Tuesday, January 10, 2006

what exactly defines a hobby as “expensive?”

yes, i know i suck at updates.

world of warcraft has conquered my life.  i have (as of sunday night) a lvl 14 troll hunter named course who’s been eating up most of my free time since last thursday.

danielle and i will spend an evening at home tonight, sans gaming, and i shall elaborate on house and car repairs. 

in the meantime… a guy that sits next to me at work is a member of AHRMA , a vintage motorcycle racing association.  he collects and races vintage czech dirtbikes from the 1970’s and has all sorts of jawa stuff plastered around his desk.  here’s his website, czechpoint, where he has lots of info on the jawa bike lineage.


one of reese’s many CZ bikes

i was actually pretty surprized that these were sold in the states.  kinda like the yugo, i figured that they would have been technologically backward by western standards, and according to reese, that’s pretty much what happened to them after the soviets sent tanks to czechoslovakia in 1968 to crush the “prague spring” and solidify communist control of the region.


thank you wikipeda

anyways, for some reason today, he today suggested i start collecting vintage motorcycles.  as i was saying that if i felt like adopting THAT hobby, i’d have to get a divorce and move to a house in the boonies so i’d have room to store their rusting corpses in the yard, he interjected with “ROTARY motorcycles” and immediately caught my attention.  i instantly was forced to break off from the productive work i was accomplishing and do some research.


the suzuki RE-5.  this is where i started.

most people dont even know what a rotary “wankel” engine is, let alone its history, but when felix wankel originally developed the concept, he was creating it for a motorcycle manufacturer called NSU as a powerplant for their bikes.  mazda may be the only company building them now, but there was a time when everybody and their uncle had licensed the engine, including general motors and ford.  then came the oil crunch in the 70’s and pretty much killed the engine in its infancy.  before that though, almost every major (and minor) motorcycle company on the planet had a line of wankel powered bikes.  honda, yamaha, kawasaki, norton, (british), van veen (dutch), and even MZ (a east german mfg) had rotary powered machines.  this site is in german, but there are plent of cool pics of several of them down below.  this one is my favorite.


the hercules W-2000.  the german contribution

the hercules W-2000 is where i would start if i was i was stupid enough to buy one of these things.  not because its’s mechanically superior (that i know of) but because it’s the only one that doesnt have the engine transversly mounted.  instead the driveshaft is inline, giving it that unique look above.

i was reading that german site and saw that the nickname of this bike was the “staubsauger.”  i nearly dropped out of my chair laughing at that when i read that.  staubsauger means vacuum cleaner (dust sucker) in german, which is exactly what it looks like.  almost like u have a big electric motor mounted down there.

rotary recycle actually has for sale listings. looks like i better start checking ebay…

more tonight.  hopefully

Posted by sand at 20:53:16 | Permalink | Comments (4)

Monday, May 9, 2005

oldie but goodie

think i’ve kinda been coming up short in the “nerd humor” department lately.  if anything, it’s been leaning towards jock jockularity.  so i’m gonna resurrect this thing i wrote last october when i wrecked my bike on I-5.  a lot of u guys have read it once before, but hey!  i always wanted it circulated on the web anyways! =D

and i’m lazy.

as usual, i make no promises for spelling, grammar, or physics.  so, without further adieu…


This morning I was riding my motorcycle to class.  Traffic was moving at 10 mph and, while it had been sunny in Everett when I left, by the time I had gone three miles, it had started raining hard.  45 minutes later, at the point where express lanes diverged from the main part of the freeway, my lane opened up for a ways and I began to speed up.  I looked to my left at the traffic stopped in the expressway on-ramp and saw another guy on a bike stalled out and blocking traffic.  When I turned my head back around the car in front of me was slamming on his breaks.

As one naturally does in such a situation, I applied pressure to my own breaks and proceeded to begin a swerve as taught by the Washington Motorcycle Safety Council.  Strangely enough, this put the bike in a sideways skid and the next thing I knew both the bike and I were headed for the freeway surface.  As I began to fall, being nominally an engineer I thought, “Wow, seeing as how I’ve obviously overcome the friction force holding my tires to the road, what an excellent opportunity I now have to derive the coefficient of friction between my tires and the concrete!”

