Mayor Eric Garcetti came by for a photo-op with the Bike Babes, and when informed of the source of electrical energy for our little dance party said “That’s awesome.” We agree.
The BBBs came out in force, equipped with sparkly hotpants and miniskirts:
And I caught the duo that is KnotworkLA dancing while generating power:
The system performed beautifully, enabling CicLAvia guests to produce 733 Watt-hours of clean energy, of which 630 was used for music, meaning that we used none of the power generously sold to me by the DWP the night before. Great job CicLAvia!
As usual, our best customers were the ones too small to fit our bikes (a kid’s bike with generator will be coming soon!)
We’ve just received many of the parts for the generator, and will test them out this week! Suddenly all of the planning and fund-raising and cogitating is going to be attached to a couple of bikes with power cables coming out of them. This is a big step, so I suppose it’s time to update everybody on how this thing is going to work.
Hub Motors
We bought our motors from ebikes.ca in Vancouver BC. There are more local options, but these come highly recommended, and there is a wealth of information and support at their website. The motors are “brushless DC motors,” which is a bit of a misnomer, as the motor itself runs on (or outputs) three phase AC. In a motor application, that AC comes from a motor controller which converts 12V DC into a variable frequency, variable voltage power signal according to the desired speed and power. Since we’re using the motors backward, taking power out instead of putting it in, we’ll need to make sense of that 3 phase AC.
Nine Continent Rear Hub from ebikes.ca
The motors come in three different windings, from 6 turns to 8 turns. This is equivalent to using gears of different sizes on your bike; if you supply a given voltage, the 6 turn motor turns faster than the 8 turn motor, but with less torque. What this means to us is that the 8 turn motor will supply our target of 14V at a lower speed, meaning that we can use the low gears we’ll need for hauling cargo. However, it might be too much, and we’ll have to use super low gears to keep our voltage low. We ordered a 7 and an 8 turn motor, and we’ll figure out which one we need once we have the bike in the trainer and a load attached.
Rectifiers
A rectifier takes the alternating output of a motor and converts both the positive and negative peaks into positive current, effectively flipping all the troughs into peaks. It works by feeding the alternating current through an arrangement of diodes (which only allow current in one direction, like a check-valve). Ours are packaged in neat little boxes with spade terminals and a must be mounted on a heat sink; the diodes don’t put out a lot of heat, but it’s enough to damage them if they can’t dissipate it.
Load
We’re using the element from a ceramic space heater as a load. This is basically a big resistor; current has to pass through a series of special ceramic blocks that are poor electrical conductors. These heat up, normally to heat the air blown through them. This element is unfortunately a bit too strong, with a resistance of 180 ohms, but since there two elements, we can connect them in parallel, cutting that resistance down to 90 ohms. If I’d been able to find a traditional coil element, we could clamp on anywhere along the coil to adjust the resistance.
For a more visible effect, we picked up three 100Watt light bulbs. These have a resistance of 144ohms apiece, but connected in parallel we’ll get 48 ohms, which is a pretty reasonable load to power.
Metering
One of the toys we received is the Watt’s Up meter. This little guy connects in line with our power, allowing us to see just how much power, in volts, amps, and watts (just so you don’t have to compute the product). This means we can finally get a good idea of what a person puts out on our system! This is really exciting.
My first human power project, the Seattle Bicycle Music Festival in 2010, was an amazing success. This, in large part, is why I want I’m so excited to put on another show! We built our own generator, inspired by Rock The Bike‘s Biker Bar (which has since been discontinued for reasons I will discuss later). Like the Biker Bar, our generator used a single generator coupled to the bikes by a long tire driven shaft. Like the Biker Bar, our generator folded in half to become an 8 foot long trailer. Unlike the Biker Bar, however, our shaft folded too, allowing us to squeeze five bikes onto the contraption, instead of three! A 90amp VW Bus alternator, with it’s own voltage regulation circuitry built in, converted those pedaler’s work to clean 12V, variable current DC. The volunteer cyclists were able to power all the acts, including quite a loud rock band who brought along three tube amplifiers! We had our share problems though, and I learned a great deal.
The bikes should be on display
Seattle Bicycle Music Festival, Miriam Halsey, 2010
One of the best parts of the bike powered concert is that the folks powering the concert are right next to the band, facing the audience. They’re on display. The audience knows that this is part of they act, and it’s their turn next! With a system like this, the volunteers are close enough to have a conversation with each-other. This, I think, kept people coming back to the bikes more than anything else.
Mechanical transmission is lossy
Setting up at Cal Anderson Park, Chrystal Lin, 2010
for all it’s simplicity, The common-shaft approach has a major downfall in the form of mechanical losses; the tires contacting the shaft, the support bearings, the flexible shaft couplers, all of these are big energy sinks, which is why Rock the Bike has stopped building their Biker Bar system, and why Movable Parts is using a different system.
Don’t skimp on critical components!
We made the mistake of taking our shaft bearings from the cheapest skateboards we could find ($25 apiece). Within an hour of use, the loose ball bearings inside had burned up all their lubrication and had moved on to burning up the polyurethane wheels:
Melted and deformed skateboard wheels. Chrystal Lin, 2010
The wheels rapidly conformed to the shape of the shaft and stopped spinning, polishing the shaft nicely and sprinkling shredded polyurethane all over the generator floor:
The above photographer was sent on a mission to a nearby skateshop (which kindly opened an hour early) for 20 high quality skateboard wheels and bearings (which cost about as much as five complete $25 skateboards), and the show went on.
Home