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Thread: quick question about hydrolics

  1. #1 quick question about hydrolics 
    Forum Freshman
    Join Date
    Jun 2009
    St Helens< near Liverpool, UK
    ok 2 questions pretty simple if you know the answers im sure

    1. do hydrolics work in a similar fashion to bike gears in referance to the ratio of pushing the fluid from the higher volume chamber to the lower volume chamber.
    i.e. the higher the gear ratio the slower you need to turn you legs but the harder it is to turn.

    2. what is the minimum size a hydrolic cyclinder can be, im thinking for a human sized robotic hand, i know pnumatics would be an alternative, but im looking for strength. so hydrolics is preferable

    thanks for any and all help, i know some of this is pretty basic, please be patient.

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  3. #2  
    Forum Freshman Solveer's Avatar
    Join Date
    Dec 2009
    well... there is obviously a difference between gears and hydraulics but the thing that is the same is that the Work performed is the same (ignoring losses, that is). So Force x Distance still holds. With hydraulics, the determining parameter is the surface area of the working piston. So if one piston has an Area of 1 and the second one of 2, then you will need to move piston one by twice the distance you want to move piston two, however the force exerted will be double of what you input.

    Second question is somewhat open. Hydraulics don't really define what the minimum surface area of the piston can be. Obviously once you get to the size of one molecule of your fluid, you will start having issues.
    In a real world scenario, the size is determined by what can be manufactured (at a given cost) and what makes sense (again, the smaller you go, the less force you will have). For example, if you have a 1/4 inch diameter piston and a hydraulic line at 100psi (you could of course also have 3000 or 10000 psi, but your lines would be thicker than the piston), the force exerted will be 4.9lbf. So you either need to increase the piston size (area) or pressure (and therefore plumbing requirements).

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