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Vibration conundrum in motorcycles

A friend of mine rides motor bikes, and is fed up with hand-numbing vibration.

The conventional way to reduce vibration in the bars is to add mass inside the end, decreasing the resonant frequency to below that of the engine.

I had an idea that a carefully-tuned second resonant system inside the bars – a cantilever with a mass on the end – could be used to upset the main resonance – maybe with some form of partial coupling to the inside of the bars at the more mobile end.

handlebarvib250.jpgBearing in mind I know nothing about mechanical engineering, imagine my pleasure when I discovered such things exist, and reviews elsewhere suggest that they are effective – to varying extents.  

Further googling revealed that a roll of coins glued into the end of the bars with silicone elastomer can have a similar effect.

Looking at diagrams of the mass damper in the Taipei 101 tower block, it looks like the partial coupling needs to be in the system – the huge Taipei mass has dampers to the building.  

A similar technique was used hundreds of years ago in some Japanese pagodas which have a tree trunk loosely mounted inside them to improve earthquake resistance.

On the subject of vibration damping, I finally put a name to the pairs for weights that can be seen attached to overhead power and suspension bridge cables.

They are Stockbridge dampers, invented by US engineer George Stockbridge in the 1920s, which reduce wind-induced vertical waves at tens of Hertz.

‘Alice’

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1 Comment

  1. Steve Kurt
    January 24, 2013 01:44

    the wiki page for tuned mass dampers is pretty informative too…
    http://en.wikipedia.org/wiki/Tuned_mass_damper
    Specialized, the bicycle company, did make a tuned mass for the ends of the handlebars. It was sold as being some sort of tuning fork gadget, IIRC. No idea if it worked or not, but they really did put a lot effort into adding elastomers to the fork blades and chainstays of some of their bikes in order to damp vibration