3 ms·

Mechanical bouncing should be pretty predictable - ie. A particular bit of metal briefly resonating at a frequency based on the speed of sound in the material.

Mechanical bouncing should be pretty predictable - ie. A particular bit of metal briefly resonating at a frequency based on the speed of sound in the material. However, these traces look more chaotic. Anyone know why?

lambdaone 2y ago
The system is hit so violently that it goes into a non-linear regime, repeatedly hitting the end-stops of its motion. Consider how adding even a small amount of nonlinearity to a simple harmonic oscillator can create chaos, and I think you should be able to see how this generates chaos.
- tonyarkles 2y ago
  Plus, at the interface, there’s some small amount of oxide that has grown on the surfaces. When those pieces of metal are being banded together and separated there’s tiny electric arcs that are working at getting rid of that.
progbits 2y ago
A bad switch will simply put contacts together at the same rate as the human pressing it, so it's very random and variable as you press with different strength and speed. A good switch will decouple your finger from the contact by some nonlinear/bistable linkage, so once you accumulate a fixed amount of travel distance it will snap the contacts with the same speed/force. But of course even that isn't perfectly decoupled nor perfectly deterministic.
deleted 2y ago
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photon_rancher 1y ago
Did some similar testing with an on-off rocker switch for a project last year. Traces were highly predictable if you pressed it just gently past the detent. But if you did it too slowly (restricting the detent force) or used too much follow through (adding to the detent force) the result was very chaotic. Sometimes you could get the bounce period to extend by 10x if you took enough samples. And if there’s too much current or other problems i saw decent ground and supply bounce too. That definitely makes it toucher to measure the behavior- in some respects a diff or current probe gave even more interesting results.

lambdaone 2y ago

The system is hit so violently that it goes into a non-linear regime, repeatedly hitting the end-stops of its motion. Consider how adding even a small amount of nonlinearity to a simple harmonic oscillator can create chaos, and I think you should be able to see how this generates chaos.

tonyarkles 2y ago
Plus, at the interface, there’s some small amount of oxide that has grown on the surfaces. When those pieces of metal are being banded together and separated there’s tiny electric arcs that are working at getting rid of that.

progbits 2y ago

A bad switch will simply put contacts together at the same rate as the human pressing it, so it's very random and variable as you press with different strength and speed. A good switch will decouple your finger from the contact by some nonlinear/bistable linkage, so once you accumulate a fixed amount of travel distance it will snap the contacts with the same speed/force. But of course even that isn't perfectly decoupled nor perfectly deterministic.

deleted 2y ago

[deleted]

photon_rancher 1y ago

Did some similar testing with an on-off rocker switch for a project last year. Traces were highly predictable if you pressed it just gently past the detent. But if you did it too slowly (restricting the detent force) or used too much follow through (adding to the detent force) the result was very chaotic. Sometimes you could get the bounce period to extend by 10x if you took enough samples. And if there’s too much current or other problems i saw decent ground and supply bounce too. That definitely makes it toucher to measure the behavior- in some respects a diff or current probe gave even more interesting results.