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11-02-2013 #1
Ah yes, it's all wrong!:)
Here's the right formula (taken from http://www.clag.org.uk/beam.html):
δ = FL3 ∕ 3EI
I = πr4 ∕ 4 = πd4 ∕ 64
(for round beam)
which means that deflection at a given F and L, for a 20mm dia beam is:
δ = FL3 * 0.0002358
Assuming L = 0.18m and F=100N the maximum deflection is:
δ = 100 * 0.005832 * 0.0002358 m = 0.0001375m = 0.1375mm
Which makes much more sense than the previously calculated value.
The funny thing is that changing the dia from 20mm to 22mm gives you a maximum deflection drop from 0.1375mm to 0.094mm. That's just by making the shaft 2mm thicker. Quite amazing me thinks.
Regards,
dsc.
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