Jake wrote:
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?

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?

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).

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

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?

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.

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.

DAGS on "air muscles". They're marketed by a British company. While
you're on the site, check out how their built their robotic hand -- and
watch the video of it picking up a pint.

There's a lot of good information there on how they built their hand,
including stuff on power sources.

--RC