*It's not that complicated, our factory installed ramp/door has the normal*
*garage door torsion spring and cable arrangement . . the gate just*
*floats at ground level but allows a one hand lift to within a foot of*
*being closed;** an easy push finishes the chore . .It doesn't need*
*to be spring-slammed shut but that would be okay.* * Another case where*
*close enough is just right.*
**
On Fri, Dec 3, 2010 at 6:48 PM, Randall <tr3driver@ca.rr.com> wrote:
Well, you want the force from the spring to be zero with the ramp closed, so
the spring needs to be fully relaxed/retracted at that point. And the force
should be just slightly less than what it takes to lift the ramp off the
ground at full extension. So figure out how far it can stretch between
those two extremes, and choose a spring that supplies that much force at
that much extension.
But unless I'm missing something, I think you will be unhappy with the
result. The force from the spring is more or less linear with displacement,
while the force to lift the door depends on the cosine of the angle between
the door & the ground. If your spring is strong enough to nearly lift the
door off the ground, I suspect it's going to slam into the trailer plenty
hard enough to smash fingers, tear up the trailer and so on. Swinging
garage doors actually have multiple cam actions built into the hinges, to
deal with this problem.
-- Randall
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