Finding engineering data on shock absorbers
Tim Wescott
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.
Jim Wilkins
Googling "shock dampeners" lead to this:
http://www.taylordevices.com/pdf/M-series-specifications.pdf
Perhaps instead of a fixed device you could use an adjustable heavy-
duty door closer, like for a fire door.
jsw
Tim Wescott
It'd have to be a damn heavy fire door.
I figure that -- assuming that automotive shocks are close enough -- I'll
get an adjustable one and tinker with it. It still needs to be close,
though, or I'll be repeating a lot of effort.
Steve Austin
Tim Wescott
There's a difference in nomenclature between industrial and American
automotive usage.
In industrial usage a "shock absorber" is a thingie that, when you run
something heavy into it, absorbs the shock. That's what you've sent me a
data sheet for. It's not what I need.
In American automotive usage a "shock absorber" is a thingie that, when
you push or pull on it, resists motion with (usually) an increasing
resistance force for increasing velocity. In industrial and British
automotive usage such a thingie is a "damper". That's what I need.
I'd love to have enough $$ to get an industrial damper, and the contacts
to be able to easily buy more when the first one wears out (or if it
turns out that I've mis-specified it). But I can swing down to the
corner auto parts store and get something that may well be what I need,
at an affordable price, on a Saturday, in less than an hour. So if I can
use that instead, that's what I want.
cl...@snyder.on.ca
Check Koni and other "race/performance" shocks - they usually have
jounce and rebound valving specs and are adjustable.
Richard J Kinch
> At the least I need things like stroke and mounting data, ...
Sir, this is a metalworking group. You do not need such data, because you
will sand-cast the parts in your backyard foundry and finish them on a
lathe in your basement, to whatever specs you like.
Don Foreman
wrote:
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.
Pete Keillor
Or a flow control valve (parallel needle and check) if you only need
damping when lowering.
Pete Keillor
DT
>>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
DanG
constant resistance on the way down. There are many lengths and
ratings.
--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgri...@7cox.net
"Tim Wescott" <t...@seemywebsite.com> wrote in message
news:UpydnQN-9rK5IPXW...@web-ster.com...
scs
wrote:
>Kinda oddball question, hoping that someone will know.
This may help. British Publication
The Shock Absorber Handbook
John C. Dixon, Ph.D, F.I.Mech.E., F.R.Ae.S.
Email (for orders and customer service enquiries):
cs-b...@wiley.co.uk
Visit our Home Page on www.wiley.com
ISBN 978-0-470-51020-9 (HB)
Tim Wescott
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.