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To make LEGO properly hydraulic, some kind of real hydraulic fluid pumping
system would be needed. And it would have to take either water or a special
hydraulic fluid.
I believe it may be possible to achieve control with airflow alone. But I
would agree that it would be very difficult. You would need feedback both
on pressure of air and position of cylinder, and a means of combining the
two to make the air flow smoothly without the sudden decompression.
What this basically means is that both sides of the pistons would probably
need to be filled with compressed air at the same time, and not just one
side. This would allow the cylinders to take advantage of the air pressure
difference between the two sides of the cylinders in order to control their
extension and retraction, instead of just letting the air rush freely out of
the end of the valve controlling the cylinder that is not taking in air, as
is done in the current system. Of course, to balance things out,
depressurisation equivalent to the amount of movement required would have to
happen, which is why electronic control would likely be necessary.
--
Cheers ...
Geoffrey Hyde
"bisgaard" <bisgaard@e-mail.dk> wrote in message
news:GAJx9x.J8A@lugnet.com...
> In real life pneumatic is not used where more than two position is • accuired,
> and when it is done ither more pneumatic cylinders are placed after each
> other to make more fixed positions.
> Or there is placed an hydraulic brake on the cylinder to holde it in • place.
> (an hydraulic brake is bacicly an hydraulic cylinder where an valve either
> allow free passage ore close the connection between the two chambers).
>
> The solution my be to make lego hydraulic, by placing the air pump in • water
> (warning after placing pneumatic elements in water they will not be able • to
> hold air presure again!)
> This will make the movement of the cylinder much slower and when the valve
> is turned in middle position it will stop and hold its position.
>
> As Mario typed liquid is not able to compress, whitch means that you • either
> have to pump all the time or store the pressure somehow. This can be done • by
> filling an tank halfway up with liquid and halfway air, when pressure is
> applied the air will compress, and in that way store the pressure.
> I used an lego air tank for this, and since there is no moving parts in • the
> tank it can be used for air again after it has dryed.
>
> Some other observasions:
>
> The return air is released in the valve, so when using water the water • is
> comming out the same way, meaning something under the valve have to • catch
> the water.
>
> The air pump take in air from the middle so it is not enought to put the • end
> in water.
>
> Pipes, t-joint and air tank can be dryed and used for air again.
>
> Pump, cylinder and valve can't, so be sure to put an mark on them, and • store
> them for other creations that accuire hydralic control.
>
> If the pipes used are air proof there should not be any danger of leaking
> water around the cylinder.
>
> Liqiud are harder to pump than air so an electric pump have to be geared
> more down.
>
> And at the end: none of the electric parts are water proof so make sure
> there are no leak before putting in the electric, and don't put to much
> presure on since the pipes will then jump off.
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