Spindle lessons

kyle luttrell · Posted: Thu Feb 28, 2013 6:09 pm Post subject:

[quote="Keith Freber"][quote="kyle luttrell"]

joseph hollinger · Posted: Thu Feb 28, 2013 6:10 pm Post subject:

Michael Purnell · Joined: 27 Sep 2006 Posts: 29

mike clements · Posted: Thu Feb 28, 2013 9:28 pm Post subject:

At the end of the day, the guy that walks away with the Duffy is the winner.
If winning isn't enough proof for you, then you are out of luck.
I'm not playing your hate game any more.
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Mike Goebel · Posted: Thu Feb 28, 2013 9:33 pm Post subject:

Bruce Woodrow · Posted: Thu Feb 28, 2013 10:34 pm Post subject:

There seem to be several issues here:

1. The pervasive attitude that kart tuning is a 'black art' and that the Laws of physics do not apply to karts, or anything attached to them

2. Terminology - i.e. the terms strength and stiffness seem to have been confused

3. A lack of engineering/physics knowledge (root cause of 1 and 2, above)

Solutions:

1. The Laws (yes - Laws, NOT theory) of physics DO apply to karts - get over it! Every change made to a kart can be analyzed and its effect calculated/simulated. Sorry to burst anyone's bubble, but magic isn't real.

2. Some explanation:

STRENGTH refers to how much force can be applied before an item is either permanently deformed (doesn't spring back to original shape) - referred to as yield strength, or fails - referred to as ultimate strength.

STIFFNESS is the inverse of flexibility. It is a measure of how much force must be applied to cause a certain deflection or deformation

Although dimensionally identical parts made from different carbon steels have widely varying strengths, they ALL have virtually the same stiffness. I.E. changing the material of an axle or spindle does not change its deflection for a given load (force) - changing component dimensions is the only way to achieve different stiffness of steel parts.

There is however another material property that affects the behavior of parts under dynamic (rapidly changing) load conditions - Internal damping. 'Soft' steels have more internal damping than 'Hard' steels. So, although parts made from different grade steels will deflect by the same amount when a fixed load is applied, when the load is varied, the rate of change of deflection will be different for the different steel grades. This is somewhat demonstrated by the different 'ringing' sounds made by dimensionally identical rear axles made from different grade steels - 'soft' axles are relatively dead (well damped) and don't ring as well, or as long, as 'hard' (less damped) axles.

So, there are two ways to affect the influence of a steel spindle on kart handling (without changing steering geometry):

a) Change the spindle dimensions (stiffness)
b) Change the grade of steel (damping)

Both have an effect on the strength pf the spindle, but as long as the spindle doesn't permanently deform or break, strength has no influence on the behavior of the spindle - it just tells you how hard a hit the spindle can take, without causing a problem.

In the case of a); if a hole is drilled through the center of the spindle and no other dimensions are changed, there will be 2 effects:

i) The stiffness will be reduced (easy to calculate due to reduction in moment of inertia (I))
ii) The strength will be reduced (easy to calculate due to increased bending stress (bending strength) and reduced cross sectional area (shear strength))

However, I think that what is causing confusion here is that for the same weight spindle (i.e. uses the same volume of steel), a spindle with a hollow shaft will be stiffer than one with a solid shaft - but this means increasing the outside diameter of the shaft. Alternatively, a hollow shaft spindle made to have the same stiffness as a solid shaft spindle, will be lighter.

3. Do some research - it's NOT Rocket Science!

There is no pot to stir, facts are facts.

Bruce

Bruce Woodrow · Posted: Thu Feb 28, 2013 10:44 pm Post subject:

patrick slattery · Posted: Fri Mar 01, 2013 9:27 am Post subject:

[quote="Keith Freber"][quote="kyle luttrell"]

Andy Seesemann · Posted: Fri Mar 01, 2013 12:10 pm Post subject:

I love it when you get fired up, Woodrow.

A
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Really Good Guy.

Keith Freber · Joined: 27 Jul 2001 Posts: 88

Mike Goebel · Posted: Fri Mar 01, 2013 5:55 pm Post subject:

michael schorn · Posted: Fri Mar 01, 2013 9:25 pm Post subject:

kyle the chassis looks real nice. I do have a question Why isn't the master cylinder bolts drilled and pinned? Just curious?
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kyle luttrell · Posted: Fri Mar 01, 2013 10:00 pm Post subject:

michael schorn · Posted: Sat Mar 02, 2013 1:02 am Post subject:

Okay that makes sense thanks.
_________________
OK everyone It's my opinion only, no one elses, and does not reflect any organization or office that I belong to or hold. Thank you for your support.
Portland Karting Association
Host 2013 IKF 4 Cycle Sprint
& Road Race Grand Nationals