JoelP
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| posted on 20/6/07 at 06:41 PM |
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quote:
Originally posted by short track 123
If you put a set of scales under the wheel with a block supporting the chassis and remove the bolts from the shock is this unsprung weight ?
not to me...
Unsprung mass represents more than just the literal mass that is unsprung, it must also take into account its position in order to represent how much
affect it has on the ability of the wheel to move fast.
If you extended your wishbone 10 feet out to the side, a kilo weight would make it very hard to move the wheel. That same weight attached 1cm away
from you inner pivot (on the wishbone still) wouldnt affect the wheel at all. An inch of wheel travel would move the weight 10" in the first
example but maybe only 1mm in the second, this obviously involves very different amounts of energy.
The same idea applies to the rocker and rods.
For simplicity of comparison, you could break items into a few groups. Stuff at the wheel and moveing with it, ie your wheel itself, tyre, discs,
calipers, cycle wings etc. Stuff that is only moving at one end, which you could roughly halve for comparison with the first group. This would be
wishbones, brake flexis, your spring etc. Another group would be the things that dont fall easily into the first groups, and this group is where
rockers and pushrods would fall. Stuff at 45 degrees like your pushrod would move 70% less than the wheel items, so would be less important. Your
rocker would be roughly 35% biased, as its both pivoting and only moving with the 70% of the pushrod.
That gets a bit complex though, which is never a good start.
The most accurate way to measure your unsprung mass would be to apply a force and measure acceleration, as this would automatically include the
bias's above. However, you would then also have to exclude gravity, which takes us in a neat circle as to the use of bathroom scales - measure
the weight at the wheels, covert to newtons, add balast to round the weight at the wheel to a comparable amount (ie 20kgs), measure the
acceleration under gravity, work out the actual mass from that, deduct the balast added, and VOLIA, several hours wasted on an internet discussion. 
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gazza285
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| posted on 20/6/07 at 07:41 PM |
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I'm not getting invlolved in this one again.
DO NOT PUT ON KNOB OR BOLLOCKS!
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short track 123
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| posted on 21/6/07 at 05:55 AM |
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Do you know of any good books, web site's where i can find info that cover this area of suspension design all the books i have only quote
unsprung mass as mass (moments of inertia are covered i.e mass and distance from pivot point) and have nothing about including force of shocks benning
included in the un-sprung mass but do cover wheel and spring rates as separate areas.
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JoelP
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| posted on 21/6/07 at 07:10 AM |
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no idea im afraid, i wrote/made that up myself. With your moment of inertias though you're not far off, works fine for outboard suspension but
for inboard it needs tweeking.
[Edited on 21/6/07 by JoelP]
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