On Tue, 02 Feb 2010 18:02:44 -0600, Tim Wescott
wrote:

Kinda oddball question, hoping that someone will know.

I'm almost ready to re-hang my driveway gate - we've been surviving with
a roll of chicken wire for way too long - but before it goes on it needs
a shock absorber to keep it from breaking exactly the way it did before.

(It's a scissors gate, about 120 pounds, 18 feet long and it pivots up
and down on one end. It's counterbalanced on springs, but when an
enthusiastic kid closes it the crash is a thing to behold -- and a thing
to break welds.)

I don't want to cut and try a bazillion different things, and I'm an
engineer so I have the delusion that I can design things from first
principals.

Is there any place I can find engineering data on vehicle shock
absorbers? Not "buy this here shock for that there truck, and get 'em
heavy duty if you want to put two cows in there", but real honest-to-gosh
tables with numbers and other useful things for folks who are blatantly
mis-applying a vehicle shock absorber.

At the least I need things like stroke and mounting data, but something
that gives the damping rate of the thing would be uber-cool. In the
absence of damping rate a vehicle weight / shock chart would be useful,
but it'd be a distant second best.

Stroke and mounting data are obvious (if I can match what's in my truck
I'll be quite happy), but if I had the force vs. velocity curves for a
number of different shocks then I'd know from the get-go if I'm in the
right ball park, and where to put my pivot points, and that sort of thing.

Your 120-lb load is much lighter than any vehicle load, and your
requirement is mearly to limit velocity rather than to critically damp
a resonant mass-spring suspension.

Find a small surplus hydraulic cylinder, make your pivot points
compatible with the cylinder's throw, use an adjustable needle valve
to achieve desired viscous damping factor.

On Wed, 03 Feb 2010 00:11:07 -0600, Don Foreman
wrote:

On Tue, 02 Feb 2010 18:02:44 -0600, Tim Wescott
wrote:

Kinda oddball question, hoping that someone will know.

I'm almost ready to re-hang my driveway gate - we've been surviving with
a roll of chicken wire for way too long - but before it goes on it needs
a shock absorber to keep it from breaking exactly the way it did before.

(It's a scissors gate, about 120 pounds, 18 feet long and it pivots up
and down on one end. It's counterbalanced on springs, but when an
enthusiastic kid closes it the crash is a thing to behold -- and a thing
to break welds.)

I don't want to cut and try a bazillion different things, and I'm an
engineer so I have the delusion that I can design things from first
principals.

Is there any place I can find engineering data on vehicle shock
absorbers? Not "buy this here shock for that there truck, and get 'em
heavy duty if you want to put two cows in there", but real honest-to-gosh
tables with numbers and other useful things for folks who are blatantly
mis-applying a vehicle shock absorber.

At the least I need things like stroke and mounting data, but something
that gives the damping rate of the thing would be uber-cool. In the
absence of damping rate a vehicle weight / shock chart would be useful,
but it'd be a distant second best.

Stroke and mounting data are obvious (if I can match what's in my truck
I'll be quite happy), but if I had the force vs. velocity curves for a
number of different shocks then I'd know from the get-go if I'm in the
right ball park, and where to put my pivot points, and that sort of thing.

Your 120-lb load is much lighter than any vehicle load, and your
requirement is mearly to limit velocity rather than to critically damp
a resonant mass-spring suspension.

Find a small surplus hydraulic cylinder, make your pivot points
compatible with the cylinder's throw, use an adjustable needle valve
to achieve desired viscous damping factor.

Or a flow control valve (parallel needle and check) if you only need
damping when lowering.

Pete Keillor

Find a small surplus hydraulic cylinder, make your pivot points
compatible with the cylinder's throw, use an adjustable needle valve
to achieve desired viscous damping factor.

Or a flow control valve (parallel needle and check) if you only need
damping when lowering.


And you may only want damping at the end, just before it closes. If you hook
the damper directly to the gate it will slow down the gate for its entire
motion, which will be frustrating. Or is that what you want, to be able
to just drop it and go? Perhaps mount the damper so that the gate contacts it
just before the end, and then it will damp the last foot or so of travel.


--
Dennis

On Wed, 03 Feb 2010 06:28:41 -0600, Pete Keillor wrote:

On Wed, 03 Feb 2010 00:11:07 -0600, Don Foreman
wrote:

On Tue, 02 Feb 2010 18:02:44 -0600, Tim Wescott
wrote:

Kinda oddball question, hoping that someone will know.

I'm almost ready to re-hang my driveway gate - we've been surviving
with a roll of chicken wire for way too long - but before it goes on it
needs a shock absorber to keep it from breaking exactly the way it did
before.

(It's a scissors gate, about 120 pounds, 18 feet long and it pivots up
and down on one end. It's counterbalanced on springs, but when an
enthusiastic kid closes it the crash is a thing to behold -- and a
thing to break welds.)

I don't want to cut and try a bazillion different things, and I'm an
engineer so I have the delusion that I can design things from first
principals.

Is there any place I can find engineering data on vehicle shock
absorbers? Not "buy this here shock for that there truck, and get 'em
heavy duty if you want to put two cows in there", but real
honest-to-gosh tables with numbers and other useful things for folks
who are blatantly mis-applying a vehicle shock absorber.

At the least I need things like stroke and mounting data, but something
that gives the damping rate of the thing would be uber-cool. In the
absence of damping rate a vehicle weight / shock chart would be useful,
but it'd be a distant second best.

Stroke and mounting data are obvious (if I can match what's in my truck
I'll be quite happy), but if I had the force vs. velocity curves for a
number of different shocks then I'd know from the get-go if I'm in the
right ball park, and where to put my pivot points, and that sort of
thing.

Your 120-lb load is much lighter than any vehicle load, and your
requirement is mearly to limit velocity rather than to critically damp a
resonant mass-spring suspension.

Find a small surplus hydraulic cylinder, make your pivot points
compatible with the cylinder's throw, use an adjustable needle valve to
achieve desired viscous damping factor.

Or a flow control valve (parallel needle and check) if you only need
damping when lowering.

Pete Keillor

I like that. I don't think it's going to be small -- 120 lbs on a 9 foot
(average) lever arm, working against a cylinder on a lever arm that's
effectively less than a foot, adds up to lots-o-pounds.

But a cylinder -- hydraulic or pneumatic -- should be easy to find in
lots of sizes, ditto valves, and it should certainly have a wide
adjustment range.

--
www.wescottdesign.com