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  #1   Report Post  
Jake
 
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Default Complicated Project (Hydraulics & More)

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.

  #2   Report Post  
Richard J Kinch
 
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Jake writes:

So here is what the first step of my project is: I want to create a
large mechanical hand.


It's called, "robotics", a 10 megahit Google term.
  #3   Report Post  
Rick Cook
 
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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
  #4   Report Post  
Rick Cook
 
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David R Brooks wrote:
snip of lots of good stuff
Pneumatics are very hard to use when you want precision of movement.
This is because air is compressible: it's like trying to position
something accurately, when you have to push it through a large spring.
Very difficult.

Using sensors and feedback make pneumatics a whole lot more accurate.
Given that OP is apparently trained as a programmer, I'd think this
would be a good way to go.

See:
http://www.shadow.org.uk/products/airmuscles.shtml

for the air muscles and
http://www.engineeringtalk.com/news/msy/msy100.html

for a little on sensors and feedback with pneumatics in robotic
applications.

--RC
  #5   Report Post  
Anthony
 
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"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.

Remove sp to reply via email


  #6   Report Post  
Tim Shoppa
 
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Should I be considering something besides hydraulics?

Pneumatics can be easier and cheaper to deal with in some
circumstances. It's certainly a lot less messy when you spring a leak!

Get to know your local industrial surplus sources. Lots of pneumatic
and hydraulic surplus is available, but you have to know where to look.
If you're in southern california, one retail-friendly surplus house is
C&H Surplus in Pasadena.

  #7   Report Post  
 
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Richard J Kinch wrote:
Jake writes:

So here is what the first step of my project is: I want to create

a
large mechanical hand.


It's called, "robotics", a 10 megahit Google term.


Hello Jake,
Try this site.
http://www.robotbuilder.co.uk/forum/...C_id=3298#2413
John.

  #8   Report Post  
Larry Jaques
 
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On 14 Feb 2005 06:37:04 -0800, the inscrutable
spake:

Hello Jake,
Try this site.
http://www.robotbuilder.co.uk/forum/...C_id=3298#2413


The page cannot be found
The page you are looking for might have been removed, had its name
changed, or is temporarily unavailable.

Please try the following:

* If you typed the page address in the Address bar, make sure that
it is spelled correctly.
* Open the www.robotbuilder.co.uk home page, and then look for
links to the information you want.
* Click the Back button to try another link.

HTTP 404 - File not found
Internet Information Services


----------------------------------
VIRTUE...is its own punishment
http://www.diversify.com Website Applications
==================================================

  #9   Report Post  
Tim Shoppa
 
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Pneumatics are very hard to use when you want precision of movement.
This is because air is compressible: it's like trying to position
something accurately, when you have to push it through a large

spring.

But if you want precision force, rather than precision positioning,
then a natural spring of the right force constant is a good thing.

Imagine trying to pick up an egg with a robotic hand when you have
hydraulic positioning - very accurate but no automatic control of
applied force. Then imagine it when you've got low-precision
positioning but good control over the force applied.

What you really need for a robotic hand is the "right" mix of position
accuracy with adjustable force. You won't always be picking up eggs!

Tim.

  #10   Report Post  
Robin S.
 
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"Jake" wrote in message
oups.com...

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.


All these questions and you forgot to say what you wanted the hand to do.

Oddly, no one else has asked this question before me. By asking non-specific
questions, you either get the shotgun effect of everyone posting little
tid-bits that may or may not be helpful, or you don't get very many (any)
answers at all.

So:

1. What do you want the hand to do? This is _the_ most important question
to answer, the first question to answer, and the ONLY question that you
absolutely must answer _completely_ before you can go any further.

Once you've got the answer to #1:

2. How much money do you have?

3. How much time do you have?

4. Do you personally know people who can design and machine/fabricate
mechanical parts, install hydraulic fittings/valves/pumps/actuators, design
and build control circuits, etc., etc.?

The above questions have to do with "feasibility". There will be other
questions, but start above.

Regards,

Robin




  #11   Report Post  
Don Foreman
 
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On 14 Feb 2005 00:27:01 -0800, "Jake" wrote:

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


You need to define what you want your project to do before you decide
(or ask others) how to do it. You need to know what forces, speeds,
and precisions it should have, and what budget and capabilities you
have or can obtain or develop.

