how to design a variable torsional spring
April 19, 2008 3:53 AM Subscribe
how do i design a cheap spring to attach to a small plastic lever, that will only act over a portion of the rotation of that lever?
posted by edtut to science & nature (4 answers total)
i am designing something with a small straight plastic lever, about 40mm long. it is attached to a plastic door by fitting into the shaft at the end, and the lever rotates over about 40 degrees to open and close the door. the door opens from a flat bottom position to a top position, and seals at both ends.
the lever is rotated by a mating pivot lever, that has a pin. the pin runs down a straight slot in the lever. the ratio is just slightly amplified, but the rotation of each lever is near enough to equivalent.
i want to add a torsional spring to the lever to help lift weight of the door from the bottom position. the spring is a simple 3 coil torsional spring, with one fixed end, and the other end rotating with the lever.
but when i do, of course, the door doesnt seal well at the bottom most point (because the mechanism force is too low). the spring works against the pin force, to open the door slightly.
is there a type of torsional spring that can be free of tension at the bottom point, but then help lift the lever through most of the travel.
or alternatively, is there a simple way to fix the end of the torsional spring to have the same effect?