Re: Analysis of Dual Pivot Brake
- From: jim beam <spamvortex@xxxxxxxxxxxxxxx>
- Date: Mon, 19 Nov 2007 20:05:56 -0800
Joe Riel wrote:
As a followup, we can look at the relative pad movement. Let x1 be
the movement of the left pad, x2 the movement of the right pad. For
small movements, the vertical movement of the contact point of the
two arms is
dy = dx1*L5/L2 = -dx2*L6/L4.
The (negative) ratio is
-dx1/dx2 = L4*L5/L2/L6.
Expressed in terms of k we get
-dx1/dx2 = L4/L2*k/(1-k)
Ideally we'd like this ratio to be 1, so that both pads open equally.
that is ideal, but presumptive. the y-arm is actually free to compress
independently.
Solving for k we get
k = L2/(L2+L4)
Plugging that into the gain ratio and simplifying we get
F/T = 1/2*(L1/L2 + L3/L4)
So, with k set so the pads move equally, the gain of
the brake is the average of the gain of the two
lever arms without the connection (the connection is required
for operation.
the connection is required to help swing the two arms together when
free, but under load, that connection is small beer compared to the
force exertion from compressing the rim. the connection never sees more
than caliper spring loading.
.
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