Consider the following free body diagram.

figure 1

Approximating the angle of the tire to be 60 degrees, we should be able to calculate the friction force F and from that derive the coefficient of moving friction ¼.

All of a sudden, I’m sitting almost fully upright and sliding effortlessly down the freeway in a deep snow tire rut like a kid on a waterslide.  Once I realize that it doesn’t hurt at all and that I’m not leaving a large portion of my skin on the pavement, I stop screaming long enough to think, “Hmmm, u know, applying the same principles I just did for the tire, I can figure out the coefficient of moving friction between the exposed, large-aggregate stones in the concrete surface of the freeway and my bouncing ass! (Or more specifically, the pants covering my bouncing ass).”

Consider the following free body diagram.


figure 2

For this example, we’ll assume an angle of about 74 degrees.  Once again, we should be able to calculate the friction force F and from that derive the coefficient of moving friction ¼.

Interestingly enough, I noticed that the bike itself was now careening on ahead of me a good sight faster than I was.  Obviously, while the bike was more than three times my mass, possibly creating a larger friction force to slow it down, that same mass also gave it more inertia than I had, causing it to slow less rapidly.  I could tell from the position it was sliding in that the contact surface between the bike and the road was about 8 square inches.

Consider the following free body diagram.


figure 3

Content that the bike in front of me would hit anything before I did, I spun around on my rear while continuing to slide another 90 ft and concentrated on the traffic coming from behind me.

This brings up another value that could be used to derive the coefficient of friction between the pavement and my ass.  knowing that I slid about 120 ft, with an initial velocity of Vx = 30mph, taking into account my weight and neglecting air resistance, the friction force necessary to bring my body to a rest can be calculated and ¼ can be derived.

Hint: ¼ will be very small.  Not only did I not loose any skin, there was not so much as a frayed thread on the seat of my cotton pants.

The entire experiment lasted all of 5 minutes from start to finish and was concluded when I applied a vertical force to the reposed bike, creating a moment about the bottom of the tire and rotating it to an upright position, thus demonstrating the mechanical advantage gained by a long moment arm.

Consider the following diagram.


figure 4

Assuming the CG of the motorcycle is 1ft above the base of the tires and assuming it moves through a 90 degree arc while being set upright, one can calculate the distance it was moved and use that to derive work W done during the lift.

Amazingly enough, with all the kinetic energy in that system I walked away with out so much as a bruised tailbone to show for it.  The most unpleasant part of the whole experience (experiment?) was that my pants and underwear were wet from 8:30 AM when this happened till 2:30 PM when I got home and changed them.

NOTE:  UNDERWEAR CHANGED DUE TO CLAMMY WETNESS FROM RAIN WATER.  NOT BECAUSE I LOST CONTROL OF MY BODILY FUNCTIONS IN AN EMERGENCY!

I estimate the starting volume of water held in the fibers of my pants (Vs) to be (gonna switch to SI units here) 300mL.  By the time I got home, around 25% was still there, mostly around my butt because I had been sitting on it for several hours, not allowing it to dry.

Consider the following system diagram.


figure 5

Given the relative humidity to be 98% and approximating my body heat Tb = 37 degrees C (plus another 10 degrees C for the love in my pants) and the outside temp To = 12 degrees C, we should be able to find the energy in Joules used in evaporating that volume of water from my pants.  (Or not… thermodynamics was never my strongest subject…)

All this is a very interesting physics experiment that anyone can perform given the appropriate environmental conditions and possessing the correct equipment.

Equipment list:

  • Heavy motorcycle with nonfunctional rear brake.
  • Helmet (never did hit my head, but safety first!)
  • leather jacket
  • pants
  • rain
  • road

It also doesn’t hurt to have a lady driving behind u that also rides and likes to follow bikers to give them some rear protection.  Special thanks to her for turning on her hazards and putting down my kickstand after I lifted the bike.  Props for not running me over.

Good luck!


i’ll post some pix of the bike later.  right now it’s in pieces in the garage while i replace most of the electrical system so i can get rid of it.  damn, it feels good to be a gangsta!
Posted by sand at 06:48:05 | Permalink | Comments (9)