Thursday, October 31, 2013

The design- range

During the early phase of planning, I had range anxiety.  Would the bike go far enough to be practical?  I set the goal at a trip to the food coop, or about 33 miles.   It took a while before I figured out that it is not like an electric car, if the battery goes dead, I can pedal.  But if someone else used the bike that had a health problem, how far could they go?

Other electric bikes seemed to use a battery in an aluminum case, which fit under the rear luggage rack or between the seat tube and rear wheel.
Trek Transport electric longtail with battery under rear rack.  (Photo credit Trek)

These were usually 24 or 36 volt, and somewhere between 5 to 10 Amp hours capacity.  (Volts is the zing, like the octane rating on gas, and Amp hours is like the gallons in a car fuel tank.  Bigger numbers on either one can give you more range.)  These batteries had a nice package that could take falling down, and also a built in key for turning the bike on and off, but they seemed kind of small, even though manufacturers were promising a 30 to 40 mile range.  Then it occurred to me that range would depend greatly on how much extra the rider pedaled.

Another thing that influences range is drag.  Bicycles have been in development for over two hundred years, and they roll pretty nicely now.  Their main energy loss is air friction, which is proportional to size, and an upright riding posture is not very aerodynamic.  A rule of thumb is about 300 watts of force to push an average size rider along in an upright posture at 20 mph.  (This results in many electric bike motors being built at the 300 watt size, as many national laws use around 20 mph as the registration threshold.)

Three graphs, like this one for a forward leaning (i.e. racing) posture, (less is energy needed), and a wattage calculator, (I'm not sure of who to credit for this graph the way the website is written), can be found at this website:
American Road Cycling's Cycling Performance Simplified

If the wind is blocked by a fairing so that air resistance is removed, it is possible to go quite fast using just human pedal power:
Fred Rompelberg (Netherlands) on a bicycle drafting a dragster at the Bonneville Salt Flats in 1995, setting a world bicycle speed record of 166.9 mph (photo credit Strausberg racing team)

Of course, since aerodynamic drag increases proportional to the square of speed, I could ride slow (5 to 10 mph, which is not very likely to happen) and not worry about the range...

After spending far too many late nights reading electric bike forums, I decided a step or two bigger battery was needed.

Wednesday, October 30, 2013

The design- speed

I started out building both bikes last winter, but as you can tell from the pictures only the bakfiets was done in time for the Fourth of July parade.  That's ok, as it has been a blast to ride, and I'll use some of the lessons learned from it when I finish the longtail this winter.

A solar electric cargo bike looked like a decent car substitute, but there were several problems to think about.  One of the first questions was speed, because I didn't want to take half the day to get to White River Junction and another half getting back.  However I also knew that the average speed in a car is much lower than the driving speed.  The travel time might be more dependent on stop signs and traffic than on a car's superior speed.  After carefully measuring 13 trips over the last several months, it's turned out that a trip to the center, (6 miles one way), takes 13 minutes in my car, and 21 minutes on the bike, which is 1.6 times longer.  Surprisingly, the longer trip to WRJ (16 miles one way) didn't give the car a huge advantage, taking 29 minutes in the car, and 56 on the bike, or 1.9 times as long.  The bike trip computer usually shows my riding speed between 16 to 19 mph, and improvements are planned for the second bike that I think will raise the speed a few mph more, reducing the time difference.

Getting groceries at the Upper Valley Food Coop

A stop at recycling on the way.

Thirty five miles has turned out to be a soft limit of this first design for a few reasons.  First of all I'm not in shape, and a trip of 1 hour 52 minutes riding time is a fair amount for someone who is not used to sitting on a bike.  Secondly, I used the gearset from an old mountain bike and it has a small front gear.  When I'm going 20 mph, I'm pedaling pretty fast, and at 25 mph I'm pedaling really fast.  I find that I'm riding around in top gear 98% of the time, and shift down to the middle front gear only for the really steep hills.  The speed then drops to 12 to 14 mph with moderately hard pedaling.

On the other hand, I routinely hit 35 mph going down hills, and a few times have gone 41 mph.

This is probably a good point to talk about the line when a bike becomes a motor vehicle and has to be registered.  I'm using Federal Law HR 727, and here is a copy of the subsection:
This formatted copy is from Electric Bike Solutions (GoCarLite), click on image to enlarge.

Obviously I wish to go fast enough to replace my car, but not fast enough to make it a registered vehicle.  There are at least a half dozen ways I can legally improve the speed, but I don't wish to game the system so much that it causes trouble.  There are bikes out there that are topping out in the 60 to 80 mph range, and electric bicycles have been banned in parts of NYC because the bicycle messengers were abusing their power.  I'll cover more of this in a later post, but for now I'll just say that the solar electric cargo bike tops out under motor power at 20 mph on a flat level road with me on it.

Monday, October 14, 2013

The basics

I wanted to use my car less.

I'm not against cars, I love Porsches.  But there are several reasons I would like to use a car less, centered mostly around connections.  So I started looking for bikes with big luggage racks, and ended up with cargo bikes.  Of course it would have to have an electric motor, as I live in Vermont, which is not flat, and I wanted to carry a load.  And I've lived 27 years off grid, as well as working on Solar Hartland for the last three years, so it might as well have solar panels.

I asked many people for donor bikes, started shopping for parts, and then built a bike.   I thought a blog about what happened, the results, and the next plans, might be a good idea.

My first solar electric cargo bike in the Hartland Fourth of July Parade.

The first cargo bikes I saw were trikes, with a box between two front wheels.  They didn't look like much fun, and also the roads around me are mostly narrow, so I decided to stick with two wheels.  This was supposed to be a car substitute, I wanted to lean into corners going fast.

The next searches found longtails, because I was looking for regular type bikes with electric motors:
Surly Big Dummy longtail with load.  (unsure of photo credit, probably one of the owners of Xtracycle.)

There are several manufacturers making longtails in the US Pacific northwest area, and the design was a good fit for my needs, so the project seemed all set.  Turning to the electric motor however, trouble set in.  There were two kinds of motors!
The motor on the left has gears and a slip clutch, the right motor is direct drive.

The geared motor has more push for loads, and it's slip clutch allows you to coast.  The DD motor gives you regeneration- it makes electricity to put back into the battery when going down hills.

To make matters worse, I then discovered the bakfiets style bike (Dutch-  bak=box, fiets=cycle):
These seem to be used for hauling kids around.  (photo credit Babboe company)

The longtail seemed to be better for me, but all the blogs chose the bakfiets.  And the motor did not have a clear cut choice,  The obvious answer was to build one of each.