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hi guys,
i'm doing a project at uni based around a bicycle brake lever, however i've become a bit stuck...
what i need to know...
basically i need to know the how the geometry for the lever is determined, i've seareched everywhere, all i can fine is geometry for the brakes themselves, but there is nothing for the lever...
can anyone help
To hazard a guess its all about average hand sizes/ leverage ratios?
The force required to pull the brakes against the rim is a function of the lever arm distance between the pin and the cable end and the lever arm of point at which force is applied by the hand.
Imagine a see saw with one side shorter than the other.
The rest is ergonomics.
Could you clarify what you mean by geometry of the lever? Ergonomics of the lever, or specifics of the pivots, etc. and amounts of cable pull?
Do you know what a free body diagram is? That will tell you all about it.
Lever = L shaped
Pivot at short end of the L
Cable at the bend in the L
Cable follows a circular path centred on the pivot (assuming cable doesnt move - it could in some levers iirc)
Cable pull and amount of lever movemnt required would dictate the length of the corner to pivot dimension
Lever shape and length then dictated by a compromise of required pull and ergonomics
I have assumed a cable but hydro levers would have similar considerations.
Unless of course someone has invented a dw link brake lever.
Or did i.completely miss the point - quite likely!
Found an old XT v brake lever in the garage the other day....if its any use? It is just the lever, it got bent in an accident....but it's your for a donation to Debra charity.
Sorry the cable anchor follows a circular path relative to the pivot.
The cable itself cuts the corner.
Changes the maths a bit but not much.