Example: hydraulics are good where force and motion is needed from a
relatively small actuator but nowhere is it written in stone that
they must run at 3000 PSI, use oil, or even be made of metal. Nearly
all industrial hydraulics do use metal, oil and high pressure to get
the very high forces usually associated with hydraulics, but you may
not need your "hand" to be able to crush rocks. If ounces of force
would suffice, then small electric motors and leadscrews might work
well.

I've seen all-plastic hydraulic devices that were all plastic and
used water as fluid: remote throttle actuators in a dynomometer cell
where the operator simply wanted to be outside the region of loud
noise.


  #12   Report Post  
Emmo
 
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you should go to a toy store and buy a Lego Tecnics set. Pneumatic
actuators, lots of connectors, very cheap...


  #13   Report Post  
Jake
 
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I'm going to lead off by saying I'm very pleased by the responses you
have all given - they have been helpful in getting me off to a good
start. I like the idea of the air muscles mentioned earlier. They
certainly look promising. But you have raised some very important
issues, Robin S. Here are some more details:

I'm probably not interested in spending any more than $2000USD on the
hand. It would be nice if it could crush rocks but not necessary. As
far as size and strength goes you might imagine one of these hands
attached to the arm of one of those big pieces of construction
equipment. I think the general idea is to get a hand working, and then
build an arm to attach it to, and then a shoulder, working all the way
until I have a giant ... "robot"?

I'm very much intrigued by the idea of an exoskeleton, only I think it
would be quite difficult to make one that is close to the size a human
- at least for a person working on it in their garage without some sort
of big financial backing. I think it would be easier from a
design/engineering standpoint to build a large-scale exoskeleton, like
a large humanoid vehicle. That is why I want to build this "hand". It
seems like a good starting point, I will have to work out the actual
construction of said hand as well as the system used to control it. As
much as possible I would like the operators hand movements to be
translated to the mechanical hand for the most part 1 to 1. So if the
operator does a thumbs up, the mechanical hand would do one too, in as
close to realtime as possible, meaning that the mechanical hand forms
the thumbs up as the operator forms the thumbs up and they both stop
moving at approximately the same time.

Some sort of force-feedback mechanism would come in handy here, because
it would allow the operator to control the gripping strength of the
mechanical hand just by interpreting the feedback from whatever
pressure/force sensors are installed on the hand. What may be required
is some sort of computer layer in between the operator and the hand, so
as to allow for the gripping of squishy or delicate objects like eggs
or people (Imagine a big hand pulling off the wall of a tall burning
building and extricating the people who may be unconscious inside)
without crushing the held object. I doubt the size of the mechanical
hand I have in mind would allow for the gripping of an object the size
of an egg. Perhaps the smallest object it could grasp would be a
softball or a mushball (about 6" in diameter, like a cabbage).

At any rate... I figure before I go off to build a 20 foot walking
mechanical robot suit thing I should start small - thus, the hand. At
the very least if I were to be able to build such a hand there might be
some market for it in construction or other areas if it were to advance
enough to really be useful.

How strong is the human hand? I envision my mechanical hand to be on
the order of 5 to 20 times stronger than that. Probably close to ten
times as strong. But I don't have any specific application for it as
of yet so it is hard to say. I just want to build one. I want it to
be articulate, and I want to be able to control it with my own hand.

I can't remember the name but someone mentioned Legos and the Technic
pneumatic pieces - that's a stunning idea. I'll try that out as far as
prototyping goes to get the structure/design/frame figured out.

A couple of questions that just came to mind - or just one:

If you have two identical hydraulic cyclinders next to each other,
operating on the same object and working off of the same base, is the
net force just the sum of the forces of the two cylinders?
In other words, if I have a platform that is lifted by 4 hydraulic
cylinders attached at each corner, and each cylinder can exert a force
of 25 newtons, is the total force 25 newtons or 100 newtons? I think
it would be 100 newtons.

Ok I'll let you guys comment now on how insane I must be to dream of
making something like this...

  #14   Report Post  
B.B.
 
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In article .com,
"Jake" wrote:

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


[...]

