Springs made from PhysicsContrainsActors

Development World Creation
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1

Hi everyone,
I’m having some trouble figuring out which properties of a PhysicsContraintActor correspond to the physical constants of a spring system.

If I understood correctly, in order to create a non-damped spring - aka simple harmonic oscillator - one has to create a PhysicsContraintActor and link it between e.g. a ceiling (some static non-physics object) and e.g. a cylinder, which has physics enabled and some mass defined. Then, one has to set everything in the PhysicsConstraintActor to “locked”, except for the linear Z-motion (spring will swing “up” and “down”), which will be set to “free”. Then, we need to set the spring constant (usually described as “K” in physics formulas), which I believe is “Linear Position Drive” in combination with a value for “Linear Position Strength”. If I do that, I get:

47804-springproblem.png
47804-springproblem.png649×755 38.2 KB

However, the oscillation seems to be damped (oscillation decreases in amplitude each swing and stops altogether after n swings). As you can see from the screenshot, I did not setup any linear velocity drive (which I assume is the velocity-dependent damping).

Please let me know, what I’m doing or understanding wrong here.

Thanks very much in advance,
Sven

2

I need to add that I did set “Linear Damping” on the cylinder (and also my ceiling, just in case) to 0.0. So this cannot cause the damping effect either.

Again my question is basically how to setup a harmonic oscillator (non-damped spring).

Thanks,
Sven

3

Check the physics damping in the physics objects themselves. They default to a small amount, pretty much analogous to air drag.

4

No, that’s not it. As I said in my first comment, both physics damping values of the cylinder and the ceiling are set to 0.0. I’m using compiled 4.11.0-0+UE4 and still have the same problem. I’m suspecting a Physx bug?

5

Could someone please find a solution to this problem?