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Mechanism Design

Mechanism Design

Mechanism Design

What is the mechanism behind car sunglass compartments and cup holder flaps that you press down and they open very smoothly. I want to know:

- What is the latching mechanism and how is it released?
- How does it open on its own and how is it so smooth?

Visuals would help a lot, and if there is a website/thread that explains this outside of the context of car repair, I would really appreciate that.


RE: Mechanism Design

Thanks IRstuff! I'd love to see the design of the latch and trigger, and spring mechanism if anybody knows where I can find that!

RE: Mechanism Design

You won't find one single design for latching that is used by all- I've owned cars where the door had a button to be pressed, and doors with a travel activated latch, etc.

Pretty much all of them will use a dashpot in some configuration so that the door doesn't just fall open.

RE: Mechanism Design

Do a websearch on "push push latch", there are many design variations on the same basic theme (a retractable ball point pen is one example). Here is a video showing the basic concept in action:

RE: Mechanism Design

Usually a gear driving a rotary dashpot, I think.

RE: Mechanism Design


Check out products made by Sugatsune and Southco.


RE: Mechanism Design

We can liken this to magnetic control shock absorbers that can vary the softness or harshness of closing the cup holder by sensing the weight of the coffee and using an ecu to adjust the viscosity of the damping medium for the coffee weight. Imagine that previously mentioned grease filled with iron particles. Sort of.

Ps: this is a blatant, but relevant ad for magnetic shocks on the new Corvette. You owe me big, Jimmie.

RE: Mechanism Design

The rotary dampers are rated at a given rpm but they don't list how they vary with speed. Am I missing something? This would seem important. (I'm not selling magnetic grease).

RE: Mechanism Design

The little rotary dampers used on cassette player doors and such (basically a rotating gear and a fixed flange) are produced in huge quantities. I have seen them priced at ~$.05 in quantity.
One drawback is you have to buy a bunch to get a good price.
Another is that when you go back in a year for more, they will have transitioned to a different design, and you won't be able to get the ones that you had before.

Similarly for push/push latches, except that there are some standard types that will continue to be available for a while, from e.g. Southco, but not for a nickel.

I don't know how they make the rotary dampers; the ones I looked at seemed to have a lot of tiny parts inside.

There was for a while a linear damper comprising a rubbery tube of varying wall that slid on a rod and through a hole. It was fairly expensive, and didn't really work very well.

I have seen a homemade linear damper that worked fairly well, comprising two pieces of magnetic tape (not recording tape, but the thick stuff that has permanent magnetic domains in it), one stuck to a stationary plate and one stuck to a planar surface on a plastic part that slid on polished steel rails, arranged so the magnets slid past each other in proximity but never touched. The magnetic attraction caused a nice steady friction force on the rails.

Mike Halloran
Pembroke Pines, FL, USA

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