Ending the School Year with a Bang!

... or at least a lot of smoke!

I was working with my advanced physics students building a bicycle generator. We had all the wiring purchased and ready to set up. We were about to hook it all up to the alternator, when...

We got one of the connections switched, and in the process of pulling it out to fix it there were some sparks, and then there was some smoke, and then there was LOTS of smoke.

Long story short, we got to pull the fire alarm, use the fire extinguisher, and evacuate the entire school. That was an exciting day! It really was the best possible situation though.  No one got hurt, no property was damaged (except we melted some wires), and some genuine (and I mean genuine) learning occurred as a result. In hind sight there were at least three things we should have done differently: 


1. Don't bolt down the wires until you're sure they're where they should be.
2. You can never have too many fuses.
3. Don't forget: the frame is negative.

The best part was we couldn't figure out why it happened until we were outside, and THEN we realized it. Ok - the best part might have been that everyone was SUPER supportive: the superintendent, all the teachers who were outside with me, all the students. It was awesome. And there's no better advertisement for physics!

But there's one more portion of this story to write. The rest of that day we had class outside because my classroom was COVERED in fire extinguisher dust. For anyone who's experienced that stuff, oh man, I commiserate. That stuff gets EVERYWHERE, and it's NOT easy to clean up. The custodial staff at the high school did a _great_ job cleaning things up, but the thing they were not excited to touch: my closet.

Unfortunately, the door to my closet had been open and every surface was covered in white powder.

Truth be told, I have never cleaned out my closet in 8 years of teaching. There are boxes in there that I inherited which were never opened when I arrived, and I have never opened them. There were objects in there for which I have NO CLUE what they're for or how they work. So here was my opportunity. After school was out I got a couple of supplementary custodial workers to help me go through EVERYTHING in my closet and make the decision to either wipe it off or throw it out.

I didn't think to take a "before" picture, but here's the after picture with everything cleaned out:

And the rest of the room: 

I was able to donate a lot of the stuff I didn't want - most of it was electronic equipment from the 1980's, like oscilliscopes, multimeters, a centrifuge, etc. Great stuff. I hope some shopper at Resource in Barre will want those things!

KSTF Summer Meeting: Turns Out I Voluntarily Left the State of VT (!?!)

Albeit for a very short while...

Not too much to say at the moment since it's past midnight, and I'm definitely tired :P but I'm hanging out in Philadelphia at the Knowles Science Teaching Foundation summer meeting: the first KSTF meeting I've voluntarily attended since my fellowship ended last year. What can I say? I just couldn't stay away. I love these people. Tomorrow I'm presenting with two other fellows in a seminar called "Off the Grid" in which two guys were inspired by my bike generators of a few years ago, and went on to build super sweet bicycle generators to take their classrooms off the grid. Very nice. They drove to the meeting so that they could bring their bike generator to the meeting, so people have been donating energy so that the presentation itself can be run off of the human-energy-filled battery. Best of all, these guys made shirts for us. Pictures to come.

"Simple" Bike Generator

My former co-teacher (and professor at Yestermorrow Design/Build School), Ben Cheney, called me up the other day looking for a voltmeter and an ammeter that could read up to 120 Volts and 10 Amps (respectively), and unfortunately, I didn't have anything besides a multi-meter to lend him, but turns out he needed these devices for a bike generator he's building for Efficiency Vermont to do demonstrations in schools. And the electrical design is similar to the "simple" one I was planning to put up anyway - so here it is:

It's merely a DC motor, but instead of supplying electricity to it, you turn the shaft, which then makes the process work backwards, generating electricity. The light bulb doesn't care which direction the current is flowing, so you can turn the shaft in whatever direction is convenient. According to the Simple Bike Generator I've got in my room (errr... rather which is out on loan to a Canadian college), the generator shaft is in direct contact with the wheel via a rubber stopper, which fits on the end for good contact. That's really have the job right there, though, is making good contact between the wheel of the bike and the generator shaft. It's not easy. But... you're creative, you'll be able to figure it out ;)

Student-Built Bicycle Generators

Today I stopped at the high school to meet up a with a former student who wanted to borrow our bicycle generator. Her college in Canada (I forget which one now) is having a green fair, and she and he compatriots are hoping to rehabilitate our delapitated machine.

Two summers ago we built 5 bicycle generators with a group of summer school students using Subaru alternators and deep cycle batteries... and some wires and stuff (heh heh). All 5 worked by the end of the 2-week session (which seems amazing to me now), and since it was the first time anyone in the group (myself and my co-teacher included) had ever done something like this we made a lot of mistakes that would certainly affect the way we would build them in the future.

In any case, this is what we did:
We took Subaru alternators (cause we could get them for free, and Subaru is like the official car of Vermont, so they're pretty abundant), and we made sure there was a good electrical connection between the outside of the metal alternator and the metal bicycle frame (grounding), likewise with the negative side of the battery (use a high-gauge well-insulated wire).

The Large Bolt on the alternator carries the majority of the current, so you need a pretty hefty, well-insulated wire connected to the positive side of the battery, but that's not going to be enough to produce electricity once the alternator's turning.

The reason is because the alternator has no permanent magnet. It's an electro-magnet, which means that it needs just a little bit of juice to start production (lighter-gauge wire should be fine). Thus the idiot light. When you flick the switch to "on", the battery sends a little bit of current through the bulb, which provides resistance and tells us that there's electricity flowing through there. And when the bulb is lit, that means the electromagnet is juiced and its ready to produce electricity on its own.

The alternator is built to cease using electricity from the battery once it's going, so after a few turns the idiot light should go off indicating that it's sufficiently powering itself as it turns. When you stop, however, the light should come back on.

Be sure to turn the switch to "off" when you're done, so you don't drain the battery.

Advantages:

• This system would be great for long-term power use - if you were actually trying to fill a battery with human-generated power.
• It was super cheap - each bike was built for less than $100!
• All the parts are readily available at an auto-parts store.
  

Disadvantages:

• The way we built them ... (heh heh) they were almost impossible to move. Those deep cycle batteries were freaking heavy.
• We ended up attaching a tiny inverter to our battery (with the cigarette-lighter end cut off) so that we could actually plug in some devices for our parent/community exhibition. But what we didn't anticipate was that those inverters were the type of device that is "always on", and as long as it was plugged in they were sucking energy from battery :( thus killing them.
• They did not demonstrate the correlation between the wattage of a device and how hard you would have to pedal to power it. Because of the electro-magnet, you couldn't get around needing a battery. So as an educational tool to demonstrate power it wasn't so good. As a tool to teach circuitry, it was great.

The bicycle generator I lent to the college student was of a different (simpler) design, which I'll notate tomorrow probably.