"Jake" wrote in news:1108369621.374189.304230
@f14g2000cwb.googlegroups.com:

I'm posting this to this group because it seems that this is where most
of the hydraulics related questions go.

I am planning to start a rather ambitious project that doesn't seem to
have been attempted very much so far, as far as I can tell.

One of the largest obstacles to completing this project is that I
really have no experience in metalworking. I certainly don't know
anything about hydraulics but what I've learned on the internet. I
know very little of electronics, or at least the kind that will
probably help in this project. I am a computer guy first and foremost,
and I can write programs in many languages, but I just haven't done
much work creating machines.

So here is what the first step of my project is: I want to create a
large mechanical hand. I also want to create a "device" or "interface"
to control said hand.

I have the general concept worked out in my head - I haven't actually
drawn up a blueprint or schematic yet. The main reason I'm only at
this point is that I don't really know a lot about hydraulics. I know
that:
Hydraulics are strong, that's why they are used in construction.
They are expensive.
They can be dangerous if not treated well.
And that's pretty much all I know.

What I'm hoping for from you guys, is some input on the following:
How small can hydraulic cylinders be? I'm shooting for something like
a 5:1 scale. Would it be feasable or possible to put one cylinder on
each "knuckle" to act as a muscle for that part of the finger? Or
should I be looking at having a kind of "tendon" control system where
each finger is controlled by a series of cables that are in turn pulled
on by one hydraulic cylinder per finger? Bluntly, are there hydraulic
cylinders that are less than a foot long and only about 1 or 2 inches
in diameter? How much power would one of those generate?

Force = surface area of piston x pressure. You need to subtract the rod
area from the piston area on the rod end to get the real surface area.

Yes, hydraulic cylinders can be fairly small indeed. But I really do not
recommend them for this application.


Should I be considering something besides hydraulics? Such as electric
step motors or pneumatics? If so, what would the pros/cons of going
with one of these alternatives be?

Yes. The cheapest method is probably going to be stepper/servo control
and actuation.


As far as controling the hydraulic cylinders - is there a way to tell
the cylinder to only go out a certain distance or to only come in a
certain distance? The only control system I've ever seen for a
hydraulic cylinder is basically a simple extend/retract/stop system,
that has to be attended to by the operator (i.e. I want to say
"Cylinder: Extend 3 inches and stop." and then have that happen).

Yes there is, but it is not easy, nor cheap. You will need a
proportioning valve for each cylinder you wish to control, you will also
need a feedback device for each cylinder (encoder), and you will need
control electronics (a drive). Proportioning valves alone will be in the
several hundred dollars _each_ range.

A pneumatic system is basically the same in principle of hydraulics.


What is the maintenance like on hydraulic systems? What is the most
often replaced piece of a h.system?

Hydraulic systems are somewhat maintenance intensive, if properly
maintained. If you are using proportioning valves, maintenance becomes
critical, as even tiny contamination is your dire enemy.
Then consider all the hoses you have, that are going to be moving within
this arm, being abraded. Having a 3000 psi hydraulic hose spring a leak
of 120° oil is not a fun thing if you are nearby.


What do you do to power a hydraulic system? Do you have to lug around
a huge battery or do you somehow convert energy from an engine into
hydraulic power?

Well..you might want to bring several batteries to drive a hydraulic
pump, depending on the pressures/force you need available.



Once more on controlling these things - do you know of any way to hook
a hydraulic system up to a computer and control it via the computer?
Like if I were to create a program that could talk to the hydraulic
system through my computer then I could just control the whole thing
from my computer screen.

Yes, we have many machines which do this, but as I stated, it is _not_
cheap.



I think that is enough for now, that's an awful lot of questions!
Please help me if you can. If you know of another place I might ask
these questions please feel free to let me know, the more information I
can get on these topics, the better.







--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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