the wind).

 

Now here's something critically important -- the power needed to overcome air resistance goes up as the cube of your airspeed.  A bicycle or ebike has a drag factor nearly fifty times as great as a velomobile.² The homemade design I rode was "dirty" compared to modern velomobiles, but was still probably thirty times better than a bike or ebike.  That made an astonishing difference.  Once rolling, cruising at twenty five miles per hour was easier than fifteen on a bicycle.  

 

Velomobiles are difficult to get up to speed.  Stop and go driving is far from fun.  But the problem vanishes with electric assist plus,  in stop and go  riding you can recover much of that energy using regenerative braking.³

 

Properly executed they offer some protection from the elements and storage space for a few grocery bags.  In cold weather you don't need a heater because you're pedaling away at with about 300 watts of waste heat (a human pedaling a bike is about 75% efficient) - more than enough to heat a small enclosed volume.  In the Summer you can use the motor more and open the lid.  And you can run on the order of a hundred of them with the same amount of energy your family car needs.  It would place a very small load on the grid... so low that no changes would be required.

 

There are issues with infrastructure as they're larger than bikes. You're not going to sling one over your shoulder and carry it up to the office.  It may be they're more useful for longer commutes and suburban use.  You can fit about six of them in the parking space necessary for a car.  Currently non-electricxs are handmade and go from $5,000 to $12,000 - about the price of a high end road bike.  In moderate production that could quickly drop below $4,000 even with electric assist.  

 

The most interesting e-velomobile I've seen is the eWAW from a small company in Belgium. It has a carbon fiber roll cage/frame, very light weight (33 kg with motor and battery) and a very low center of gravity for cornering and stability.  It has a tiny 250 watt motor and a lithium ion battery about three times as big as what's in your laptop.   It will go nearly 100 miles on just battery power.   All of these numbers could be improved, but it's quite impressive as is..  Improving the breed would be a great project for a mechanical engineering class.  Back of the envelopes suggest it could be very safe under 30 mph assuming calmed traffic - potentially safer than a conventional bike.

 

It wouldn't be the best first for all areas .. nothing is.  The US is particularly unfriendly to cycling, but I wonder how this would work in the many cities with populations under 100,000 that often have large areas with 25 or 30 mph speed limits? 

 

Cities are beginning to realize curbspace is some of their most important real estate and I think part of the mix to deal with traffic in the future is to take into account the area a vehicle takes up when figuring out how to charge for road and parking use.  Bicycles are set to capitalize on this. I'd had discussions with two cities in the EU that are thinking in terms of banning cars from city centers and relying on bikes, and in one case, velomobiles, as important elements of access.   It is likely the future will not play out as tech writers suggest it will.

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¹ She isn't an ideal case.. she's very tall and the bicycle had upright handlebars giving her a lot of projected surface area.  Here's an earlier bit on bike efficiency.

² The coefficient of drag or C_d multiplied by the area facing the oncoming air.   On a bike the C_d is 0.8 to 1.0 and the area is about a square meter.  On a velomobile the C_d is generally under 0.15 and the projected area is about a third of a square meter.  You can push much lower.. the human powered land speed record car - the Canadian Eta - has a C_d of 0.03 and an non athlete could easily power it to normal legal highway speeds in the US.  I wrote about it earlier. 

³ Turn the motor into a generator slowing you down and charging your battery.

 

heat by chance

minipost 

We still have a bit of snow on the ground - slushy stuff that is partly translucent.  I tried forming someone of it into a sphere.  With clear enough ice and some polishing with your gloves you can make a spherical lens good enough to start a fire.  (from several years ago)  I didn't get there today, but a neighbor asked what I was doing and how could I stand all of that cold going to my hands.  I said it wasn't bad, but that's not what's going on.  Cold isn't moving from the snow to my hands - rather heat is moving from my hands to the snow.  There was a puzzled look.  

It turns out to be easy to understand what's going on and that discovery was part of a revolution taking place in physics at the end of the 19^th century that led directly to quantum mechanics.   It's not some fundamental law, but rather just chance .. nothing deeper than that.

Boltzman figured it out.  You can think of heat in terms of molecules vibrating in a solid or shooting around in a gas.  The more energy they have, the greater this agitation.  Consider a tank of air with a divider.  Make one side hotter than the other.  It's air molecules are zipping around faster than those on the other side.  Remove the divider and the hot and cold gases mix.  (you could do this with liquids or solids - same idea)

It is more probable that a faster moving molecule collides with a less energetic molecule than the other way around.  In the process it leaves a bit of its energy.  Energy is conserved and given enough of these collisions the extra energy in from the faster molecules tends to get equally distributed and everything eventually comes to the same temperature.

At the time it was crazy to think that something as how heat flows might be governed by chance.  It would take years to understand his result.  In the process a very deep understanding of heat would emerge and prepare people for a radical rethinking of what the microworld was. 

In the meantime enjoy the fact that you're heating up a bit of the cool March air when you go outside.