You can make your cylinders basically any size you like--the force
generated equals the oil pressure times the area of the piston, so you
can scale 'em down a bunch if you're willing to deal with higher
pressures. And with a "hand" you probably won't be needing a whole
buttload of force on the intricate bits like fingers--you can easily
build a system using different pressures in different sections.
A piston less than 1/4" across has an area of 1/2 a square inch, so
20psi oil pressure gets you ten pounds of force, which ought to be
plenty for a finger. Step it up to 50psi for hand-smashing fun and
you're still dealing with negligible pressures and won't need
hydraulic-use rated hardware. Safe to work with, too.
Generally, as components shrink they can handle higher pressures more
easily, too, since there will be less surface area internally. (for
example, a hypo needle has a burst pressure in the neighborhood of
10,000psi) If you don't need a whole lot of flow use small lines.
Cheaper fittings to boot. Size it so fluid won't have to move faster
than 20 feet per second.
If you use hydraulics your biggest headache in terms of construction
would be the lines and hoses--that can be mitigated somewhat if you
place all of your valves as close as possible to the cylinders, so you
might prefer the tendons option. Also, if you go with a tendon setup
you have more room to install positional sensors either out at the
joints or along the tendons themselves. And with a tendon setup the
cylinders won't have to move around, so you could plumb them all with
rigid lines, which are better/cheaper than hoses to work with.
I assume you've read about open center and closed center hydraulic
systems. Open center basically has a low-pressure standby mode where
oil just gets pumped straight through the valves and back to the tank.
It's easy to do if all of your valves will be located on the same
manifold, but gets quite a bit more complex if you don't. Closed center
would be the way to go in that case, but you'll need either a variable
displacement pump or some sort of unloader valve arrangement. With a
variable displacement pump you'll wind up with a rather high pressure
standby that could make the hand difficult to control. If the valves
will all be computer-controlled and not in a common manifold, closed
center with an unloader activated by the computer would probably be
best. Make sure to always have a pressure relief valve in case
something goes wrong.
Maintenance depends on how cleanly you assemble the system and how
hot it'll run. You'll probably be running pretty cool, so it's not too
likely that you'll wear out or burn the fluid any time soon. Make sure
your reservoir has a low spot in it and the pump's intake is higher than
it. That way any water that might get in will stay out of the
hydraulics.
You'll get mixed opinions on where to place the filter--some say on
the return to the tank, some say before the pump, some say after the
pump if working pressures allow it. On the return to the tank is a
logical choice if you know you can put the system together cleanly.
Pump intake is a somewhat dangerous place because if your filter gets
clogged too badly it could either cavitate the pump, or worse, get
sucked into the pump.
You could also use a bypass filter setup--a secondary high flow, low
pressure pump that does nothing but take fluid from the reservoir, pump
it through a filter, and back. Tie the main pump's intake to the
filter's output and you'll get the best of all systems and a
low-pressure filter.
If you decide to build parts yourself you can make hydraulic
cylinders pretty efficiently with DOM (drawn over mandrel) tubing. You
only need to clean up and thread the ends and install your plug and
gland nut. Of course, you'll need to make plugs, pistons, and gland
nuts. (:
As far as hydraulic positioning systems, I know some hydraulic
cylinders that need accurate positional feedback have a ballscrew that
is attached to a rotary converter in the base of the cylinder. The nut
is on the end of the rod and the rod is hollow to make room for the
screw. But I think something like that would be extremely expensive and
not available in smaller sizes. Also, some cylinders actually have
threaded rods that are then built back up. The rod is smooth when all
is said and done, but you can place a magnetic pickup by the rod and
count as the threads pass by below the surface. Again, expensive, but I
think more readily available in small sizes.
You'd probably be better off using a sensor outside the cylinder or
even at the joint.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/
  #15   Report Post  
Robin S.
 
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"Jake" wrote in message
ps.com...

I can't remember the name but someone mentioned Legos and the Technic
pneumatic pieces - that's a stunning idea. I'll try that out as far as
prototyping goes to get the structure/design/frame figured out.


I would recommend you go in this direction before you invest some very
siginificant funds into something that could take years of work to get
going.


A couple of questions that just came to mind - or just one:

If you have two identical hydraulic cyclinders next to each other,
operating on the same object and working off of the same base, is the
net force just the sum of the forces of the two cylinders?
In other words, if I have a platform that is lifted by 4 hydraulic
cylinders attached at each corner, and each cylinder can exert a force
of 25 newtons, is the total force 25 newtons or 100 newtons? I think
it would be 100 newtons.


The only thing that matters is the area of the surface which is
perpendicular to your force and on which hydraulic (or pneumatic) pressure
is acting upon. In the case of a group of hydraulic cylinders, this is the
total area of all the pistons.

