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# How to calculate shock absorber constants from known c and k values

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## How to calculate shock absorber constants from known c and k values

(OP)
We are trying to put a spring-damper system on a drone to act as landing gear (very small scale, only about 300 grams total). We created a MATLAB simulation to describe spring and damper constants, taking into account drone weight, free fall height, and stroke length of the spring-damper. The simulation tells us k constants, c constants, damping ratios, and compression lengths for an input maximum acceleration, stroke length, mass, and fall height. Those are the constants we then need to find a spring damper (aka shock absorbers) for. The issue is, the datasheets associated with commercially available shock absorbers don't have these constants. I have linked two datasheets for reference.

One datasheet we have found uses constants of: Max in.-lbs/cycle (Nm/cycle), Max in.-lbs/hour (Nm/hour), Max Velocity in/sec (m/sec), and max reaction force lbf (N). In this case, what is the meaning of these variables? i.e. is Max Velocity an impact velocity? That would be perfect for our free fall application. Or is it velocity of the stroke of the shock absorber? How do we take c, k, and damping ratios and calculate these values? Datasheet found here: https://www.toolots.com/ea-non-adjustable-hydrauli...

Another datasheet uses different variables: Load (kg), Max absorption energy J (kgf * m), Speed Range (m/s), and extension force N (kgf). In this case, is the Load a continuous load? Is the speed Range the speed of the physical stroke? Is the extension force a direct F = k*x relationship? Datasheet attached.

Hopefully you can either give me some advice on how to approach these variables or some equations on how to calculate them. Any help is appreciated. Thanks!

### RE: How to calculate shock absorber constants from known c and k values

Your first one says 100N at 2 m/s, therefore c is 50 N/m/s

It may not be linear but it'll be sufficiently in the ballpark. Frankly these little ones rely on friction as much as damping.

Personally I think you'd be better off with a bit of foam wrapped around your spring.

Cheers

Greg Locock

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