In Last Week’s Lab
Mikhail: worked on the Clutch
Caitlin: worked on removing paint from the Racers (where the ball-bearing hits)
Mark: gasket work
Mun: tried to get points onto the wires, but could only find 6, so were trying to figure out if we could use some that were on the extra wires
Kate: (same)
Francesco: worked on the fork assembly, tried to figure out what goes where and started putting the front end together
Max: figured out the configuration of the brake and clutch levers ; calculated the mechanical advantage for each of the levers.
Phil: pressed the gearing into the engine cover; cleaned out and started to put the front end back together.
Mary Kate: put the bottom end back together
Sydney: put bottom end back together
Leslie: put bottom end back together.
Max B: put the top end together, switched one of the springs in the carburetor, painted the cylinder
Jaime: helped paint the cylinder head so that it wouldn’t get rusty (with the silver paint) so that it wouldn’t oxidize and get rusty
Samone: figured out how to put the transmission together; there was a broken tooth, with a washer that had welded with one of the gear shafts; figuring out how to put separate it
Devon: putting the clutch back together, working with the missing/fused washer.
Guest Lecturer – Bill Becker
Bill Becker: The Wheel as a Structural Subsystem on a Motorcycle
-Background:
· From Philadelphia
· Works on mostly vintage machines, but also enjoys bringing them up to modern standards… attracted to the “beauty of mechanical work”
· goes to his shop, and “creates problems and then solves problems”
-Some Basic Physics:
· Need to understand Mass, Matter, and Force
o Forces are what act on mass
o With a motorcycle, dealing with forces like gravity, inertia, momentum, and velocity
o Velocity is a force acting in a direction
· It takes work to stop momentum and to stop inertia
For Manufacturing:
· If you’re designing for racing, staying streamlined is very important for becoming faster and better… this means reducing mass and reducing friction.
· If you’re producing for mass production, materials have to be affordable and not too expensive
-Looking at the wheel:
· On Japanese motorcycles, there’s usually 36 spokes (9×4), but on our British bike there’s 40 spokes (10×4)… it doesn’t really make a difference.
· Outer piece: “rim”, connected via the “spokes” to the “hub”
o The hub contains a brake, with shoes that expand (for the brake), and some bearings.
-Materiality of Motorcycle wheels
· In the modern motorcycle, there’s 12 different materials used on every wheel
o Why so many? Because each material is good for different things! For example…
§ Aluminum, for the rim
§ Stainless steel, for the spokes
§ Cast iron for the hubs
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Strength
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Flexibility
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Weight
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Hard/Soft
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Workability
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Resist Corrosion?
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Conductivity
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Cost
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Available?
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Aluminum
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x
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Light
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very
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X
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very
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Cast Iron
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X
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Heavy
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Good
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Mild Steel
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Hardened Steel
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Stainless Steel
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X
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X
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Heavy
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X
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X
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X
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Exp
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X
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|
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Rubber
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X
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X
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Light
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X
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X
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cheap
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very
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Polyester
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Brass
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Chromium
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Asbestos
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Plastic
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Air
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-Because Rubber is so readily available, that’s why it was chosen as the material that undergoes a large amount of friction between the bike and the road.
-Basic Forces that work on the wheels:
· Compression, Tension, Shear (and Bending, which is a combination of all 3)
· Young’s Modulus of Elasticity: describes how different materials respond under stress (load) and strain (deformation)
o The stronger the material, the steeper the slope
o This chart also measures the yield point and the fracture point.
· In a wheel, only about a quarter of the spokes are working at a time (bearing a load)
o Each spoke can support about 850 pounds
o So each wheel can support about 8000-8500 pounds.
· However, a wheel is supporting a much bigger load than just the rider’s weight.
o Especially with gravity, impact, acceleration and deceleration/braking, there’s a lot of stress on the spokes of the wheel.
o At any given time, you could get have as many as 50% of the spokes contributing to the wheel’s strength
o The spokes’ orientation provides different triangulations, which strengthen the wheel for different motions (like banking, etc…)
§ Only for the rear wheel…. The front wheel doesn’t provide any braking or any power, so radial spokes are OK
HW for next meeting (Thursday 4/9): CHS 16-18 in Zen (next three chapters, first three chapters of part III)