You should be aware of the forces you are (possibly) dealing with here.

Lets say a system pressure of 1500psi (~100 bar), a cylinder with a piston
diameter of 1" (~25mm).

F=pi*r^2*P

Whe
F is force in pounds
pi is pi (~3.14159...)
r is radius of pison (circle) in inches
P is pressure in pounds per square inch

F=pi*.5^2*1500
=1178lbs
(Which turns into roughly 5200N)

Obviously, this is a _lot_ of force. While it's fun to see rocks get
crushed, you may not personally enjoy the feeling. Hydraulic systems are not
designed to fail when they get bloody, so you really only get one chance
(and typing code without a full compliment of fingers must suck).

A guy at work recently got caught in an automatic surface grinder's
hydraulic feed mechanism. It nearly sheared his finger off.


Ok I'll let you guys comment now on how insane I must be to dream of
making something like this...


Well, at least you see what we're seeing. You should definately see what you
can do with this Lego Tecnics set (if it even exists). Anything that speeds
up the prototyping stage of development is going to be a _huge_ help.

You've got a lot on your plate...

Regards,

Robin




  #16   Report Post  
 
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The "snakes" in the movie _Anaconda_ had Hundreds of hydraulic
cylinders at every joint. All controlled by a computer program. Th
central hydraulic pump was pretty impressively large too. Programmers
worked all night to program the scene for the next day.
Pete

  #17   Report Post  
Lloyd E. Sponenburgh
 
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"B.B." u wrote in message
news
A piston less than 1/4" across has an area of 1/2 a square inch, so
20psi oil pressure gets you ten pounds of force,


No, that would be 5/100 sq" (.049) for a 1/4" dia. piston (extend, only.
The rod would reduce the retract area and force.)

So, for a 1/4" piston, you get just under ONE pound for 20psi.

LLoyd


  #18   Report Post  
B.B.
 
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In article t,
"Lloyd E. Sponenburgh" wrote:

"B.B." u wrote in message
news
A piston less than 1/4" across has an area of 1/2 a square inch, so
20psi oil pressure gets you ten pounds of force,


No, that would be 5/100 sq" (.049) for a 1/4" dia. piston (extend, only.
The rod would reduce the retract area and force.)

So, for a 1/4" piston, you get just under ONE pound for 20psi.

LLoyd


Ah, crap, I was thinking radius and using diameter. Or the other way
around. Sorry, Valentine's Day ****s me all up.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/
  #19   Report Post  
Sunworshipper
 
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On Mon, 14 Feb 2005 16:56:15 -0600, Don Foreman
wrote:

On 14 Feb 2005 00:27:01 -0800, "Jake" wrote:

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


You need to define what you want your project to do before you decide
(or ask others) how to do it. You need to know what forces, speeds,
and precisions it should have, and what budget and capabilities you
have or can obtain or develop.

Example: hydraulics are good where force and motion is needed from a
relatively small actuator but nowhere is it written in stone that
they must run at 3000 PSI, use oil, or even be made of metal. Nearly
all industrial hydraulics do use metal, oil and high pressure to get
the very high forces usually associated with hydraulics, but you may
not need your "hand" to be able to crush rocks. If ounces of force
would suffice, then small electric motors and leadscrews might work
well.

I've seen all-plastic hydraulic devices that were all plastic and
used water as fluid: remote throttle actuators in a dynomometer cell
where the operator simply wanted to be outside the region of loud
noise.


Somewhere I have a letter from the DOE/NIST stating that water
pressure can not work for hydraulic devices. And furthermore if water
pressure is lost the solar device will burn down cause the sun will
still be tracked.
  #20   Report Post  
OldNick
 
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On Tue, 15 Feb 2005 20:36:25 -0600, "B.B."
u vaguely proposed
a theory
.......and in reply I say!:

remove ns from my header address to reply via email


Sorry, Valentine's Day ****s me all up.


Well half your luck.....unles your name is Buggsy.....



  #21   Report Post  
Don Foreman
 
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On Tue, 15 Feb 2005 21:40:02 -0800, Sunworshipper
Somewhere I have a letter from the DOE/NIST stating that water
pressure can not work for hydraulic devices. And furthermore if water
pressure is lost the solar device will burn down cause the sun will
still be tracked.


All generalities are false....

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